Ultrahigh-strength hot continuous rolling magnet yoke steel plate and manufacturing method thereof

Abstract

The invention relates to the technical field of hot-rolled high-strength hydroelectric steel production, in particular to an ultrahigh-strength hot continuous rolling magnet yoke steel plate and a manufacturing method thereof. The steel plate comprises the following components in percentage by weight: 0.16%-0.19% of C, 0.21%-0.49% of Si, 0.70%-0.95% of Mn, less than or equal to 0.013% of P, less than or equal to 0.003% of S, 0.11%-0.15% of Al, 0.041%-0.068% of Nb, 0.03%-0.05% of V, 0.02%-0.03% of Ti, 0.30%-0.70% of Cr, 0.30%-0.40% of Mo, 0.25%-0.50% of Ni and the balance of Fe. The alloy comprises the following components in percentage by weight: 0.30%-0.50% of Cu, 0.0008%-0.0018% of B, less than or equal to 0.004% of N and the balance of Fe and The steel plate disclosed by the invention not only has relatively high strength, but also has good comprehensive mechanical properties such as plasticity and toughness, and the steel plate has high same plate difference, unevenness level and relatively high magnetic induction intensity, and can be stably applied to a rotor body of a hydro-generator of a hydroelectric generating set.

Description

Technical Field

[0001] The present invention relates to the technical field of hot-rolled high-strength steel production for hydropower, and in particular to an ultra-high-strength hot-rolled yoke steel plate and a manufacturing method thereof. Background Art

[0002] The yoke is a key component of a hydro-turbine generator rotor. It is constructed from laminated hot-rolled steel sheets with a thickness of 3 to 6 mm and an overall height of 2 to 4 meters. Assembly accuracy must be controlled to within 0.5 parts per thousand, making it the largest component in a hydro-turbine unit. Because the yoke operates directly under a magnetic field of 50 to 100 gauss and experiences significant rotational inertia, its performance directly impacts the generator's efficiency and stability. Therefore, the yoke steel must simultaneously meet the requirements of high strength, high dimensional accuracy, and excellent magnetic properties. On the one hand, the yoke steel must possess excellent mechanical properties to withstand complex loads. On the other hand, high dimensional accuracy ensures assembly accuracy, while high magnetic permeability and low iron loss reduce eddy current losses, thereby improving the unit's overall power generation efficiency.

[0003] Patent CN103451533A discloses a hot-rolled yoke steel with a yield strength of ≥800 MPa and a production method. Its components and weight percentages are: C: 0.03% to 0.15%, Si: ≤0.15%, Mn: 1.20% to 2.00%, P: ≤0.015%, S: ≤0.005%, Ti: 0.08% to 0.18%, Nb: 0.04% to 0.08%, Mo: 0.10% to 0.50%, Al: 0.02% to 0.10%, N: ≤0.006%. The production steps include smelting and continuous casting into billets; heating the continuous cast billets; rough rolling; finish rolling; laminar cooling; and conventional coiling for standby use. The resulting steel has a yield strength of ≥800 MPa, a tensile strength of ≥850 MPa, an elongation A ≥11%, and a magnetic induction property B 50 ≥1.5T hot-rolled high-strength yoke steel.

[0004] Patent CN107794449A discloses an ultra-high-strength yoke steel and its manufacturing method. Its chemical composition, calculated by weight percentage, is C: 0.10% to 0.15%, Si: ≤0.15%, Mn: 1.85% to 2.00%, P: ≤0.015%, S: ≤0.010%, Ti: 0.20% to 0.30%, Nb: 0.05% to 0.07%, Mo: 0.35% to 0.55%, B: 0.001% to 0.003%, Als: 0.02% to 0.10%, N: ≤0.010%, and the remainder is Fe and unavoidable inclusions. This method obtains a bainite structure by adding an appropriate amount of bainite-forming elements and combining it with an ultra-fast cooling process, thereby obtaining an ultra-high-strength yoke steel with a yield strength ≥900MPa, a tensile strength ≥980MPa, an elongation A ≥10%, and a magnetic induction performance B 50≥1.50T.

