An ultra-wide and super-thick 1200 MPa grade steel for hydropower engineering and a preparation method thereof

Abstract

This invention provides an ultra-wide, extra-thick 1200 MPa grade steel for hydropower engineering and its preparation method, relating to the field of steel manufacturing technology for hydropower engineering. The steel composition is: C 0.12%~0.15%, Cr 0.45%~0.55%, Ni 1.80%~2.50%, Mo 0.40%~0.50%, Cu 0.20%~0.50%, Mn 0.6%~1.20%, Si 0.25%~0.45%, Alt 0.03%~0.08%, Ti 0.02%~0.05%, Nb 0.02%~0.05%, B 0.0015%~0.0018%, P≤0.006%, S≤0.002%, with the remainder being Fe and unavoidable impurities. The preparation method includes: smelting according to predetermined element mass percentages; LF-RH refining; continuous casting and controlled rolling; and conditioning treatment. This invention employs a segregation reinforcement strategy to address the insufficient core strength of extra-thick steel plates, significantly improving the uniformity of strength in the thickness direction. Through a modulation process, it produces ultra-wide, extra-thick 1200 MPa grade hydropower engineering steel. This ultra-wide, extra-thick 1200 MPa grade hydropower steel exhibits dimensions and mechanical properties better suited to the harsh application environments of current hydropower steel applications, representing the future trend in hydropower steel development.

Description

Technical Field

[0001] This invention relates to the field of high-strength hydropower steel manufacturing technology, and particularly to the demand for hydropower steel in special environments and under stringent strength requirements in hydropower projects, characterized by ultra-wide and extra-thick steel. Background Technology

[0002] Against the backdrop of a "dual carbon" environment, fully leveraging the advantages of renewable resources is a crucial direction for national development. Hydropower, as a typical renewable and environmentally friendly energy source, is gradually gaining importance in national energy development. Similarly, the hydropower steel required for the construction of hydropower stations is also continuously evolving. Currently, the construction of hydropower stations involves a high demand for high-strength hydropower steel for core components such as pressure pipelines, branch pipes, and spiral casings, primarily at the 600 MPa, 800 MPa, and a small amount at the 1000 MPa level. However, with the rapid development of deep-water engineering and high-power motors, hydropower equipment faces increasingly demanding service environments and operating conditions. The development of high-strength, thick-walled, and ultra-wide hydropower steel is a key solution to this problem.

[0003] Currently, domestic research and development on high-strength hydropower steel mainly focuses on steel grades with a strength of 1000 MPa, and plate thicknesses are mostly below 100 mm. Patent CN 116219289 A discloses a 1000 MPa grade high-toughness hydropower steel and its production method. This invention proposes a multiphase microstructure composed of tempered sorbite and tempered bainite, with a yield strength greater than 890 MPa, tensile strength greater than 950 MPa, elongation after fracture greater than or equal to 20%, and an impact strength of 250 J at -60℃. This product exhibits excellent toughness, but its thickness is no greater than 70 mm, and its tensile strength is less than 1000 MPa. Patent CN 108359879 A discloses a DQ-T method for 1000 MPa grade hydropower steel with a thickness no greater than 60 mm. This invention proposes an online quenching process for 1000 MPa grade hydropower steel, applicable to steel plates with a thickness no greater than 60 mm, but still facing difficulties in environments requiring large-scale, high-strength applications. Patent CN 116254471 A discloses a 1000 MPa grade easily weldable extra-thick hydropower steel and its manufacturing method. This invention achieves a balance between strength, toughness, and weldability by optimizing the alloy composition to control the carbon equivalent and weld crack sensitivity index. The finished product has a maximum thickness of 110 mm, a yield strength ≥900 MPa, a tensile strength ≥980 MPa, and an impact energy ≥150 J at -40℃, which basically meets the requirements for use of extra-thick hydropower steel of 1000 MPa and below. However, it is difficult to cope with the stringent conditions of ultra-high strength and large dimensions.

