Low-alloyed, containing no boron steel

 

The invention relates to metallurgy, namely to find a heavy-duty welded steel plate, which is used for manufacture of pipelines. The proposed low-alloyed, containing no boron steel having a tensile strength of at least 900 MPa, impact strength, measured in test samples with a V-notch on Charpy at -40oC at least 120 j and microstructure containing predominantly fine-grained lower banit, fine mesh martensite or a mixture formed from almost precrystallization grains of austenite. Steel contains components in the following ratio, wt. %: carbon 0,03-0,10; manganese 1,6-2,1; niobium 0,01-0,10; vanadium 0,01-0,1; molybdenum 0,3-0,6; titanium from 0.005 to 0.03; iron - rest, and a carbon equivalent of UOE steel is in the range of 0.5Seto 0.7, and the weldability of RSM0,35. The technical result of the invention is to improve the strength of steel without a vacation to obtain secondary hardening. The ratio of yield strength to ultimate tensile strength is not more than 0,93. 13 C.p. f-crystals, 13 ill., table 2.

The present invention can be used in the manufacture of piping and structural steel.

The prior art In the following description of the various terms. For convenience in description of the Glossary, located immediately before the claims.

Currently in industrial use of its pipeline steel has the highest yield strength of approximately 550 MPa. In industry there are pipeline steel with high yield strength, for example to approximately 690 MPa, but as far as known to the applicant, they are not used in industrial production pipelines. Moreover, as described in U.S. patent 5545269, 5545270 and 5531842 (CoE and Luton), it was found that practical to produce surpr is their at least about 900 MPa as source material for pipelines. The strength of the steel described CoE and Luton in U.S. patent 5545269, achieved by compensation between the steel chemistry and processing technology, the result of which was obtained a homogeneous microstructure, which consists mainly of fine-grained, tempered martensite and banit, which strengthened again by deposition-phase copper and some carbides or nitrides, or carbonitrides of vanadium, niobium and molybdenum.

In U.S. patent 5545269 CoE and Luton have described a method of obtaining a high-strength steel in which the steel is quenched from the final temperature of the hot rolling to a temperature not higher than 400oWith speeds of at least 20oWith a second, preferably about 30oWith a second to get mainly microstructure of martensite and bainite. Moreover, to achieve the target microstructure and properties of the invention CoE and Luton requires that the steel plate was subjected to secondary hardening process additional process steps, including vacation chilled water sheet at a temperature not higher than the point of turning Ac1, i.e. the temperature at which during heating begins to form austenite, teching carbides or nitrides, or carbonitrides of vanadium, niobium and molybdenum. This additional process stage tempering after hardening significantly increases the cost of production of steel sheet. It is therefore desirable to develop a new methodology for the processing of steel, in which the dispense stage of annealing and at the same time has achieved the desired mechanical properties. In addition, the phase vacation, though necessary for the desired hardening to obtain the desired microstructure and properties, also leads to the ratio of yield strength/tensile strength above 0,93. From the point of view of a preferred construction of the pipeline it is desirable to maintain the ratio of yield strength/tensile strength below 0,93, while maintaining high yield strength and tensile strength.

There is a need for pipelines with increased strength compared to existing transport crude oil and natural gas at a very far distance. This need is driven by the need and increase transport efficiency through the application of high pressure gas and (b) reduce the cost of materials and the laying of the track by reducing the wall thickness and external diameter of the pipeline. Aasee time.

Therefore, the aim of the present invention to provide compositions of steel and alternative technologies for cheap low alloy heavy-duty plate steel and production of her pipe, high strength which is achieved without the involvement stage of tempering to obtain a secondary hardening. In addition, another objective of the present invention is the development of high-strength steel plate for pipe, which is suitable for constructing pipelines and for which the ratio of yield strength/tensile strength is lower than approximately 0,93.

The problem with extremely durable steel, i.e. a steel having a yield strength greater than about 550 MPa, is softening in the heat-affected zone (HAZ) after welding. In this HAZ may occur local phase transformation or annealing during thermal cycles caused by welding, which leads to significant, i.e. approximately 15% or more, the softening of the HAZ compared to the base metal. Although there were obtained a heavy-duty steel with a yield strength of 830 MPa or higher, usually these are not possessed of toughness required for the pipeline have a relatively high rate PCM (well-known technical term for expressing the ability to weld), which is usually higher than around 0.35.

Therefore, another objective of the present invention to provide a low alloy heavy-duty plate steel as a starting material for the pipeline, which has a yield strength of at least about 690 MPa, a tensile strength of at least about 900 MPa and sufficient toughness for use at low temperatures, i.e. up to -40oC, and at the same time saves compatible product quality with minimal loss of strength in the HAZ during thermal cycle caused by welding.

An additional objective of the present invention to provide a heavy-duty steel with the toughness and weldability, which are required for the pipeline and having an indicator RSM less than around 0.35. Although both measures are widely used in connection with the ability to weld, and REM, and Se (carbon equivalent), another well-known technical term used to measure the ability to weld), also reflect the ability of the steel to be hardened, in that they provide guidance regarding the tendency of steel to the formation of solid microstructures of the base metal. When the u + wt.% Cr)/20 + wt.% Ni/60 + wt.% Mo/15 + wt.% V/10 + 5 (wt.% In); and Se is defined as: Se = wt.% With + wt. % Mn/6 + (wt.% Cr + wt.% Mo + wt.% V)/5 + (wt.% Cu + wt.% Ni)/15.

The invention As described in U.S. patent 5545269, it was found that under these conditions the stage quenching in water to a temperature not higher than 400oWith (preferably to ambient temperature), followed by a final heavy-duty rolling steel cannot be replaced by air cooling, because under such conditions, the cooling air can cause the transformation of austenite into aggregates of ferrite/pearlite, which leads to deterioration of the strength of the steel.

In addition, it was found that the interruption of the cooling water such steel above 400oWith may lead to the lack of transformation hardening in the cooling process and the strength of steel decreases.

In the steel plate obtained by the method described in U.S. patent 5545269 applies vacation after cooling with water, for example by reheating to a temperature in the range from about 400 to 700oC for a given time interval in order to provide uniform quenching in the whole volume of steel plate and to improve the impact toughness of the steel. Test specimens with a V-notch on Sari can be obtained using test specimens with a V-notch in Sharpie, represents the energy absorbed in breaking the specimen steel (impact energy) at a given temperature, for example, the impact energy at -40oWith (vE-40).

After improvements, described in U.S. patent 5545269, it was found that heavy-duty steel with high toughness can be obtained without the use of expensive final vacation. It was found that this desirable result can be achieved by interrupted quenching in a specific temperature range, depending on the specific chemical composition of steel, in which the microstructure of the steel is a predominantly fine-grained lower banit, fine mesh martensite, or mixtures thereof, which develop when the temperature is interrupted cooling or during subsequent cooling to ambient temperature. In addition, it was found that this new sequence of process steps provides the unexpected and unobvious result - plate steel with higher strength and toughness in comparison with the existing level of technology.