[0005] Patent CN112176251A discloses an 850MPa-grade high-strength magnetic yoke steel plate with low internal stress and its manufacturing method. The components and weight percentages are as follows: C: 0.081% to 0.158%, Si: ≤0.13%, Mn: 1.22% to 1.70%, P ≤0.012%, S ≤0.005%, Ti: 0.156% to 0.223%, Nb: 0.038% to 0.057%, Mo: 0.250% to 0.407%, B: 0.002% to 0.003%, Al: 0.04% to 0.08%, N ≤0.008%, and the remainder is Fe and unavoidable impurities. The resulting magnetic yoke steel plate has a yield strength of ≥865MPa, a tensile strength of ≥933MPa, an elongation A ≥12%, an impact energy KV2 of ≥76J at -20°C, and a magnetic induction performance of B. 50 ≥1.62T, unevenness less than 3mm / m.

[0006] However, there are significant contradictions and constraints among the key performance indicators of the yoke steel plates of the above-mentioned prior art. Specifically, its strength, plastic toughness, magnetic properties, plate difference control level and unevenness retention ability are difficult to achieve coordinated optimization, and each performance indicator shows a mutually exclusive characteristic of one increasing while the other decreases. Therefore, the research and development of new yoke steel plates that have comprehensive mechanical properties of high strength and excellent plastic toughness, as well as excellent plate difference control level, good unevenness retention ability and high magnetic induction intensity, is of great significance for promoting technological progress in related fields and improving product performance. Summary of the Invention

[0007] The purpose of the present invention is to provide an ultra-high strength hot-rolled yoke steel plate and a manufacturing method thereof, which not only has high strength, but also has comprehensive mechanical properties such as good plasticity and toughness. The steel plate has a high plate difference, unevenness level and high magnetic induction intensity, and can be stably used in the rotor body of the hydro-turbine generator of a hydro-power unit.

[0008] In order to achieve the above object, the technical solution of the present invention is as follows:

[0009] On the one hand, the present invention provides an ultra-high strength hot-rolled yoke steel plate, which includes the following components in weight percentage: C: 0.16% to 0.19%, Si: 0.21% to 0.49%, Mn: 0.70% to 0.95%, P≤0.013%, S≤0.003%, Al: 0.11% to 0.15%, Nb: 0.041% to 0.068%, V: 0.03% to 0.05%, Ti: 0.02% to 0.03%, Cr: 0.30% to 0.70%, Mo: 0.30% to 0.40%, Ni: 0.25% to 0.50%, Cu: 0.30% to 0.50%, B: 0.0008% to 0.0018%, N≤0.004%, and the rest are Fe and unavoidable impurities.

[0010] The reasons for designing the types and contents of the above alloying elements in the present invention are as follows:

[0011] C: C can effectively improve the strength of steel plates and has the advantage of low cost. However, too high a C content will reduce the plasticity and toughness of the steel and also affect the magnetic properties of the steel. Therefore, the C content is controlled to be 0.16% to 0.19%.

[0012] Mn: Mn is usually dissolved in steel and improves the strength of the steel through solid solution strengthening. Mn can also reduce the phase transition point by expanding the y-phase region, expand the hot working range, refine the ferrite, and improve strength and toughness. Therefore, the Mn content is controlled at 0.70% to 0.95%.

[0013] Si: Si dissolves in ferrite and austenite in steel, which can significantly improve the strength and hardness of the steel. Si will cause the toughness and formability of the steel to decrease, so the Si content is controlled to 0.21-0.49%.

[0014] P: P is easy to precipitate in steel and form Fe3P and segregate, which reduces the impact toughness and magnetic induction properties of the steel. The content of P in steel should be controlled.

[0015] S: Sulfur in steel will form MnS inclusions with manganese. MnS can easily cause banded structure in the steel, resulting in decreased toughness and formability under lateral impact. The S content in steel should be controlled as much as possible.

