Two-phase steel and method of its manufacture

 

(57) Abstract:

The invention relates to high-strength steel and its production. Steel can be used in building structures, pipelines, etc., two-phase steel contains ferrite and martensite-bainite phase. Ferritic phase has a reinforcing particles mainly carbides and carbonitrides of vanadium and niobium. The steel obtained by rolling into sheets, with the first pass rolling is carried out at a temperature above the recrystallization of austenite, the second pass rolling at a temperature below the recrystallization temperature of the austenite and the third highest in the temperature range between the points of turning Ar3and Ar1and cooling water to a temperature below approximately 400°C. the Proposed steel may contain components in the following ratio, wt.%: carbon 0,05-0,12, silicon from 0.01 to 0.50, manganese 0.4 to 2.0, niobium 0,03-0,12, vanadium 0.05 to 0.15, molybdenum 0.2 to 0.8, titanium 0,015-0,03, aluminum 0,01-0,03, Fe rest. When this option proclaimest steel SSR 0,24. If the steel contains the heat-affected zone of the weld, the strength of the steel is not less than 95% of the strength of the base metal. The technical result of the invention is to provide essentially homogeneous Sobranie relates to high-strength steel and its production. This steel is suitable for building structures and can be used as a semifinished product for a line pipe. More specifically the invention relates to the production of two-phase high-strength steel sheet, which contains ferrite and martensite/bainite phase and the microstructure and mechanical characteristics of which are essentially isotropic throughout the thickness of the sheet, and the sheet has excellent toughness and weldability.

Two-phase steel containing ferrite as a relatively soft phase and martensite/banit as a relatively solid phase, is obtained by annealing at a temperature between the transformation of Ar3and Ar1and then cooled to room temperature with a speed within the speed of the cooling air and the cooling rate of the water. The choice of annealing temperature depends on the chemical composition of steel and the desired volume ratio of the phases ferrite and martensite/bainite.

On low-carbon and low-alloy two-phase steels, which are the object of active research metallurgists, there are many publications, for example: materials of the conference "Fundamentals of Dual-Phase Steels" ("fundamentals of two-phase steels") and "Formable HSLA and Dual Phase Steelss" ("the Shape of the s steels mainly limited by the automobile industry, where their unique abilities to mechanical hardening is used to improve formemost automotive sheet steel processing and stamping. Therefore, the application of two-phase steels limited thin (typically 2-3 mm and less than 10 mm) leaves from outside the yield strength and tensile strength, respectively 345-415 MPa (50-60 ksi) and 485-620 MPa (70 to 90 ksi). In addition, the martensite/bainite phase is typically about 10-40% of the volume of the microstructure, and the rest is softer ferritic phase.

For example, application Japan 02 070019 A, 1990, the known two-phase steel strength 70 kg/mm2(686 MPa) containing ferritic phase in an amount up to 60% vol. and the martensite-bainite phase, as the rest. However, the known steel does not have the necessary high yield, which does not allow to use it in preparations for the pipe of the pipeline.

From U.S. patent 4273838 known welded steel containing the heat-affected zone in the weld. However, the known steel does not have sufficient strength in the heat affected zone.

Proposal from Japan 62 174322 A, 1987, a method of manufacturing a two-phase steel, which includes heating the workpiece to a temperature of 950-1200oC, rolling in the sheet when the temperature is P>oC speed 2-40oC/s, obtaining the structure of steel 3-15 vol.% martensite and 20-40% of bainite in the martensite-bainite phase and the rest of the ferrite. However, the known method of manufacturing steel is not possible to obtain a two-phase steel with high yield strength and toughness in the heat-affected zone for use in preparations for the pipe of the pipeline.

Object of the invention is the use of high capacity two-phase steel to mechanical hardening is not to improve formemost, and to achieve a relatively high yield strength - up to 690 MPa (100 ksi), preferably 760 MPa (110 ksi) after deformation of the steel sheet by 1-3% in the formation of pipes for pipeline and, thus, to apply the two-phase sheet steel with characteristics described here as blanks for tubes.