In accordance with the above objectives of the present invention was developed methodology process is tolegenovna steel plate with specified chemical composition is rapidly cooled, at the end of hot rolling, by quenching a suitable fluid medium, such as water, to a suitable Temperature termination quenching (SMI) with subsequent cooling to ambient temperature, to obtain a microstructure containing predominantly fine-grained lower banit, fine mesh martensite, or mixtures thereof. Used to describe the present invention, the term hardening refers to accelerated cooling by any means, which uses fluid is selected to provide a larger cooling rate of steel compared with steel cooling air to the ambient temperature.

According to the present invention it is steel with a capacity of negotiation speed cooling temperature settings stop the hardening that provides reinforcement to the way partial quenching, which is called PNZ, with subsequent cooling phase air to get in the final sheet product microstructure containing predominantly fine-grained lower banit, fine mesh martensite, or mixtures thereof.

From the field of technology it is well known that the addition of small amounts of radistai low alloy steel. Thus, the addition of boron in the steel used effectively in the past for the formation of solid phases such as martensite in low-alloy steel with a depleted chemical composition, i.e., with low carbon equivalent (Se) to get a cheap high-strength steel with excellent weldability. However, appropriate control of the desirable small additives of boron difficult is implemented. It requires technically advanced production facilities and trade secrets. In the present invention is the spacing of the chemical composition of the steels with the addition of boron and without additives, which can be processed according to the methodology of Interrupted direct quenching, to obtain the desired microstructure and properties of steel.

In accordance with this invention equilibrium is reached between the chemical composition of steel and the technology of its processing, in which it is possible to obtain high-strength steel plate having a yield strength of at least about 690 MPa, more preferably at least about 760 MPa and even more preferably at least about 830 MPa, with a preferred ratio of yield strength/tensile strength of less than approximately 0.85, from which it is possible to produce pipes. After welding this steel plate for use in pipelines, loss of strength in the heat-affected zone (HAZ) is less than about 10 %, preferably less than about 5 %, relative to the strength of the base steel. In addition, these heavy-duty low-alloy steel plate, suitable for manufacture of pipelines, have a thickness of preferably at least about 10 mm, more preferably at least about 15 mm and even more preferably at least approximately 20 mm in Addition, these heavy-duty low-alloy steel plate or may not contain additives of boron, or for specific purposes contain boron additive in the amount of approximately between 5 and 20 M. D. and preferably approximately between 8 and 12 m D. the quality of the product - pipeline - remains substantially dense, and generally the product does not have the tendency to cracking under the action of hydrogen.

The preferred product is the steel has a substantially uniform microstructure, which preferably consists predominantly of fine-grained lower bainite, fine mesh mA is hydrated fine mesh martensite. Used in the description of the present invention and in the claims, the term "predominantly" means at least about 50 about. %. The remainder of the microstructure may consist of more fine-grained mesh of martensite, the upper bainite or ferrite. More preferably, the microstructure contains at least about 60 to about 80. % fine-grained lower bainite, fine mesh martensite, or mixtures thereof. Even more preferably, the microstructure contains at least about 90 about. % fine-grained lower bainite, fine mesh martensite, or mixtures thereof.

As the lower banit and net martensite can prosnetsja due to precipitation of carbides or carbonitrides of vanadium, niobium and molybdenum. These sediments, especially those that contain vanadium, can help minimize softening in the heat-affected zone, probably by preventing any substantial reduction of the dislocation density in the areas heated to a temperature not exceeding the point of turning Ac1or causing dispersion strengthening in areas that are heated to a temperature above the point of turning Ac1and who in one variant embodiment, the steel contains iron and the following alloying elements in the following weight percentages: 0,03 - to 0.10% carbon (C), preferably 0,05 - 0,09% C, 0 to 0.6% silicon (Si), 1,6 - 2,1% manganese (Mn), 0 to 1.0% copper (Cu), 0 to 1.0% Nickel (Ni), preferably from 0.2 to 1.0% of Ni, from 0.01 to 0.10% of niobium (Nb), preferably 0.03 to 0.06% of Nb, 0.01 to 0.10% per vanadium (V), preferably of 0.03 to 0.08% V,
0.3 to 0.6% of molybdenum (Mo),
0 to 1.0% of chromium (Cr),
0.005 to 0.03% of titanium (Ti), preferably of 0.015 to 0.02% Ti,
0 - 0,06% aluminum (Al), preferably 0.001 to 0.06% of (Al),
0 - 0,006% calcium (CA),
0 - 0,02% of rare earth metals (REM),
0 - 0,006% of magnesium (Mg),
and additionally differs in that
Se0.7 and
RSM0,35.

Alternative to the above chemical composition change, and it includes 0,0005-0,0020 wt.% boron, preferably 0,0008-0,0012 wt.% boron and molybdenum content is 0.2-0.5 wt.%.

For steel of the present invention, containing no boron, preferably the value of Se is greater than about 0.5 and less than approximately 0.7. For steel of the present invention containing boron, preferably the value of Se is greater than about 0.3 and less than approximately 0.7.

In addition, the contents are well known nitrogen (N), phosphorus (P) and sulfur (S) in the steel is preferably minimized, even if some amount of nitrogen, the nitrogen is preferably approximately from 0.001 to 0.006 wt.%, the sulfur concentration of not more than about 0.005 wt.%, more preferably not more than about 0.002 wt. %, and the phosphorus concentration is not more than approximately of 0.015 wt.%. When such chemical composition of the steel or practically does not contain boron, in the sense that the addition of boron is missing, and the concentration of boron is preferably less than about 3 M. D., more preferably less than about 1 M. D. or steel contains an additive of boron, as indicated above.

In accordance with the present invention a preferred method of obtaining heavy-duty steel having microstructure comprising predominantly fine-grained lower bainite, fine mesh martensite, or mixtures thereof, is heated steel billet to a temperature sufficient to dissolve almost all carbides and carbonitrides of vanadium and niobium; reducing the size of the workpiece to the sheet, laminating it one or more times on a hot roll mill in the first temperature range in which the recrystallization of austenite; further reducing the size of the sheet, laminating it one or more times on a hot roll mill in the second temperature range, below t is reversine AG3, i.e. the temperature at which austenite begins to transform to ferrite during cooling; tempering finally laminated sheet to a temperature at least lower than the point of turning Ar1, i.e. the temperature at which completes the transformation of austenite to ferrite or to ferrite plus cementite when cooled preferably to a temperature between approximately 550 and 150oS and more preferably to a temperature between approximately 500 and 150oC; termination quenching and cooling the tempered sheet of air to the ambient temperature.

Each of the temperature THPpoint transformations Ar1and the point of turning AG3depend on the chemical composition of the steel billet, and they are easily determined either experimentally or by calculation using suitable models.

Heavy-duty low-alloy steel in accordance with the first preferred embodiment of the invention has a tensile strength, preferably equal to at least about 900 MPa, more preferably at least about 930 MPa, has a microstructure containing predominantly fine-grained lower banit, fine mesh vydeleny carbides or carbonitrides of vanadium, niobium and molybdenum. Preferably fine mesh martensite includes spontaneously released fine mesh martensite.