[0016] Ti: Ti forms carbides and nitrides in steel. Carbonitrides inhibit grain growth during reheating and high-temperature rough rolling in the austenitic region, refining the grains and improving the steel's strength and toughness. The precipitation of fine, dispersed TiC during coiling can produce significant precipitation strengthening, effectively increasing the steel's strength. Therefore, the Ti content is controlled to 0.020% to 0.030%.

[0017] Nb: A certain amount of Nb can significantly refine grains and improve tensile strength. During the controlled rolling process, Nb can increase the recrystallization temperature of steel and reduce the rolling mill load. At the same time, it can refine the austenite grain size by inhibiting recrystallization and preventing grain growth. During cooling after rolling, NbC and NbN precipitate, which can produce second-phase strengthening. Therefore, the Nb content is controlled to 0.041% to 0.068%.

[0018] Al: A1 forms effective fine dispersions with N or O to inhibit grain growth, which helps to improve the strength and toughness of the steel plate. Therefore, the Al content is controlled to 0.11% to 0.15%.

[0019] Cr: Cr is a carbide-forming element. In metal materials, it can react with carbon to form metal compounds such as Cr3C. This metal compound has high strength and hardness. It is dispersed in the metal matrix in a granular form and can improve the strength and toughness of the material. Therefore, the Cr content is controlled at 0.30% to 0.70%.

[0020] Mo: Mo can significantly refine the structure, improve strength and toughness, and promote the strength and toughness matching of steel; Mo can effectively improve the temper brittleness of steel, and at the same time, it can precipitate very fine carbides during tempering, significantly strengthen the steel matrix, and reduce the strength drop during tempering. Therefore, the Mo content is controlled at 0.30% to 0.40%.

[0021] Ni: Ni and Fe are infinitely miscible. Ni can not only improve the hardenability of steel and thus increase the strength of steel, but also effectively improve the low-temperature performance of steel, especially the low-temperature toughness of steel. Therefore, the Ni content is controlled to be 0.25% to 0.50%.

[0022] Cu: Cu can improve the wear resistance, strength, fatigue resistance and impact resistance of steel. Cu precipitates before austenite transformation, which can refine the austenite grains, increase the anisotropy ratio of steel, and improve the formability of steel. Therefore, the Cu content is controlled to 0.30% to 0.50%.

[0023] V: V can form hard vanadium carbide (VC) particles, strengthen the grain boundaries and intergranular spaces of steel, and improve the hardness, strength, plasticity and toughness of steel by refining the grains. Therefore, the V content is controlled to be 0.030% to 0.050%.

[0024] Boron (B): Dissolved B in steel segregates to austenite grain boundaries, reducing interfacial energy and hindering the formation of ferrite nuclei. This prolongs the incubation period for the transformation to proeutectoid ferrite and upper bainite, while having little effect on the transformation to lower bainite and martensite. Therefore, the primary function of B in low-alloy wear-resistant steel is to significantly improve the hardenability of the steel. At the same time, replacing some precious alloying elements such as Ni, Cr, and Mo with trace amounts of B helps reduce alloy costs. When the B content is too high, the excess dissolved B at the austenite grain boundaries combines with C, reducing the steel's hardenability and impact toughness. The steel's fracture mode gradually shifts from cleavage to intergranular fracture. Therefore, the B content is controlled to be between 0.0008% and 0.0018%.

[0025] N: N is a residual element in steel, which can combine with titanium and niobium in steel to form titanium nitride and niobium nitride, which can prevent the growth of austenite grains and strengthen precipitation. Therefore, N is controlled to be ≤ 0.0040%.

[0026] In the above technical solution, further, the yield strength of the steel plate is ≥1000MPa, the tensile strength is ≥1050MPa, and the elongation after fracture is A 50mm ≥15%, -20℃ impact energy KV2≥60J, magnetic induction performance B 50 ≥1.63T.

[0027] In the above technical solution, further, the difference in yield strength between the transverse and longitudinal directions of the steel plate is ≤20MPa, and the difference in -20°C impact energy KV2 between the transverse and longitudinal directions of the steel plate is ≤10J.