The technical effect of this invention is the provision of essentially homogeneous microstructure throughout (component of at least 10 mm) the thickness of the sheet. As the effect of the invention is to achieve such a fine distribution of the phase components in the microstructure, which will allow you to extend the useful boundary volume fraction of bainite/martensite about DSE one effect of the invention is to create a high-strength two-phase steel with good weldability and high resistance to softening in the heat affected zone (hereinafter referred to HAZ).

This task is solved in that two-phase steel containing ferrite and martensite-bainite phase, contains martensite-bainite phase in the amount of 40 to 80 vol.%, in which the volume fraction bainite does not exceed 50% and the ferritic phase comprises particles of carbide or carbonitride of vanadium, niobium or molybdenum, or a mixture thereof with a particle diameter of not more than 50 angstroms, while the yield strength of steel after 1 to 3% strain is at least 758 MPa.

The steel may have a homogeneous microstructure at a thickness of at least 15 mm

The steel may contain residual films of austenite thickness less than 500 angstroms in the composition of the martensite-bainite phase.

The heat in thermal cycles of welding can be from 1 to 5 kJ/mm

The objective of the invention is to create a high-strength two-phase steel with good weldability and high resistance to softening in the heat affected zone (hereinafter - HAZ).

This task is solved in that the welded steel, including the base metal and heat-affected zone, contains a ferrite phase and 40-80% vol. martensite-bainite phase, and the content of bainite not more than 50 vol.%, and ferritic phase includes Cheam, the strength of the steel in the heat-affected zone is not less than 95% of the strength of the base metal having a yield strength of at least 758 MPa after 1 to 3% strain.

The strength of the heat-affected zone may be at least 98% of the strength of the base metal.

The steel may contain residual films of austenite thickness less than 500 angstroms in the composition of the martensite-bainite phase.

When heated in a thermal cycles of welding in steel can form additional particles of carbide or carbonitride of vanadium, niobium or molybdenum.

The heat of welding may be about 1 to 5 kJ/mm

The steel may contain components in the following ratio, wt. %:

Carbon - 0,05 - 0,12

Silicon - 0,01 - 0,50

Manganese - 0,4 - 2,0

Niobium - 0,03 - 0,12

Vanadium 0.05 to 0.15

Molybdenum - 0,2 - 0,8

Titanium - 0,015 - 0,03

Aluminum - 0,01 - 0,03

Iron - Rest

Particle- less than or equal to 0.24,

where Particleis a parameter of proclaimeth that represents the following value:

< / BR>
where C, Si, Mn, Cu, Ni, Cr, Mo and V contents of the respective elements in the steel, wt.%.

The amount of niobium and vanadium in Stalin> The invention is also a method of manufacturing steel, which allows to obtain a two-phase steel with high yield strength and toughness in the heat-affected zone for use in preparations for the pipe of the pipeline.

This task is solved in that in the method of manufacturing a two-phase steel comprising heating a steel billet, the first compression by rolling the blank in the sheet, at least one passage in the temperature interval recrystallization of austenite, the second compression by rolling the sheet at least in one pass, and the final cooling of the laminated sheet, the heating is carried out to a temperature sufficient to dissolve substantially all of the carbonitrides of vanadium, niobium, rolling the sheet at the second compression is carried out in a temperature range below the temperature of recrystallization of austenite, but above the point of turning ANDr3then spend the additional cooling compressed sheet to a temperature selected between the points of turning Ar3and Ar1and additionally spend the third compression by rolling the cooled sheet, at least one pass, and the final cooling of the sheet hold water to a temperature not Whiteley deformation at 1-3%.

Heating can be performed up to a temperature of 1150-1250oC.

The first compression can be performed with the degree of deformation of 30-70%, a second - 40-70% and the third - 15-25%.

Cooling to a temperature between the transformation of Ar3and Ar1can be air.

Cooling operation after the second compression can be performed with a duration, sufficient to 20-60 vol.% steel moved in the ferritic phase.

Final cooling of the laminated sheet can be performed with a speed of at least 25oC/s

Cooling after the second compression can be started from a temperature above 725oC, but below 800oC.

The sheet may be additionally formed in the annular or tubular material.

The annular or tubular material can be given for 1-3%.

