A 1000 mpa grade hot-rolled steel and method of manufacture

Abstract

The application provides a 1000MPa-grade hot-rolled steel and a preparation method, and belongs to the technical field of steel production, the chemical components of the hot-rolled steel include C, Mn, P, S, Al, Ti, Si, N and Fe; the content of C is 0.01-0.03% in mass fraction, the content of Mn is 2.5-5.5%, the content of P is ≤0.02%, the content of S is ≤0.005%, the content of Al is 0.1-0.15%, the content of Ti is 0.4-0.8%, the content of Si is 0.3-0.8%, and the content of N is ≤0.008%; the preparation method includes processes such as smelting, heating, hot rolling and cooling, etc. The application can make the steel have excellent mechanical properties, the yield strength of the steel is ≥1000MPa, the tensile strength is ≥1200MPa, the elongation is ≥15%, the cold bending radius is 2 times the thickness size, the cold bending angle is 180°, and the fatigue strength is ≥850MPa, which meets the use requirements of commercial vehicle high fatigue strength steel. Thus, the technical problem that the current existing high-strength steel cannot meet the high fatigue performance is solved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of steel production, in particular to a 1000MPa-grade hot-rolled steel and a preparation method thereof. BACKGROUND

[0002] In 2017, the automobile industry basic compulsory national standard GB1589-2016 was officially implemented, and the remediation efforts for illegal phenomena such as overload and over-limit were greatly increased. In addition, the emission standards are becoming increasingly stringent, and the demand for lightweighting of commercial vehicles is imminent. Research shows that the thickness of the steel plate is reduced by 0.05, 0.10, and 0.15 mm, and the vehicle body can be reduced by 6%, 12%, and 18%, respectively. When the vehicle is reduced by 10% of its total mass, the emission can be reduced by 5% to 6%, and the fuel consumption can be reduced by 6% to 8%. Therefore, the lightweighting of commercial vehicles is of great significance, and the commercial lightweighting gradually rises to the national strategic level.

[0003] However, at present, the commercial vehicle industry uses a large amount of steel plates below the 700MPa grade, and the thickness of the steel plate is large, which causes the vehicle to be heavy and generates large fuel consumption, and there are deficiencies in environmental protection and economy. With the development trend of automobile lightweighting, high-strength steel is increasingly used in the automobile industry to replace the previous low-strength grade automobile steel. The yield strength and tensile strength of high-strength automobile steel are much higher than those of low-strength grade automobile steel, and the plasticity and fatigue performance are reduced a lot, which is prone to low-stress fracture. The low fatigue performance and fracture problem seriously restrict the use and development of high-strength steel in the manufacturing process of commercial vehicles. Therefore, it is of great significance to develop high-strength automobile steel with high fatigue performance. SUMMARY

[0004] The application provides a 1000MPa-grade hot-rolled steel and a preparation method thereof to solve the technical problem that the existing high-strength steel cannot meet the high fatigue performance.

[0005] In a first aspect, the application provides a 1000MPa-grade hot-rolled steel, and the chemical composition of the hot-rolled steel comprises C, Mn, P, S, Al, Ti, Si, N and Fe, wherein the mass fraction of C is 0.01% to 0.03%, the mass fraction of Mn is 2.5% to 5.5%, the mass fraction of P is ≤0.02%, the mass fraction of S is ≤0.005%, the mass fraction of Al is 0.10% to 0.15%, the mass fraction of Ti is 0.4% to 0.8%, the mass fraction of Si is 0.3% to 0.8%, and the mass fraction of N is ≤0.008%.

[0006] The content of C is 0.01% to 0.03%, the content of Mn is 2.5% to 5.5%, the content of P is ≤0.02%, the content of S is ≤0.005%, the content of Al is 0.10% to 0.15%, the content of Ti is 0.4% to 0.8%, the content of Si is 0.3% to 0.8%, and the content of N is ≤0.008%.

[0007] Optionally, the microstructure of the hot-rolled steel comprises 15% to 20% ferrite, 65% to 75% bainite, and 0% to 10% austenite in terms of volume fraction.