[0028] In the above technical solution, further, the thickness of the steel plate is 3 to 6 mm.

[0029] Another aspect of the present invention provides a method for manufacturing the ultra-high strength hot-rolled yoke steel plate, the method comprising the following steps:

[0030] 1) Smelting and casting: After molten iron pretreatment, converter smelting, LF furnace refining, RH vacuum treatment, continuous casting is performed to obtain continuous casting billets;

[0031] 2) Heating: The continuous casting billet is hot charged into the heating furnace, the charging temperature of the continuous casting billet is ≥300℃, the heating temperature is 1231~1260℃, the holding time is 150~250min, of which the soaking and holding time is 40~60min;

[0032] 3) Rolling: The total reduction rate of rough rolling is ≥80%, the end temperature of rough rolling is 1110-1160°C, the entrance temperature of finishing rolling is ≥1080°C, the final rolling temperature is 850-910°C, and the crown of the strip is controlled to be C25 ≤35μm, and the absolute value of the wedge C25 is ≤20μm;

[0033] 4) Cooling: laminar cooling is adopted, and the coiling temperature is 660-700℃;

[0034] 6) Cross-cutting: Straighten the steel coil and cut it into fixed-length steel plates. The unevenness of the steel plates after cross-cutting should be ≤15mm / m;

[0035] 6) Quenching + tempering: Before quenching, the steel plate is heated to 880-930°C, and the holding time T1, min = steel plate thickness × (2.0-2.5) min. After the holding is completed, it is water quenched to room temperature with a cooling rate of 30-60°C / s. The quenched steel plate is tempered at 550-650°C, and the tempering holding time T2, min = steel plate thickness (mm) × (3.0-3.5) min;

[0036] 7) Straightening: Straighten the steel plate so that the unevenness of the entire steel plate is ≤1mm.

[0037] In the above technical solution, further, in step 1), electromagnetic stirring and dynamic soft reduction are used for continuous casting, and the thickness of the continuous casting billet is 170 to 250 mm.

[0038] In the above technical solution, further, in step 3), the rough rolling is performed in 4 to 7 passes.

[0039] In the above technical solution, further, in step 3), the finishing rolling adopts 7-stand PC rolling mill, the PC angles of the finishing rolling F2~F4 PC rolling mills are 0.6~0.8°, 0.4~0.6°, and 0.2~0.5°, respectively, the bending roll force of the finishing rolling F1-F3 is set to 950~1250KN, the bending roll force of F4 is set to 800~1050KN, the bending roll force of F5 is set to 600~900KN, the bending roll force of F6 is set to 450~750KN, and the bending roll force of F7 is set to 300~650KN.

[0040] In the above technical solution, further, in step 4), the cooling rate is 10 to 30°C / s.

[0041] The beneficial effects of the present invention are:

[0042] 1) The yoke steel plate of the present invention has a yield strength of ≥1000MPa, a tensile strength of ≥1050MPa, and an elongation after fracture of A 50mm ≥15%, with high strength and high elongation, achieving good strength and plasticity of steel plate;

[0043] 2) The yoke steel plate of the present invention has a -20°C KV2 impact energy value of ≥60J and has high low-temperature impact toughness;

[0044] 3) The yoke steel plate of the present invention has no cracks on the surface during a 180° cold bending test with d=2a (a is the thickness of the steel plate), indicating excellent cold bending performance;

[0045] 4) The yoke steel plate of the present invention has low anisotropy, the difference in yield strength between the transverse and longitudinal directions of the steel plate does not exceed 20 MPa, and the difference in KV2 impact energy value between the transverse and longitudinal directions at -20°C of the steel plate is within 10 J;

[0046] 5) The yoke steel plate of the present invention has an excellent plate thickness difference level, and the thickness difference of the whole plate is controlled within 0.05mm;

[0047] 6) The yoke steel plate of the present invention has excellent plate quality, and the unevenness of the entire steel plate is ≤1mm, which is conducive to stacking processing with yoke steel;

[0048] 7) The yoke steel plate of the present invention has high magnetic induction performance, B 50 ≥1.63T. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a microstructure photograph of the yoke steel plate prepared in Example 1. DETAILED DESCRIPTION

[0050] The following are examples of the present invention. These examples are merely descriptions of the best mode of carrying out the present invention, but are not intended to limit the scope of the present invention in any way.

