Steel for 800MPa-grade torsion beam and preparation method thereof

Abstract

The invention relates to steel for an 800MPa-grade torsion beam and a preparation method of the steel, and the method comprises the following steps: a steel billet with set chemical components is obtained, and the set chemical components comprise 0.06%-0.10% of C, 1.20%-1.80% of Mn, 0.30%-0.60% of Cr, 0.10%-0.40% of Mo, 0.01%-0.03% of Nb and 0.05%-0.20% of V; heating and rolling the steel billet to obtain a hot-rolled plate; the hot-rolled plate is subjected to water cooling, the first cooling speed of water cooling and the final temperature of water cooling are controlled, the steel for the torsion beam is obtained, and in the water cooling process, a corresponding water outlet device within the first set length of the edge of the hot-rolled plate is controlled to be in a closed state; and controlling a second cooling speed within a second set length of the head and within a second set length of the tail of the hot-rolled sheet. The mechanical property uniformity of the steel for the torsion beam is improved.

Description

Technical Field

[0001] The present application relates to the technical field of steel preparation, and in particular to an 800MPa grade torsion beam steel and a preparation method thereof. Background Art

[0002] The torsion beam of a car is a semi-independent suspension, which connects the left and right longitudinal arms through a crossbeam. When the car rolls during driving, the crossbeam will twist and deform, thereby providing torsional rigidity to improve the handling stability of the car. The traditional torsion beam is stamped into an open shape with a stabilizer bar in the middle. Figure 1 A schematic diagram of a torsion beam structure provided in an embodiment of the present application; see Figure 1 ,like Figure 1 (a) shows good fatigue performance, but the component structure is complex and the deadweight is large. The latest structural form uses a torsion beam formed into a closed cross-section of the tube, such as Figure 1 (b) This closed-section torsion beam can better meet the needs of space and load, has a significant weight reduction effect, and is in line with the trend of green and low-carbon development of automobiles. However, this closed-section torsion beam needs to be formed after welding, which has higher requirements on the mechanical properties of the material.

[0003] Therefore, there is an urgent need for a closed-section torsion beam steel with good mechanical properties and uniform mechanical properties in all directions without increasing the process cost. Summary of the invention

[0004] The present application provides an 800MPa grade torsion beam steel and a preparation method thereof to solve the following technical problem: how to improve the uniformity of the mechanical properties of the torsion beam steel.

[0005] In a first aspect, the present application provides a method for preparing 800MPa-grade torsion beam steel, the method comprising:

[0006] A steel billet with a set chemical composition is obtained; wherein the set chemical composition includes: C, S, Mn, Cr, Mo, Nb and V, and in terms of mass fraction, the content of C is 0.06% to 0.10%, the content of Mn is 1.20% to 1.80%, the content of Cr is 0.30% to 0.60%, the content of Mo is 0.10% to 0.40%, the content of Nb is 0.01% to 0.03%, and the content of V is 0.05% to 0.20%;

[0007] Heating and rolling the steel billet to obtain a hot-rolled plate;

[0008] The hot-rolled plate is water-cooled, and a first cooling rate of the water-cooling and an end temperature of the water-cooling are controlled to obtain 800MPa-grade torsion beam steel; wherein, during the water-cooling process, a corresponding water outlet device within a first set length of the edge of the hot-rolled plate is controlled to be in a closed state, and a second cooling rate within a second set length of the head and a third set length of the tail of the hot-rolled plate is controlled.

[0009] Optionally, the first cooling rate is ≥100°C / s, and / or the end temperature of the water cooling is 400°C to 500°C.

[0010] Optionally, the first set length is 500mm to 1000mm.

[0011] Optionally, the second set length is within 50m, and the third set length is within 50m;

[0012] The second cooling rate is 40°C / s to 80°C / s.

[0013] Optionally, the set chemical composition also includes: Si, Als, P and S, wherein:

[0014] The content of Si is 0.05% to 0.20%, the content of Als is 0.02% to 0.04%, the content of P is ≤0.02%, and the content of S is ≤0.009%.

[0015] Optionally, the method further includes:

[0016] The 800 MPa torsion beam steel is air-cooled, and then coiled and slowly cooled to obtain a finished 800 MPa torsion beam steel product.

[0017] Optionally, the heating process parameters include: temperature of 1180° C. to 1280° C., and time of 120 min to 160 min.

[0018] Optionally, the rolling includes rough rolling and finish rolling; wherein, the process parameters of the rough rolling include: the total deformation of the rough rolling is ≥60%, and the outlet temperature of the rough rolling is 1050°C to 1100°C.

