High-strength steel having excellent low-temperature viscosity and excellent viscosity in thermally affected zone of welding joint (options), method for manufacturing such steel, method for manufacturing sheet from indicated steel, high-strength steel tube (option), and a method for manufacturing high-strength steel tube

FIELD: steel making.

SUBSTANCE: invention relates to such type of steel that is employed in welded structures such as gas conduits, petroleum pipelines, as well as in high-pressure vessels. Steel according to invention contains, wt %: C 0.02-0.10, Si up to 0.6, Mn 1.5-2.5, P up to 0.015, S up to 0.003, Ni 0.01-2.0, Mo 0.2-0.6, Nb below 0.010, Ti up to 0.030, Al up to 0.070, N up to 0.0060, Fe and unavoidable impurities - the rest, provided that parameter P = 2.7C+0.4Si+Mn+0.8Cr+0.45(Ni+Cu)+2V+Mo-0.5 is within a range of 1.9 to 3.5. Microstructure of steel is mainly composed of martensite and bainite. Steel sheet is manufactured by heating casting to at least Ac3, subjecting it to hot rolling, and cooling sheet at a rate 1°C/sec to temperature not exceeding 550°C. Sheet is further used to manufacture a tube. When laying multilayer welding joint, energy absorbed in the Charpy impact test at -40°C is at least 200 J.

EFFECT: achieved elongation strength at least 800 MPa.

21 cl, 1 dwg, 9 tbl, 5 ex

 

Background of invention

The technical field to which the invention relates.

The present invention relates to very high-strength hot-rolled steel having ultimate tensile strength of at least 800 MPa, in particular at least 900 MPa, with excellent viscosity base steel and excellent toughness in the heat-affected zone of the weld in the temperature range from -60°0° (hereinafter referred to as ″viscosity at low temperatures″ and ″toughness in the heat-affected zone of the weld″) and the way it is received, and the method of manufacturing a steel sheet and steel pipes of the above hot rolled steel.

Such very high-strength hot-rolled steel after further processing and welding are widely used in pipeline pipes for transportation of natural gas or crude oil, pressure vessels, welded structures, etc.

Description of the prior art

In recent years, to a steel sheet for pipe pipes used for pumping water (for example, in the case of the discharge pipe or pressure vessel is considered to require high strength and toughness at low temperatures. For example, in the case of sheet steel piping pipe already undertaken various studies in connection with and is cooking, extra high strength steel sheet, having ultimate tensile strength of at least 800 MPa (at least X100 standard American petroleum Institute (API)), and high-strength steel with excellent toughness at low temperatures, excellent toughness in the heat-affected zone of the weld and excellent weldability, described in Japanese patent No. 3244986 and 3262972. In addition, very high-strength pipeline pipe having ultimate tensile strength of not less than 900 MPa, and the method of its manufacture are described in not subjected to the examination of Japanese patent publication No. 2000-199036.

However, while the energy absorbed during the impact test on Charpy at -20°in the heat-affected zone, on which is placed a single layer of weld in steel plate for pipe pipe, described in the aforementioned Japanese patent No. 3244986 and 3262972 is not less than 100 j, which is very good, the viscosity of the metal in the zone of the weld is sometimes reduced in the heat-affected zone, in which lay a weld bead comprising two or more layers, under certain welding conditions.

In addition, although the energy absorbed during the impact test on Charpy main steel at a temperature of -40°With steel plate for pipe pipe, described in the aforementioned Japanese patent No. 3244986 and 3262972, and not in the above paragraph is dargavskaya examination of Japanese patent publication No. 2000-199036, an average of not less than 200 j, when the number (hereinafter denoted by the symbol n) of the samples under test using the same material and the same test conditions, is three, and the above-mentioned result is very good, still a problem arises, namely that the energy absorbed during the impact test on Charpy some samples, is less than 200 j, and some examples of its variance is greater.

In the detailed study of the problem of dispersion viscosity at low temperatures it was found that the energy absorbed during the impact test on Charpy, with a probability of 20 percent was less than 200 j, when the impact test on Charpy conducted at a temperature of -40°With the increase of n, and in addition, the energy absorbed during the impact test on Charpy some samples did not exceed 100 j, and on the fracture surfaces of the samples were observed verge of brittle fracture when the impact test on Charpy were conducted in the temperature range from -60° to a temperature not exceeding -40°C.

By the way, the authors of this invention have proposed a method for increasing the viscosity at low temperatures due to the adaptation to this purpose, the welding method described in Japanese patent application No. 2001-336670. However, in this case found the camping, the proposed method is not ready for immediate use, because it was not suitable for mass production and demanded the introduction of new equipment. Due to the above situation requires the development of high-strength pipeline pipe with excellent toughness at low temperatures characteristic of main steel and (steel) weld.

Summary of the invention

The present invention proposed, extra high strength steel having ultimate tensile strength of at least 800 MPa, and the steel pipe made of such steel and this steel has excellent toughness in the heat-affected zone of the weld, in particular, excellent energy, characterizing the work of brittle fracture, in the case of overlapping multi-layer weld has the energy absorbed during the impact test on Charpy main steel at a temperature of -40°With an average of at least 200 j and a small variance, has excellent toughness at low temperatures, and is easily welded on the construction site. In the context of the invention, the energy that characterizes the work of brittle fracture, is the energy absorbed during the impact test on Charpy measured in the temperature range in which some material undergoes a wholly plasticheskiye, when the impact test on Charpy at different temperatures is subjected to the same material that undergoes brittle fracture at low temperature.

The authors of this invention have conducted intensive studies of the chemical components of the steel material and its microstructure to obtain a high-strength steel having ultimate tensile strength of at least 800 MPa (at least X100 standard ANI), with the energy that characterizes the work of brittle fracture, not less than 100 j in the heat-affected zone of the weld, which impose multi-layer weld bead having energy absorbed during the impact test on Charpy, an average of at least 200 j and a small variance in the temperature range not exceeding -40°and easily welded on the construction site.

The result of these studies, the authors of the present invention, firstly, it was found that the decrease in viscosity at low temperatures when welding with two-layer overlay weld was caused by the niobium carbonitride, and further have provided evidence that the number Nb is extremely important when trying to avoid the mentioned reduction. Secondly, in connection with the main steel was that sometimes under certain test conditions were observed small amounts of energy absorbed during the impact test on Charpy, and the Torah of the present invention have found, this small energy absorbed during the impact test on Charpy, was caused, in particular, the existence of large grains, and found that reducing the number Nb proved extremely effective countermeasure.

In accordance with this invention high strength steel with excellent toughness at low temperatures was obtained at the expense of additional control parameter P, which was a measure of proclaimeth, in a suitable range to increase the tensile strength that got smaller as he reduced the number Nb.

This invention is made on the basis of the above discoveries, and its essence is described below.

(1) high-Strength steel with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of the weld, characterized in that it contains by weight:

From: 0,02-0,10%,

Si: not more than 0.6%,

Mn: 1.5 to 2.5%,

P: less than 0.015%,

S: not more than 0.003 per cent,

Ni: 0.01 to 2.0 percent,

Mo: 0,2-0,6%,

Nb: less than 0,010%,

Ti: not more than 0,030%,

Al: not more than 0,070%, and

N: not more than 0,0060%,

the rest is Fe and inevitable impurities, with the parameter P in steel, defined in the following expression, is in the range from 1.9 to 3.5, and the microstructure of the steel consists mainly of martensite and bainite:

P=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+Mo 0.5 in.

(2) high-Strength steel excellent in what Scott at low temperatures and excellent toughness in the heat-affected zone of the weld, characterized in that it contains by weight:

From: 0,02-0,10%,

Si: not more than 0.6%,

Mn: 1.5 to 2.5%,

P: less than 0.015%,

S: not more than 0.003 per cent,

Ni: 0.01 to 2.0 percent,

Mo: 0.1 to 0.6%,

Nb: less than 0,010%,

Ti: not more than 0,030%,

In: 0,0003-0,0030%,

Al: not more than 0,070%, and

N: not more than 0,0060%to satisfy the expression Ti-3,4N≥0,

the rest is Fe and inevitable impurities, with the parameter P in steel, defined in the following expression, is in the range from 2.5 to 4.0, and the microstructure of the steel consists mainly of martensite and bainite:

P=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+1,mo.

(3) high-Strength steel with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of the weld on PP(1) or (2), characterized in that it further contains, by mass, one or more of the elements such as

V: 0.001 to 0.10%per,

Cu: 0.01 to 1.0%in,

Cr: 0.01 to 1.0%in,

Sa: of 0.0001 to 0.01%,

rare earth metal (REM): of 0.0001 to 0.02%, and

Mg: 0,0001-0,006%.

(4) high-Strength steel with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of a welded seam on any of the points(1)to(3), characterized in that the average diameter of the initial austenite grains in the steel does not exceed 10 microns.

(5) high-Strength steel with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of the weld, characterized in that the holding by weight:

To: from 0.02 to less than 0.05%,

Si: not more than 0.6%,

Mn: 1.5 to 2.5%,

P: less than 0.015%,

S: not more than 0.001%,

Ni: 0.01 to 2.0 percent,

Mo: 0.1 to 0.6%,

Nb: less than 0,010%,

Ti: not more than 0,030%,

In: 0,0003-0,0030%,

Al: not more than 0,070%, and

N: not more than 0,0060%to satisfy the expression Ti-3,4N≥0, and one or more of the elements such as

V: 0.001 to 0.10%per,

Cu: 0.01 to 1.0 percent, and

Cr: 0.01 to 1.0%in,

the rest is Fe and inevitable impurities, with the parameter P in steel, defined in the following expression, is in the range from 2.5 to 4.0, the microstructure of the steel consists mainly of martensite and bainite, and the average diameter of the initial austenite grains in the steel does not exceed 10 μm:

P=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+1,mo.

(6) high-Strength steel with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of the weld, characterized in that it contains by weight:

To: from 0.02 to less than 0.05%,

Si: not more than 0.6%,

Mn: 1.5 to 2.5%,

P: less than 0.015%,

S: not more than 0.001%,

Ni: 0.01 to 2.0 percent,

Mo: 0.1 to 0.6%,

Nb: less than 0,010%,

Ti: not more than 0,030%,

In: 0,0003-0,0030%,

Al: not more than 0,070%, and

N: not more than 0,0060%to satisfy the expression Ti-3,4N≥0, and one or more of the elements such as

V: 0.001 to 0.10%per,

Cu: 0.01 to 1.0%in,

Cr: 0.01 to 1.0 percent, and

Sa: of 0.0001 to 0.01%,

the rest is Fe and inevitable impurities, with the parameter P in steel, defined in the following expression, is dia is the azone from 2.5 to 4.0, the microstructure of the steel consists mainly of martensite and bainite, and the average diameter of the initial austenite grains in the steel does not exceed 10 μm:

P=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+1,mo.

(7) the Method of manufacturing a high strength steel plate with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of the weld, which is a method of manufacturing a steel sheet of the casting containing components according to any one of p.p.(1)-(3), (5) and (6), characterized in that the re-heat the casting to a temperature not lower than the temperature AU3perform hot rolling of this casting, and then cooling the obtained steel sheet with a cooling rate of not less than 1°C/sec to a temperature of not more than 550°C.

(8) the Method of manufacturing a high strength steel plate with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of the weld under item(7), characterized in that the carry out molding in a cold condition of the cooled steel sheet to receive the pipe, and then put on her abutting portion of the longitudinal weld seam.

(9) high-Strength steel pipe with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of the weld, characterized in that the duct part, Saltykova the ing with the application of longitudinal welded seam, most steel contains, by mass:

From: 0,02-0,1%,

Si: not more than 0.8%,

Mn: 1.5 to 2.5%,

P: less than 0.015%,

S: not more than 0.003 per cent,

Ni: 0.01 to 2%,

Mo: 0.2 to 0.8%,

Nb: less than 0,010%,

Ti: not more than 0.03%,the

Al: not more than 0.1%, and

N: not more than 0,008%,

the rest is Fe and inevitable impurities, with the parameter P in steel, defined in the following expression, is in the range from 1.9 to 4.0, and the microstructure consists mainly of martensite and bainite:

P=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+Mo 0.5 in.