[0051] Examples 1-8

[0052] The chemical compositions of the ultra-high strength hot-rolled yoke steel plates of Examples 1-8 of the present invention are shown in Table 1.

[0053] Table 1 Chemical composition (wt%) of ultra-high strength hot-rolled yoke steel plates of Examples 1-8 of the present invention

[0054] C Si Mn P S Al Cr Ni Mo Nb Ti V Cu B N Example 1 0.17 0.30 0.81 0.012 0.001 0.113 0.52 0.41 0.37 0.063 0.027 0.038 0.37 0.0012 0.0023 Example 2 0.18 0.42 0.76 0.011 0.001 0.135 0.65 0.46 0.33 0.040 0.024 0.030 0.30 0.0008 0.0011 Example 3 0.16 0.21 0.95 0.009 0.003 0.150 0.70 0.38 0.35 0.059 0.025 0.042 0.42 0.0015 0.0037 Example 4 0.19 0.25 0.86 0.013 0.002 0.144 0.48 0.31 0.32 0.056 0.024 0.047 0.50 0.0018 0.0005 Example 5 0.19 0.39 0.70 0.010 0.001 0.127 0.30 0.25 0.30 0.068 0.020 0.035 0.42 0.0011 0.0040 Example 6 0.17 0.49 0.92 0.007 0.002 0.140 0.34 0.29 0.40 0.045 0.030 0.050 0.35 0.0013 0.0028 Example 7 0.18 0.43 0.79 0.009 0.003 0.110 0.59 0.35 0.38 0.049 0.028 0.045 0.46 0.0014 0.0009 Example 8 0.16 0.28 0.88 0.007 0.002 0.122 0.67 0.50 0.031 0.053 0.022 0.033 0.41 0.0009 0.0032

[0055] The manufacturing method of the yoke steel plate comprises the following steps:

[0056] 1) Smelting and casting: After molten iron pretreatment, converter smelting, LF furnace refining, and RH vacuum treatment, continuous casting is carried out. Electromagnetic stirring and dynamic soft reduction are used for continuous casting. The thickness of the continuous casting billet is 170-250mm.

[0057] 2) Heating: The continuous casting billet is hot loaded into the heating furnace. The charging temperature of the continuous casting billet is ≥300℃ to avoid crack defects caused by the high alloy content of the continuous casting billet after cooling. The heating temperature is 1231-1260℃ and the holding time is 150-250min, including a soaking and holding time of 40-60min to ensure that the alloy elements can be fully dissolved, the continuous casting billet can be evenly burned through, and the original austenite grains are fully homogenized without growing too much.

[0058] 3) Rolling: Rolling is divided into two stages: rough rolling and finishing rolling. Rough rolling is carried out in 4 to 7 passes. The total reduction rate of rough rolling is ≥80%. The large reduction rate can effectively break the columnar crystals of the continuous casting billet and refine the structure. The end temperature of rough rolling is 1110-1160℃. The higher rough rolling temperature can ensure the entrance temperature of finishing rolling. The intermediate roller insulation cover between rough rolling and finishing rolling is put into use. The entrance temperature of finishing rolling is ≥1080℃. The finishing rolling is carried out in a 7-stand PC rolling mill. The final rolling temperature is 850-910℃. This entrance temperature and final rolling temperature can ensure that the finishing rolling load does not exceed the limit and the rolling is stable. The structure is not excessively coarsened. Finishing rolling F2-F4 The PC angles of the PC rolling mill are 0.6-0.8°, 0.4-0.6°, and 0.2-0.5°, respectively. The bending roll force of finishing rolling F1-F3 is set to 950-1250KN, the bending roll force of F4 is set to 800-1050KN, the bending roll force of F5 is set to 600-900KN, the bending roll force of F6 is set to 450-750KN, and the bending roll force of F7 is set to 300-650KN. By setting the PC angle and bending roll force of each stand, the crown C25 of the strip is controlled within 35μm, and the absolute value of the wedge C25 is controlled within 20μm, in order to ensure that the steel plate has a good transverse plate difference.