[0019] Optionally, the process parameters of the finishing rolling include: the total deformation of the finishing rolling is ≤40%, and the outlet temperature of the finishing rolling is 820°C to 920°C.

[0020] In a second aspect, the present application provides an 800 MPa grade torsion beam steel prepared by the method described in any embodiment of the first aspect.

[0021] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0022] The preparation method of the 800MPa torsion beam steel provided in the embodiment of the present application obtains a steel billet with a set chemical composition; wherein, in terms of mass fraction, the set chemical composition includes: C, S, Mn, Cr, Mo, Nb and V, in terms of mass fraction, the content of C is 0.06% to 0.10%, the content of Mn is 1.20% to 1.80%, the content of Cr is 0.30% to 0.60%, the content of Mo is 0.10% to 0.40%, the content of Nb is 0.01% to 0.03%, the content of V is The amount is 0.05% to 0.20%; heating the steel billet; rolling the heated steel billet to obtain a hot-rolled plate; water-cooling the hot-rolled plate, and controlling the first cooling rate of the water cooling and the terminal temperature of the water cooling to obtain 800MPa grade torsion beam steel; wherein, during the water cooling process, the corresponding water outlet device within a first set length of the edge of the hot-rolled plate is controlled to be in a closed state, and the second cooling rate within a second set length of the head and the second set length of the tail of the hot-rolled plate is controlled. The C content is 0.06% to 0.10%, and the Mn content is 1.20% to 1.80%. C can realize interstitial solid solution in the Fe lattice and substitutional solid solution of Mn and Fe atoms, ensuring the basic strength of the steel at about 600MPa. The Cr content is 0.30% to 0.60%, and the Mo content is 0.10% to 0.40%. Cr and Mo inhibit the diffusion of C during the phase change process, thereby obtaining a hard phase structure at a higher temperature and increasing the strength of the steel by about 100MPa. The Nb content is 0.01% to 0.03%. Nb has a significant dragging effect on the diffusion of C in the high temperature stage, inhibits the dynamic recrystallization and growth of austenite in the finishing rolling stage, refines the grains, and can increase the strength of the steel by about 100MPa. The V content is 0.05% to 0.20%. V is easy to combine with C atoms to generate VC. VC has good thermal stability and small size. In the embodiment of the present application, the strength of the steel can be further increased by about 100MPa, so the above-mentioned composition design ensures that the strength of the steel is above 800MPa; heating the billet can improve the uniformity of the composition of the billet; rolling the heated billet can refine the austenite grains of the billet; water cooling the hot-rolled plate, and controlling the first cooling rate of the water cooling and the terminal temperature of the water cooling can obtain a hard phase structure with a suitable supersaturated C solid solubility; and in the water cooling process, controlling the corresponding water outlet device within the first set length of the edge of the hot-rolled plate to be in a closed state, and controlling the second cooling rate within the second set length of the head of the hot-rolled plate and the second set length of the tail of the hot-rolled plate can ensure the cooling uniformity of the hot-rolled plate in the width and length directions, and avoid the hot-rolled plate The strip edge, strip head and strip tail are cooled too fast, thereby improving the uniformity and stability of the mechanical properties of the hot-rolled plate. In summary, the uniformity of the mechanical properties of the steel used for the torsion beam is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0024] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0025] Figure 1 A schematic diagram of a torsion beam structure provided in an embodiment of the present application; wherein (a) is an open type, and (b) is a closed type;

[0026] Figure 2 A schematic flow chart of a method for preparing 800MPa grade torsion beam steel provided in an embodiment of the present application;

[0027] Figure 3 A microstructure diagram of an 800MPa-grade torsion beam steel after welding provided in an embodiment of the present application;

[0028] Figure 4 A microstructure diagram (enlarged view) of an 800MPa grade torsion beam steel after welding process provided in an embodiment of the present application. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0030] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0031] In the present application, unless otherwise specified, the directional words used, such as "upper" and "lower", refer specifically to the directions of the drawings in the accompanying drawings. In addition, in the description of the specification of the present application, the terms "include", "comprise", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: the existence of A alone, the existence of A and B at the same time, and the existence of B alone. Among them, A and B can be singular or plural.