[0008] Optionally, the microstructure grain size grade is 13-14.

[0009] Optionally, the hot-rolled steel satisfies at least one of the following properties: yield strength ≥ 1000 MPa, tensile strength ≥ 1200 MPa, elongation ≥ 15%, cold bending radius is 2 times the thickness size, cold bending angle is 180 degrees, fatigue strength ≥ 850 MPa.

[0010] In a second aspect, the application provides a method for preparing a 1000 MPa grade hot-rolled steel, for preparing the hot-rolled steel of any one of the embodiments of the first aspect, the method comprising:

[0011] subjecting the molten steel to converter smelting, vacuum treatment and continuous casting to obtain a casting blank having the chemical composition;

[0012] heating the casting blank in stages and controlling the process parameters of the heating;

[0013] rolling the heated casting blank in stages and controlling the first process parameters of the rolling to obtain a hot-rolled steel;

[0014] cooling the hot-rolled steel and controlling the second process parameters of the cooling, and then coiling to obtain a 1000 MPa grade hot-rolled steel.

[0015] Optionally, the heating the casting blank in stages and controlling the process parameters of the heating comprises:

[0016] adopting a high-temperature charging method for the casting blank and controlling the charging temperature, then carrying out two-stage rapid heating and controlling the temperature and time of the two-stage rapid heating, and controlling the temperature fluctuation of different parts of the casting blank.

[0017] Optionally, the charging temperature is 500-1000°C; and / or,

[0018] the two-stage rapid heating comprises a preheating stage and a soaking stage, the preheating stage temperature is 1100-1150°C, the preheating stage time is 80-100 min, the soaking stage temperature is 1150-1200°C, and the soaking stage time is 30-40 min; and / or,

[0019] the temperature fluctuation of different parts of the casting blank is ≤ 50°C.

[0020] Optionally, the first process parameters include the rough rolling end temperature and the finish rolling finish rolling temperature; wherein,

[0021] the rough rolling end temperature is 950-1040°C, and the finish rolling finish rolling temperature is 750-810°C.

[0022] Optionally, the second process parameter comprises a cooling speed, a cooling temperature and a temperature of cooling water; wherein,

[0023] The cooling speed is > 50℃ / s, the cooling temperature is 500℃-550℃, and the temperature of the cooling water is ≤ 30℃.

[0024] Optionally, the time of the vacuum treatment is > 25min.

[0025] The above technical solution provided by the embodiments of the present application has the following advantages compared with the prior art:

[0026] The 1000MPa grade hot-rolled steel provided by the embodiments of the present application has a high proportion of ferrite content by reasonably designing the chemical composition, improves the forming performance of the material, and strictly controls the Ti, S and N content in the steel, reduces the size and quantity of impurities such as TiN and MnS in the steel, thereby further improving the fatigue performance of the steel. BRIEF DESCRIPTION OF DRAWINGS

[0027] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and serve to explain the principles of the present application together with the specification.

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0029] Figure 1 A flowchart of a preparation method of a 1000MPa grade hot-rolled steel provided by the embodiments of the present application. DETAILED DESCRIPTION

[0030] In order to make the purposes, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0031] Various embodiments of the present application can exist in a range of forms; it should be understood that the description in a range form is merely for the convenience and brevity, and should not be understood as a hard limitation to the scope of the present application; therefore, it should be considered that the described range has disclosed all possible sub-ranges and single values within the range. For example, it should be considered that the range description from 1 to 6 has 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 values within the described range, such as 1, 2, 3, 4, 5, and 6, which applies to any range. In addition, whenever a numerical range is indicated in the present text, it is meant to include any cited number (fraction or integer) within the indicated range.