(10) high-Strength steel pipe with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of the weld, characterized in that the duct part, costacabana by imposing a longitudinal weld, the main steel contains, by mass:

From: 0,02-0,10%,

Si: not more than 0.8%,

Mn: 1.5 to 2.5%,

P: less than 0.015%,

S: not more than 0.003 per cent,

Ni: 0.01 to 2%,

Mo: 0,1-0,8%,

Nb: less than 0,010%,

Ti: not more than 0,030%,

In: 0,0003-0,003%,

Al: not more than 0.1%, and

N: not more than 0,008%, to satisfy the expression Ti-3,4N≥0,

the rest is Fe and inevitable impurities, with the parameter P in steel, defined in the following expression, is in the range from 2.5 to 4.0, and the microstructure consists mainly of martensite and bainite:

P=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+1,mo.

(11) high-Strength steel pipe with excellent toughness at low temperatures prevoshodnoy toughness in the heat-affected zone of the weld by p.p.(9) or (10), characterized in that it further contains, by mass, one or more of the elements such as

V: 0,001-0,3%,

Cu: 0.01 to 1%,

Cr: 0.01 to 1%,

Sa: of 0.0001 to 0.01%,

REM: of 0.0001 to 0.02%, and

Mg: 0,0001-0,006%.

(12) high-Strength steel pipe with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of a welded seam on any of p.p.(9)-(11), characterized in that the average diameter of austenite grains in the steel pipe does not exceed 10 microns.

(13) high-Strength steel pipe with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of the weld, characterized in that the duct part, costacabana by imposing a longitudinal weld, the main steel contains, by mass:

To: from 0.02 to less than 0.05%,

Si: not more than 0.8%,

Mn: 1.5 to 2.5%,

P: less than 0.015%,

S: not more than 0.001%,

Ni: 0.01 to 2%,

Mo: 0,1-0,8%,

Nb: less than 0,010%,

Ti: not more than 0,030%,

In: 0,0003-0,003%,

Al: not more than 0.1%, and

N: not more than 0,008%, to satisfy the expression Ti-3,4N≥0, and one or more of the elements such as

V: 0,001-0,3%,

Cu: 0.01 to 1%, and

Cr: 0.01 to 1%,

the rest is Fe and inevitable impurities, with the parameter P in steel, defined in the following expression, is in the range from 2.5 to 4.0, the microstructure consists mainly of martensite and bainite, and the average diameter of austenite the grains is not more than 10 μm:

P=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+1,mo.

(14) high-Strength steel pipe with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of the weld, characterized in that the duct part, costacabana by imposing a longitudinal weld, the main steel contains, by mass:

To: from 0.02 to less than 0.05%,

Si: not more than 0.8%,

Mn: 1.5 to 2.5%,

P: less than 0.015%,

S: not more than 0.003 per cent,

Ni: 0.01 to 2%,

Mo: 0,1-0,8%,

Nb: less than 0,010%,

Ti: not more than 0,030%,

In: 0,0003-0,0030%,

Al: not more than 0.1%, and

N: not more than 0,008 %, to satisfy the expression Ti-3,4N≥0, and one or more of the elements such as

V: 0,001-0,3%,

Cu: 0.01 to 1%.

Cr: 0.01 to 1%,

Sa: of 0.0001 to 0.01%,

the rest is Fe and inevitable impurities, with the parameter P in steel, defined in the following expression, is in the range from 2.5 to 4.0, the microstructure consists mainly of martensite and bainite, and the average diameter of austenite grains is not more than 10 μm:

P=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+1,mo.

(15) a method of manufacturing a high strength steel pipe with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of the weld, characterized in that the re-heat the casting containing components according to any one of p.p.(9)-(14), to a temperature not lower than the temperature AU3carry out hot th rolling this casting, and then cooling the obtained steel sheet with a cooling rate of not less than 1°C/sec to a temperature of not more than 550°To carry out molding in a cold condition of the cooled steel sheet to give it shape pipe, then carry out arc welding submerged arc welding abutting portion with inner and outer sides of the pipe, and then subjected to steel pipe expanders.

(16) a method of manufacturing a high strength steel pipe with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of the weld under item(15), characterized in that the heat costacabana by overlapping the longitudinal weld of the steel pipe to a temperature of from 300°500°before the flare pipe.

(17) a method of manufacturing a high strength steel pipe with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of the weld under item(15), characterized in that the heat costacabana by overlapping the longitudinal weld of the steel pipe to a temperature of from 300°500°after expanding pipe.

Brief description of drawings

The drawing shows a graph illustrating the influence of the amounts of Nb on the viscosity of the re-heated parts of the coarse grains.

Description of the preferred concretehuman implementation

First of all, below is an explanation of the nature of the heat-affected zone of the weld. High-strength steel of various types imposed a two-ply seams and evaluate the toughness in the weld in the heat-affected zone of welds at -20°by conducting impact test on Charpy samples, each of which had a cut in the intersection of the inner and outer welds or in part, located at a distance of 1 mm from the intersection of internal and external welds. The term "mating portion" means the place where the layers two-layer weld bead overlap with each other in the cross section perpendicular to the direction of welding. The evaluation of almost all fracture surfaces were faces of brittle fracture, and in some cases the energy absorbed during the impact test on Charpy, was small, not exceeding 50 j.

A careful study of the fracture surfaces revealed that brittle fracture began with the following parts: (1) the region extending from the fillet part to part, separated from it by 1 mm, the heat-affected zone of the weld, which was heated once to a temperature less than the melting temperature, and then heated to a temperature somewhat higher than the temperature AU3; (2) the area to the Yu was re-heated to a temperature a little less than the melting temperature; and (3) the area that was heated once to a temperature less than the melting temperature. The probability of brittle fracture in their respective fields accounted for about 60% to in paragraph (1), about 30% in part (2) and about 10% in paragraph (3).

This result means that the viscosity in the re-heated part, where grain was enlarged under the influence of the disposable heating should increase. Then the authors present invention further careful observation of the fracture surfaces were convinced that a combination of niobium carbonitride was present in the original moment of brittle fracture, and found the possibility of increasing the viscosity of the heat-affected zone of the weld, in particular, re-heated part with large grains, which is twice subjected to heat, by reducing the number Nb.

Based on the above discoveries, the authors of this invention have examined the effect of Nb on the toughness in the heat-affected zone of the weld, after modeling the influence of heat caused by the imposition of a two-layer weld, by testing for playback cycle heat weld. Made of steel sheets, by adjusting the content of additional quantities of elements other than niobium in the range of the zone, specified in items 1 or 2 of the claims, and changing the amount of Nb in the range from 0.001 to 0.04 wt.%, and prepared the samples. Created conditions of cyclic heating corresponding to the magnitude of the applied energy of 2.5 kJ/mm, that is, The first heat treatment of the samples was conducted under such conditions that the test sample was heated at a speed comprised 100°C/sec, to a temperature of 1400°C, held at this temperature for 1 sec, and then cooled with a cooling rate, which constituted 15°C/s, introducing the sample in the temperature range from 500°800°and in addition to this, the second heat treatment of the samples was conducted under such conditions that the temperature of the heating was set equal to 1400°or 900°With the heating rate, holding time at a given temperature, cooling temperature and the cooling rate was kept identical to the first heat treatment. After this the samples to the standard size for impact testing of samples with V-shaped cuts on Sharpie prepared in accordance with Japanese industrial standard (APS) z (JIS Z 2202 and conduct impact test on Charpy in accordance with APS z 2242.

The results are shown in the drawing. It was found that in those steels in which the additive Nb was not less than 0.01%, the energy absorbed during the impact test on the Arpi, in a few cases not exceeding 50 j but in those steels in which the additive Nb was less than 0.01%, there were no cases when the energy absorbed during the impact test on Charpy, not exceeding 50 j but noted that the viscosity of the re-heated part with large grains was significantly increased. When observing the surface of the destruction of the first sample of the steel with the addition of Nb, in which the energy absorbed during the impact test on Charpy, does not exceed 50 j, it was found that almost the entire surface was the face of brittle fracture, and that at the initial moment on the verge of brittle fracture was present combined niobium carbonitride. On the other hand, when observing the surface of the destruction of the steel, the content of Nb in which amounted to less than 0.01%, after the impact test on Charpy at the starting point on the verge of brittle fracture was not combined niobium carbonitride. As a consequence, the authors of this invention have achieved increasing the viscosity in the above mentioned areas of brittle fracture, reducing the amount of Nb to a value of less than 0.01%.

The following are clarifications in connection with the viscosity at low temperatures the main steel. To ensure excellent toughness at low temperatures in very high-strength steel pipe having a tensile strength at elongation of at least 800 MPa, in particular at least 900 MPa, the mu who needs to create a structure, consisting mostly of bainite and martensite, have undergone a phase transformation from precrystallization austenite containing large particles. When mixed with large grains or when the share of bainite and martensite is not large enough, the energy absorbed during the impact test on Charpy, it turns out small, and meanwhile, the energy absorbed during the impact test on Charpy, is the termination rate fast plastic fracture. The authors of this invention were subjected to basic steel tests to strike Sharpie at a temperature of 60°and carefully examined the patterns in the immediate vicinity survived the destruction of parts of the samples that failed to reach the energy absorbed during the impact test on Charpy, not less than 200 j. The study found that in the structure there was a large grain diameter of 10-100 μm, and it was they who caused the reduction of the energy absorbed during the impact test on Charpy.

The structure of the castings obtained by the method of continuous casting containing a relatively small amount of alloying elements and having a tensile strength of 800 MPa, is usually a complex structure of ferrite and bainite or ferrite and perlite. When such a re-casting is heated for conducting hot rolling, is a rich education is Finance a new austenite mainly from the borders of ferritic grains, and when the temperature of the heating reaches approximately 950°, teensolo exceeds the temperature AU3this complex structure undergoes a phase transformation to austenite with controlled grain size, the average diameter is about 20 μm. When through the subsequent hot rolling is made of steel sheet, grain patterns become smaller due to recrystallization, and the structure becomes almost uniform, with variable grain size and has the austenitic grains with an average diameter of about 5 μm. However, on the basis of estimates, we can conclude that if the steel that adds elements that provide additional hardening, and example of which can be high-strength steel having ultimate tensile strength of at least 800 MPa, is subjected to hot rolling, the steel is partially remain large grains, and its viscosity at low temperatures is reduced.

Having in mind this situation, the authors of the present invention in detail investigated the influence of the components on the structure and found that when the amount of Nb was reduced to values of less than 0.01%, the grains after hot rolling was small, and partly existing large grains were observed. The effect of reducing the number of Nb can be explained as follows.

Let's start with explaining the reason chastichno the preservation of large grains with a large number of Nb. Extra high strength steel having ultimate tensile strength of at least 800 MPa, in particular at least 900 MPA, typically contains relatively large amounts of alloying elements such as Mn, Ni, Cu, Cr and Mo, which leads to high proclaimest. When continuously casting etc. of this steel, the structure of the casting after cooling to room temperature, it is contains a separate phase of a major banita (hereinafter referred to as "Bantam"), the diameter of the crystal grains is not less than 1 mm in terms of diameter of the original austenite grains, single phase martensite (hereinafter referred to as "martensite"), or a structure consisting mainly of bainite and martensite (hereinafter referred to as "the dominant structure bainite and martensite"). Beans such structure contains fine-grained residual austenite. Note that, although patterns as bainite and martensite are rack structures and are difficult to identify using an optical microscope, they can be identified by measuring the hardness.

When casting having such a structure as that described above, is heated to a temperature in the range from 900°With up to 1000°With, such reactions occur as a reaction to the emergence of new austenite grains formed due to phase transformation, going from the borders of the outcome of the s austenitic grains (hereinafter referred to as "normal phase ferrite-austenite transformation"), and the reaction of the formation of large austenite grains of a size not less than 1 mm due to lung growth and consolidation above the remaining austenite (hereinafter referred to as "anomalous phase ferrite-austenite transformation").