[0004] Therefore, given the rapid development of hydropower projects in my country, the increasingly stringent operating conditions, and the demand for high-strength, large-scale hydropower steel from large hydropower stations, the research and development of ultra-wide, thick, high-strength hydropower steel is an effective means to support the development of hydropower projects in my country. Summary of the Invention

[0005] This invention provides an ultra-wide, extra-thick 1200 MPa grade hydropower engineering steel and its preparation method. By optimizing the addition of Cu element, a 120 mm thick ultra-wide, extra-thick 1200 MPa grade hydropower steel with uniform mechanical properties is designed and developed, in which the core is supplemented by appropriate Cu micro-segregation to compensate for its insufficient strength. While meeting the current high strength requirements of hydropower steel, it also meets the special large-scale environment requirements of ultra-wide and extra-thick steel.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] An ultra-wide, extra-thick 1200 MPa grade steel for hydropower engineering contains the following chemical composition by mass percentage: C 0.12%~0.15%, Cr 0.45%~0.55%, Ni 1.80%~2.50%, Mo 0.40%~0.50%, Cu 0.20%~0.50%, Mn 0.6%~1.20%, Si 0.25%~0.45%, Alt 0.03%~0.08%, Ti 0.02%~0.05%, Nb 0.02%~0.05%, B 0.0015%~0.0018%, P≤0.006%, S≤0.002%, with the remainder being Fe and unavoidable impurities.

[0008] Furthermore, the properties of the 1200 MPa grade hydropower engineering steel are as follows: thickness ≥ 120 mm, width ≥ 4500 mm, yield strength ≥ 960 MPa, tensile strength ≥ 1200 MPa, elongation after fracture A ≥ 12%, and impact energy at -60 ℃ ≥ 70 J.

[0009] This invention also provides a method for preparing the above-mentioned ultra-wide and extra-thick 1200 MPa grade steel for hydropower projects, comprising the following steps:

[0010] S1. The steel is smelted according to its designed composition.

[0011] S2. Refining molten steel using LF-RH;

[0012] S3, continuous casting and controlled rolling;

[0013] S4, Modulation Processing.

[0014] Furthermore, the S1 smelting process includes: after pre-desulfurization of molten iron, molten iron, scrap steel and pig iron are added to the converter for conventional top and bottom composite blowing; during tapping, slag washing and full-process bottom blowing argon are used, and deoxidizer, high-carbon ferromanganese, ferrosilicon and ferrochrome are added to the ladle to complete the preliminary deoxidation and alloying.

[0015] Furthermore, the S2 refining process includes: bottom blowing with argon at a rate of 80-120 L / min throughout the LF furnace, adding the required alloying elements to ensure alloy melting and homogenization in the ladle, controlling the content of each element within the required range, and performing deoxidation, desulfurization, and inclusion removal to reduce secondary oxidation and nitrogen addition during the refining process; further alloying and control of the molten steel in the RH furnace, and degassing and decarburization to control the content of each element within a suitable range; and performing net circulation treatment for more than 12 minutes when the vacuum degree is less than 2 mbar.

[0016] Furthermore, the S3 continuous casting controlled rolling process includes:

[0017] The molten steel from the RH furnace refining process is cast into a continuous casting billet under the protective casting conditions of carbon-free or ultra-low carbon protective slag. The cross-sectional size of the continuous casting billet is 460 mm.

[0018] The rolling process includes roughing and finishing rolling. The steel billet obtained from continuous casting is heated in a heating furnace at a temperature of 1180~1250 ℃. In order to ensure that the alloying elements are fully dissolved, the heating coefficient is controlled at 12 min / mm during heating.

[0019] The roughing temperature is 950~1150 ℃. The roughing process adopts large reduction rolling, with a total reduction rate ≥50% and a single pass reduction ≥30mm.

[0020] The total reduction rate of finishing rolling is ≥40%, the single-pass reduction rate is ≥7%, the starting rolling temperature of finishing rolling is 890~920 ℃, and the finishing rolling temperature is 800~830 ℃;

[0021] After rolling, laminar flow cooling is adopted, with an initial cooling temperature of 790 ℃~830 ℃ and a cooling rate of ≥5 ℃ / s, cooling to room temperature.

[0022] Furthermore, the S4 modulation process includes: quenching and tempering the rolled slab, wherein the quenching temperature is 830 ℃~880 ℃, the tempering temperature is 590 ℃~620 ℃, the heating coefficient of the tempering process is 1~3 min / mm, and the holding time is 60~150 min.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) The ultra-wide and extra-thick 1200 MPa grade hydropower engineering steel prepared by the present invention has ultra-high tensile strength (≥1200 MPa), good plasticity and toughness (elongation after fracture A≥12%), and stable strength in the thickness direction.

[0025] (2) The preparation process of this invention is relatively simple, efficient and energy-saving, and produces steel for hydropower projects with both high strength and large size and good economic efficiency in harsh and complex environments. Attached Figure Description

[0026] Figure 1 This is a process flow diagram of the present invention.