It is possible to produce a steel that contains components in the following ratio, wt. %:

Carbon - 0,05 - 0,12

Silicon - 0,01 - 0,50

Manganese - 0,4 - 2,0

Niobium - 0,03 - 0,12

Vanadium 0.05 to 0.15

Molybdenum - 0,2 - 0,8

Titanium - 0,015 - 0,03

Aluminum - 0,01 - 0,03

Iron - Rest

Particle- No more than 0,24,

where Particleis a parameter of proclaimeth, as indicated above.

The steel may further contain chromium in amounts of from 0.3 to 1.0 wt.%.

The task is solved according to the invention by the fact that the chemical composition of the steel thus consistent with thermo-mechanical regime rolling, provided that the production of high-strength, i.e., having a yield strength of more than 690 MPa (100 ksi) and at least 760 (110 ksi) after 1-3% deformation of two-phase steel, which is suitable as preparation for a pipe of the pipeline and has a microstructure comprising 40-80, preferably 50-80% vol. martensite/bainite in the ferritic matrix, and the share of bainite in the martensite/bainite phase is less than 50%.

In a preferred variant embodiment of the invention the ferrite matrix additionally strengthen the high-density dislocations, i.e. more than 1010cm/cm3and fine particles of at least one, and preferably all of the components from a number of carbides or carbonitrides of vanadium, niobium and molybdenum carbide, i.e., (V,Nb)(C,N) and Mo2C. These very small (diameter less than 50 angstroms) particles are formed in the ferrite phase due to interfacial reactions precipitation, which caused the austenite-ferrite transformation temperature below Ar3. Such particles are glaski composition and thermomechanical characteristics of rolling, possible to obtain a two-phase steel of a thickness of at least about 15, preferably about 20 mm ultra-high strength.

The strength of the steel depends on the presence of martensite/bainite phase, the increase in volume fraction which increases the strength. However, the strength must be combined with toughness (ductility), provide a ferritic phase. For example, after 2% strain yield strength of at least 690 MPa (100 ksi) when at least about 40 vol.% martensite/bainite, but at the level of at least about 830 MPa (120 ksi) when at least about 60 vol.% martensite/bainite.

Required, i.e. with a high density of dislocations and particles of vanadium and niobium in the ferritic phase, the steel is produced by compression when the finishing rolling at temperatures between points of turning Ar3and Ar1and cooling to room temperature, in contrast to the method of production of two-phase steels for the automotive industry is not thicker than 10 mm and yield strength 345-415 MPa (50-60 ksi) in which to provide the required formemost ferritic phase should not contain reinforcing particles. These particles are formed intermittently in the mobile phase boundary ferrite and austenite. However, they wypadkow rolling and heat treatment. Thus, vanadium and niobium are key elements in the chemical composition of steel.

In Fig.1 presents a snapshot of the executed scanning electron microscope, where visible (grey) ferrite and (lighter) martensite/bainite phase tempered alloy A3. This figure shows the resulting two-phase steel according to the invention.

In Fig. 2 presents the performed transmission electron microscope picture contained in the ferrite strengthening particles of carbonitrides of niobium and vanadium size of less than about 50, preferably in the range of about 10-50 angstroms.

In Fig. 3A and 3b presents made in accordance with the method of the bright and dark field transmission electron of microsemi fragment of the microstructure of the solid phase (martensite).

In Fig. 4 presents graphs of Vickers hardness in the HAZ (ordinate) for steel according to the invention (solid line) and similar commercially available pipeline steel X100 (dashed line). In the HAZ claimed were hardly noticeable decrease in strength, whereas the steel X100 this loss of strength is around 15%.

Thus, the steel according to the invention provides high strength, otlichnoooo 0,07-0,09

Si - 0,01-0,5

Mg is 0.4 to 2.0, preferably 1.0 to 2.0, especially 1,2-2,0

Nb - 0,03-0,12, preferably of 0.05-0.1

V - 0,05-0,15

Mo - 0,2-0,8

Cr - 0,3-1,0 (desirable for the hydrogen-containing environment)

Ti - 0,015-0,03

Al - 0,01-0,03

Particle- no more than 0,24

Fe and incidental impurities - rest

The sum of the concentrations of vanadium and niobium is not less than 0.1 wt.%, while the preferred concentration of each is not less than 0.04%. The presence of such well-known impurities like nitrogen, phosphorus and sulfur, reduced to a minimum, although a certain amount of nitrogen, as explained below, it is desirable to obtain inhibiting the grain growth of TiN particles. In a preferred embodiment, the nitrogen content is in the range 0.001 to 0.01%, sulfur not over 0.01% of phosphorus - not more than 0.01%. This chemical composition of the steel does not contain boron in the sense that boron is not added and the amount should be less than 5 ppm, preferably less than 1 ppm.