When implementing the additional additive Nb in this steel, formed fine-grained niobium carbide, resulting in grain growth during heating is suppressed. Therefore, when the steel is heated in the temperature range from a temperature slightly above the temperature AU3for example to 1100°suppressed the growth of austenite grains formed by normal phase austenitic transformation, namely the secondary recrystallization. In the austenitic grain size not less than 1 mm, i.e. having almost the same size as the original austenite grains in the casting, partially formed due to anomalous phase ferrite-austenite transformation. If such large austenite grains are formed in the steel during heating, since the recrystallization after hot rolling is hard austenitic grain is partially stored in the form of grains of a size not less than 50 μm, and these large grains cause a decrease in viscosity at low temperatures.

When steel is heated, by entering it in the temperature range of not less than 1150°C, combined niobium carbide, the impact of the cat is, which is to consolidate grains, dissolved, and the growth of the grains formed by conventional austenitic phase transformation from the boundaries of austenite grains, that is, the secondary recrystallization, is accelerated, and thus there is proper regulation of the size of austenitic grains. Although during hot rolling, casting, having such a structure, the average diameter of the grains increases slightly, the large grain size of about 50 μm are not observed at all. However, the large grain size smaller than about 20 μm, still remain.

In contrast to the above, since the casting of steel in which the amount of Nb is reduced to a value of less than 0.01%, it contains very little of niobium carbide, the effect of suppressing secondary recrystallization is weak. Therefore, when the casting is heated by typing it in the temperature range from 950°1100°S, secondary recrystallization is accelerated, and thus the grain, which is formed by normal phase austenitic transformation, cause the destruction of large grains formed by the abnormal phase ferrite-austenite transformation, and the structure becomes homogeneous. During hot rolling, casting, having such a structure is uniform structure in which the average diameter of the grains is about 10 μm, and it no longer remains a large grain size not less than 20 μm. Mark is m, because the coarsening of austenite grains after secondary recrystallization is suppressed as lowering the heating temperature, the grains after hot rolling are small.

As explained above, the authors of this invention have found that even in the casting, in which the alloying elements, providing high proclaimest and contributing to the formation of large austenite grains, in particular, due to anomalous phase ferrite-austenite transformation during heating made in relatively large quantities to achieve high strength and which had a separate phase bainite, single phase martensite or dominant structure bainite and martensite have been able noticeable suppression of the formation of large grains by reducing the amount of Nb to a value of less than 0.01%. Based on this discovery, the authors present invention has succeeded in developing a high-strength steel as the main steel having excellent toughness at low temperatures, equivalent to not less than 200 j of energy absorbed during the impact test on Charpy when this basic steel is subjected to impact test on Charpy temperature range from -60°With temperatures of less than -40°C.

However, it is clear that reducing the number of Nb decreases the temperature of recrystallization, and implemented the e rolling without recrystallization is invalid. The authors of this invention have investigated the occurrence of recrystallization of austenite in the steel, which was added 0.005% of Nb, and steel, to which was added 0,012% Nb, with both steel contains, by weight, 0.05% of C, 0.25% of Si, 2% Mn, 0.01% P, 0,001% S, 0.5% of Ni, 0.1% of Mo, 0,015% Ti, 0,0010%, 0,015% Al, 0,0025% N, 0.5% of Cu and 0.5% Cr. The study found that the temperature of recrystallization either of these two steels were in the temperature range from 900 to 950°Since, whatever additional amount of Nb, and steel, which are abundantly added Mn, Ni, Cu, Cr and Mo, the recrystallization temperature is not changed regardless of the additive Nb. Therefore, it is proved that the influence of additives Nb were insignificant from the point of view of the recrystallization of austenite.

Further, since the decrease in the number of Nb causes a decrease in tensile strength, the authors of this invention have examined the effect of additional elements to improve proclaimest and found the opportunity to guarantee the proper tensile strength and adequate toughness at low temperatures by regulating parameter P, which was a measure of proclaimeth, in a proper range. In the detailed study of the effect of alloying elements on proclaimest steel, the additional amount of Nb which reduced to a value of less than 0.01%, it was found that in the case of steel, not containing, by determining the parameter P according to the expression R=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+Mo+0,5, proclaimeth, it is estimated that turned out to be a proper and suitable range of parameter P ranged from 1.9 to 3.5. On the other hand, it was found that in the case of steel, which was added In, the value of the parameter P was determined by the expression R=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+1,mo, and a suitable range of parameter P ranged from 2.5 to 4.0. By adjusting the parameter P and introducing it into the proper range, the authors of this invention have succeeded in obtaining an acceptable balance between the target values of tensile strength and toughness at low temperatures without adverse effect on the toughness in the heat-affected zone of the weld and the welding at the construction site.

In addition, when the heat-affected zone of the weld is heated to a temperature of at least 300°S, fine-grained martensite-austenite (MA) underwent vacation, whereupon the energy absorbed during the impact test on Charpy, consistently turned out great. On the other hand, when the heat-affected zone of the weld steel, which was added to Nb before reaching the content is not less than 0.01%, was heated to a temperature of at least 300°With, despite the fact that fine-grained martensite-austenite (MA) underwent vacation, took place simultaneously and embrittlement caused osuzhdeni the m Nb, therefore the effect expected in this invention, is clearly not observed.

Next, explanation will be given of the reasons for limiting the contents of components of steel and components of the main steel pipe.

Carbon (C) exceptionally effective to increase the tensile strength and proclaimeth steel due to the dissolution or precipitation of carbonitride in steel, and the lower limit of the content is set equal to 0.02%in order to achieve the target strength by creating a structure consisting of bainite, martensite or dominant patterns of bainite and martensite. On the other hand, when the content is excessive, the viscosity at a low temperature in the steel material and the heat-affected zone of the weld is reduced, resulting in significantly deteriorates the weldability at the construction site, for example, there are low-temperature cracks after welding, and therefore the upper limit of the content is set at 0.10%. For additional increase in viscosity at low temperatures, it is preferable to set upper limit content to 0.07%. In addition, to increase the tensile strength, it is preferable to regulate the content until the value of not less than 0.03%. On the other hand, if the tensile strength is too large, it may affect the shape of the donkey expanding, this may decrease the roundness, so it is preferable to regulate the content until the value of less than 0.05%. In this case, the roundness parameter is obtained by measuring the diameter of the steel pipe in several parts, for example, by measuring the diameter passing through the center of the steel pipe, in four parts, not including the welded seam, every 45 degrees, calculating the average value, subtracting the minimum diameter of the maximum diameter and the subsequent dividing the difference by the average value.

Si performs the function of deoxidation and creates the effect of increasing the tensile strength. However, excessive addition of Si toughness in the heat-affected zone of the weld and the welding at the construction site is markedly reduced, and therefore the upper limit of the content of Si is set equal to 0.8%. The preferred limit on the amount of Si is 0.6%. In this case, since Al and Ti, and Si also performs the function of deoxidation in steel, corresponding to this invention, it is preferable to regulate the content of Si in accordance with the contents of Al and Ti. The lower limit of the Si content does not indicate specifically, but in General the content of Si as an impurity in the steel is not less than 0.01%.

Manganese (MT) is a mandatory element for receiving mi is restructure steel corresponding to this invention and consisting of the dominant patterns of bainite and martensite, as well as to ensure an acceptable balance between tensile strength and ductility at low temperatures, resulting in lower limit of the content of Mn is set equal to 1.5%. On the other hand, excessive addition of Mn, not only increases proclaimest and reduced viscosity in the heat-affected zone of the weld and the welding at the construction site, but also accelerated segregation in the centre and decreases the viscosity of the steel material at low temperatures. For these reasons, the upper limit of the content of Mn is set equal to 2.5%. In this case, the term "segregation center" means a state in which the segregation of the resulting components due to hardening in the vicinity of the center of the casting during the casting process, does not disappear even after the subsequent processes and stored in the vicinity of the center of thickness of the steel sheet.

Phosphorus and sulfur (R and S) are impurity elements inevitably included in the steel. Phosphorus (P) accelerates segregation in the centre and at the same time increases the viscosity at low temperatures due to irregular fracture. Sulfur (S) reduces the ductility and toughness due to the effect of the compounds of MnS, which continues to remain in the steel during the mountains the whose rolling. Therefore, in this invention the upper limits of the content of P and the content of S is set equal respectively 0,015%, and 0.003% for an additional increase in viscosity at low temperatures. Note that R and S are impurities, and the lower limits of their content when modern technologies are about 0,003%, and 0.0001%. In addition, it is possible to suppress deposition of such a sulfide, as MnS in the steel due to the limitations of the content's value is not more than 0.001%. For this reason, it is preferable to limit the content's value is not more than 0.001%in order to prevent the decrease in ductility and toughness.

Compared with Mn, Cr or Mo Nickel (Ni) is able to reduce harmful for viscosity at low temperatures the formation of hardened structures in the area of segregation in the centre, created during hot rolling. Ni is also effective for increasing the viscosity of the heat-affected zone of the weld. Since this effect is negligible when the content of Ni, amounting to less than 0.01%, the lower limit of this content and set equal to 0.01%. In addition, for increasing the viscosity of the heat-affected zone of the weld is preferable to setting the lower limit of the Ni content of 0.3%. On the other hand, the excessive Ni content not only reduces economic efficiency due to the high cost of Ni, but also reduces the tsya viscosity in the heat-affected zone of the weld and the welding at the construction site, and therefore, the upper limit of the content of Ni is set equal to 2.0%. Note that the additive Ni also carried out for the purpose of preventing the occurrence of surface cracks caused by the presence of Cu, in continuous casting and hot rolling. When Ni adds to this end, the preferred is the addition of Ni, wherein the content is one third of the Cu content.

Molybdenum (Mo) is added to increase proclaimest steel and receiving bainite, martensite or dominant patterns of bainite and martensite, providing an excellent balance between tensile strength and ductility at low temperatures. The above results become more significant with the addition of Mo in combination with the addition of boron (B). In addition, due to the combination of additives Mo and achieved the phenomenon of suppression of recrystallization of austenite during controlled rolling, as a result get austenitic structure with smaller grains. To obtain these results add Mo the lower limit of the Mo content set equal to 0.2% in the case of steel, which does not add In, and set mentioned lower limit is 0.1% in the case of steel, which adds Century. on the other hand, if you add Mo in excess of 0.8%, not only increase production costs, but also decrease the viscosity of the heat-affected zone of the weld W is a, and weldability at the construction site, regardless of the additive Century, Therefore, the upper limit of the Mo content set equal to 0.8%. In this case, the preferred upper limit of the Mo content is 0.6%.

Niobium (Nb) suppresses the recrystallization of austenite during controlled rolling, makes fine-grained austenitic structure due to the precipitation of carbonitride, and also contributing to the increase proclaimest. In particular, the effect of increasing proclaimest due to additives Nb synergy is further enhanced by the coexistence of the element boron (B). However, if Nb is added so that its content is not less than 0.01%, the partially formed large grains, resulting in a decrease in the percentage of samples that can withstand the impact test, and the reduction of viscosity in the heat-affected zone of the weld, when impose weld containing two or more layers. Moreover, in this case also decreases weldability at the construction site. For these reasons, the upper limit of the content of Nb is set at the level of less than 0.01%. The preferred content of Nb is less than 0,005%. In addition, in the steel containing no additive Ni is not required because the parameter P defined by the expression R=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+Mo-0,5, is in the range from 1.9 to 4.0, preferred is compulsory from 1.9 to 3.5, or the parameter P defined by the expression R=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+1,mo, is in the range from 2.5 to 4.0. However, the usual content of Nb in the steel as an impurity is not less than 0.001%.