Heavy-duty low-alloy steel in accordance with the second preferred embodiment of the invention has a tensile strength, preferably equal to at least about 900 MPa, more preferably at least about 930 MPa, and has a microstructure containing predominantly fine-grained lower banit, fine mesh martensite, or mixtures thereof, and further includes boron and fine sediment particles of cementite and not necessarily even smaller particles precipitate carbides or carbonitrides of vanadium, niobium and molybdenum. Preferably fine mesh martensite includes spontaneously released fine mesh martensite.

Description of drawings
In Fig.1 schematically shows a processing stage according to the present invention with the overlap of the various components of the microstructure associated with specific combinations of elapsed processing time and temperature.

In Fig.2A and 2B shows electron microscopic images of an x, respectively, in the bright and testigo net martensite steel, moreover, in Fig.2B one can see well-developed sediment particles of cementite within the grid of martensite.

Fig.3 is an electron microscopic picture for the knockouts in the light field, which is mainly found microstructure of fine-grained lower bainite for steel treated at a Temperature termination quenching approximately 385oC.

In Fig.4A and 4B shows electron microscopic images of an x, respectively, in bright and dark field, steel treated at a Temperature termination quenching approximately 385oS, and in Fig.4A shows the microstructure of predominantly fine-grained lower bainite, and Fig. 4B illustrates the presence of particles of carbides of molybdenum, vanadium and niobium, which has a diameter less than approximately 10 nm.

Fig. 5 is a composite diagram that includes the schedule and electron-microscopic images of an x, which demonstrate the effect of Temperature termination hardening on the relative values of impact strength and tensile strength for a particular chemical compounds boron steel, indicated in the table. 2 this description as N and T (circles) and depleted Bo is given impact energy Charpy in Joules, at -40oWith (vE-40); the abscissa is the tensile strength in MPa.

Fig. 6 is a graph showing the influence on the relative values of impact strength and tensile strength for a particular chemical compounds boron steel, indicated in the table. 2 describe how N and T (circles) and containing no boron steel, indicated in the table. 2 descriptions as "" (squares), all in accordance with the present invention. The ordinate shows the impact energy by Sharpie in Joules at -40oWith (vE-40); the abscissa is the tensile strength in MPa.

Fig. 7 is an electron microscopic picture for the knockouts in the light field, which is detected net martensite with dislocations in the steel sample D, which was treated with PNZ Temperature termination quenching of approximately 380oC.

Fig. 8 is an electron microscopic picture for the knockouts in the light field, which is detected by the microstructure predominantly lower bainite in the sample steel D (according to the table. 2 descriptions), which was treated with PNZ Temperature termination quenching of approximately 428oC. Inside the grid bainite can the th bainite.

Fig.9 is an electron microscopic picture for the knockouts in the light field, which is detected by the microstructure of the upper bainite in the sample steel D (according to the table. 2 descriptions), which was treated with PNZ Temperature termination quenching of approximately 461oC.

Fig.10A is an electron microscopic picture for the knockouts in the light field, which is detected by the region of martensite (center), surrounded by ferrite in the steel sample D (according to the table. 2 descriptions), which was treated with PNZ Temperature termination quenching of approximately 534oC. Inside the ferrite near the boundary between the ferrite/martensite you can see small particles of sediment carbide.

Fig. 10B is an electron microscopic picture for the knockouts in the light field, which is detected by the high-carbon twinned martensite in the steel sample D (according to the table. 2 descriptions), which was treated with PNZ Temperature termination quenching of approximately 534oC.

Although this invention will be described in connection with its preferred variant embodiment, it should be understood that invented the Toms, modified and equivalent variations that can be covered within the spirit and scope of the invention as defined in the attached claims.

Detailed description of the invention
In accordance with one concept of the present invention billet processed with a substantially uniform heating of the workpiece to a temperature sufficient to dissolve almost all carbides and carbonitrides of vanadium, niobium, preferably in the range from about 1000 to 1250oS and more preferably in the range from about 1050 to 1150oWith; the first hot rolling of the billet to the preferred reducing its thickness by approximately 20-60% with the formation of the sheet, in one or several passes, in the first temperature range in which the recrystallization of austenite; the second hot rolling preferable to reduce the thickness of about 40-80%, in one or several passes, in the second temperature range, which is slightly below the first temperature interval, in which no recrystallization of austenite, and above the point of turning AG3; hardening the laminated sheet by quenching with speed, pribek, more preferably at least about 30oC/sec, even more preferably at least approximately 35oC/sec, the temperature not lower than the point of turning AG3until the Temperature of the termination quenching (SMI), which is at least not higher than the point of turning Ar1, preferably in the range from about 550 to 150oS and more preferably in the range from about 500 to 150oWith, and termination hardening, leaving the steel plate to cool in air to ambient temperature in order to facilitate the completion of the transformation of steel in a predominantly fine-grained lower banit, fine mesh martensite, or mixtures thereof. It is understood by experts in the field of technology used here, the expression "thickness reduction percentage" means the percentage reduction of the thickness of the steel billet or plate steel to discuss reduction. Only for the purpose of example, without limiting the present invention, in the first temperature range, the thickness of the steel billet approximately 25.4 cm can be reduced by approximately 50% (50% reduction) to a thickness of approximately 12.7 cm, then the second temperature isomer, referring to Fig.1, a steel plate treated according to this invention, is subjected to controlled rolling 10 in the specified temperature range (described in more detail in the following); then the steel is quenched from 12 point vintage 14 to a Temperature termination quenching (SMI) 16. After the termination of hardening steel is allowed to cool in air 18 to the ambient temperature, in order to facilitate the completion of the transformation of steel in a predominantly fine-grained lower banit (in the region of the lower bainite 20), fine mesh martensite (in the area of martensite 22), or a mixture thereof. The area of the upper bainite 24 and the region of the ferrite 26 is fixed.

For a heavy-duty steel, you must have many properties that are provided by the combination of alloying elements and thermomechanical treatment; usually small changes in the chemical composition of the steel can lead to significant changes of the obtained characteristics. This is the role of different alloying elements and the preferred limits of their concentrations in the steel of the present invention.

Carbon provides a matrix hardening steel and welded joints, regardless of their microstructure, and also provides dirbantiems niobium [Nb (C, N)], carbonitrides of vanadium [V (C, N)] and particles or precipitation Mo2(View of the molybdenum carbide), if they are sufficiently small and numerous. In addition, the precipitation of carbonitrides of niobium, during hot rolling, usually provides inhibition of recrystallization of austenite and inhibits grain growth thus appears to be the cleanup tool austenite grains, which leads to improvement of the yield strength, tensile strength and impact strength at low temperature (for example, the impact energy in the test Sharpie). Carbon also increases the hardenability, i.e., the ability to form more rigid and stable microstructure during cooling of the steel. Usually, if the carbon content is less than about 0.03 wt.%, these effects hardening does not occur. If the carbon content is greater than about 0.10 wt.%, the steel is usually susceptible to cold cracking after welding in the field, and reduced toughness in the steel plate and the heat-affected zone of welds.