In General the material according to the invention is manufactured in the usual way in the form of a piece of steel of the above composition. This workpiece is heated to sufficient to dissolve substantially all of the carbonitrides of vanadium and niobium temperature, preferably within 1150-1250oC. as a result, essentially all of the elements hirokatsu procurement: for the first compression up to 30-70% - in the first temperature range in which the recrystallization of austenite; for the second compression by 40-70% in the second, lower temperature range in which no recrystallization of austenite, but the above points Ar3the beginning of the transformation of austenite into ferrite during cooling of the steel; and after cooling the air to a temperature in the range between the points of turning Ar3and Ar1(the complete transformation of austenite into ferrite during cooling of steel where 20-40% of the austenite transforms into ferrite) - for the third compression 15-20%. Compressed workpiece is quenched in water cooling speeds of at least 25oC/s, preferably at least about 35oC/s to a temperature not higher than 400oWith, which excluded a further transformation into ferrite, and, if desired, laminated tempered high-strength sheet steel, suitable for the production of pipes for pipeline, cool air to room temperature. As a result, the steel becomes uniform in grain size not more than 10 μm, and preferably not more than 5 μm.

High-strength steel must possess a number of properties achieved by the combination of chemical analysis with thermo-mechanical processing. Described below

Carbon provides a matrix any hardening steels and welds regardless of their microstructure and dispersion hardening is mainly due to the formation of small particles NbC and VC, if they are sufficiently small and numerous. In addition, the allocation NbC during hot rolling slow recrystallization and prevents the grain growth, and thus serves as a means of improving the quality of grain austenite, helping increase both strength and toughness at low temperature. Carbon also increases the ability to take the training, i.e., to form a more solid and stronger microstructure during cooling of the steel. When the carbon content of < 0.01% of this strengthening effect is not observed, and when > 0,12% of the steel is susceptible to cracking when welding on cold in the field and its viscosity, including HAZ in the weld seam area will be below.

Manganese strengthens the matrix of the steel and the weld and significantly improves the ability to take the training. At least Mn, necessary to achieve the required strength of 0.4%. Like carbon, Mn in excess affects the viscosity of the sheet and seam and also causes cracking when welding on cold field, so its upper limit is 2.0%. This limit also n is rovodnik steels, which promotes cracking under the influence of hydrogen (hereinafter - PBB).

Silicon is always injected into the steel as a deoxidizer in an amount of at least 0.1 percent. Taken in excess silicon adversely affects the toughness in the HAZ, which, with its concentration of > 0.5% is reduced to an unacceptable level.

Niobium is added to improve the quality of grain in the microstructure of the steel after rolling, which increases both strength and ductility. Allocation NbC during hot rolling slows and inhibits the recrystallization grain growth, serving as a means of improving the quality of grain of austenite. He tells extra strength after annealing due to the precipitation of NbC particles. However, its excess adversely affects the weldability and toughness in the HAZ, therefore, the upper limit of its concentration of 0.12%.

Titan adding in a small amount forms fine particles of TiN that improve fine grain structure after rolling in the HAZ of steel, thereby increasing the viscosity. Ti add so much to the ratio of Ti/N ranged from 2.0 to 3.4. Excess Ti affects the viscosity of steel and welded joints due to the formation of larger particles of TiN or TiC. The concentration of Ti is less than 0,002% cannot provide sufficient is t to these steel as a deoxidizer. At high (>0.05%) of the aluminium content tends to the formation of inclusions of type Al2O3adversely affecting the toughness of steel and its HAZ.