[0032] In the description of the present application, the terms "comprise", "contain" and the like mean "comprise but not limited to". In the present text, relational terms such as "first" and "second" and the like are merely 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 the entities or operations. In the present text, "and / or" describes the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B can represent the cases of A alone, A and B together, and B alone. Where A and B can be singular or plural. In the present text, "at least one" means one or more, and "multiple" means two or more. "At least one", "at least one of the following" or the like means any combination of the items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can represent a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

[0033] Unless otherwise specifically stated, the various raw materials, reagents, instruments and equipment, etc. used in the present application can be purchased on the market or can be prepared by existing methods.

[0034] In a first aspect, the present application provides a 1000 MPa grade hot-rolled steel, the chemical composition of the hot-rolled steel can include: C, Mn, P, S, Al, Ti, Si, N and Fe; in terms of mass fraction,

[0035] The content of C can be 0.01-0.03%, the content of Mn can be 2.5-5.5%, the content of P can be ≤0.02%, the content of S can be ≤0.005%, the content of Al can be 0.1-0.15%, the content of Ti can be 0.4-0.8%, the content of Si can be 0.3-0.8%, and the content of N can be ≤0.008%.

[0036] In the embodiments of the present application, the positive effect of controlling the content of C to be 0.01-0.03% is that C, as an important alloying element in steel, is important for improving the strength of the steel plate and promoting the precipitation of the second phase. However, if the content of C is too high, the welding performance and forming performance will be affected. Specifically, the content of C can be 0.01%, 0.02%, 0.03%, etc.

[0037] The positive effect of controlling the content of Mn to be 2.5-5.5% is that Mn can reduce the phase transition temperature of austenite to ferrite, expand the austenite region in the iron-carbon phase diagram, promote the microstructure transformation of the steel at medium temperature, and obtain uniform microstructure, so that the steel has excellent corrosion resistance and higher strength. However, if the content of Mn is too high, the degree of intermediate segregation will increase, which is not conducive to corrosion resistance and fatigue performance. Specifically, the content of Mn can be 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, etc.

[0038] The positive effect of controlling the content of P to be ≤0.02% is that P, as a harmful inclusion in steel, has a great damaging effect on the low-temperature impact toughness, elongation, weldability, and fatigue crack propagation characteristics of the steel. Specifically, the content of P can be 0%, 0.006%, 0.012%, 0.015%, 0.02%, etc.

[0039] The positive effect of controlling the content of S to be ≤0.005% is that S, as a harmful inclusion in steel, has a great damaging effect on the low-temperature toughness and fatigue crack propagation characteristics (mainly long sulfide) of the steel. More importantly, S combines with Mn in the steel to form MnS inclusions, and the plasticity of MnS during hot rolling makes MnS extend along the rolling direction to form MnS inclusion bands along the rolling direction, which severely damages the low-temperature impact toughness and fatigue crack propagation characteristics of the steel plate. Specifically, the content of S can be 0%, 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, etc.

[0040] The positive effect of controlling the content of Al to be 0.10-0.15% is that Al is a good deoxidizing element that can reduce the austenite phase region. However, if the content of Al is too high, aluminum oxide clumps are easily formed and the continuous casting process is not conducive. Specifically, the content of Al can be 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, etc.

[0041] The positive effect of controlling the content of Ti to be 0.4-0.8%: Ti is a good fine-grain strengthening element, and meanwhile, when the titanium carbonitride precipitates in the steel plate reach a certain density, the corrosion resistance of the steel plate can be significantly improved. However, if the content of Ti is too high, Ti-containing metal inclusions are easily formed. Specifically, the content of Ti can be 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, etc.

[0042] The positive effect of controlling the content of Si to be 0.3-0.8%: Si can improve the strength of the steel in the form of solid solution strengthening, can also expand the medium-temperature phase transition zone, inhibit the precipitation of carbides, improve the fatigue crack propagation resistance of the steel, and can also improve the corrosion resistance of the steel. However, if the content of Si is too high, the segregation of the steel plate, the low-temperature toughness and the weldability of the steel plate will be seriously deteriorated. Specifically, the content of Si can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, etc.

[0043] The positive effect of controlling the content of N to be ≤0.008%: Ti has a great affinity with N, and TiN particles are dispersedly generated to inhibit the excessive growth of austenite grains during the heating and hot rolling of the slab. Specifically, the content of N can be 0%, 0.002%, 0.004%, 0.006%, 0.008%, etc.