Manganese is essential for obtaining microstructures required for the steel of the present invention, which contain fine-grained lower banit, the ary viscosity at low temperature. For this purpose, the lower limit of the manganese content is set to about 1.6 wt. %. The upper limit is set at about 2.1 wt.%, because when the content is greater than about 2.1 wt.% manganese contributes to axial segregation in continuously cast steel, and can also lead to deterioration of the toughness of steel. Moreover, the high content of manganese tends excessive increase proclaimest steel, resulting in reduced weldability in field conditions by reducing the toughness in the heat-affected zone of welds.

Silicon is added for deoxidation and increase the strength of steel. The upper limit of the silicon content is set to about 0.6 wt.%, in order to avoid significant deterioration of weldability in the field and toughness in the heat-affected zone, which may be due to the excessive content of silicon. For deoxidation of steel is not always necessary silicon, because for this purpose you can use aluminum or titanium.

Niobium added to facilitate purification of the grain microstructure of the steel after rolling, which improves both strength and toughness. The deposition of niobium carbonitride during hot PR is about for cleansing grains of austenite. It may also provide additional hardening during the final cooling due to the formation of sludge niobium carbonitride. In the presence of molybdenum niobium effectively cleans the microstructure, suppressing the recrystallization of austenite during controlled rolling, and hardens steel, providing a dispersion strengthening and giving a contribution in increasing the ability to hardening. In the presence of boron niobium results in a synergistic improvement in proclaimest. For the achievement of such effects is preferable to add at least about 0.01 wt.% niobium. However, if the content of niobium is greater than approximately 0.1 wt.%, niobium usually has a deleterious effect on the weldability and toughness in the heat-affected zone, so that the preferred content is a maximum of approximately 0.1 wt.%. More preferably add approximately from 0.03 to 0.06 wt.% niobium.

Titanium forms fine particles of titanium nitride and contributes to a clean microstructure, suppressing the coarsening of austenite grains during re-heating of the workpiece. In addition, the presence of particles of titanium nitride inhibits the enlargement of the grains in the heat-affected zone during welding. Accordingly Titus the CSO impacts. As titanium binds to nitrogen in the form of titanium nitride, it prevents worsening the effect of nitrogen on proclaimest due to the formation of boron nitride. Preferably the amount of added this purpose titanium is at least about 3.4 times greater than the amount of nitrogen (by weight). At low concentrations of aluminum (i.e., less than about 0.005 wt.%) titanium forms an oxide, which serves as an embryo for the formation of ferrite inside the grains in the heat-affected zone during welding, and thus cleanses the microstructure in these areas. To achieve these goals, it is preferable to add at least about 0.005 wt.% titanium. The upper limit is set to about 0.03 wt.%, since the high content of titanium leads to coarsening of the particles of titanium nitride and dispersion hardening caused by the precipitation of titanium carbide, both these processes lead to the deterioration of impact strength at low temperature.

Copper increases the strength of the base metal and the heat-affected zone of welds, however, the addition of excess copper strongly affects the toughness in the heat-affected zone and weld ability in the field of plods improve the properties of low-carbon steel, obtained according to the present invention, without deterioration of weldability in the field and impact strength at low temperature. Unlike manganese and molybdenum additives of Nickel reduces the tendency to form components of hardened microstructures, which degrades toughness steel plate at a low temperature. It turned out that the addition of Nickel in the amount of more than 0.2 wt.% is effective to improve toughness in the heat-affected zone of welds. In General, the Nickel is improving additive, except propensity for sulfide cracking under the action of stresses in some environments, when the Nickel content is greater than about 2 wt.%. For steels, obtained according to the invention, the upper limit is set at approximately 1.0 wt.%, since Nickel is becoming an expensive alloying element, and it can degrade the toughness in the heat-affected zone of welds. Furthermore, the addition of Nickel is effective to prevent cracking of the surface, caused by the copper in the process of continuous casting and hot rolling. The addition of Nickel to this end is preferably greater than pribliziteljny effective cleaning of the microstructure of steel. Aluminum can also play an important role in ensuring toughness in the heat-affected zone, by removing the free nitrogen in the major grain heat-affected zone in which heat welding provides a partial dissolution of titanium nitride, resulting in outstanding free nitrogen. If the aluminum content is too large, i.e., about 0.06 wt. % there is a tendency to the formation of inclusions of type aluminum oxide (Al2O3), which can degrade the toughness of steel, including the heat-affected zone. The deoxidation of steel can be made additives titanium or silicon, and it is not necessary to add aluminum.

Vanadium has a similar niobium, but less pronounced effect. However, the addition of vanadium to a heavy-duty steel gives a noticeable effect when introduced in combination with niobium. The joint introduction of niobium and vanadium further enhances the excellent properties of the steel according to the invention. Although the preferred upper limit is approximately 0.10 wt.% vanadium, from the viewpoint of the toughness in the heat-affected zone of welds and, therefore, the weldability in the field, especially p is proclaimed steel and thereby facilitates the formation of the microstructure of the lower bainite. A strong effect of molybdenum on proclaimest became especially pronounced in the boron-containing steels. When molybdenum is added together with niobium, molybdenum enhances the suppression of recrystallization of austenite during controlled rolling, and thereby it contributes to the purification of the microstructure of austenite. To achieve these effects, the amount of molybdenum added to the steel, containing no boron in steel containing boron is preferably at least about 0.3 wt. % and about 0.2 wt.% respectively. The upper limit for molybdenum is approximately 0.6 wt.% and about 0.5 wt.% accordingly, for steel, containing no boron, and a steel containing boron as an excessive amount of molybdenum degrades toughness in the heat-affected zone formed by welding in the field, impairing weldability in the field.

Chrome usually increases proclaimest steel with direct quenching. It also increases resistance to cracking under the action of corrosion and hydrogen. As in the case of molybdenum, with an excess of chromium, i.e., more than 1,the impact toughness of the steel and the heat-affected zone, so preferably the maximum chromium content is approximately 1.0 wt.%.

Nitrogen suppresses the coarsening of austenite grains during re-heating of the workpiece and the heat-affected zone of welds, forming a titanium nitride. Therefore, the nitrogen contributes to the improvement of impact strength at low temperature as the base metal and the heat-affected zone of welds. For this purpose, the minimum nitrogen content is approximately of 0.001 wt.%. The upper limit is preferably supported at the level of approximately 0,006 wt.%, because excess nitrogen increases the scope of the surface defects of the workpiece and reduces the effective ability of boron to the padding. In addition, the presence of free nitrogen causes the deterioration of the toughness in the heat-affected zone of welds.