Vanadium is added to the dispersion hardening at the loss of small particles VC in the steel during annealing and HAZ during cooling after welding. Being in solution, V contributes to increasing the hardness of steel after quenching. Therefore, it is useful to maintain the strength of high-strength steel in the HAZ. The upper limit of 0.15% installed because the excess of V leads to cracking when welding on cold field conditions, and also deteriorates the toughness of steel and its HAZ. Due to interfacial allocation of particles V(C,N) having a diameter of not more than about 50, preferably 10-50 angstroms, it also serves as a strong reinforcer eutectoid ferrite.

Molybdenum increases proclaimest steel by direct quenching with the formation of the solid microstructure of the matrix and provides the dispersion hardening during tempering due to the particles Mo2C and NbMo. Excess Mo contributes to cracking when welding on cold in the field and deteriorates the toughness of steel and its HAZ, so set the upper limit of 0.8%.

Chromium also increases prochitat to prevent access of hydrogen, for promotes the formation on the steel surface oxide film with a high content of Cr2O3. When the concentration of Cr < 0.3% of the resistant layer Cr2O3on the steel surface is not formed. Like molybdenum, excess Cr contributes to cracking when welding on cold in the field and deteriorates the toughness of steel and its HAZ, therefore, the upper limit of its concentration of 1.0%.

The penetration and the inclusion of nitrogen in the steel cannot be prevented when it is melting. In the claimed steel its admixture useful for forming small particles of TiN, which prevent grain growth during hot rolling with the quality of laminated steel and its HAZ. To obtain the required number of fractions TiN need at least 0.001% of nitrogen. However, its excess adversely affects the toughness of steel and its HAZ, therefore, the maximum nitrogen concentration is set at a level of 0.01%.

Thermomechanical treatment has two objectives: to obtain a fine tapered grain of austenite and to provide a high density of dislocations and shear zones in two phases.

The first goal is achieved by intensive rolling at temperatures above and below the recrystallization temperature of austenite, but always above point is scoi temperature flatten it. Eventually cooling to a temperature below the point Ar3the beginning of the transformation of austenite into ferrite is formed a mixture of finely dispersed austenite and ferrite, and when rapid cooling to a temperature below the point Ar1- a mixture of fine ferrite and martensite/bainite.

The second goal is achieved by a third compression by rolling the flattened grains of austenite at temperatures between points ar1and Ar3when 20-60% of the austenite has passed into the ferrite.

In achieving the desired fine distribution of phases that are component parts of the alloy plays an important role in the claimed method of thermal processing.

The temperature boundary between the temperature ranges recrystallization and exceptions recrystallization of austenite depends on the heating temperature before rolling, the concentrations of carbon and niobium and the degree of compression achieved in the aisles rolling. For each composition of steel, this temperature can be determined either experimentally or by calculations on the model.

The pipe is manufactured from a sheet known has been operating a UOE method, according to which the sheet bend U - and then-shaped and O-shaped workpiece give 1-3%. Formation and distribution with related/P> The following examples serve to illustrate the invention.

500-pound (226,8 kg) portion of the alloy with the following chemical composition was obtained by vacuum-induction melting, poured into blanks, pulled in plate thickness of 102 mm (4 inch), heated for two hours before 1240oC and subjected to hot rolling mode according to table 2.

Alloy and thermomechanical processing were designed to provide the following distribution of strong sources of carbonitrides, in particular Nb and V: (a) about one-third of their compounds released in the austenite before quenching (loose particles provide resistance to recrystallization, penetrating grain of austenite, which is why they are before the transformation of austenite become fine); b) about one-third of their compounds is released during the transformation of austenite into ferrite in the area between critical points and below the critical point (loose particles contribute to the hardening of the ferritic phase); C) about one-third of their compounds remains in solid solution, to stand out in the HAZ for the reduction or elimination of normal for other steels loss of hardness.

The finished product had a thickness of 20 mm and contained 45% of ferrite and 55% martensite/bainite.

oC gives 100% austenite, for point Ar3is below 800oC. As seen in Fig.1, the quenching from about 725oC provides a conversion of 75% of austenite, for point Ar1is near this temperature. Therefore, the temperature window for obtaining a two-phase alloy is approximately 75oC. table 3 summarizes data about the temperature at the finishing rolling temperature hardening, volume fractions and microhardness Vickers.