Titanium (Ti) forms a fine nitride in the steel and prevents escalation (grains) of austenite during re-heating. In addition, in the steel containing the additive In, Ti reduces the amount of dissolved N, which is harmful to increase proclaimeth, by fixing N in the form of nitride, which provides an additional increase in proclaimest. In addition, when the Al content is not greater than 0.005%, Ti forms an oxide in the steel. The Ti oxide performs the functions of embryos product phase transformations inside the grains in the heat-affected zone of the weld and so does structure influence zone of the weld is fine. To guarantee the above-mentioned result of adding Ti, it is preferable to setting the lower limit of the Ti content of 0.001%. Additionally, for stable reception of effects that are due to the formation of nitride and fixation of dissolved N, it is preferable to regulate the lower limit of the Ti content at a level of not less than increased 3.4 times the content of N. on the other hand, if the additional amount of Ti is excessive, the nitride being consolidated, formed Melk the granular carbide, occurs hardening by precipitation, and therefore the toughness in the heat-affected zone of the weld is reduced. In addition, in this case, as in the case of adding Nb to achieve content of not less than 0.01%, partially formed of large grains, and therefore there is a reduction in the viscosity at low temperatures. For these reasons, the upper limit of the content of Ti is set equal to 0,030%.

Aluminum, Al add in steel as a deoxidizer, and it also performs the function of reducing grain patterns. However, if the Al content exceeds 0.1%, increase of non-metallic inclusion system of aluminum oxide, and therefore decreases the purity of steel, and the viscosity in the steel material and the heat-affected zone of the weld. For these reasons, the upper limit of the content of Al is set to 0.07%, and the optimum Al content is not more than 0,06%. In addition, since Si and Ti have the same function deoxidation, and Al in the steel according to the invention, it is preferable to regulate the content of Al with regard to the content of Si and Ti.

The lower limit of the content of Ti is not set specifically, but the Al content is usually not less than 0,005%.

Nitrogen (N), when it is added, bringing its content to a number greater than 0,008%, contributes to the formation of surface defects in the casting and cause a decrease in viscosity in the zone of thermal influence the Oia of the weld due to dissolved N and niobium nitride. Therefore, the upper limit of the content of N is set equal 0,008%. The preferred upper limit of the N content is 0,006%. The lower limit of the N content of don't ask specifically, but the N content as an impurity is typically about 0.003 per cent.

The steel according to the present invention contains the components, the explanation of the above as the main component. In addition, to ensure an additional increase of tensile strength and viscosity and expanding the range of materials they can add one or more elements such as b, V, Cu, Cr, CA, rare earth metal (REM) and Mg, the content of which is specified below.

Boron (B) is an element effective for increasing proclaimest steel by adding a slight amount, and upon receipt of the dominant patterns of bainite and/or martensite, which is one of the objectives of the present invention. In addition, enhances the effect of Mo with increasing proclaimest steel in accordance with this invention, as well as synergy accelerates the effect of increasing proclaimest due to the coexistence and Nb. These effects are not guaranteed when the content is less than 0,0003%. Therefore, the lower limit of the content is set equal 0,0003%. On the other hand, excessive addition is not only accelerates the formation of groupcentered, for example, Fe3(C, b)6and because of this reduced viscosity at low temperatures, but also reduces the impact on the increase of proclaimest. Therefore, the upper limit of the content is set equal 0,0030%.

Vanadium (V) performs almost the same function as Nb. While some additive V the effect of V is weaker than the influence of Nb, the coexistence of V with Nb enhances the effects of increasing viscosity at low temperatures and viscosity in the heat-affected zone of the weld. Because these effects are minor, when the V content is less than about 0.001%, it is preferable to setting the lower limit of the content of 0.001%. On the other hand, if the amount of added V exceeds 0.3%, the viscosity of the heat-affected zone of the weld, in particular the toughness in the heat-affected zone of the weld in the case of overlapping weld containing two or more layers, is reduced, the formation of large grains, due to the anomalous phase ferrite-austenite transformation during heating during hot rolling, and therefore decreases the viscosity at low temperatures, and also deteriorates the weldability at the construction site. For these reasons, it is preferable to set upper limit of the content of V is equal to 0.3%. Also preferred upper limit of the content of V is 0.1%.

Copper and HRO is (Cu and Cr) are elements, which increase the tensile strength in the base steel and in the heat-affected zone of the weld, so the content necessary to achieve the above effects, respectively, shall be not less than 0.01%. On the other hand, if the content of Cu or Cr is excessive, the toughness in the heat-affected zone of the weld and the welding at the construction site is much worse. Therefore, each of the upper limits of the contents of Cu and Cr set equal to 1.0%.

Calcium (CA) and rare earth metal (REM) regulate the form of a sulfide such as MnS in the steel and increase the toughness of this steel at low temperatures. It is preferable to set each of the lower limits of the content of CA and REM equal to 0.0001%. On the other hand, if the additive Sa exceeds 0.01% or additive REM exceed 0.02%, in large quantities is formed CaO-CaS or REM-CaS, which leads to the formation of large clusters and large inclusions, resulting in a reduction of cleanliness of the steel and deterioration of weldability at the construction site. For these reasons, it is preferable to set upper limits of the content of CA and REM respectively equal to 0.01%and 0.02%. In addition, the preferred upper limit of the content of CA is 0,006 %.

In addition, when necessary tensile strength not less than 950 MPa, prefer inim is additional regulation of sulfur content S and oxygen, in steel to achieve values of 0.001%and 0.002 per cent respectively. In addition, it is preferable to regulate the value of the ESSP, which is an indicator associated with the regulation of the form of mixtures of the system sulphides (ESSP is determined by the expression ESSP=(Sa)[1-124(O)]/(1,25S) and is in the range from 0.5 to 10.0).

Magnesium (Mg) performs the function of forming fine oxide suppressing enlargement of austenite grains in the heat-affected zone of the weld and therefore increases the viscosity at low temperatures. To ensure these effects, the lower limit of the content of Mg is set equal to 0.0001%. On the other hand, if the Mg content exceeds 0,006%, a coarse-grained oxide, resulting in the viscosity at low temperatures is reduced. Therefore, the upper limit of the content of Mg is set equal to 0,006%.

In addition to the restrictions placed on the content of each of the added elements, the present invention provides for the regulation parameter P, which is a measure of proclaimeth, within a suitable range to obtain an excellent balance between tensile strength and ductility at low temperatures. The parameter P determines differently in accordance with the presence of boron (B) in steel: the parameter P is determined by the expression P=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+Mo-0.5 V was the Sabbath., not containing, in the steel containing, the parameter P is determined by the expression R=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+1,mo. When the parameter P is less than 1.9 in the steel without additives or less than 2.5 in steel In addition, the ultimate tensile strength of at least 800 MPa, it is impossible, so these values are taken as lower limits in the respective steels. On the other hand, when the parameter P exceed 4.0 in any of the just mentioned steels, deteriorate the toughness in the heat-affected zone of the weld and the welding at the construction site, so this value is adopted as the upper limit in any of these steels. In addition, it is preferable to define the upper limit of the parameter P is equal to 3.5 in steel without the addition of boron. In conclusion, it should be noted that an adequate range of the parameter P is defined as follows: from 1.9 to 3.5 in steel without additives and from 2.5 to 4.0 in steel with the addition of Century

Below is an explanation of the microstructure.

To achieve high tensile strength not lower than 800 MPa, if we talk about the ultimate tensile strength, and guarantee acceptable viscosity at low temperatures it is necessary to adjust the relative amount of bainite, martensite or dominant patterns of bainite and martensite in the range from 90 to 100 %, if we talk about the proportion of bainite the martensite. Note that the remainder is preserved austenite, but it is difficult to detect using an optical microscope. In this case, the fact that the share of bainite and martensite is in the range from 90 to 100%, will be determined following two conditions. First, (1) through micrograph obtained using an optical microscope micrograph obtained by scanning electron microscope, or a micrograph obtained with a transmission electron microscope confirmed by the fact that it is not formed of polygonal ferrite; secondly, (2) determining the percentage of bainite and martensite, as being in the range from 90 to 100% is carried out in accordance with hardness: to calculate the hardness to 100%martensite at the base of the number To use the expression Hv=270+1000C, where C is the number of carbon, expressed wt.% percent; when the hardness of the steel material is in the range from 70 to 100%determine that the share of bainite and martensite for the steel material is in the range from 90 to 100%.

In addition, when the share of bainite and martensite is in the range from 90 to 100%, ultimate tensile strength and quantity To satisfy the following expression: 0,7×(3,720P+869)<CPD, where CPD is the ultimate tensile strength (expressed in MPa) obtained steel, and carbon (expr the TES wt.%).

To obtain excellent viscosity at low temperatures in the direction of the cross section in the case of steel pipes used, for example, as a pipe of a pipe, it is necessary to optimize the phase of austenite before this phase of the austenite will transform to ferrite phase or in what is called the initial phase of austenite during cooling, and it is necessary to make the structure of the steel material, essentially fine. For this reason you want the original austenite consisted of precrystallization austenite, and that the average diameter of the grains was limited to the amount not exceeding 10 μm. This gives an exceptionally good balance between tensile strength and ductility at low temperatures. In this case, the term "diameter of the original austenitic grain" means the diameter of grains, including strip deformation and twin boundary, which perform the same function as the boundary of the austenite grains. The diameter of the original austenite grains determine, for example, in accordance with APS JI (JPS G) 0551, dividing the full length of the straight line drawn in the direction of thickness of the steel sheet, on the number of points where the straight line intersects with the grain boundaries of the original austenite present on a straight line as determined by the micrograph obtained using an optical microscope. Bottom is th limit of the average diameter of the initial austenite grains is not specifically ask, and find the lower limit is about 1 μm in accordance with the test conducted on the micrograph obtained using an optical microscope. In this case, the preferable range of the diameter of the original austenite grains is from 3 to 5 microns.

When receiving a high-strength steel with excellent toughness at low temperatures, it is desirable to hot rolling under conditions described below. The temperature re-heating define so that she was in the temperature range in which the structure of the casting, consists essentially of a single phase of austenite; in particular, as the lower temperature limit re-heating take the temperature AU3. When the temperature re-heating exceeds 1300°C, the crystal grains become larger, and therefore it is preferable to limit the temperature re-heating value of not more than 1300°C. with regard to rolling after re-heating, it is preferable to conduct, first, rolling with recrystallization, and secondly, conducting rolling without recrystallization. Note that, although the recrystallization temperature is changed in accordance with components of the steel, it is in the range from 900°With temperatures of re-heating, and therefore, the preferred is the temperature range during rolling with recrystallization is from 900° With up to 1300°and the preferred temperature range during rolling without recrystallization is from 750°880°C. After that, apply cooling with a cooling rate of not less than 1°C/sec up to some arbitrary temperature not exceeding 550°C. the Upper limit of the cooling rate is not set specifically, but the preferred range is from 10 to 40°C/sec. The lower limit of the end temperature of the cooling too, don't ask specifically, but the preferred range is from 200°With up to 450°C.

Conducting hot rolling under such conditions as those described above and determine the components of the steel, heating and cooling, you can get very high-strength steel with excellent toughness at low temperatures. In addition, by forming in the cold pipe of the hot-rolled steel sheet with the subsequent imposition of a weld containing two or more layers in abutting portion, it is possible to make very high-strength steel pipe with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of the weld. That is, this invention makes it possible to mitigate the conditions of welding in the manufacture of steel pipe having a thickness of the sheet, causing the need for overlay weld containing two and more layers. When the overlapping longitudinal seam preferred is the use of arc welding, including arc welding submerged arc welding.

The sizes of high-strength steel pipe that is used as a pipeline pipe, in accordance with the present invention typically comprise about 450-1500 mm in diameter and about 10-40 mm wall thickness. As for the method of manufacturing a steel pipe of such size, it should be noted that this manufacturing method essentially involves the operation, which made the pipe during UO operations, when the steel sheet is first attached U-shaped, and then O-shaped, impose tack welds on the abutting portion, followed by arc welding submerged arc welding with inner and outer sides, and then provide roundness by expanding the pipe.