Calcium and rare earth metals (REM) usually regulate the form of inclusions of manganese sulphide (MnS) and improve the impact strength at low temperature (for example, the impact energy in the test Sharpie). To regulate the form of sulfide, it is desirable to have at least approximately to 0.001 wt.% calcium or approximately of 0.001 wt.% REM. However, if the calcium content exceeds the 0,006 maize-sulfide calcium) or REM-CaS (REM-sulfide calcium) and turn into large clusters and large inclusions which not only pollute the steel, but also have a deleterious effect on the weldability in the field.

Preferably the concentration of calcium is limited to approximately 0,006 wt. % and the concentration of REE is limited to about 0.02 wt.%. In a heavy-duty steel for pipelines may be particularly effective for improving the toughness and weldability decrease in the sulfur content of approximately lower than 0.001 wt.% and reducing the oxygen content below approximately of 0.003 wt.%, preferably below approximately 0.002 wt.%, when saving values ESSP preferably higher than about 0.5 and less than about 10, where the ESSP is an indicator associated with the regulation of the shape of sulfide inclusions in steel, which is determined by the ratio ESSP = (wt.% Sa) [1 - 124 (wt.% O)]/1,25(wt.% S).

Magnesium usually forms finely dispersed oxide particles, which can suppress the coarsening of the grains and/or to promote the formation of ferrite in the grains in the heat-affected zone, thereby improving toughness in the heat-affected zone. In order for magnesium to be effective, it is desirable that the amount was at least approximately 0,0 is deteriorating toughness in the heat-affected zone.

Boron in small additives, from about 0.0005 to 0,0020 wt.% (from 5 to 20 M. D.), low-carbon steel (carbon content less than about 0.3 wt.%) can dramatically improve proclaimest such steels, contributing to the formation of strongly reinforcing components, bainite or martensite, and at the same time, boron slows the formation of softer components, ferrite and pearlite during cooling of steel from high temperature to the ambient temperature. Excess boron in the amount of about 0.002 wt.% may promote the formation of brittle particles of type borocarbide iron Fe23(C, b)6. Therefore, the preferred upper limit of the boron content is 0,0020 wt.%. To obtain the maximum effect in terms of their ability to strengthen the desired concentration of boron lies
between approximately 0.0005 and 0,0020 wt.% (from 5 to 20 M. D.). Given the above, it is possible to use boron as an alternative to expensive alloying additives to provide microstructural uniformity throughout the thickness of steel sheets. In addition, boron enhances the efficiency of both molybdenum and niobium at increasing the ability of the steel to the padding. Therefore, the additive of boron allows the, obuvki boron in steel provide the possibility of combining high strength with excellent weldability and resistance to cold cracking. Boron can also increase the strength of the intergranular phase, and hence the resistance to intergranular cracking under the action of hydrogen.

The first aim of thermomechanical processing according to the invention, which is schematically illustrated in Fig.1, is to achieve a microstructure containing predominantly fine-grained lower banit, fine mesh martensite, or mixtures thereof, obtained by the transformation of practically precrystallization grains of austenite and preferably also containing a dispersion of fine particles of cementite. The components of the lower bainite and net martensite can be additionally hardened even more fine dispersion of carbide precipitation of molybdenum (Mo2C), carbonitrides of vanadium, niobium or mixtures thereof, and in some cases may contain boron. Highly dispersed microstructure of fine-grained lower bainite, fine mesh martensite and their mixtures provides a material with high strength and good toughness at low temperature. To obtain the desired microstructures and flatten so the size across the thickness of the austenite grains is smaller, for example preferably less than approximately 5-20 μm, and thirdly, these flattened grains of austenite are filled with dislocations (to a high density and shear zones. These boundary surfaces limit the growth of transformed phases (i.e., lower banit and net martensite), when the steel plate is cooled after hot rolling.

The second purpose is to hold sufficient quantities of molybdenum, vanadium and niobium, mainly in the solid solution, after cooling the sheet to a Temperature termination hardening, so that the molybdenum, vanadium and niobium were available for deposition in the form of Mo2With, Nb (C,N) and V (C, N) during the transformation of bainite or during thermal cycles of welding to strengthen and preserve the strength of the steel. Temperature reheating a steel billet to hot rolling must be high enough to maximize the dissolution of vanadium, niobium and molybdenum, and at the same time preventing the dissolution of the particles of titanium nitride (TiN), which was formed during continuous casting of steel and serve to prevent the enlargement of the grains of austenite prior to hot rolling. To achieve this the rolling should be at least approximately 1000oWith and not higher than about 1250oC. Preferably the workpiece is re-heated by suitable means to raise the temperature of almost all of the blanks, preferably the entire workpiece to a predetermined temperature, for example, placing the workpiece in an oven for a certain time. The specific value of the temperature re-heating, which must be used for any steel composition within the present invention can easily identify the expert in this field of technology or experimentally, or calculated using an appropriate model. In addition, the oven temperature and time of re-heating, which is necessary to raise the temperature of almost all of the blanks to the preset value can be easily determined by the expert in this field of technology with reference to published industry standards.

For any steel composition within the present invention the temperature, which defines the boundary between the region of recrystallization and the area where there is no recrystallization temperature THPdepends on the chemical composition of steel and more specifically the temperature re-heating prior to rolling, the concentration of carbon, the concentration of niobium and T this temperature for each steel composition or experimentally, or by using model calculations.

Except for the temperature re-heating, which applies to almost all the harvesting, the following temperature values that are referenced in the description of the processing method of this invention, are the values measured on the surface of the steel. The temperature of the steel surface can be measured, for example, using an optical pyrometer or any other device suitable for measuring the surface temperature of steel. The values listed here speed quenching (cooling) belong to the center or nearly the center of the thickness of the sheet, and the Temperature of the termination quenching (SMI) is the highest or almost the highest temperature, which is implemented on the surface of the sheet after the termination of hardening due to heat transferred from the mid-thickness of the sheet. Specialist in this field technicians will be able to determine the desired temperature and rate of flow of quenching fluid to achieve a high cooling rate, referring to published industry standards.

Conditions of hot rolling of the present invention, in addition to surgery to reduce the size of the small grains of austenite, providing the additional cleaning of the microstructure, by limiting the size of the transformation products, i.e., fine-grained lower bainite and fine mesh martensite during cooling after rolling. If the thickness during rolling at the temperature of recrystallization decreases below described herein interval, while the thickness during rolling in the temperature range where there is no recrystallization increases above described here interval, grains of austenite will usually be small enough in size, i.e., produces large grain of austenite, resulting in reduced strength and toughness of steel and there is increased susceptibility to cracking under the action of hydrogen. On the other hand, if the thickness during rolling at the temperature of recrystallization increases above described here interval, while the thickness during rolling in the temperature range where there is no recrystallization decreases below described herein interval, the formation of zones of deformation and dislocation substructures in the grains of austenite may not correspond to a sufficient degree of purification of products of transformation, when the steel is cooled after rolling.