Although more volumetric fractions of a second (martensite/bainite phase is usually characterized by poor fluidity and viscosity, steel according to the invention are distinguished by a fluidity sufficient for the formation and distribution of the alloy has been operating a UOE process. It ensures the maintenance of an effective amount of such elements of the microstructure, as the unit of martensite (less than 10 microns) and every single particle in it (less than 1 µm). In Fig.1 (scanning electron microscope micronance) is seen in a two-phase containing ferrite and martensite microstructure obtained in the mode A3. All two-phase steel progeny a micrograph in Fig. 2 shows a very thin interfacial dispersion of particles in the zone of ferrite steel A3. As a rule, near the borders of the second phase is visible, evenly distributed on the amount of eutectoid ferrite volume fraction increases with decreasing temperature quenching.

The transmission electron microsemi on figures 3A and 3b show the nature of the second phase of the declared steels. Here are seen predominantly lamellar martensite microstructure with some bainite phase. In the martensite visible thin (thickness less than 500 angstroms), the film residual austenite near the borders of the plates, as shown on a dark image of Fig. 3b. The morphology of martensite provides not only durable, but also viscous phase, and contributes to a strengthening and maintaining good viscosity two-phase steel.

Table 4 shows the tensile strength at break and fluidity of two samples of alloy A.

Thanks to the excellent mechanical hardening of these microstructures after 2% elongation of the tube forming the desired minimum tensile strength is at least at the level of 689 MPa (100 ksi), preferably 758 MPa (110 ksi).

Table 5 shows the impact strength of the Sha, the technical conditions e ASTM).

In table 5 the values of impact energy show excellent viscosity of the claimed steel at -40oC level of at least 100 joules, preferably about 120 j.

A key aspect of the invention is a high-strength steel with good weldability and high resistance to loss of strength in the HAZ. For testing cracking in the cold and loss of strength of the HAZ were performed laboratory welds. Shown in Fig. 4 clearly shows that in contrast to the known articles, such as commercially available steel for pipelines X100, declared a two-phase steel is not exposed to significant or noticeable loss of strength in the HAZ. In the same steel X100, on the contrary, there is a softening of the HAZ by 15% in comparison with the base metal. In the claimed steel HAZ retains at least about 95%, preferably at least about 98% strength of the base metal. This strength is achieved when the heat for welding is within 1-5 kJ/mm.

1. Two-phase steel containing ferrite and martensite-bainite phase, characterized in that it contains a martensite-bainite phase in the amount of 40 to 80 rpm. % where volume fraction bainite does not exceed 50% and the ferritic phase includes h is the yield strength of steel after 1 - 3% strain is at least 758 MPa.

2. Steel under item 1, characterized in that it has a homogeneous microstructure at a thickness of at least 15 mm

3. Steel under item 1, characterized in that it contains residual films of austenite thickness less than 500 in the composition of the martensite-bainite phase.

4. Steel under item 1, characterized in that the heat for welding is from 1 to 5 kJ/mm

5. Welded steel, including the base metal and heat-affected zone, characterized in that it contains a ferrite phase and 40 - 80% vol. martensite-bainite phase, in which the content of bainite not more than 50 vol.%, and ferritic phase comprises particles of carbide or carbonitride of vanadium, niobium or molybdenum, or a mixture thereof with a particle size of not more than 50 , and the strength of the steel in the heat-affected zone is not less than 95% of the strength of the base metal having a yield strength of at least 758 MPa after 1 to 3% strain.

6. Steel under item 5, characterized in that the strength of the heat affected zone is not less than 98% of the strength of the base metal.

7. Steel under item 5, characterized in that it contains residual films of austenite thickness less than 500 in the composition of the martensite-baniatsa additional particles of carbide or carbonitride of vanadium, niobium or molybdenum.

9. Steel under item 8, characterized in that the heat for welding is approximately from 1 to 5 kJ/mm

10. Steel under item 5, characterized in that it contains components in the following ratio, wt.%:

Carbon - 0,05 - 0,12

Silicon - 0,01 - 0,50

Manganese - 0,4 - 2,0

Vanadium 0.05 to 0.15

Molybdenum - 0,2 - 0,8

Titanium - 0,015 - 0,03

Aluminum - 0,01 - 0,03

Iron - Rest

Particle- less than or equal to 0.24,

where Particleis a parameter of proclaimeth that represents the following value:

< / BR>
where C, Si, Mn, Cu, Ni, Cr, Mo and V contents of the respective elements in the steel, wt.%.