[0032] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0033] In a first aspect, the present application provides a method for preparing 800MPa grade torsion beam steel. Figure 2 A schematic diagram of a process for preparing a 800MPa grade torsion beam steel provided in an embodiment of the present application; see Figure 2 , the method comprising:

[0034] S1. Obtain a steel billet with a set chemical composition; wherein the set chemical composition includes: C, S, Mn, Cr, Mo, Nb and V, and in terms of mass fraction, the content of C is 0.06% to 0.10%, the content of Mn is 1.20% to 1.80%, the content of Cr is 0.30% to 0.60%, the content of Mo is 0.10% to 0.40%, the content of Nb is 0.01% to 0.03%, and the content of V is 0.05% to 0.20%;

[0035] In the embodiment of the present application, the C content is 0.06% to 0.10%, and the Mn content is 1.20% to 1.80%. C can realize interstitial solid solution in the Fe lattice and substitutional solid solution of Mn and Fe atoms, ensuring the basic strength of the steel at about 600MPa; the Cr content is 0.30% to 0.60%, and the Mo content is 0.10% to 0.40%. Cr and Mo inhibit the diffusion of C during the phase change process, thereby obtaining a hard phase structure at a higher temperature, and increasing the strength of the steel by about 100MPa. Right; the Nb content is 0.01% to 0.03%. Nb has a significant dragging effect on the diffusion of C in the high temperature stage, inhibits the dynamic recrystallization and growth of austenite in the finishing rolling stage, refines the grains, and can increase the strength of the steel by about 100MPa; the V content is 0.05% to 0.20%. V is easy to combine with C atoms to generate VC. VC has good thermal stability and small size. In the present invention, the strength of the steel can be further increased by about 100MPa. Therefore, the above-mentioned component design ensures that the strength of the steel is above 800MPa. Exemplarily, the C content can be 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, etc., the Mn content can be 1.20%, 1.30%, 1.40%, 1.50%, 1.60%, 1.70%, 1.80%, etc., the Cr content can be 0.30%, 0.40%, 0.50%, 0.60%, etc., the Mo content can be 0.10%, 0.20%, 0.30%, 0.40%, etc., the Nb content can be 0.01%, 0.02, 0.03%, etc., and the V content can be 0.05%, 0.10%, 0.15%, 0.20%, etc.

[0036] In addition, the chemical composition of the steel used for the torsion beam of the embodiment of the present application is designed to have a low carbon equivalent, the welding process is simple, and air cooling can be performed directly after welding. Figure 3 A microstructure diagram of an 800MPa-grade torsion beam steel after welding provided in an embodiment of the present application; Figure 4 A microstructure diagram (enlarged diagram) of a 800MPa torsion beam steel after welding process provided in the embodiment of the present application; please refer to Figures 3-4 The addition of a certain amount of Cr and Mo elements in the composition design ensures that the weld and its heat-affected zone still obtain hard phase structure under air cooling conditions (see Appendix Figure 3 ), at the same time, during the welding heating process, the diffused C atoms combine with V atoms to form VC, which is secondary precipitation strengthened in the weld and heat affected zone (see Appendix Figure 4 ), which makes up for the strength drop caused by coarse grains under air cooling conditions, ensures that the hardness of the base material and the weld is close, which is beneficial to the forming performance of the welded pipe.

[0037] In some embodiments, the set chemical composition further includes: Si, Als, P and S, wherein:

[0038] The content of Si is 0.05% to 0.20%, the content of Als is 0.02% to 0.04%, the content of P is ≤0.02%, and the content of S is ≤0.009%.

[0039] In an embodiment of the present application, further, the above-mentioned set chemical composition also includes: Si, Als, P and S, the Si content can be 0.05%, 0.10%, 0.15%, 0.20%, etc., the Als content can be 0.02%, 0.03%, 0.04%, etc., the P content can be 0.02%, 0.01%, etc., and the S content can be 0.009%, 0.008%, etc.

[0040] S2, heating and rolling the steel billet to obtain a hot-rolled plate;

[0041] In some embodiments, the heating process parameters include: a temperature of 1180° C. to 1280° C. and a time of 120 min to 160 min.

[0042] In the embodiments of the present application, a high temperature and short time heating method is adopted to ensure uniform solid solution of alloy elements, effectively reduce or eliminate dendrite segregation during solidification of the ingot, improve the uniformity of the composition of the ingot, and provide basic conditions for uniform final organization and mechanical properties. Exemplarily, the above heating temperature can be 1180°C, 1200°C, 1220°C, 1240°C, 1260°C, 1280°C, etc., and the heating time can be 120min, 125min, 130min, 135min, 140min, 145min, 150min, 155min, 160min, etc.

[0043] In some embodiments, the rolling includes rough rolling and finish rolling; wherein the process parameters of the rough rolling include:

[0044] The total deformation of rough rolling is ≥60%, and the outlet temperature of rough rolling is 1050℃~1100℃.