[0059] 4) Cooling: Laminar cooling is used with a cooling rate of 10-30°C / s and a coiling temperature of 660-700°C. This process is to further refine the grains and provide a uniform and fine original structure for subsequent heat treatment, thereby obtaining higher strength and ensuring good coil quality after coiling by the coiler;

[0060] 5) Cross-cutting: Straighten the steel coil and cut it into fixed-length steel plates. The unevenness of the steel plates after cross-cutting should be ≤15mm / m;

[0061] 6) Quenching + tempering: Before quenching, the steel plate is heated to 880-930℃, and then kept warm. The holding time is T1, min = steel plate thickness × (2.0-2.5) min. After the holding is completed, it is water quenched to room temperature to form a martensite structure. The cooling rate is 30-60℃ / s. The steel plate is heated and kept warm to ensure that the austenite of the steel plate is homogenized and the austenite grains of the steel plate are appropriately coarse, which can ensure that the steel plate obtains better magnetic properties. Higher cooling rate quenching can produce finer The lath martensite structure improves the strength of the steel plate. The steel plate after quenching is tempered at 550-650℃. The tempering holding time T2, min = steel plate thickness (mm) × (3.0-3.5) min. The microstructure of the steel plate after tempering is tempered bainite. The strength of the tempered steel plate is greatly improved after quenching. Through high temperature tempering, the residual stress of the steel plate can be completely eliminated, the strength and hardness of the steel plate can be appropriately reduced, and the plasticity, toughness and cold bending performance of the steel plate can be greatly improved.

[0062] 7) Straightening: Use 11-17 roller high-strength steel plate straightening machine to straighten the steel plate so that the unevenness of the entire steel plate is ≤1mm.

[0063] The continuous casting and heating process parameters of Examples 1-8 are shown in Table 2.

[0064] Table 2 Continuous casting and heating process parameters of Examples 1-8

[0065] Continuous casting slab thickness / mm Furnace charging temperature / ℃ Heating temperature / ℃ Holding time / min Soaking time / min Example 1 250 412 1260 250 60 Example 2 170 535 1247 222 40 Example 3 190 370 1237 185 50 Example 4 180 482 1231 160 44 Example 5 240 308 1255 238 56 Example 6 210 406 1242 205 48 Example 7 220 557 1235 176 54 Example 8 230 584 1254 150 58

[0066] The rolling process parameters of Examples 1-8 are shown in Table 3.

[0067] Table 3 Rolling process parameters of Examples 1-8

[0068]

[0069]

[0070] The finishing PC mill parameters of Examples 1-8 are shown in Table 4.

[0071] Table 4 Parameters of the finishing PC mill of Examples 1-8

[0072]

[0073] The cooling, quenching and tempering parameters of Examples 1-8 are shown in Table 5.

[0074] Table 5 Cooling, quenching and tempering parameters of Examples 1-8

[0075]

[0076] The performance results of the steel plates prepared in Examples 1-8 are shown in Table 6.

[0077] Table 6 Performance results of the steel plates obtained in Examples 1-8

[0078]

[0079] The test results show that the yield strength of the yoke steel plate of the present invention reaches more than 1000MPa, and has a high elongation and a small difference in transverse and longitudinal strength. The steel plate has good low-temperature toughness, high cold bending performance, excellent magnetic properties, and the steel plate also has excellent same-plate difference and unevenness.

[0080] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. The scope of protection of the present invention shall be determined by the scope defined in the claims. Other variations or modifications may be made based on the above description. Obvious variations or modifications derived therefrom shall remain within the scope of protection of the present invention.