Arc welding submerged arc welding is a welding during which the dilution of the weld metal core steel is great. Therefore, to regulate the chemical components of the weld metal in the range where obtained the desired properties, it is necessary to choose the material of the weld reasons dilution of primary steel. As an example, note that welding can be performed with ispolzovanii.ochen wire containing Fe as a main component, from 0.01 to 0.12% of C, not the m ore than 0.3% of Si, 1.2 to 2.4% of Mn, 4.0 to 8.5% of Ni and 3.0-5.0% of Cr+Mo+V and the flux glomerulosa type or fused type.

The dilution ratio is the main steel varies depending on the welding conditions, in particular heat input for welding, but in the General case, the dilution ratio is the main steel increases with increasing heat input. However, in low welding speed, the dilution ratio is the main steel does not increase even when increasing the applied heat. To ensure sufficient depth of penetration when applied welding in a single pass of a joined part (impose a single-layer weld bead on the abutting portion with its outer side and inner side, it is preferable to limit the heat input and welding speed the following ranges.

When heat input is less than 2.5 kJ/mm, decreases the depth of penetration, and on the other hand, when the heat input is more than 5 kJ/mm, softened heat-affected zone of the weld, and slightly decreases the viscosity of the heat-affected zone of the weld. Therefore, it is preferable to limit the heat input range from 2.5 to 5.0 kJ/mm

When the welding speed is less than 1 m/min, the committed work of several welding insufficient for applying longitudinal weld is and pipeline pipe, and, on the other hand, when the welding speed exceeds 3 m/min, it is difficult to stabilize the shape of the roller. Therefore, it is preferable to limiting welding speed range from 1 to 3 m/min

Roundness can be increased by applying the flare pipe after imposition of the longitudinal weld. It is preferable to set the degree of flaring of the pipe at the level not less than 0.7% to increase its roundness through the implementation of plastic deformation. On the other hand, if the degree of flaring of the pipe exceeds 2%, the viscosity as in the base steel and the weld is somewhat reduced, which is caused by plastic deformation. For these reasons, it is preferable to determine the degree of flaring of the pipe in the range from 0.7 to 2%. In this case, the degree of flaring of the pipe is determined by the value obtained by subtracting the length of the circle after expanding the tube from the circumference before the flare pipe and expressions have values in percent.

After overlapping longitudinal seam, when the longitudinal weld seam is heated to a temperature of at least 300°before the flare pipe and/or after such expanding, solid mixture of martensite and austenite (denoted hereinafter by the symbol "MA"), formed in the heat-affected zone of the weld, can decompose to the dominant structure bainite and March the sieve and fine-grain carbide cementite, resulting in increased viscosity in the heat-affected zone of the weld. On the other hand, if the temperature of the heating exceeds 500°With, there is a softening of the core steel. For these reasons, it is preferable to limit the temperature range from 300°500°C. Although the influence of time is small, the time (heating) is preferably from about 30 seconds to 60 minutes. Its preferred range is from about 30 seconds to 50 minutes. In addition, when using the heat after expanding pipes, technological deformation, leading to the edge of the outer surface of the weld is restored, whereupon the viscosity of the heat-affected zone of the weld is increased.

When the test sample is cut out from the heat-affected zone of the weld, mirror polished and poisoned, and then consider using a scanning electron microscope, it becomes evident that the structure of MA formed in the heat-affected zone of the weld, is composed entirely of white solid substance. When the structure of the MA is heated to 300-500°C, it decomposes into the dominant structure bainite and martensite with small precipitates in the grains and cementite, which can be distinguished from MA. In addition, when the test sample is etched with OSU reflector particles or etching nitrogen compounds after mirror polishing and also consider using a scanning electron microscope, it is possible to distinguish patterns MA from the other patterns MA, decayed to the dominant structure bainite and martensite and cementite, and it can be done by identifying the presence or absence of small precipitates in the grains.

In this case, when heat welded longitudinal seam, it is preferable to bring the heat to the weld metal and heat-affected zone of the weld, available in basic steel. The heat-affected zone of the weld is the area within about 3 mm from the intersection of weld metal and base steel, so it is preferable to heat at least the area that includes basic steel within 3 mm from the intersection of weld metal and base steel. However, heating a narrow zone fraught with technical difficulties, so the more real is the application of heat treatment to the area within approximately 50 mm from the intersection of weld metal and base steel. In this case, there occurs such an inconvenience, as the deterioration of the properties of the main steel caused by heating to a temperature in the range from 300°500°C. For heating the longitudinal weld, you can use a gas burner of radiant type or induction heater.

As explained above, the present invention provides the ability to get very high-strength steel is sheet, having ultimate tensile strength of not less than 800 MPA, and also gives the possibility to manufacture steel pipe of the steel sheet, which also has excellent toughness in the heat-affected zone of the weld, when the sheet lay a weld bead comprising two or more layers, and has the energy absorbed during the impact test on Charpy main steel in the temperature range of not more than -40°With, on average, not less than 200 j, and a small variance, and the steel sheet has excellent toughness at low temperatures, and in addition, this steel sheet has excellent weldability on the construction site. By the way, it becomes possible to use the mentioned steel sheet for manufacturing a pipe pipe and said steel pipe as pipe pipe designed for the transportation of natural gas or crude oil, and to provide pumping water, manufacturing of pressure vessel, welded, etc. and in all cases we are talking about the use in harsh environmental conditions.

Example 1

Steel chemical compositions are given in tables 1 and 2 (table 2 is a continuation of table 1), was melted and subjected to continuous casting castings of the thickness of 240 mm is Perceived by the major re-casting was heated to a temperature of 1100° With, and then subjected to rolling in the temperature range recrystallization from 900°1100°and then subjected to rolling in the temperature range of the absence of recrystallization, ranging from 750°880°S, and then cooled with a cooling rate of 5-50°C/sec to a temperature not exceeding 420°C by cooling with water was obtained steel sheets of a thickness of 10-20 mm

The average diameter of the initial austenite grains was obtained by the method of line segments of intersection of the straight line in the direction of thickness in accordance with APS g 0551. The proportion of bainite and martensite were obtained using the following procedures. Started with the fact that by examining patterns in the micrograph obtained using an optical microscope in accordance with APS g 0551, confirmed the fact that it is not formed of polygonal ferrite. Then measured the hardness according to Vickers, applying the load through a load of 1 kg, and determine the measured value as HvVMin accordance with APS z 2244. Received denoted by the symbol αVMthe relation HvVMto hardness of 100%martensite, calculated by using the expression Hv=270+1300C, namely αVM=Hvbm/Hv. Then, using the definition of the share of bainite and martensite as a component of 90% if αVM=0.7 and 100% if αVM=1, Vici the Lyali share bainite and martensite by using the expression F VM=100×(1/3×αVM+2/3).

Yield strength and ultimate tensile strength in the rolling direction of the steel sheet (hereinafter referred to as "direction L and in the direction (hereinafter referred to as "direction")perpendicular to the rolling direction, were evaluated using tensile tests over the entire thickness in accordance with the methodology ANI. Impact test on Charpy conducted at a temperature of -40°at a frequency of n repeated trials of the three, in accordance with APS z 2242, using the samples with a V-shaped notch having a standard size, length, oriented in the directions of L and C, prepared in accordance with APS z 2202. The energy absorbed during the impact test on Charpy, was estimated as the average of the values obtained by three repeated measurements. In addition, spent another impact test on Charpy temperature range from -60°With temperatures of below -40°With a frequency of n repeated trials, adjustable from 3 to 10, and assessed expressed as a percentage probability that the energy absorbed during the impact test on Charpy, will be not less than 200 j (this probability is below referred to as "reliability evaluation of viscosity at low temperatures").

The toughness in the heat-affected zone of the weld was evaluated by subjecting the sample to heat treatments, according to stoysin double overlay weld with providing heat input of 2.5 kJ/mm during each overlay weld using setup to playback cycle heat weld. That is, the first heat treatment of the sample was carried out in the conditions under which the sample was heated at a rate of 100°C/sec to a temperature of 1400°C, kept at this temperature for one second, and then cooled with a speed of 15°C/s, giving a temperature range from 500°800°and in addition carried out a second heat treatment of the sample under conditions in which the temperature of the heating was set equal to 1400°or 900°and has complied with the conditions of the cooling rate, holding time, cooling temperature and cooling rate, identical to the corresponding conditions of the first heat treatment. In addition, prepared the standard size of the samples with a V-shaped incision in accordance with APS z 2202 and subjected the samples to the impact test on Charpy at a temperature of -30°at a frequency of n repetitions of the three, in accordance with APS z 2242, and the energy absorbed during the impact test on Charpy, was estimated as the average of the values obtained by three repeated measurements.

The results are shown in table 3. Steel a-E is steel, which contain the components within the ranges specified in this invention and provide target levels of tensile strength, viscosity at low rate is Torah and viscosity in the heat-affected zone of the weld. On the other hand, the amount of carbon (C) in steel F and the number of Mn in steel I is less than the corresponding number in the ranges specified in this invention, so that the tensile strength is low. Quantity in steel With G, the amount of Si in the steel H, the number of Mn in steel J and the amount of Mo in the steel To more than the corresponding number in the ranges specified in this invention, resulting in decreased viscosity at low temperatures, the reliability of the estimate of the viscosity at low temperatures and toughness in the heat-affected zone of the weld. The amount of Nb in steel L larger than the corresponding number in the range specified in this invention, therefore, although the energy absorbed during the impact test on Charpy at -40°was acceptable, while decreased the reliability of the estimate of the viscosity at low temperatures and toughness in the heat-affected zone of the weld. The amount of Nb in the steel Yards more than in steel L, resulting in decreased viscosity at low temperatures, the reliability of the estimate of the viscosity at low temperatures and toughness in the heat-affected zone of the weld. The amount of Ti, the quantity V, number nitrogen, N, and the number of S in steel N, O, P and R, respectively, more than in the ranges specified in this invention, resulting in reduced what were the viscosity at low temperatures, the reliability of the estimate of the viscosity at low temperatures and toughness in the heat-affected zone of the weld. The amount of Al in steel Q larger than the corresponding number in the range specified in this invention, resulting in decreased viscosity in the heat-affected zone of the weld.

Table 1

Chemical components (mass%), Ceq and Pcm material steel
SteelChemical elements (wt.%)
SiMnPSNiMoNbTiAlN
And0,030,101,950,0050,00050,500,300,0050,0080,0150,0023
In0,050,251,850,0080,00060,900,450,0070,0050,0200,0015
0,040,151,900,0030,00082,000,200,0090,010 0,0030
D0,060,251,900,0040,00031,800,400,0030,0090,0100,0025
E0,050,101,960,0040,00101,000,100,0090,0050,0200,0015
F0,010,251,850,0050,00101,200,350,0040,0110,0150,0032
G0,150,151,950,0070,00060,600,260,0070,0110,0120,0033
N0,071,002,120,0090,00180,300,480,0090,0110,0230,0032
I0,040,261,000,0100,00260,500,520,0020,0090,0150,0025
J0,050,35 3,000,0060,00030,320,420,0010,0050,0260,0016
To0,090,482,050,0080,00050,851,000,0050,0100,0230,0030
L0,040,551,980,0090,00160,130,260,0500,0100,0150,0028
M0,040,551,960,0090,00160,130,260,1500,0100,0150,0028
N0,030,491,910,0050,00060,450,320,0030,0350,0100,0016
00,070,152,000,0060,00070,500,230,0020,0120,0300,0035
P0,080,052,160,0070,00090,160,51 0,0050,0150,0260,0080
Q0,050,161,790,0090,00050,650,450,0060,012to 0.0600,0035
R0,040,201,950,0070,00400,800,300,0080,0100,0010,0030

A dash in the cell chemical component means that the amount does not exceed the detection limit.

Ceq=C/+Mn/6+(Ni+Cu)/5+(Mo+V+Cr)/5.

Pcm=C+Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10+In+S.

Setting P=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+Mo-0.5 (steel, not containing).

Setting P=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+1,mA (in steel containing C).