[0044] In addition to the range of the above chemical components being limited, from the viewpoint of improving the material formability and economy, the present application does not add valuable alloy elements such as Cu, Ni, Mo, etc.

[0045] In some embodiments, the microstructure of the hot-rolled steel can include, in volume fraction: ferrite 15-20%, bainite 65-75%, and austenite 0-10%.

[0046] In the embodiments of the present application, the positive effect of ferrite being 15-20%, bainite being 65-75%, and austenite being 0-10%: the comprehensive strength and toughness are good.

[0047] In some embodiments, the grain size level of the microstructure can be 13-14 levels.

[0048] In the embodiments of the present application, the positive effect of the grain size level being 13-14 levels: the grain boundary area is large when the grain size level is in this range, so that the steel has good mechanical properties. The embodiments of the present application obtain a good match between high strength and high fatigue performance through ultra-fine grain control technology on conventional continuous casting and hot continuous rolling production line equipment.

[0049] In some embodiments, the hot-rolled steel can satisfy the following conditions: yield strength ≥ 1000 MPa, tensile strength ≥ 1200 MPa, elongation ≥ 15%, cold bending radius is 2 times the thickness size, cold bending angle is 180 degrees, and fatigue strength ≥ 850 MPa.

[0050] In a second aspect, the present application provides a method for preparing a 1000 MPa grade hot-rolled steel, for preparing the hot-rolled steel of any one of the embodiments of the first aspect, the method comprising:

[0051] S1, converting smelting, vacuum treatment and continuous casting of molten steel to obtain a casting blank with the chemical composition;

[0052] In some embodiments, the vacuum treatment time is > 25 min.

[0053] In the embodiments of the present application, the positive effect of controlling the vacuum treatment time > 25 min is to remove N, H, O and other gas elements cleanly, reduce the generation of impurities in the steel, and improve the toughness of the steel. Specifically, the vacuum treatment time can be 26 min, 30 min, 35 min, 40 min, 45 min, etc.

[0054] S2, heating the casting blank in stages, and controlling the process parameters of the heating;

[0055] In some embodiments, the heating of the casting blank in stages and the control of the process parameters of the heating comprise:

[0056] The casting blank is heated in a high-temperature furnace, and the temperature of the furnace is controlled, then two-stage rapid heating is performed, and the temperature and time of the two-stage rapid heating are controlled, and the temperature fluctuation of different parts of the casting blank is controlled.

[0057] In some embodiments, the furnace temperature is 500℃-1000℃; and / or,

[0058] The two-stage rapid heating comprises a preheating stage and a soaking stage, the preheating stage temperature is 1100℃-1150℃, the preheating stage time is 80min-100min, the soaking stage temperature is 1150℃-1200℃, and the soaking stage time is 30min-40min; and / or,

[0059] The temperature fluctuation of different parts of the casting blank is ≤ 50℃.

[0060] In the embodiments of the present application, two-stage rapid heating is adopted, and the positive effect of controlling the heating temperature is that the cast blank passes through two stages of preheating and soaking, effectively preventing cracking of the cast blank in the furnace and during rolling, and fully solid-solution of alloy elements, uniform cast blank temperature, more uniform structure, and more stable product mechanical properties and use performance. The heating temperature is an important factor affecting fatigue performance, and in the temperature range of the present application, excessively coarse austenite grains and coarse precipitates caused by excessively high heating temperature can be avoided, thereby avoiding adverse effects on fatigue performance. Specifically, the charging temperature can be 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, etc. The temperature of the preheating stage can be 1100℃, 1110℃, 1120℃, 1130℃, 1140℃, 1150℃, etc. The time of the preheating stage can be 80min, 90min, 100min, etc. The temperature of the soaking stage can be 1150℃, 1160℃, 1170℃, 1180℃, 1190℃, 1200℃, etc. The time of the soaking stage can be 30min, 35min, 40min, etc. The temperature fluctuation of different parts of the cast blank can be 5℃, 10℃, 20℃, 30℃, 40℃, 50℃.