After rolling steel Bodvou cease at a temperature not higher than the point of turning Ar1that is , when the temperature at which completes the transformation of austenite to ferrite or to ferrite plus cementite during cooling, preferably not higher than about 550oS and more preferably not higher than approximately 500oC. Typically use quenching water; however, for the implementation of quenching can use any suitable fluid medium. In accordance with the present invention is usually not used long cooling between rolling and quenching, as it interrupts the normal flow of material passing under rolling and cooling a typical steel-rolling mill. However, it was found that by interrupting the cycle of quenching in a suitable temperature range and then cooled and hardened steel cold air having an ambient temperature to a final state, are obtained particularly advantageous components of the microstructure, without interrupting the rolling process, and thus with minimal impact on the performance of the rolling mill.

The steel sheet is subjected to hot rolling and tempering, is sent so the final processing of the cooling air, which is completed at a temperature not higher than the point listello 500oC. This final cold treatment is carried out with the aim of improving the impact toughness of the steel, providing sufficient substantially uniform deposition of fine particles of cementite throughout the microstructure of fine-grained lower bainite and fine mesh martensite. In addition, depending on the Temperature of the termination hardening and steel composition can be formed even more finely dispersed precipitated particles Mo2With and carbonitrides of niobium and vanadium, which can increase the strength.

Steel plate, obtained by the described method, has high strength and high toughness at high uniform microstructure throughout the thickness of the sheet, despite its low carbon content. For example, such a steel sheet typically has a yield strength of at least about 830 MPa, a tensile strength of at least about 900 MPa and impact strength (measured at -40oWith, for example vE-40at least about 120 joules, and these properties acceptable for use are in the pipeline. Furthermore, the reduced tendency of softening in the heat-affected zone due to the presence and complement the raised sensitivity of the steel to cracking under the action of hydrogen.

The heat-affected zone (HAZ) in the steel is developed in the course of thermal cycle caused by welding, and it may extend approximately 2-5 mm from the melt during the welding process. In the HAZ of the temperature gradient is, for example, from about 1400 to 700oWith, and this interval covers the area in which they usually occur softening phenomena, from lower to higher temperature: softening due to high-temperature tempering and softening due to the austenization are determined and slow cooling. At low temperatures, 700oWith the present vanadium, and niobium, and their carbides or carbonitrides that prevent or substantially minimize the softening due to the preservation of high density dislocations and substructures; while at elevated temperatures, of about 850-950oWith, deposited an additional amount of carbides or carbonitrides of vanadium, niobium, which minimize softening. The cumulative effect during thermal cycle caused by welding, is that the loss of strength in the HAZ is less than about 10%, preferably less than about 5%, relative to the strength of the base steel. Thus, p metal, preferably at least approximately 95% of the strength of the base metal. Strength in the HAZ is maintained, mainly due to the fact that the total concentration of vanadium and niobium is more than about 0.06 wt.%, and preferably and vanadium, and niobium are present in the steel at a concentration of greater than about 0.03 wt.%.

As is well known in the prior art pipeline is formed from a sheet using a known process, U-O-E, in which the sheet is attached U-shaped (U), then it turned into an annular shape (A), and this On the form roller after welding, extend approximately 1% (E). The formation and expansion, along with the attendant work-hardening effects, provide increased strength to the pipe.

The following examples serve to illustrate the above-described inventions.

Preferred treatment options with PNZ
According to the present invention the preferred microstructure consists of predominantly fine-grained lower bainite, fine mesh martensite, or mixtures thereof. Specifically for best combination of strength and toughness, and resistance to softening in the HAZ preferred microstructure is usernam and stable alloy carbides, containing molybdenum, vanadium, niobium or mixtures thereof. Specific examples of these microstructures is presented below.

The effect of Temperature termination hardening on the microstructure
1. Boron steel with sufficient hardenability.

The microstructure of the steel treated in the process was interrupted direct quenching (PNZ) at a speed of hardening is approximately from 20 to 35oC/C, is mainly regulated by the ability of steel for hardening, which is determined by such compositional parameters as the carbon equivalent of the AOC and Temperature termination quenching. Boron steel with sufficient hardenability of steel plate, having a preferred thickness for steel plate of the present invention, namely Se more than approximately 0.45 and less than approximately 0.7, especially suitable for processing in PNZ, providing enhanced processing capability to retrieve the target microstructures (preferably, predominantly fine-grained lower banit) and mechanical properties. The value of SMI for these steels can be in a wide range, preferably from about 550 to 150oWith, and still formed the target microstructural at 200oWith their microstructure is essentially spontaneously released net martensite. When SMI increases to approximately 270oC, the microstructure is slightly different from the one that was in SMI 200oWith, except for the weak consolidation of the particles spontaneously remitted net of martensite. In the microstructure of the sample processed by SMI approximately 295oC found a mixture of mesh martensite (the main part) and the lower bainite. But for net martensite is considerable spontaneous vacation, leading to well-developed particles spontaneously released of cementite. Refer now to Fig. 5, where micrograph 52 shows the microstructure of the above-mentioned steels processed by SMI 200oWith about 270oAnd about 295oC. consider Again Fig. 2A and 2B, which shows the micrograph in bright and dark field, demonstrating the presence of large particles of cementite in SMI approximately 295oC. These features mesh martensite can lead to a reduction in the yield strength; however, the strength of steel, shown in Fig.2A and 2B, still meets the requirements for the pipeline. Contact is a predominantly lower banit, as can be seen from Fig.3 and micrograph 54 in Fig.5. In Fig.3, electron microscopic photograph an x bright field detected characteristic of precipitated particles (fine selection) of cementite in a matrix of lower bainite. In the alloys of this example, the microstructure of the lower bainite characterized by excellent stability during thermal treatment, which resists softening even in fine-grained and microtechnical the heat-affected zone during welding. This can be explained by the presence of very fine alloy carbonitrides containing molybdenum, vanadium and niobium.

In Fig.4A and 4B shows electron microscopic images of an x, respectively, in bright and dark field, demonstrating the presence of carbide particles having a diameter less than approximately 10 nm. These small particles of carbides (fine selection) can provide a significant increase in yield strength.

In Fig. 5 presents a summary of the observations of microstructures and properties, received on the sample boron steel with a preferred variant of the chemical composition. The numbers under the points are experimental data indicate the Temperature of the termination quenching in degrees Celsius at which poluchenii>With, the predominant component of the microstructure of steel is becoming the top banit, as can be seen from the micrograph 56 in Fig.5. In addition, when SMI is about 515oWith a small, but noticeable amount of ferrite, which is also illustrated by the micrograph 56 in Fig.5. The total result is that significantly reduces the strength without a corresponding improvement of the toughness. In this experiment it was found that avoid significant amounts of upper bainite and especially the prevalence of microstructures top banita to get a good combination of strength and toughness.

2. Boron steel depleted composition.

When boron steel depleted composition (Se less than about 0.5 and more than approximately 0.3) process in PNZ, getting steel sheets having a preferred thickness for steel plate of the present invention, the resulting microstructure can contain different amounts of proeutectoid and eutectoid ferrite, which are much softer phase than the microstructure of the steel bottom bainite and net martensite. To achieve the objectives of the present invention, the total strength colcheste steel processed in PNZ, can provide a very attractive value toughness at high strength, as shown in Fig.5, for a more depleted boron steel with SMI approximately 200oC. This steel is characterized by a mixture of ferrite and spontaneously remitted net of martensite, and the last phase is predominant in this sample, as can be seen from the micrograph 58 in Fig.5.