Table 2

(continuation of Table 1)
Chemical elements (wt.%)The parameter PCeqPcm
inVCuCrCARSIMg
0,00100,0800,300,30---3,240,5400,200
--0,500,600,0012-0,00103,15to 0.6620,251
0,00230,040---0,0008-3,350,5380,202
-0,0500,300,30---3,350,6670,255
0,0010--0,60---3,220,5830,210
0,00100,0300,300,30--0,00053,480,5540,192
0,0008-0,230,50---to 3.580,6820,320
-0,0400,160,50-0,0008-3,380,6580,283
0,00080,0300,650,32---2,830,4570,00150,0260,260,450,002--4,580,7680,291
0,0016-0,320,26---4,720,7620,326
0,00130,0500,150,52---3,320,5510,221
0,00130,0500,150,52---3,320,5510,221
0,00100,0300,510,230,0023-is 0.00023,340,5280,215
-0,1500,300,42---2,980,6170,250
0,00260,0400,230,26-0,0005-3,820,6280,268
0,0023-0,320,590,0021-- 3,570,6210,243
0,00080,0500,300,30---3,420,5680,217

Example 2

Steel sheets of a thickness of 10-20 mm, containing chemical components of steels a-E, are shown in tables 1 and 2, was obtained in the same conditions as in example 1. Thereafter, the steel sheets were subjected to molding in a cold condition, and then arc welding submerged arc welding with the interconnection heat of 2.0 to 3.0 kJ/mm on each of inner surfaces and heat input of 2.0 to 3.0 kJ/mm on each of the outer surfaces with subsequent expansion of the pipe, while receiving a steel tube with an outer diameter 700-920 mm. Average diameter of the initial austenite grains, and the proportion of bainite and martensite in the core steel for each of the steel pipe was obtained in the same way as in example 1. Next was assessed properties tensile strength using a tensile tests over the entire thickness in accordance with the methodology ANI. The viscosity at low temperatures was evaluated as in example 1, the average value of energy absorbed during the impact test on Charpy and reliability of estimation of the viscosity at low temperatures was achieved by preparing the test sample for testing is to strike the Arpi thus, the length of this sample was located in the direction C. the Viscosity of the heat-affected zone of the weld was evaluated by exposing the test sample having a V-shaped cut in the intersection or in part, located at a distance of 1 mm from the intersection, another impact test on Charpy at a temperature of -30°C.

The results are shown in table 4. In any of the steels tensile strength tensile base steel is not less than 800 MPa, the viscosity of the base steel is exceptionally good; the energy absorbed during the impact test on Charpy at -40°is not less than 200 j, and the reliability of the estimate of the viscosity at low temperatures is not less than 85%. As for the heat-affected zone of the weld, then the energy absorbed during the impact test on Charpy at a temperature of -30°is not less than 100 j, and toughness in the heat-affected zone of the weld is also excellent.

Example 3

Casting of steel containing the chemical components of the steel As shown in tables 1 and 2, obtained by the method similar to that described in example 1, and after this was carried out by hot rolling the casting in the conditions shown in table 5, and cooled, thus obtaining a steel sheet thickness of 10 and 20 mm, the Average diameter of the initial austenite grains, as well as the share of bainite and martensite was obtained in the same way, as in example 1, and evaluated the properties tensile strength using a tensile tests over the entire thickness in accordance with the methodology ANI. The viscosity at low temperatures was evaluated as in example 1, the average value of energy absorbed during the impact test on Charpy and reliability of estimation of the viscosity at low temperatures was achieved by preparing the test sample for impact test on Charpy so that the length of this sample was located in the direction C. the Viscosity of the heat-affected zone of the weld was evaluated by exposing the test sample to tensile tests throughout the thickness, and then the impact test on Charpy at a temperature of -30°C.

The results are shown in table 6. In any of the steels tensile strength tensile base steel is not less than 800 MPa, and with regard to the viscosity of the base steel, characterizing its energy absorbed during the impact test on Charpy at -40°is not less than 200 j, and the reliability of the estimate of the viscosity at low temperatures is not less than 85%; as for the heat-affected zone of the weld, characterizing its energy absorbed during the impact test on Charpy at a temperature of -30°is not less than 100 j, and therefore, the high-strength steel sheet with excellent viscosity in the zones of the heat-affected weld. In addition, steel with specifications 27 and 28 obtained under conditions corresponding to the ranges specified in item 6 of the claims are even more convincing reliability assessment viscosity at low temperatures than steel with specifications 24 and 26 obtained under conditions different from those specified in item 6 of the claims.

Example 4

Steel chemical compositions are shown in table 7, were produced and subjected to continuous casting to obtain castings. The resulting casting was re-heated to a temperature of 1100°C, and then subjected to rolling in the temperature range recrystallization from 900 to 1100°and then subjected to rolling with the degree of compression equal to 5, in the temperature range of the absence of recrystallization, ranging from 750 to 880°S, and then cooled with a cooling rate of 5-50°C/sec to a temperature not exceeding 420°C by cooling with water was obtained steel sheets of a thickness of 16 mm, an Average diameter of the original austenitic grains was obtained by the method of line segments of intersection of the straight line in the direction of thickness in accordance with APS g 0551.

Yield strength and ultimate tensile strength in the direction of the steel sheet was evaluated by means of testing the tensile stresses across the thickness in accordance with the method of ANI. The energy absorbed during the impact test on Charpy, evaluating, conducting the impact test on Charpy at -40°and at a frequency of n repeated trials of the three, in accordance with APS z 2242 using samples with a V-shaped notch having a standard size, while the length of the prepared samples in the direction consistent with the requirements APS z 2202. The toughness in the heat-affected zone of the weld was evaluated as in example 1. In addition, for the simulation of thermal cycle heat-affected zone (HAZ), the samples were subjected to heat treatment twice, and then was heated to 350°and was kept for five minutes at this temperature.

Then calculate the value of TS/0,7(3720C+869), based on the magnitude limit of the tensile strength and the amount of carbon (C). When the share of bainite and martensite is in the range from 90 to 100%, satisfied the following expression:

TS/0,7(3720C 869)>0,7,

where TS is the tensile strength (expressed in MPa) tensile steel, and With (in wt.%) - the amount of carbon.

In table 8 steel AA-AF, an, FJ, AK and AR-AR is steel, which contain the components within the ranges specified in this invention, and have target levels of tensile strength, viscosity at low temperatures and viscosity in the heat-affected zone of the weld. On the other hand, to the number of carbon (C) in steel AG more than the corresponding number in the range specified in this invention, resulting in decreased viscosity at low temperatures in the core steel and the toughness in the heat-affected zone of the weld. In addition, the number of Mn in steel Al less than the corresponding number in the range specified in this invention, the resulting microstructure is not from the dominant patterns of bainite and martensite, and the tensile strength and toughness at low temperatures is reduced. The number of Nb steels, Al and AM, and the amount of Ti in the steel'AN more than the corresponding number in the ranges specified in this application, resulting in partially form large crystal grains, in some subjects the samples decreases the energy absorbed during the impact test on Charpy, and decreases the viscosity of the heat-affected zone of the weld. Steel JSC has the content of R is less than the corresponding content in the range specified in this invention, resulting in decreased tensile strength tensile.

Example 5

Steel sheets containing the chemical components of the steel AA-AE, are shown in table 7 was obtained in the same conditions as in example 4, and then the steel sheets were subjected to molding with the teachings of the pipes on the operations UO and were subjected to arc welding submerged arc welding with heat input of 2.0 to 3.0 kJ/mm on each of the inner surfaces and the heat input of 2.0 to 3.0 kJ/mm on each of the outer surfaces. Then some of the steel pipe was heated to a temperature of 350°C and kept at this temperature for 5 minutes, and then cooled to room temperature and held the tube expanders, and some of the steel pipes were subjected to tube expanders without heating the welded longitudinal seams.

For the study of the mechanical properties of the basic steel these steel pipes as in example 4, were tested in tension across the thickness in accordance with the methodology ANI and impact test on Charpy at -40°using the samples, the length of which was oriented in the direction C. the Energy absorbed during the impact test on Charpy, was obtained by measuring its frequency n of repetition is equal to three, and finding the average value of three measured values. Then got the toughness in the heat-affected zone of the weld, exposing the test sample having a V-shaped cut in the intersection or in part, located at a distance of 1 mm from the intersection, another impact test on Charpy at a temperature of -30°and finding the average value of the three obtained values.

The results are shown in table 9. In this table under the heading "After welding in the column Toughness in the heat-affected zone of the weld" displayed the toughness in the heat-affected zone of the weld steel pipe subjected to the expanding t the UBA without heating of the weld, and under the heading "After heat treatment" shows the viscosity in the heat-affected zone of the weld steel pipe subjected to the flare pipe after heating of the weld by means of induction heating. In any of the steels AA-AE tensile strength tensile base steel is not less than 900 MPa; with regard to the viscosity of the base steel, characterizing its energy absorbed during the impact test on Charpy at -40°is not less than 200 j, and as the viscosity of the heat-affected zone of the weld, characterizing its energy absorbed during the impact test on Charpy at a temperature of -30°is not less than 100 j. Thus, the high-strength steel pipe with excellent toughness at low temperatures in the primary steel and excellent toughness in the heat-affected zone of the weld.

1. High-strength steel with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of a weld containing carbon, silicon, manganese, phosphorus, sulfur, Nickel, molybdenum, niobium, titanium, aluminum, nitrogen, and iron, characterized in that it contains components in the following ratio, wt.%:

CarbonSiliconnot more than 0.6
Manganese1.5 to 2.5
Phosphorusless than 0.015
Sulfurno more than 0,003
Nickel0,01-2,0
Molybdenum0,2-0,6
Niobiumless 0,010
Titaniumno more than 0,030
Aluminumno more 0,070
Nitrogenno more 0,0060
Iron and inevitable impuritiesRest

in this case the parameter P is in the range from 1.9 to 3.5, and is determined by the following expression:

P=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+Mo-0,5,

and the microstructure of the steel consists mainly of martensite and bainite.

2. High-strength steel according to claim 1, characterized in that it further comprises, in wt.%, one or more items, such as:

Vanadium0,001-0,10
Copper0,01-1,0
Chrome0,01-1,0
Calciumof 0.0001 to 0.01
Rare earth metal (REM)of 0.0001 to 0.02
Magnesium0,0001-0,006.

3. High-strength steel according to claim 1, characterized those who, the average diameter of the initial austenite grains in the microstructure of the steel does not exceed 10 microns.

4. High-strength steel with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of a weld containing carbon, silicon, manganese, phosphorus, sulfur, Nickel, molybdenum, niobium, titanium, boron, aluminum, nitrogen and iron, characterized in that it contains components in the following ratio, wt.%:

Carbonfrom 0.02 to less than 0.05
Siliconnot more than 0.6
Manganese1.5 to 2.5
Phosphorusless than 0.015
Sulfurno more than 0,003
Nickel0,01-2,0
Molybdenum0,1-0,6
Niobiumless 0,010
Titaniumno more than 0,030
Bor0,0003-0,0030
Aluminumno more 0,070
Nitrogenno more 0,0060 and satisfies the expression:
Ti-3,4N≥0,
Iron and inevitable impurities- rest

in this case the parameter P is in the range from 2.5 to 4.0 and is determined by the following expression is the group of:

P=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+1,5Mo, and the microstructure of the steel consists mainly of martensite and bainite.

5. High-strength steel according to claim 4, characterized in that it further comprises, in wt.%, one or more items, such as:

Vanadium0,001-0,10
Copper0,01-1,0
Chrome0,01-1,0
Calciumof 0.0001 to 0.01
Rare earth metal (REM)of 0.0001 to 0.02
Magnesium0,0001-0,006.

6. High-strength steel according to claim 1, characterized in that the average diameter of the initial austenite grains in the microstructure of the steel does not exceed 10 microns.