[0061] S3, the heated cast blank is rolled in stages, and a first process parameter of the rolling is controlled to obtain a hot-rolled steel;

[0062] In some embodiments, the first process parameter can include a rough rolling end temperature and a finish rolling finishing temperature; wherein,

[0063] The rough rolling end temperature can be 950℃-1040℃, and the finish rolling finishing temperature can be 750℃-810℃.

[0064] In the embodiments of the present application, the positive effect of controlling the rough rolling end temperature to be 950℃-1040℃ is that if the rough rolling end temperature is lower than 950℃, the finish rolling finishing temperature cannot reach the set value, increasing the rolling load and energy consumption; and if it is higher than 1040℃, it will cause coarse grains. Specifically, the rough rolling end temperature can be 950℃, 970℃, 990℃, 1010℃, 1030℃, 1040℃, etc.

[0065] The positive effect of controlling the finish rolling finishing temperature to be 750℃-810℃ is that if the finish rolling finishing temperature is lower than 750℃, rolling will be performed in the two-phase region of the material, causing defects such as mixed grains; and if it is higher than 810℃, the original austenite grains of the steel will be excessively coarse, reducing the fatigue strength of the steel. Specifically, the finish rolling finishing temperature can be 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, etc.

[0066] S4, cooling the hot-rolled steel and controlling a second process parameter of the cooling, and then coiling to obtain the 1000MPa grade hot-rolled steel.

[0067] In some embodiments, the second process parameter can include a cooling speed, a cooling temperature, and a temperature of cooling water; wherein,

[0068] The cooling speed can be >50℃ / s, the cooling temperature can be 500℃-550℃, and the temperature of the cooling water can be ≤30℃.

[0069] In the embodiments of the present application, the cooling speed is controlled to be >50℃ / s, the cooling temperature is 500℃-550℃, and the temperature of the cooling water is ≤30℃. The positive effects are: ensuring uniformity of the structure, playing a fine-grain strengthening role, and preventing or delaying the premature precipitation of carbides during the cooling process, so that the carbides are dispersedly precipitated in ferrite, thereby improving the strength. Specifically, the cooling speed can be 55℃ / s, 60℃ / s, 70℃ / s, 80℃ / s, etc. The cooling temperature can be 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, etc. The temperature of the cooling water can be 10℃, 20℃, 30℃, etc.

[0070] The 1000MPa grade hot-rolled steel is realized based on the above-mentioned method for preparing the 1000MPa grade hot-rolled steel. The specific steps of the method for preparing the 1000MPa grade hot-rolled steel can refer to the above-mentioned embodiments. Since the 1000MPa grade hot-rolled 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 described here one by one.

[0071] The present application will be further described in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. The experimental methods not specified in the following examples are generally determined according to national standards. If there is no corresponding national standard, the international standard, the conventional condition, or the condition suggested by the manufacturer is used.

[0072] The steel liquid of Examples 1-8 and Comparative Examples 1-4 was prepared and cast into a slab. The chemical composition of the cast slab is shown in Table 1.

[0073] Table 1: Chemical composition of each example and comparative example (wt%)

[0074] Group C Mn P S Al Ti N Si Example 1 0.01 2.5 0.008 0.005 0.1 0.4 0.002 0.3 Example 2 0.012 2.8 0.02 0.004 0.115 0.45 0.0005 0.4 Example 3 0.015 3.2 0.015 0.002 0.125 0.55 0.0007 0.5 Example 4 0.020 3.7 0.013 0.0002 0.118 0.65 0.001 0.6 Example 5 0.022 4.0 0.01 0.0003 0.135 0.5 0.008 0.65 Example 6 0.025 4.5 0.009 0.001 0.145 0.75 0.007 0.7 Example 7 0.028 5.0 0.018 0.0008 0.15 0.7 0.006 0.75 Example 8 0.030 5.5 0.012 0.0001 0.128 0.8 0.005 0.8