[0045] In the embodiment of the present application, the rolling stage is divided into two parts: rough rolling and finish rolling. By defining the process parameters of rough rolling, it is possible to ensure that refined and uniform austenite grains are obtained; in addition, each pass of rough rolling is descaled to ensure the surface quality of the hot-rolled plate. Exemplarily, the total deformation of the above-mentioned rough rolling can be 60%, 62%, 64%, 66%, etc., and the outlet temperature of the rough rolling can be 1050°C, 1060°C, 1070°C, 1080°C, 1090°C, 1100°C, etc.

[0046] In some embodiments, the process parameters of the finishing rolling include: the total deformation of the finishing rolling is ≤40%, and the outlet temperature of the finishing rolling is 820°C to 920°C.

[0047] In the embodiment of the present application, the total deformation of the finishing rolling is limited to ≤40% to ensure the plate shape and rolling stability of the hot-rolled plate; the outlet temperature of the finishing rolling is limited to ensure that the austenite grains are further fully refined while taking into account the rolling stability of thin-gauge products. For example, the total deformation of the finishing rolling can be 40%, 38%, 36%, 34%, etc., and the outlet temperature of the finishing rolling can be 820°C, 840°C, 860°C, 880°C, 900°C, 920°C, etc.

[0048] S3. Water-cooling the hot-rolled plate, and controlling a first cooling rate of the water-cooling and an end temperature of the water-cooling to obtain 800 MPa-grade torsion beam steel; wherein, during the water-cooling process, controlling a corresponding water outlet device within a first set length of the edge of the hot-rolled plate to be in a closed state, and controlling a second cooling rate within a second set length of the head and a second set length of the tail of the hot-rolled plate.

[0049] In some embodiments, the first cooling rate is ≥100°C / s, and / or the end point temperature of the water cooling is 400°C to 500°C.

[0050] In some embodiments, the first set length is 500 mm to 1000 mm.

[0051] In some embodiments, the second set length is within 50 m, the third set length is within 50 m, and the second cooling rate is 40° C. / s to 80° C. / s.

[0052] In the embodiment of the present application, the hot rolling is followed by direct rapid cooling, and the middle temperature measuring point of the cooling line is used as the process control temperature. The hot rolled plate is water cooled, and the first cooling rate of the water cooling and the terminal temperature of the water cooling are controlled, so that a hard phase structure with a suitable supersaturated C solid solubility can be obtained; and in the water cooling process, the corresponding water outlet device within the first set length of the edge of the hot rolled plate is controlled to be in a closed state, and the second cooling rate within the second set length of the head of the hot rolled plate and the second set length of the tail of the hot rolled plate is controlled, so that the uniformity of cooling of the hot rolled plate in the width and length direction of the hot rolled plate can be ensured, and the cooling rate of the edge, head and tail of the hot rolled plate can be avoided to be too fast, thereby improving the uniformity and stability of the mechanical properties of the hot rolled plate. Exemplarily, the first cooling rate can be 100°C / s, 105°C / s, 110°C / s, 120°C / s, etc., the end temperature of water cooling can be 400°C, 420°C, 440°C, 460°C, 480°C, 500°C, etc., and the second cooling rate can be 40°C / s, 50°C / s, 60°C / s, 70°C / s, 80°C / s, etc.

[0053] In some embodiments, the method further comprises:

[0054] The 800 MPa torsion beam steel is air-cooled, and then coiled and slowly cooled to obtain a finished 800 MPa torsion beam steel product.

[0055] In the embodiment of the present application, the rear end fine-tuning water is controlled to be in a closed state (air cooling), and the steel plate is put into a slow cooling pit after coiling to improve the internal stress of the steel plate caused by sudden cooling after hot rolling and improve the performance stability of the steel plate.

[0056] In a second aspect, the present application provides an 800 MPa grade torsion beam steel prepared by the method described in any embodiment of the first aspect.

[0057] In the embodiment of the present application, the 800MPa torsion beam steel meets the following mechanical properties: yield strength Rp 0.2 : 650MPa~820MPa, tensile strength Rm: 800MPa~950MPa, elongation A: ≥15%, hole expansion rate λ: 55%.

[0058] The 800MPa-grade torsion beam steel is realized based on the preparation method of the above-mentioned 800MPa-grade torsion beam steel. The specific steps of the preparation method of the 800MPa-grade torsion beam steel can refer to the above-mentioned embodiment. Since the 800MPa-grade torsion beam steel adopts part or all of the technical solutions of the above-mentioned embodiments, it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiments, which will not be repeated here one by one.

[0059] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to national standards. If there is no corresponding national standard, then the conditions recommended by the manufacturer are followed.