7. High-strength steel with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of a weld containing carbon, silicon, manganese, phosphorus, sulfur, Nickel, molybdenum, niobium, titanium, boron, aluminum, nitrogen and iron, characterized in that it contains components in the following ratio, wt.%:

Carbonfrom 0.02 to less than 0.05
Siliconnot more than 0.6
Manganese1.5 to 2.5
Phosphorusless than 0.015
not more than 0.001
Nickel0,01-2,0
Molybdenum0,1-0,6
Niobiumless 0,010
Titaniumno more than 0,030
Bor0,0003-0,0030
Aluminumno more 0,070
Nitrogenno more 0,0060 and satisfies the expression:
Ti-3,4N≥0,

and one or more elements such as:

Vanadium0,001-0,10
Copper0,01-1,0
Chrome0,01-1,0
Iron and inevitable impuritiesrest

in this case the parameter P is in the range from 2.5 to 4.0 and is determined by the following expression:

P=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+1,5Mo,

and the microstructure of the steel consists mainly of martensite and bainite, and the average diameter of the initial austenite grains in the microstructure of the steel does not exceed 10 microns.

8. High-strength steel with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of a weld containing carbon, silicon, manganese, phosphorus, sulfur, Nickel, molybdenum, niobium, titanium, boron, aluminum, AZ is t, and iron, characterized in that it contains components in the following ratio, wt.%:

Carbonfrom 0.02 to less than 0.05
Siliconnot more than 0.6
Manganese1.5 to 2.5
Phosphorusless than 0.015
Sulfurno more than 0,003
Nickel0,01-2,0
Molybdenum0,1-0,6
Niobiumless 0,010
Titaniumno more than 0,030
Bor0,0003-0,0030
Aluminumno more 0,070
nitrogenno more 0,0060 and satisfies the expression:
Ti-3,4N≥0,

and one or more elements such as:

Vanadium0,001-0,10
Copper0,01-1,0
Chrome0,01-1,0
Calciumof 0.0001 to 0.01
Iron and inevitable impuritiesThe rest,

in this case the parameter P is in the range from 2.5 to 4.0 and is determined by the following expression:

P=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+1,5Mo,

and microstruc the round steel consists mainly of martensite and bainite, moreover, the average diameter of the initial austenite grains in the microstructure of the steel does not exceed 10 microns.

9. A method of manufacturing a high strength steel plate with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of the weld, including the manufacture of the sheet from the casting of steel containing components in the ratio according to any one of claims 1, 2, 4, 5, 7, and 8, the re-casting is heated to a temperature not lower than the temperature AU3perform hot rolling, then cooling the obtained steel sheet with a cooling rate of not less than 1°C/s to a temperature of not more than 550°C.

10. A method of manufacturing a high strength steel sheet according to claim 9, wherein after cooling the steel sheet exercise its formation in cold condition for receiving the pipe.

11. High-strength steel pipe with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of the weld, characterized in that it contains costacabana part, obtained by blending a longitudinal weld, the steel main part of the tube contains components in the following ratio, wt.%:

Carbon0,02-0,1
Siliconno more than 0.8
Manganese1.5 to 2.5
Phosphorusless than 0.015
Sulfurno more than 0,003
Nickel0.01 to 2,
Molybdenum0,2-0,8
Niobiumless 0,010
Titaniumnot more than 0,03
Aluminumnot more than 0.1 and
Nitrogenno more than 0,008,
Iron and inevitable impuritiesrest

in this case the parameter P is in the range from 1.9 to 4.0 and is determined by the following expression:

P=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+Mo-0,5,

and the microstructure of the steel consists mainly of martensite and bainite.

12. High-strength steel pipe according to claim 11, characterized in that the steel main body of the pipe further comprises, in wt.%, one or more of elements such as:

Vanadium0,001-0,30
Copper0,01-1,0
Chrome0,01-1,0
Calciumof 0.0001 to 0.01
Rare earth metal (REM)of 0.0001-0.02
Magnesium0,0001-0,006.

13. High-strength steel pipe according to claim 11, characterized in that the average is the diameter of austenite grains in the microstructure of the steel does not exceed 10 microns.

14. High-strength steel pipe with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of the weld, characterized in that it contains costacabana part, obtained by blending a longitudinal weld, the steel main part of the tube contains components in the following ratio, wt.%:

Carbon0,02-0,10
Siliconno more than 0.8
Manganese1.5 to 2.5
Phosphorusless than 0.015
Sulfurno more than 0,003
Nickel0,01-2,0
Molybdenum0,1-0,8
Niobiumless 0,010
Titaniumno more than 0,030
Bor0,0003-0,003
Aluminumnot more than 0.1
Nitrogen not more than 0,008 and satisfies the expression:
Ti-3,4N≥0,
Iron and inevitable impurities -the rest,

in this case the parameter P is in the range from 2.5 to 4.0 and is determined by the following expression:

P=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+1,5Mo, and the microstructure of the steel consists in the main of martensite and bainite.

15. High-strength steel pipe according to claim 11, characterized in that the steel main body of the pipe further comprises, in wt.%, one or more of elements such as:

Vanadium0,001-0,30
Copper0,01-1,0
Chrome0,01-1,0
Calciumof 0.0001 to 0.01
Rare earth metal (REM)of 0.0001-0.02
Magnesium0,0001-0,006.

16. High-strength steel pipe according to claim 11, characterized in that the average diameter of austenite grains in the microstructure of the steel does not exceed 10 microns.

17. High-strength steel pipe with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of the weld, characterized in that it contains costacabana part, obtained by blending a longitudinal weld, the steel main part of the tube contains components in the following ratio, wt.%:

tr>
Carbon0.02 to less than 0.05
Siliconno more than 0.8
Manganese1.5 to 2.5
Phosphorusless than 0.015
Sulfurnot more than 0.001
Nickel0,01-2,0
Molybdenum0,2-0,8
Niobiumless 0,010
Titaniumno more than 0,030
Bor0,0003-0,003
Aluminumnot more than 0.1
Nitrogenno more 0,0080
and satisfies the expression: Ti-3,4N≥0,

and one or more elements such as:

Vanadium0,001-0,30
Copper0,01-1,0
Chrome0,01-1,0
Iron and inevitable impurities -the rest,

in this case the parameter P is in the range from 2.5 to 4.0 and is determined by the following expression:

P=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+1,5Mo,

and the microstructure of the steel consists mainly of martensite and bainite, and the average diameter of the initial austenite grains in the microstructure of the steel does not exceed 10 microns.

18. High-strength steel pipe with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of the weld, characterized in that it contains costacabana part, obtained by blending a longitudinal weld, when et is m steel main part of the tube contains components in the following ratio, wt.%:

Carbon0.02 to less than 0.05
Siliconno more than 0.8
Manganese1.5 to 2.5
Phosphorusless than 0.015
Sulfurno more than 0,003
Nickel0,01-2,0
Molybdenum0,1-0,8
Niobiumless 0,010
Titaniumno more than 0,030
Bor0,0003-0,003
Aluminumnot more than 0.1
nitrogenno more 0,0080
and satisfies the expression: Ti-3,4N≥0,

and one or more elements such as:

Vanadium0,001-0,30
Copper0,01-1,0
Chrome0,01-1,0
Calciumof 0.0001 to 0.01
Iron and inevitable impuritiesrest

in this case the parameter P is in the range from 2.5 to 4.0 and is determined by the following expression:

P=2,7C+0,4Si+Mn+0,8Cr+of 0.45(Ni+Cu)+2V+1,5Mo,

and the microstructure of the steel consists mainly of martensite and bainite, and average iameter initial austenite grains in the microstructure of the steel does not exceed 10 microns.

19. A method of manufacturing a high strength steel pipe with excellent toughness at low temperatures and excellent toughness in the heat-affected zone of the weld, characterized in that the casting of steel is re-heated, it contains components in the ratio according to any one of § § 11, 13, 14, 16-17, to a temperature not less than the temperature AU3perform hot rolling, then cooling the obtained steel sheet with a cooling rate of not less than 1°C/s to a temperature of not more than 550°With, then in a cold state shall forming the cooled steel sheet to give it shape pipe, then carry out arc welding submerged arc welding abutting portion with inner and outer sides of the pipe, and then subjected to steel pipe expanders.

20. A method of manufacturing a high strength steel pipe according to claim 19, characterized in that, before expanding costacabana by overlapping the longitudinal weld of the steel pipe is heated to a temperature of from 300 to 500°C.

21. A method of manufacturing a high strength steel pipe according to claim 19, characterized in that after expanding costacabana by overlapping the longitudinal weld of the steel pipe is heated to a temperature of from 300 to 500°C.



 

Same patents:

Rail steel // 2256000

FIELD: ferrous metallurgy; production of steel of railway rails.

SUBSTANCE: proposed steel contains the following components, mass-%: carbon, 0.30-0.35; silicon,1.15-1.25; manganese, 1.50-2.60; chromium, 0.6-1.3; vanadium, 0.08-0.15; aluminum, 0.005-0.010; nitrogen, 0.012-0.020; calcium, 0.001-0.020; molybdenum, 0.10-0.40; strontium, 0.001-0.020; nickel, 0.001-0.30; the remainder being iron. Proposed steel contains limited amount of admixtures, mass-%: sulfur, no more than 0.020; phosphorus, no more than 0.020; copper, no more than 0.20.

EFFECT: improved mechanical properties and hardness of steel; increased service resistance of rails.

2 cl, 2 tbl

Low-alloy steel // 2255999

FIELD: metallurgy; structural welding steels used for manufacture of side members for heavy-duty automobiles working in Extreme North.

SUBSTANCE: proposed low-alloy steel contains the following components, mass-%: carbon, 0.08-0.15; silicon, 0.1-0.6; manganese, 1.0-1.8; chromium, 0.3-0.9; copper 0.1-0.5; vanadium, 0.02-0.1;maluminum, 0.01-0.06; nickel, 0.7-1.5; nitrogen, 0.002-0.015; calcium, 0.002-0/030; niobium, 0.01-0.05; titanium, 0.004-0.035; sulfur, no more than 0.010; phosphorus, no more than 0.020; the remainder being iron.

EFFECT: increase of impact viscosity to 44 J/cm2 at temperature of 70°C at retained weldability.

3 tbl

FIELD: metallurgy; rolling process; manufacture of electrically welded pipes for erection of oil and gas lines in northern latitudes.

SUBSTANCE: proposed method includes heating the slabs to temperature of 1160-1190°C and performing finish rolling at total relative reduction of no less than 70% at temperature of end of rolling not above 820°C. Besides that, skelps are heated to temperature of 900-950°C after rolling and are subjected to water hardening; then skelps are tempered at temperature of 600-730°C. Skelps are rolled from low-alloyed steel having the following composition, mass-%: C, 0.07-0.12; Mn, 1.4-1.7; Si, 015-0.50; V, 0.06-0.12; Nb,0.03-0.05; Ti, 0.010-0.030; Al, 0.02-0.05; Cr, no more than 0.3; Ni, no more than 0.3; Cu, no more than 0.3; S, no more than 0.005; P, no more than 0.015; N, no more than 0.010; the remainder being Fe.

EFFECT: improved mechanical properties, weldability; increased yield of good skelps.

3 cl, 3 tbl, 1 ex

FIELD: metallurgy, in particular chromium-nickel-manganese-copper austenite stainless steel.

SUBSTANCE: claimed steel contains (mass %) (a) C 0.03-0.12; (b) Si 0.2-1.0; (c) Mn 7.5-10.5; (d) Cr 14.0-16.0; (e) Ni 1.0-5.0; (f) N 0.04-0.25; (g) Cu 1.0-3.5; (h) Mo as trace element; and balance: Fe and inevitable impurities. Austenite stainless steel contains less, than 8.5 vol.% of δ-ferrite, determined as δ-ferrite = 6.77[(d)+(h)+1.5(b)]-4.85[(e)+30(a)+30(f)+0.5(c)+0.3(g)]-52.75.

EFFECT: austenite stainless steel of improved mechanical strength, high corrosion resistance, in particular in salt mist, and high phase stability during hot and cold treatment.