[0027] Figure 2 The quenched microstructure of the 1200 MPa grade hydropower engineering steel prepared in Example 1.

[0028] Figure 3 The tempered microstructure of the 1200 MPa grade hydropower engineering steel prepared in Example 1.

[0029] Figure 4 The quenched microstructure of the 1200 MPa grade hydropower engineering steel prepared in Example 2.

[0030] Figure 5 The tempered microstructure of the 1200 MPa grade hydropower engineering steel prepared in Example 2.

[0031] Figure 6 The quenched microstructure of the 1200 MPa grade hydropower engineering steel prepared in Example 3.

[0032] Figure 7 The tempered microstructure of the 1200 MPa grade hydropower engineering steel prepared in Example 3. Detailed Implementation

[0033] To better illustrate the technical solutions and advantages of the present invention, specific embodiments of the present invention are described in detail below with reference to figures and tables. It should be noted that, unless otherwise specified, any feature description of the present invention is merely an example of an entire series of equivalent or similar feature descriptions. The described embodiments are only used to explain and aid in understanding the present invention and are not intended to specifically limit the present invention.

[0034] This invention employs low-carbon Cr-Ni-Mo alloying, supplemented by Cu element strengthening and core reinforcement design, using a converter smelting-refining-continuous casting and rolling process, and applying appropriate rolling control and offline modulation process on a 5500 mm finishing mill to obtain 1200 MPa grade hydropower engineering steel with a width ≥4500 mm and a thickness ≥120 mm.

[0035] An ultra-wide, extra-thick 1200 MPa grade steel for hydropower engineering comprises the following components by mass percentage: C 0.12%~0.15%, Cr 0.45%~0.55%, Ni 1.80%~2.50%, Mo 0.40%~0.50%, Cu 0.20%~0.50%, Mn 0.6%~1.20%, Si 0.25%~0.45%, Alt 0.03%~0.08%, Ti 0.02%~0.05%, Nb 0.02%~0.05%, B 0.0015%~0.0018%, P≤0.006%, S≤0.002%, with the remainder being Fe and unavoidable impurities.

[0036] The mechanism of action of the main alloy components in the ultra-wide and extra-thick 1200 MPa grade hydropower engineering steel of the present invention is as follows:

[0037] C: The main function of C is solid solution strengthening, ensuring the strength of the steel matrix. In addition, C forms fine carbides with Nb, Ti, and Mo, playing a role in precipitation strengthening. However, excessive C content reduces the toughness and weldability of the steel. Therefore, to fully utilize the role of C in steel while ensuring the toughness of the product, the C content in this invention should not exceed 0.15%.

[0038] Si: Si is mainly dissolved in steel, playing a role in solid solution strengthening. It can also improve hardenability and inhibit carbide precipitation, ensuring the cooling rate of the core of extra-thick plates and improving tempering resistance. However, excessive Si can lead to deterioration of plasticity and weldability. Therefore, the Si content in this invention is selected as 0.25% to 0.45%.

[0039] Mn: The addition of Mn can improve the hardenability of steel plates and significantly optimize the cooling process of extra-thick steel plates. However, excessive Mn can lead to severe segregation and deteriorate welding performance. Therefore, the Mn content in this invention is selected to be 0.60% to 1.20%.

[0040] Cr: Cr can significantly improve hardenability and optimize the cooling process of extra-thick plates. Cr is also one of the strengthening elements. The Cr content in this invention is selected to be 0.45% to 0.55%.

[0041] Cu: Cu improves the hardenability of steel, plays a role in solid solution strengthening and precipitation strengthening in steel, and is also beneficial to low-temperature toughness. Here, in the composition design of extra-thick plates, a suitable Cu content is selected to utilize the micro-segregation strengthening of Cu elements in the core to compensate for the insufficient core strength of extra-thick plates and improve the uniformity of strength in the thickness direction. In this invention, the Cu content is 0.20% to 0.50%, and a suitable Cu content is the main means of segregation reinforcement and reducing plasticity deterioration.

[0042] Mo: Mo can improve the hardenability of steel and enhance tempering stability, while fine carbides play a strengthening role. The addition of Mo in this invention further improves hardenability and ensures tempering stability, thereby guaranteeing strength. Considering the influence of Mo on weldability, this invention selects a Mo content of 0.40%–0.50%.