3. Steel with sufficient proclaimedly, containing no boron.

For steels of the present invention, containing no boron, requires an increased content of other alloying elements compared to boron steels, in order to achieve the same level of proclaimest. Therefore, these steels, containing no boron, are characterized by a high carbon equivalent, preferably greater than about 0.5 and less than approximately 0.7, so that they can be efficiently process and to obtain an acceptable microstructure and properties of sheet steel having a preferred thickness for steel plate of the present invention. In Fig.6 shows measurements of the mechanical properties obtained for the steel, almost not containing the ski properties for boron steels of the present invention (circles). Numbers at each experimental point means the Temperature of the termination quenching (o(C) at which the received data. Studies have been conducted properties microstructure for steel, containing no boron. In SMI, equal 534oC, the microstructure of the steel is a predominantly ferrite with precipitation plus top banit and twinned martensite. In SMI, equal 461oC, the microstructure is a predominantly upper and lower beinit. In SMI, equal 428oC, the microstructure is a predominantly lower banit with precipitation. When SMI equal to 380 and 200oC, the microstructure is a predominantly mesh martensite with precipitation. In this example, it was found that avoid significant amounts of upper bainite and especially the prevalence of microstructures top banita to get a good combination of strength and toughness. Moreover, you should also avoid very high Temperatures termination quenching as a mixed microstructure of ferrite and twinned martensite does not provide a good combination of strength and toughness. When steel containing no boron treated in PNZ Estwenno net martensite, as shown in Fig.7. This electron-microscopic picture an x in the bright field is clearly parallel lattice structure with high dislocation density, which is high strength of this structure. It is assumed that the microstructure is desirable from the viewpoint of high strength and toughness. However, it is noteworthy that the impact strength is not so great, compared with that achieved for microstructures with a predominantly lower Bantam obtained boron-containing steels of the present invention at equivalent Temperatures termination quenching in PNZ, or, of course, at Temperatures termination hardening as low as approximately 200oC. When SMI is increased to approximately 428oC, the microstructure of the steel is rapidly changed from a structure containing mesh martensite to structures containing predominantly lower beinit. In Fig.8, electron microscopic photograph an x bright field in the sample steel D (according to the table. 2 descriptions), which was treated with PNZ Temperature termination quenching of approximately 428oWith the detected characteristic of precipitated particles of cement stability under thermal influence, resistance to softening even in fine-grained, and subcritical, and microtechnical the heat-affected zone in welded products. This can be explained by the presence of very small driftwood carbonitrides, type containing molybdenum, vanadium and niobium.

When the Temperature of the termination of hardening increases to approximately 460oWith the steel microstructure with a predominantly lower Bantam is replaced with another containing a mixture of upper and lower bainite. As you might expect, this Temperature increase stop quenching leads to a decrease in strength. This decrease in strength is accompanied by a drop in toughness, which is attributed to the presence of a significant volume fraction of the upper bainite. In Fig.9 shows electron microscopic shot at the knockouts in the light field, which shows the sample area became D (according to the table. 2 descriptions), which was treated with PNZ Temperature termination quenching of approximately 461oC. On the micrograph is manifested mesh upper bainite, characterized by the presence of the plates of cementite on the borders of ferritic grids bainite.

At even higher Temperature termination hardening, for example 534oC, the microstructure of the article on transparency in light box, presented on Fig. 10A and 10B, taken from regions of the sample steel D (according to the table. 2 descriptions), which was treated with PNZ Temperature termination quenching of approximately 534oC. this sample produced a significant amount of ferrite containing precipitates, along with brittle martensite twinning. The total result is that significantly reduced strength, without a corresponding improvement of the toughness.

To obtain acceptable properties of the steels of the present invention, containing no boron, offers the appropriate Temperature interval termination quenching, preferably from 200 to 450oWith out desired structure and properties of steel. At temperatures below approximately 150oWith mesh martensite is too rigid for optimum toughness, while at temperatures above approximately 450oWith the first steel is too much top bainite and successively increasing the number of ferrite, with harmful sediment, and finally formed twinned martensite, which leads to poor toughness of these samples.

Properties of the microstructure of these steels, virtually erevnon cooling. In the absence of additives boron education germ ferrite is not suppressed as effectively as in the case of boron steel. As a result, when high Temperatures termination hardening first formed significant amounts of ferrite in the course of turning, which causes the separation of the carbon in the remaining austenite, which subsequently turns into a high-carbon twinned martensite. Secondly, in the absence of the additive of boron in steel similarly suppress transformation in higher banit, which leads to undesirable mixed microstructures of the highest and lowest banita that do not have corresponding properties of impact strength. However, when in the steel shop no experience consistent boron steel production, processing PNZ still can be used effectively to obtain steels with exceptional strength and toughness, subject to the above rules in the processing of these steels, especially in relation to Temperature termination hardening.

Steel billets processed according to the present invention, is preferably subjected to appropriate re-heating prior to rolling, in order of vysvetiv austenite carbides and carbonitrides of molybdenum, niobium and vanadium, so that these elements can be re-deposited later, during the processing of steel, in a more desirable form, i.e. in the form of fine particles in the austenite or in the products of transformation of austenite before quenching, and cooling and welding. In the present invention re-heating is carried out at temperatures in the range from about 1000 to 1250oWith and preferably from about 1050 to 1150oC. Development of alloy composition and thermomechanical processing adapted to receive the following balance the relative strengths of the agents forming carbonitrides, especially niobium and vanadium:
approximately one third of these elements are preferably precipitated in the austenite prior to quenching,
approximately one third of these elements is preferably deposited in the products of transformation of austenite during cooling after tempering,
approximately one third of these elements preferably remains in solid solution, so that they were available for deposition in the heat-affected zone, in order to improve the normal softening observed in steels having a yield strength greater than 550 MPa.

The mode of rolling, used to get clicks is prekrashenija quenching with cooling rate of the 35oC/sec, followed by cooling to ambient temperature. When this processing PNZ get the desired microstructure, containing predominantly fine-grained lower banit, fine mesh martensite, or mixtures thereof.

Referring again to Fig.6, it can be seen that it is possible to prepare the composition and to obtain a steel D (PL. 2), which contains almost no boron (the lower the number of experimental points connected by the dashed line), and steel H and I (table. 2), which contain a specified small amount of boron (the top number of experimental points, between parallel lines), so that these steels have a tensile strength greater than 900 MPa and impact strength at -40oWith over 120 j, for example vE-40more than 120 joules. In each case, the resulting steel is characterized by predominantly fine-grained lower Bantam and/or fine mesh martensite. As shown by experimental point marked "534" (mean Temperature termination quenching in degrees Celsius at which received this sample), when the process parameters are out of limits method of the present invention, the resulting microstructure (ferrite with precipitation plus top banit and/is retene, moreover, the tensile strength or toughness, or both indicators become worse specified limits for the use of steel in pipelines.