11. Steel under item 10, wherein the amount of niobium and vanadium is at least 0.1 wt.%.

12. Steel under item 10, characterized in that it further comprises from 0.3 to 1.0 wt.% chrome.

13. A method of manufacturing a two-phase steel comprising heating a steel billet, the first compression by rolling the blank in the sheet, at least one passage in the temperature interval recrystallization of austenite, the second compression by rolling the sheet at least in one pass, and the final cooling of the laminated sheet, characterized in that h is s, rolling the sheet at the second compression is carried out in a temperature range below the temperature of recrystallization of austenite, but above the point of turning Ar3then spend the additional cooling compressed sheet to a temperature selected between the points of transformation Ar3and Ar1and additionally spend the third compression by rolling the cooled sheet, at least one pass, and the final cooling of the sheet hold water to a temperature not higher than 400oC, you get a steel with ultimate tensile strength of at least 689 MPa, after further deformation of 1 - 3%.

14. The method according to p. 13, characterized in that the heating is carried out before 1150 - 1250oC.

15. The method according to p. 13, wherein the first compression is performed with the degree of deformation of 30 - 70%, second 40 - 70% and the third 15 - 25%.

16. The method according to p. 13, characterized in that the cooling is to a temperature between the points of transformation Ar3and Ar1avodat air.

17. The method according to p. 13, characterized in that the cooling operation after the second compression spend a duration sufficient for 20 - 60% vol. steel moved in the ferritic phase.

18. The method according to p. 13, characterized in that econab on p. 13, characterized in that the cooling after the second compression start from a temperature above 725oC, but below 800oC.

20. The method according to p. 13, characterized in that the sheet is additionally formed in the annular or tubular material.

21. The method according to p. 13, characterized in that the annular or tubular material handed out at 1 - 3%.

22. The method according to p. 13, characterized in that made the steel that contains components in the following ratio, wt.%:

Carbon - 0,05 - 0,12

Silicon - 0,01 - 0,50

Manganese - 0,4 - 2,0

Niobium - 0,03 - 0,12

Vanadium 0.05 to 0.15

Molybdenum - 0,2 - 0,8

Titanium - 0,015 - 0,03

Aluminum - 0,01 - 0,03

Iron - Rest

Particle- No more than 0,24,

where Particleis a parameter of proclaimeth, as indicated above.

23. The method according to p. 22, wherein the amount of niobium and vanadium in the steel is not less than 0.1 wt.%.

24. The method according to p. 23, characterized in that the steel contains niobium in an amount not less than 0.04 wt.%.

25. The method according to p. 22, characterized in that the steel further comprises chromium in an amount of 0.3 to 1.0 wt.%.

 

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The invention relates to the field of ferrous metallurgy, in particular to the composition of steel and can be used in the production of high-strength rod deformed bars, as well as for the manufacture of prestressed concrete structures

Die steel // 2041968
The invention relates to metallurgy, in particular to steel for the manufacture of cold forming dies, and can be used in mechanical engineering, aviation and other industries

The invention relates to metallurgy, in particular to the structural steel for the manufacture of shells of containers for storage and transportation of spent nuclear fuel

Maraging alloy // 2025530
The invention relates to the field of metallurgy, to find Maraging alloys for the production of highly critical parts of the aviation and other industries

The invention relates to metallurgy, in particular to the development of Invar alloy with a low temperature coefficient of linear expansion

The invention relates to permanent magnets and can find application, in particular, Electromechanical products requiring high performance permanent magnets

Steel // 2016124
The invention relates to metallurgy, in particular to steel, and can be used in mechanical engineering, the automotive industry for the manufacture of springs, leaf springs, torsion bars, pneumatic chisels and other elastic products

The invention relates to alloys with shape memory effect, which is to be used in industry for non-threaded pipe joints, bump stops, emergency heating regulators, etc
The invention relates to the treatment (including thermal) of the rolled strip, in particular tape, designed for packaging a rolled metal
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