[0043] Ni: Ni can improve hardenability, has a certain solid solution strengthening effect, and increases corrosion resistance. The main purpose of adding Ni in this invention is to improve the low-temperature toughness of steel. Theoretically, the increase of Ni significantly optimizes the performance of steel. However, considering the cost of Ni and its impact on the quenched microstructure, the Mo content in this invention is selected to be 1.80-2.50%.

[0044] Ti and Nb: Ti and Nb are commonly used microalloying elements that play a role in precipitation strengthening and refining austenite grains. However, excessive content will deteriorate mechanical properties. Therefore, in this invention, the content of both Ti and Nb is designed to be 0.02 to 0.05%.

[0045] Alt: Alt has a certain deoxidation effect and can form AlN to refine the grains, which can improve the strength and low temperature toughness to a certain extent. In this invention, the Al content is selected to be 0.03% to 0.08%.

[0046] B: The main function of B is to regulate the hardenability of steel plates, but its content must be strictly controlled. In this invention, the B content is designed to be 0.0015% to 0.0018%.

[0047] P and S: P reduces the plasticity and toughness of steel. P and S are prone to compositional segregation and need to be controlled within a low range.

[0048] This invention designs and develops an alloyed 1200 MPa grade ultra-wide and extra-thick hydropower engineering steel by adding Cr, Mn, Ni, Mo, Nb, Ti, B and Cu elements. While meeting the strength requirements, the ductility, toughness and weldability are also guaranteed to meet the current harsh and complex service environment of hydropower engineering steel.

[0049] A method for preparing ultra-wide, extra-thick 1200 MPa grade steel for hydropower projects, such as... Figure 1 As shown, it includes the following steps:

[0050] Step 1: Smelt the steel according to the design composition of the above-mentioned extra-wide and extra-thick 1200 MPa grade hydropower engineering steel;

[0051] Step 2: Refine the molten steel using LF-RH refining. In the LF furnace, add the required alloying elements to the steel and perform deoxidation, desulfurization, and inclusion removal to reduce secondary oxidation and nitrogen addition during the refining process. In the RH furnace, further alloying and control the molten steel, and perform degassing and decarburization to ensure alloy dissolution and homogenization in the ladle and control the content of each element within the required range.

[0052] Step 3: The molten steel from the RH furnace refining process is cast into a continuous casting billet by a continuous casting machine under the protective casting conditions of carbon-free or ultra-low carbon protective slag. The cross-sectional size of the continuous casting billet is 460 mm.

[0053] The rolling process includes roughing and finishing rolling. The steel billet obtained from continuous casting is heated in a heating furnace at a temperature of 1180–1250 °C. In order to ensure that the alloying elements are fully dissolved, the heating coefficient is controlled at 12 min / mm during heating.

[0054] The roughing temperature is 950~1150 ℃. The roughing process adopts large reduction rolling, with a total reduction rate ≥50%, a single pass reduction ≥30mm, and the reduction of the first two passes after widening is greater than 35mm. The thickness of the intermediate billet is ≥230mm.

[0055] The total reduction rate of finishing rolling is ≥40%, the single-pass reduction rate is ≥7%, the starting rolling temperature of finishing rolling is 890~920 ℃, and the finishing rolling temperature is 800~830 ℃;

[0056] After rolling, laminar flow cooling is adopted, with an initial cooling temperature of 790 ℃~830 ℃ and a cooling rate of ≥5 ℃ / s, cooling to room temperature.

[0057] Step 4: Quench and temper the rolled slab. The quenching temperature is 830℃~880℃, and the tempering temperature is 590℃~620℃. Specifically, hold at 830℃~880℃ for 100~150 min, then water quench to room temperature, and then hold at 590℃~620℃ for 60~150 min. The heating coefficient during the tempering process is 1~3 mm / mm. The tempering process is then completed.

[0058] The preparation method of the ultra-wide and extra-thick 1200 MPa grade steel for hydropower projects of the present invention will be described below through specific embodiments.

[0059] The preparation methods of the ultra-wide and extra-thick 1200 MPa grade steel for hydropower projects in Examples 1-3 include the following steps:

[0060] Step 1: Smelt according to the composition in Table 1, and strictly adhere to the established composition range for the alloy composition and its mass percentage;

[0061] Table 1. Chemical composition (wt.%) of steel used in hydropower projects in Examples 1, 2 and 3

[0062]

[0063] Step 2: Refine the molten steel using LF-RH refining. In the LF furnace, add the required alloying elements to the steel and perform deoxidation, desulfurization, and inclusion removal to reduce secondary oxidation and nitrogen addition during the refining process. In the RH furnace, further alloying and control the molten steel, and perform degassing and decarburization to ensure alloy dissolution and homogenization in the ladle and control the content of each element within the required range.