Examples of steels made in accordance with the present invention, is shown in table. 2. Steel, designated as A - D, practically do not contain boron, whereas samples E - I contain boron additive.

Steel treated according to the method of the present invention, suitable for use in the production pipeline, but is not limited to this application. Such steel can be used in other areas, such as structural steels.

Although this invention is described in the form of preferred embodiments, it should be understood that they can be made other modifications without deviating from the scope of the invention which is set forth in the following claims.

Dictionary of terms
The point of turning Ac1: the temperature at which during heating begins to form austenite.

Point transformations Ar1: the temperature at which, during cooling ends with the transformation of austenite to ferrite or to ferrite plus cementite.

Point transformations AG3: the temperature at which during the OHL is t): a well-known technical term, used to measure the ability to weld, also Se = wt.% With + wt.% Mn/6 + (wt.% Cr + wt.% Mo + wt.% V)/5 + (wt.% Cu + wt.% Ni)/15.

ESSP is an indicator associated with the regulation of the shape of sulfide inclusions in steel, also
ESSP = (wt.% Sa)[1 - 124(wt.% O)]/1,25(wt.% S).

Fe23(C, b)6: type borocarbide iron.

HAZ: heat-affected zone.

PNZ: interrupted direct hardening.

Depleted chemical composition: Se less than about 0.50.

Mo2With: the type of the molybdenum carbide.

Nb (C, N): niobium carbonitride.

RSM: well-known technical term for expressing the ability to weld, also PCM = wt.% With + wt.% Si/30 + (wt.% Mn + wt.% Cu + wt.% Cr)/20 + wt.% Ni/60 + wt.% Mo/15 + wt.% V/10 + 5 wt.% C)).

Mainly: as used in the description of the present invention, means at least about 50 vol.%.

Hardening: as used in the description of the present invention, means accelerated cooling by any means, which uses fluid is selected to provide a larger cooling rate of steel, compared to steel cooling air.

The rate of quenching (cooling): the cooling rate in the center or almost generally the temperature, which is implemented on the surface of the sheet after the termination of hardening due to heat transferred from the mid-thickness of the sheet.

REE: rare earth metals.

Temperature TPR: temperature below which no recrystallization of austenite.

V (C, N): vanadium carbonitride.

vE-40: impact energy determined in test samples with a V-notch on Charpy at -40oC.


Claims

1. Low-alloyed, containing no boron steel, including carbon, manganese, niobium, vanadium, molybdenum, titanium and iron, characterized in that it has a tensile strength of at least 900 MPa, impact strength, measured in test samples with a V-notch on Charpy at -40oWith at least 120 j and microstructure containing predominantly fine-grained lower banit, fine mesh martensite or a mixture formed from almost precrystallization grains of austenite, while the steel contains components in the following ratio, wt. %:
Carbon - 0,03-0,10
Manganese - 1,6-2,1
Niobium - 0,01-0,10
Vanadium - 0,01-0,1
Molybdenum - 0,3-0,6
Titanium - 0,005-0,03
Iron - Rest
moreover, the carbon equivalent Witheone hundred is emoti Pcm0,35.

2. Steel under item 1, characterized in that it additionally contains at least one component selected from the group comprising, by weight. %:
Silicon - 0-0,6
Copper - 0-1,0
Nickel - 0-1,0
Chrome - 0-1,0
Calcium - 0-0,006
Aluminum - 0-0,06
REM - 0-0,02
Magnesium - 0-0,006
3. Steel under item 1, characterized in that it additionally contains a fine selection of cementite.

4. Steel under item 1, characterized in that it additionally contains a selection of carbides or carbonitrides of vanadium, niobium and molybdenum.

5. Steel under item 4, characterized in that the total content of vanadium and niobium more than 0.06 wt. %.

6. Steel under item 4, characterized in that the content of vanadium and niobium on each of the components more than 0.03 wt. %.

7. Steel under item 1, characterized in that its microstructure is a predominantly fine-grained lower beinit.

8. Steel under item 1, characterized in that it is made in the form of a sheet with a thickness of at least 10 mm

9. Steel under item 1, characterized in that it contains 0.05-0.09 wt. % carbon.

10. Steel under item 1, characterized in that it contains 0.2 to 1.0 wt. % Nickel.

11. Steel under item 1, characterized in that it contains 0.03 to 0.06 wt. % niobium.

12. Steel p is RIT of 0.015-0.02 wt. % titanium.

14. Steel under item 1, characterized in that it contains 0.001 to 0.06 wt. % aluminum.

 

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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.

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: 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: 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

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: 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

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: 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

FIELD: metallurgy; production of low-alloyed cold-resistant steel for underwater sea gas lines at working pressure up to 19 Mpa working at low temperatures.

SUBSTANCE: proposed method includes production of steel blank, heating it to temperature above As3, deformation in controllable mode at specific reduction processes and at total reduction of 50-60% followed by controllable cooling; proposed steel has the following composition, mass-%: carbon, 0.05-0.9; manganese, 1.25-1.6; silicon, 0.15-0.30; chromium, 0.01-0.1; nickel, 0.3-0.6; molybdenum, 0.10-0.25; vanadium, 0.03-0.10; aluminum, 0.02-0.05; niobium, 0.01-0.06; copper, 0.2-0.4; calcium, 0.001-0.005; sulfur, 0.0005-0.005; phosphorus, 0.005-0.015; the remainder being iron; preliminary deformation of blanks is performed at temperature of 950-850°C at total reduction of 50-60%; then, blank is cooled down to temperature of 820-760°C at rate of cooling of 15°C/s on controllable cooling unit and final deformation is performed additionally at temperature of 770-740°C to required thickness of skelp at total reduction of 60-76%; further cooling is performed at higher rate of 35-55°C/s to temperature of 530-350°C, after which skelp is cooled in jacket to temperature of 150±20°C and then in the air. New stage of the proposed method makes it possible to manufacture tubes of 1067-1420 mm in diameter at thickness of walls of 24-40 mm which are used for sea gas pipe lines working at pressure of up to 19 Mpa.

EFFECT: enhanced strength, ductility and cold resistance; enhanced operational reliability; increased service life.

2 tbl, 1 ex

FIELD: metallurgy, namely cold resistant steels.

SUBSTANCE: cold resistant steel for machines and apparatuses, namely in gas- and oil production industry operating in condition of cold climate. Such steel contains, mass %: carbon, 0.15 - 0.22; manganese, 0.3 - 0.6; silicon, 0.15 - 0.40; vanadium, 0.08 -0.12; titanium, 0.001 - 0.040; niobium, 0.001 - 0.040; aluminum, 0.03 - 0.06; sulfur, 0.010 - 0.020; phosphorus, 0.010 - 0.020; cerium, 0.005 - 0.05; calcium, 0.001 - 0.01; barium, 0.001 - 0.01; iron, the balance.

EFFECT: improved strength and cold resistance of steel.

5 tbl

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