Claims

1. An ultra-high strength hot-rolled yoke steel plate, characterized in that: The steel plate includes the following components in weight percentage: C: 0.16% to 0.19%, Si: 0.21% to 0.49%, Mn: 0.70% to 0.95%, P≤0.013%, S≤0.003%, Al: 0.11% to 0.15%, Nb: 0.041% to 0.068%, V: 0.03% to 0.05%, Ti: 0.02% to 0.03%, Cr: 0.30% to 0.70%, Mo: 0.30% to 0.40%, Ni: 0.25% to 0.50%, Cu: 0.30% to 0.50%, B: 0.0008% to 0.0018%, N≤0.004%, and the rest are Fe and unavoidable impurities.

2. The ultra-high strength hot-rolled yoke steel plate according to claim 1, characterized in that: The yield strength of the steel plate is ≥1000MPa, the tensile strength is ≥1050MPa, and the elongation after fracture is A 50mm ≥15%, -20℃ impact energy KV2≥60J, magnetic induction performance B 50 ≥1.63T.

3. The ultra-high strength hot-rolled yoke steel plate according to claim 1, characterized in that: The difference in yield strength between the transverse and longitudinal directions of the steel plate is ≤20MPa, and the difference in -20°C impact energy KV2 between the transverse and longitudinal directions of the steel plate is ≤10J.

4. The ultra-high strength hot-rolled yoke steel plate according to claim 1, characterized in that: The thickness of the steel plate is 3 to 6 mm.

5. A method for manufacturing the ultra-high strength hot-rolled yoke steel plate according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: 1) Smelting and casting: After molten iron pretreatment, converter smelting, LF furnace refining, RH vacuum treatment, continuous casting is performed to obtain continuous casting billets; 2) Heating: The continuous casting billet is hot charged into the heating furnace, the charging temperature of the continuous casting billet is ≥300℃, the heating temperature is 1231~1260℃, the holding time is 150~250min, of which the soaking and holding time is 40~60min; 3) Rolling: The total reduction rate of rough rolling is ≥80%, the end temperature of rough rolling is 1110-1160°C, the entrance temperature of finishing rolling is ≥1080°C, the final rolling temperature is 850-910°C, and the crown of the strip is controlled to be C25 ≤35μm, and the absolute value of the wedge C25 is ≤20μm; 4) Cooling: laminar cooling is adopted, and the coiling temperature is 660-700℃; 5) Cross-cutting: Straighten the steel coil and cut it into fixed-length steel plates. The unevenness of the steel plates after cross-cutting should be ≤15mm / m; 6) Quenching + tempering: Before quenching, the steel plate is heated to 880-930°C, and the holding time T1, min = steel plate thickness × (2.0-2.5) min. After the holding is completed, it is water quenched to room temperature with a cooling rate of 30-60°C / s. The quenched steel plate is tempered at 550-650°C, and the tempering holding time T2, min = steel plate thickness (mm) × (3.0-3.5) min; 7) Straightening: Straighten the steel plate so that the unevenness of the entire steel plate is ≤1mm.

6. The manufacturing method according to claim 5, characterized in that In step 1), electromagnetic stirring and dynamic soft reduction are used for continuous casting, and the thickness of the continuous casting billet is 170 to 250 mm.

7. The manufacturing method according to claim 5, characterized in that In step 3), the rough rolling is performed in 4 to 7 passes.

8. The manufacturing method according to claim 5, characterized in that In step 3), the finishing rolling adopts 7-stand PC rolling mill, the PC angles of the finishing rolling PC mills F2 to F4 are 0.6 to 0.8°, 0.4 to 0.6°, and 0.2 to 0.5°, respectively, the bending roll force of the finishing rolling F1-F3 is set to 950 to 1250 kN, the bending roll force of F4 is set to 800 to 1050 kN, the bending roll force of F5 is set to 600 to 900 kN, the bending roll force of F6 is set to 450 to 750 kN, and the bending roll force of F7 is set to 300 to 650 kN.

9. The manufacturing method according to claim 5, characterized in that In step 4), the cooling rate is 10 to 30°C / s.

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