[0064] Step 3: The molten steel from the RH furnace refining process is cast into a continuous casting billet by a continuous casting machine under the protective casting conditions of carbon-free or ultra-low carbon protective slag. The cross-sectional thickness of the continuous casting billet is 460 mm.

[0065] For details of the rolling in step 3 and the heat treatment in step 4, please refer to the respective embodiments.

[0066] Example 1

[0067] The rolling and conditioning processes in this embodiment are as follows:

[0068] The steel billet obtained by continuous casting is heated in a heating furnace at a temperature of 1180 ℃. In order to fully dissolve the alloying elements, the heating coefficient is controlled at 12 min / mm during heating, and the temperature is held for 40 min after reaching the temperature.

[0069] During the rolling process, the roughing rolling temperature is 1150 ℃. After widening, the reduction in the second and third passes is 40.5 mm and 39 mm, respectively, and the reduction in the last pass of the roughing rolling is 35 mm. The finishing rolling temperature is 890 ℃, and the finishing rolling temperature is 802 ℃. The reduction rate in the last pass of the finishing rolling process is 10%.

[0070] Post-rolling cooling adopts laminar flow cooling, with an initial cooling temperature of 790 ℃, a cooling rate of 7 ℃ / s, and cooling to room temperature.

[0071] The final rolled product in this embodiment has a thickness of 120 mm and a width of 4500 mm.

[0072] Subsequently, offline quenching heat treatment was performed, with a quenching temperature of 850 ℃ and a tempering temperature of 610 ℃. Specifically, the temperature was held at 850 ℃ for 120 min, followed by water quenching to room temperature, and then held at 610 ℃ for 150 min. The heating coefficient during the tempering process was 3 mm / mm. After the tempering treatment was completed, the final product was obtained.

[0073] Micromorphology such as Figure 2 and Figure 3 As shown. Figure 2 It exhibits a typical lath martensite structure in the quenched state. Figure 3After tempering, carbide precipitation and blurred martensite lath boundaries can be observed, which is a typical tempered martensite structure.

[0074] Example 2

[0075] The rolling and conditioning processes in this embodiment are as follows:

[0076] The steel billet obtained by continuous casting is heated in a heating furnace at a temperature of 1223 ℃. In order to fully dissolve the alloying elements, the heating coefficient is controlled at 12 min / mm, and the temperature is held for 40 min after reaching the temperature.

[0077] During the rolling process, the roughing rolling temperature is 1150 ℃. After widening, the reduction in the second and third passes is 38 mm and 35 mm respectively, and the reduction in the last pass of the roughing rolling is 30 mm. The finishing rolling temperature is 900 ℃, and the finishing rolling temperature is 815 ℃. The reduction rate in the last pass of the finishing rolling process is 7%.

[0078] Post-rolling cooling adopts laminar flow cooling, with an initial cooling temperature of 800 ℃, a cooling rate of 8 ℃ / s, and cooling to room temperature.

[0079] The final rolled product in this embodiment has a thickness of 120 mm and a width of 4600 mm.

[0080] Subsequently, offline quenching heat treatment was performed, with a quenching temperature of 850 ℃ and a tempering temperature of 610 ℃. Specifically, the temperature was held at 850 ℃ for 120 min, followed by water quenching to room temperature, and then held at 610 ℃ for 150 min. The heating coefficient during the tempering process was 3 mm / mm. After the tempering treatment was completed, the final product was obtained.

[0081] Micromorphology such as Figure 4 and Figure 5 As shown. Figure 4 It exhibits a typical lath martensite structure in the quenched state. Figure 5 After tempering, carbide precipitation and blurred martensite lath boundaries can be observed, which is a typical tempered martensite structure.

[0082] Example 3

[0083] The rolling and conditioning processes in this embodiment are as follows:

[0084] The steel billet obtained by continuous casting is heated in a heating furnace at a temperature of 1223 ℃. In order to fully dissolve the alloying elements, the heating coefficient is controlled at 12 min / mm, and the temperature is held for 40 min after reaching the temperature.