[0075] Based on the chemical composition of the above-mentioned 1000MPa grade hot-rolled steel, the embodiments of the present application provide a method for preparing a 1000MPa grade hot-rolled steel, which comprises:

[0076] S11, carrying out converter smelting, vacuum treatment and continuous casting of molten steel to obtain a casting blank with the chemical composition;

[0077] S21, heating the casting blank in stages and controlling the process parameters of the heating;

[0078] S31, rolling the heated casting blank in stages and controlling the first process parameters of the rolling to obtain hot-rolled steel;

[0079] S41, cooling the hot-rolled steel and controlling the second process parameters of the cooling, and then coiling to obtain 1000MPa grade hot-rolled steel. For specific preparation process parameters, see Table 2.

[0080] Table 2 Main process parameters of each example and comparative example

[0081]

[0082] Table 3 Mechanical properties of each example and comparative example

[0083]

[0084]

[0085] Table 3 shows that the automobile steel in the examples of the present application has a yield strength of ≥1000MPa, a tensile strength of ≥1200MPa, an elongation of ≥15%, and a fatigue strength of ≥850MPa, and has excellent mechanical properties.

[0086] The above description is merely a specific implementation of the present application, enabling those skilled in the art to 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 scope consistent with the principles and novel features disclosed herein.

Claims

1. A 1000 MPa grade hot-rolled steel, characterized in that, The chemical composition of the hot-rolled steel includes C, Mn, P, S, Al, Ti, Si, N, the rest is Fe and inevitable impurities, and the mass fraction is The content of C is 0.01-0.03%, the content of Mn is 2.5-5.5%, the content of P is ≤0.02%, the content of S is ≤0.005%, the content of Al is 0.10-0.15%, the content of Ti is 0.4-0.8%, the content of Si is 0.3-0.8%, and the content of N is ≤0.008%. The microstructure of the hot-rolled steel includes 15-20% ferrite, 65-75% bainite and 0-10% austenite in volume fraction. The grain size of the microstructure is 13-14 levels. The hot-rolled steel satisfies at least one of the following performances: yield strength ≥1000 MPa, tensile strength ≥1200 MPa, elongation ≥15%, cold bending radius is 2 times the thickness size, cold bending angle is 180 degrees, and fatigue strength ≥850 MPa.

2. A method of manufacturing a 1000 MPa grade hot-rolled steel, characterized in that, The method for preparing the hot-rolled steel of claim 1 comprises: converter smelting, vacuum treatment and continuous casting of molten steel to obtain a casting blank with the chemical composition; high-temperature charging of the casting blank, control of the charging temperature, two-stage rapid heating, control of the temperature and time of the two-stage rapid heating, and control of the temperature fluctuation of different parts of the casting blank; staging rolling of the heated casting blank, control of the first process parameters of the rolling to obtain a hot-rolled steel; cooling of the hot-rolled steel, control of the second process parameters of the cooling, and then coiling to obtain a 1000 MPa grade hot-rolled steel; the two-stage rapid heating includes a preheating stage and a soaking stage, the preheating stage temperature is 1100-1150 ℃, the preheating stage time is 80-100 min, the soaking stage temperature is 1150-1200 ℃, and the soaking stage time is 30-40 min; and / or the temperature fluctuation of different parts of the casting blank is ≤50 ℃.

3. The method of claim 2, wherein, The charging temperature is 500-1000 ℃.

4. The method of claim 2, wherein, The first process parameters include the rough rolling end temperature and the finish rolling finish rolling temperature; wherein the rough rolling end temperature is 950-1040 ℃, and the finish rolling finish rolling temperature is 750-810 ℃.

5. The method of claim 2, wherein, The second process parameters include the cooling speed, the cooling temperature and the cooling water temperature; wherein the cooling speed is >50 ℃ / s, the cooling temperature is 500-550 ℃, and the cooling water temperature is ≤30 ℃.

6. The method of claim 2, wherein, The vacuum treatment time is >25 min.

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