[0060] The embodiment of the present application provides a method for preparing 800MPa-grade torsion beam steel. Please refer to Table 1 for the chemical composition (wt%) of the 800MPa-grade torsion beam steel, and Table 2 for the preparation process parameters of the 800MPa-grade torsion beam steel.

[0061] Table 1 Composition of 800MPa grade hot-rolled high-performance torsion beam steel (wt%), the remainder is Fe and unavoidable impurities)

[0062]

[0063] Table 2 Preparation process parameters of 800MPa grade torsion beam steel

[0064]

[0065] The mechanical properties and hole expansion performance tests were conducted on the torsion beam steels prepared in Examples 1 to 3 and Comparative Examples 1 to 2. Please refer to Table 3, Table 4 and Table 5 for the test results.

[0066] Table 3 Mechanical properties and hole expansion properties of 800MPa grade torsion beam steel - width direction (within 50m of coil head)

[0067]

[0068]

[0069] Table 4 Mechanical properties and hole expansion properties of 800MPa grade torsion beam steel - width direction (middle of coil: 50m from the head and 50m from the tail)

[0070]

[0071]

[0072] Table 5 Mechanical properties and hole expansion properties of 800MPa grade torsion beam steel - width direction (within 50 meters of the tail of the coil)

[0073]

[0074]

[0075] From Tables 3 to 5, it can be seen that the 800MPa torsion beam steel provided in the embodiment of the present application has excellent mechanical properties, and the uniformity of mechanical properties in all directions is good. However, in Comparative Example 1, the contents of C and Cr are not within the scope of the present application, and no Mo element is added, and the cooling process is not within the scope of the present application. The mechanical properties and hole expansion performance of the final steel plate cannot meet the target requirements, and the mechanical properties and hole expansion performance in the width direction are quite different, and the mechanical properties and hole expansion performance differences in the head, middle and tail in the length direction are also large; in Comparative Example 2, the cooling process is not within the scope of the present application, and the mechanical properties and hole expansion performance of the final steel plate in the width direction are quite different, and it is difficult to meet the mechanical properties and hole expansion requirements of the steel within the width edge of 500mm.

[0076] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for preparing 800MPa grade torsion beam steel, characterized in that: The method comprises: A steel billet with a set chemical composition is obtained; wherein the set chemical composition includes: C, S, Mn, Cr, Mo, Nb and V, and in terms of mass fraction, the content of C is 0.06% to 0.10%, the content of Mn is 1.20% to 1.80%, the content of Cr is 0.30% to 0.60%, the content of Mo is 0.10% to 0.40%, the content of Nb is 0.01% to 0.03%, and the content of V is 0.05% to 0.20%; Heating and rolling the steel billet to obtain a hot-rolled plate; The hot-rolled plate is water-cooled, and a first cooling rate of the water-cooling and an end temperature of the water-cooling are controlled to obtain 800MPa-grade torsion beam steel; wherein, during the water-cooling process, a corresponding water outlet device within a first set length of the edge of the hot-rolled plate is controlled to be in a closed state, and a second cooling rate within a second set length of the head and a third set length of the tail of the hot-rolled plate is controlled.

2. The method according to claim 1, characterized in that The first cooling rate is ≥100°C / s, and / or the end point temperature of the water cooling is 400°C to 500°C.

3. The method according to claim 1, characterized in that The first set length is 500 mm to 1000 mm.

4. The method according to claim 1, characterized in that The second set length is within 50m, and the third set length is within 50m; The second cooling rate is 40°C / s to 80°C / s.

5. The method according to claim 1, characterized in that: The set chemical composition also includes: Si, Als, P and S, wherein, The content of Si is 0.05% to 0.20%, the content of Als is 0.02% to 0.04%, the content of P is ≤0.02%, and the content of S is ≤0.009%.

6. The method according to claim 1, characterized in that The method further comprises: The 800 MPa torsion beam steel is air-cooled, and then coiled and slowly cooled to obtain a finished 800 MPa torsion beam steel product.

7. The method according to claim 1, characterized in that The heating process parameters include: temperature of 1180° C. to 1280° C. and time of 120 min to 160 min.

8. The method according to claim 1, characterized in that The rolling includes rough rolling and finish rolling; wherein the process parameters of the rough rolling include: the total deformation of the rough rolling is ≥60%, and the outlet temperature of the rough rolling is 1050°C to 1100°C.

9. The method according to claim 8, characterized in that The process parameters of the finishing rolling include: the total deformation of the finishing rolling is ≤40%, and the outlet temperature of the finishing rolling is 820°C to 920°C.

10. A 800MPa grade torsion beam steel prepared by the method according to any one of claims 1 to 9.

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