[0085] During the rolling process, the roughing rolling temperature is 1150 ℃. After widening, the reduction in the second and third passes is 39.5 mm and 38 mm, respectively, and the reduction in the last pass of the roughing rolling is 37 mm. The finishing rolling temperature is 900 ℃, and the finishing rolling temperature is 812 ℃. The reduction rate in the last pass of the finishing rolling process is 10%.

[0086] Post-rolling cooling adopts laminar flow cooling, with an initial cooling temperature of 790 ℃, a cooling rate of 7 ℃ / s, and cooling to room temperature.

[0087] The final rolled product in this embodiment has a thickness of 130 mm and a width of 4500 mm.

[0088] Subsequently, offline quenching heat treatment was performed, with a quenching temperature of 850 ℃ and a tempering temperature of 610 ℃. Specifically, the temperature was held at 850 ℃ for 120 min, followed by water quenching to room temperature, and then held at 610 ℃ for 150 min. The heating coefficient during the tempering process was 3 mm / mm. After the tempering treatment was completed, the final product was obtained.

[0089] Micromorphology such as Figure 6 and Figure 7 As shown. Figure 6 It exhibits a typical lath martensite structure in the quenched state. Figure 7 After tempering, carbide precipitation and blurred martensite lath boundaries can be observed, which is a typical tempered martensite structure.

[0090] The mechanical properties and dimensions of the steels for hydropower engineering prepared in Examples 1-3 are shown in Table 2.

[0091] Table 2 Mechanical properties of the steels for hydropower engineering prepared in Examples 1, 2 and 3

[0092]

[0093] In summary, within the range of components and processes designed in this invention, the technical solution of this invention can achieve the expected results.

Claims

1. A type of ultra-wide, extra-thick 1200 MPa grade steel for hydropower projects, characterized in that, It contains the following chemical composition by mass percentage: C 0.12%~0.15%, Cr 0.45%~0.55%, Ni 1.80%~2.50%, Mo 0.40%~0.50%, Cu 0.20%~0.50%, Mn 0.6%~1.20%, Si 0.25%~0.45%, Alt 0.03%~0.08%, Ti 0.02%~0.05%, Nb 0.02%~0.05%, B 0.0015%~0.0018%, P≤0.006%, S≤0.002%, with the remainder being Fe and unavoidable impurities.

2. The ultra-wide, extra-thick 1200 MPa grade steel for hydropower projects according to claim 1, characterized in that, The properties of the 1200 MPa grade steel for hydropower projects are as follows: thickness ≥ 120 mm, width ≥ 4500 mm, yield strength ≥ 960 MPa, tensile strength ≥ 1200 MPa, elongation after fracture A ≥ 12%, and impact energy at -60 ℃ ≥ 70 J.

3. A method for preparing ultra-wide, extra-thick 1200 MPa grade steel for hydropower projects as described in claim 1 or 2, characterized in that, Includes the following steps: S1. The steel is smelted according to its designed composition. S2. Refining molten steel using LF-RH; S3, continuous casting and controlled rolling; S4, Modulation Processing.

4. The preparation method according to claim 3, characterized in that, The S3 continuous casting controlled rolling process includes: The molten steel from the RH furnace refining process is cast into a continuous casting billet under the protective casting conditions of carbon-free or ultra-low carbon protective slag. The cross-sectional size of the continuous casting billet is 460 mm. The rolling process includes roughing and finishing rolling. The steel billet obtained from continuous casting is heated in a heating furnace at a temperature of 1180~1250 ℃. In order to ensure that the alloying elements are fully dissolved, the heating coefficient is controlled at 12 min / mm during heating. The roughing temperature is 950~1150 ℃. The roughing process adopts large reduction rolling, with a total reduction rate ≥50% and a single pass reduction ≥30mm. The total reduction rate of finishing rolling is ≥40%, the single-pass reduction rate is ≥7%, the starting rolling temperature of finishing rolling is 890~920 ℃, and the finishing rolling temperature is 800~830 ℃; After rolling, laminar flow cooling is adopted, with an initial cooling temperature of 790 ℃~830 ℃ and a cooling rate of ≥5 ℃ / s, cooling to room temperature.

5. The preparation method according to claim 3, characterized in that, The S4 modulation process includes: quenching and tempering the rolled slab, wherein the quenching temperature is 830 ℃~880 ℃, the tempering temperature is 590 ℃~620 ℃, the heating coefficient of the tempering process is 1~3 min / mm, and the holding time is 60~150 min.

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