4 cl, 1 dwg, 4 tbl, 22 ex

FIELD: material for glass industry, in particular forming material for machinery pressurized glasses.

SUBSTANCE: claimed material contains (wt. %) carbon 0.01-0.25; silicium 0.35-2.5; manganese 0.4-4.3; chromium 16.0-28.0; nickel 15.0-36.0; nitrogen 0/01-0/29; molybdenum at most 1; oxygen not more than 0.05; phosphorus not more than 0.03; sulfur not more than 0.03; and balance: iron, provided that Ni >= Cr+1.5xSi-0.12xMn-18xN-30xC-6. Material of the present invention has hardness 230-300 HB and high oxidation resistance up to 7500C.

EFFECT: material of high reactionlessness.

11 cl, 2 dwg

Steel // 2243288
The invention relates to metallurgy, in particular to low-alloy plate welded structural steels intended for the manufacture of platforms, heavy-duty trucks operating in the Far North

The invention relates to metallurgy, and more particularly to rolling production, and can be used in the manufacture of welded pipes for oil pipeline construction in seismic zones

The invention relates to metallurgy, and more particularly to rolling production, and can be used in the manufacture of the sheet reversing mills low alloy steel for the construction of offshore platforms

Rail steel // 2241779
The invention relates to ferrous metallurgy, in particular to the production of steel for rails

The invention relates to metallurgy, and more particularly to rolling production, and can be used in the manufacture of welded pipes for oil pipeline construction in seismic zones

FIELD: ferrous metallurgy; motor-car industry; production of steels intended for manufacture of items of a complex configuration with the help of cold sheet stamping.

SUBSTANCE: the invention is pertaining to the field of ferrous metallurgy and motor-car industry, in particular, to methods of production of steels intended for manufacture by cold sheet stamping of items of a complex configuration, predominantly details for motor cars. The technical problem is to boost steel stamping, to improve the quality of a surface of a steel strip and hence to improve adhesion of a protective cover. The method includes a steel smelting, casting, hot rolling, strips reeling in rolls, a cold rolling, a recrystallization annealing and a temper rolling. The steel contains components in the following ratio (in mass %): Carbon - 0.002 - 0.008, silicon - 0.005-0.025, manganese - 0.05-0,20, phosphorus - 0.005-0.025, sulfur - 0.003-0.012, aluminum - 0.02-0.07, titanium - 0.02-0.05, niobium - 0.001 0.080, iron and imminent impurities - the rest. The hot rolling is completed at the temperature determined from the ratio: Tf.r≥ 7300 / (3.0-Ig [Nb] [C]) - 253, where Tf.r - temperature of the end of the rolling, °C; [Nb] and [C] - the shares of niobium and carbon in the steel accordingly in mass %, and the recrystallization annealing is carried out in a pusher-type furnace at the temperature assigned depending on the contents of niobium in steel according to the equation: Tan= (750+ 1850 [Nb]) ± 20, where Tan - a temperature of the thermal treatment, °C; [Nb] - the contents of niobium in the steel, in mass %.

EFFECT: the invention allows to boost the steel stamping, to improve the quality of the steel strip surface and adhesion of a protective cover.

4 ex, 1 tbl

FIELD: metalwork operating in cold climates at static loads.

SUBSTANCE: proposed iron-based cold-resistant alloy includes the following components, mass-%: titanium, 1-2; carbon, 0.009 max; silicon, 0.1 max; aluminum, 0.003 max; copper, 0.03 max; nickel, 0.2 max; the remainder being iron. Proposed alloy possesses high strength at retained ductility; embrittlement of this alloy at cooling to temperature below minus 78°C is excluded; content of carbon is considerably reduced due to increased content of titanium, thus enhancing resistance to cold.

EFFECT: enhanced efficiency; enhanced cold resistance.

1 dwg, 1 tbl

Structural steel // 2251587

FIELD: metallurgy, in particular structural steel composition.

SUBSTANCE: claimed steel contains (mass %): carbon 0.42-0.54p; silicium 0.15-0.50; manganese 0.90-1.50; niobium 0.01-0.08; molybdenum 0.06-0.20; aluminum 0.005-0.060; titanium 0.019-0.045; sulfur 0.001-0.045; phosphorus 0.001-0.045; nitrogen less than 0.012; chromium, nickel and copper each not more than 0.30, and balance: iron. Steel of present invention is useful in production of pipelines for oil industry operating at temperature from 50°C to -10°C.

EFFECT: steel with optimum combination of strength and viscous properties.

2 tbl, 1 ex

FIELD: metallurgy; production of important rolled stock for oil-well tubing of increased service life.

SUBSTANCE: proposed method includes making steel of definite chemical composition in electric furnace, tapping metal from furnace into ladle, treatment of metal in ladle and teeming steel into ingot molds. Alloying with molybdenum is performed by introducing molybdenum-containing materials into furnace in making steel. After teeming, ingots are rolled, cooled and heated for rolling in preset temperature range and are subjected to preliminary and final deformation; process is completed by final cooling of rolled blanks to surrounding temperature.

EFFECT: improved strength characteristics and cold resistance of metal; enhanced reliability of metal products.

1 ex

FIELD: metallurgy; high-titanium-bearing foundry alloy production.

SUBSTANCE: the invention is dealt with the field of metallurgy, in particular, with production of the foundry alloy containing mainly titanium and also a small amount of other useful metals reduced from oxides of a charge together with the basic components of a foundry alloy. The method includes the following stages: after melting-down of the first portion of the charge representing an ilmenite concentrate formed on the rotating melt of the high-titanium-bearing foundry alloy and reduction by titanium and silicon of a part of oxides from the melted portion of ilmenite they use aluminum to reduce all oxides in a cinder melt. The obtained slag is added with the first portion of calcium oxide in the amount ensuring fluidity of the cinder. The second portion of the charge is introduced in the melt in the amount corresponding to the possibility of to reduce oxides by titanium. The produced titanium oxide is merged with the earlier produced cinder. A determined part of the produced melt in conditions of its rotation is poured out through a side tap hole. Using aluminum reduce titanium oxide from the merged cinder and the reduced titanium merge with the rest metal melt. In the formed final cinder enter the second portion of calcium oxide. A part of the produced foundry alloy is poured out through a side tap hole. Then a final cinder is also poured out and they feed a new portion of ilmenite onto the residue of the foundry alloy. The invention allows to reduce at least twice the power input used for reprocessing of the ilmenite concentrate, as in the process of reduction of the metals from oxides there are no endothermic reactions but exothermic reactions; to use ilmenite concentrates with a share of titanium oxide up to 45% and a strong metal reductant - aluminum, and also to realize a progressive technology of the liquid-phase reduction of metals from oxides in conditions of rotation of the melt by an electromagnetic field.

EFFECT: the invention allows to reduce at least twice the power input used for reprocessing of the ilmenite concentrate, to use ilmenite concentrates with a share of titanium oxide up to 45% and a strong metal reductant - aluminum, to realize a progressive technology of the liquid-phase reduction of metals from oxides.

5 cl, 1 ex, 1 dwg

FIELD: ferrous metallurgy.

SUBSTANCE: invention provides round-profiled iron smelted from low-carbon steel composed of, wt %: carbon 0.17-0.25, manganese 0.30-0.65, silicon 0.01-0.17, sulfur 0.005-0.020, vanadium 0.005-0.07, niobium 0.005-0.02, calcium 0.001-0.010, iron and unavoidable impurities - the balance. When following relationships are fulfilled: 12/C-Mn/0.02 ≥ 27; 0.46 ≥ 6V+8Nb ≥ 0.22; Ca/S ≥ 0.065, rolled iron has following characteristics: maximum degree of pollution with nonmetal inclusions, in particular sulfides, oxides, silicates, and nitrides, does not exceed 3 points for each type of inclusions; longitudinally uniform spheroidized structure composed of at least 80% grainy perlite; effective grain size 5-10 points; diameter 10-25 mm; carbon-free layer not exceeding 1.5% of diameter; cold setting value at least 1/3 height; point of maximum load not higher than 550 MPa; relative elongation at least 20%; and relative contraction at least 60%.

EFFECT: ensured optimal conditions for cold die forging of high-strength geometrically complex fastening members and simultaneously ensured improved characteristics of in-process plasticity and low level of stray hardening.

FIELD: ferrous metallurgy.

SUBSTANCE: invention provides round-profiled iron smelted from alloyed steel composed of, wt %: carbon 0.06-0.11, manganese 0.30-0.9, silicon 0.001-0.15, boron 0.0005-0.0050, vanadium 0.005-0.08, aluminum 0.02-0.06, titanium 0.01-0.04, sulfur 0.005-0.020, nitrogen 0.005-0.015, calcium 0.001-0.010, iron and unavoidable impurities - the balance. When following relationships are fulfilled: Ti/48+Al/27-N/14 ≥ 0.6 x 10-3; Mn+5.0C ≥ 0.80; Ca/S ≥ 0.065, rolled iron has following characteristics: maximum degree of pollution with nonmetal inclusions, in particular sulfides, oxides, silicates, and nitrides, does not exceed 3 points for each type of inclusions; longitudinally uniform spheroidized structure composed of at least 60% grainy perlite; effective grain size 5-10 points; diameter 10-16 mm; carbon-free layer not exceeding 1.0% of diameter; cold setting value at least 1/3 height; throughout hardenability in circles up to 16 mm in diameter; point of maximum load not higher than 500 MPa; relative elongation at least 22%; and relative contraction at least 70%.

EFFECT: ensured optimal conditions for cold die forging of high-strength geometrically complex fastening members and simultaneously improved steel hardenability characteristics.

The invention relates to metallurgy, and more particularly to rolling production, and can be used in the manufacture of welded pipes for oil pipeline construction in seismic zones

The invention relates to metallurgy, and more particularly to rolling production, and can be used in the manufacture of the sheet reversing mills low alloy steel for the construction of offshore platforms

The invention relates to the field of metallurgy, in particular to the production of long-rolled products of boron steel for cold massive forming of high-strength fasteners particularly complex form

FIELD: metallurgy; pipe rolling.

SUBSTANCE: the invention is pertaining to the field of pipe rolling, in particular, to the methods of production of triblets of pilgrim-step rolling mills and may be used at production of triblets of pilgrim-step rolling mills for rolling of hot-rolled pipes of large and average diameters (273-550 mm). The method provides for casting of steel ingots, production of triblets out of the steel ingot blanks by, a heat treatment of the triblet ingot blanks, their mechanical working to obtain the finishing dimension with subsequent hardening by a roller run, casting of carbon steel ingots, application by surfacing on the ingot blanks of a heat-resistant and abrasive resistant layer and production of triblets out of the steel ingots by the pilgrim-step rolling, and in the process of operation after appearance of a net flame erosion cracks conduct a triblet multiple remachining till removal of the heat-resistant and abrasive resistant layer, application of a new heat-resistant and abrasive resistant layer by surfacing, machining till the finishing dimension and hardening by a roller running and determination of the thickness of the heat-resistant and abrasive resistant layer from the following equation Δ = A*µ* (l÷D/S*K), where: A - is the minimal thickness of the surfacing layer after the final mechanical working of a triblet and equaled to 10 mm; D - the maximal diameter of the pipes rolled on the given triblet, mm; S - the minimal wall thickness of the pipes rolled on the given triblet, mm; µ - a reduction ratio at rolling of ingots into the hollow triblet blanks and K - a coefficient equal to 0.02. The invention ensures production of triblets of pilgrim-step rolling mills for rolling of hot-rolled pipes of large and average diameters, usage as the basis of the triblet ingot blanks produced out of a carbon steel instead of alloyed steel, increased resistibility of triblets and as a result of it a decreased share of cost of the technological tools in the cost of production of pipes.

EFFECT: the invention ensures production of triblets of pilgrim-step rolling mills for rolling of hot-rolled pipes of large and average diameters, usage of carbon steel in production of triblet ingot blanks, increased resistibility of triblets, decreased share of triblets cost in the cost of the pipes production.

2 cl, 1 tbl

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