Rare earth high-performance EH40 marine steel plate and production method thereof

Abstract

The invention discloses a rare earth high-performance EH40 marine steel plate and a production method thereof. The rare earth high-performance EH40 marine steel plate provided by the invention comprises the following chemical components in percentage by mass: 0.06 to 0.09 percent of C, 0.20 to 0.30 percent of Si, 1.45 to 1.60 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, 0.035 to 0.050 percent of Nb, 0.035 to 0.050 percent of V, 0.012 to 0.022 percent of Ti, 0.020 to 0.035 percent of Als, 0.0005 to 0.0020 percent of rare earth Ce, less than or equal to 0.40 percent of CEV, less than or equal to 0.20 percent of Pcm and the balance of Fe and inevitable impurities. The performance meets the requirements that the yield strength is larger than or equal to 390 MPa, the tensile strength is 510-660 MPa, the percentage elongation after fracture is larger than or equal to 20%, and the impact energy at the temperature of minus 40 DEG C is larger than or equal to 270

Description

TECHNICAL FIELD

[0001] The present application relates to the production technology of ship steel plate, in particular to a rare earth high-performance EH40 ship steel plate and a production method thereof. BACKGROUND

[0002] In recent years, China's marine engineering equipment and large container ships have developed rapidly. With the improvement of marine oil and gas exploration and development technology and the development of large container ships, the demand for marine platform and container ship steel has developed towards high strength, thick gauge, good weldability, low temperature toughness, and resistance to lamellar tearing.

[0003] Hot mechanical rolling process steel plate has the advantages of low cost, low yield ratio, good weldability, etc. In recent years, with the substantial improvement of medium plate equipment level, the process is widely used in ship steel plate.

[0004] EH40 ship plate steel is a grade in GB / T 712-2022 "Structural Steel for Ships and Marine Engineering", which requires yield strength ≥ 390 MPa, tensile strength 510-660 MPa, elongation after fracture ≥ 20%, -40℃ impact energy ≥ 39J, and bending performance is qualified. At the same time, there are strict requirements on harmful elements and gas content.

[0005] Patent application CN 116121659 A discloses "a low carbon equivalent EH40 grade extra-thick marine high-strength steel and its production method". The chemical composition is as follows: C: 0.13-0.16%, Si: 0.35-0.50%, Mn: 1.45-1.60%, P≤0.015%, S≤0.005%, Als: 0.015-0.045%, Nb: 0.035-0.050%, V: 0.050-0.065%, Ti: 0.008-0.020; the balance is Fe and unavoidable impurities. EH40 steel plate is produced by normalizing and weak cooling process. The shortcomings are: first, the carbon content is high, the carbon equivalent is high, which deteriorates the welding performance; second, the normalizing and weak cooling process is used for production, which increases the cost and requires high equipment capacity, and is not suitable for all steel plants.

[0006] Patent application CN 105525203 A discloses "a high-strength EH40 extra-thick steel plate and its production method", which adds a certain amount of Ni and adopts a specific rolling and cooling process to produce an extra-thick EH steel plate with a thickness of 80mm or more. The shortcomings are: this patent uses ultra-low carbon + alloy composition design, high alloy addition amount, high cost, and high cooling equipment requirement.

[0007] Patent application CN 108517462 B discloses "a high ductility EH40 grade ship plate steel and a preparation method thereof". The chemical composition is as follows: C: 0.04-0.08%, Si: 0.04-0.16%, Mn: 0.90-1.20%, Nb: 0.03-0.04%, Ti: 0.01-0.02%, Als: 0.02-0.04%, P: ≤0.02%, S: ≤0.01%. The controlled rolling and controlled cooling technology is adopted to obtain the structure of soft phase ferrite and hard phase bainite; in addition, no Cr, V, Ni and other elements are added, and the cost is low; by using the method of rapid cooling, the final rolling temperature can be appropriately increased, the rolling mill load can be reduced, the rolling efficiency can be improved, and the low-cost, easy-rolling and high-efficiency production of the high-ductility EH40 grade ship plate steel is realized. The shortcoming of the patent is that the three-stage cooling of water cooling-air cooling-water cooling is adopted, the cooling equipment is required to be high, the control difficulty is large, and it is not suitable for all thick plate production lines. SUMMARY

[0008] In view of the above shortcomings of the patent, the present application provides a high-performance EH40 hot mechanical rolling ship plate with a thickness of 10-50mm, a yield strength of ≥390MPa, a tensile strength of 510-660MPa, an elongation after fracture of ≥20%, and an impact energy of ≥100J at-40℃, and has the characteristics of easy welding and easy forming. Preferably, the performance of the high-performance EH40 hot mechanical rolling ship plate provided by the present application can meet: a yield strength of ≥460MPa, a tensile strength of 540-660MPa, an elongation after fracture of ≥20%, and an impact energy of ≥270J at-40℃.

[0009] The present application is mainly realized by the following technical solutions.

[0010] One aspect of the present application provides a rare earth high-performance EH40 ship plate, which has a chemical composition according to mass percentage: C: 0.06-0.09%, Si: 0.20-0.30%, Mn: 1.45-1.60%, P≤0.015%, S≤0.005%, Nb: 0.035-0.050%, V: 0.035-0.050%, Ti: 0.012-0.022%, Als: 0.020-0.035%, rare earth Ce: 0.0005-0.0020%, CEV≤0.40%, Pcm≤0.20%, and the balance is Fe and inevitable impurities.

[0011] The performance of the rare earth high-performance EH40 ship plate meets: a yield strength of ≥390MPa, a tensile strength of 510-660MPa, an elongation after fracture of ≥20%, and an impact energy of ≥270J at-40℃.

[0012] In some embodiments, the rare earth high-performance EH40 marine steel plate has the following properties: yield strength ≥ 460 MPa, tensile strength 540-660 MPa, elongation after fracture ≥ 20%, and impact energy at -40℃ ≥ 270 J.

[0013] In some embodiments, the rare earth high-performance EH40 marine steel plate has uniform and stable properties at the head, tail, transverse, longitudinal, 1 / 4 thickness, and 1 / 2 thickness, excellent tensile properties after stress relief, and a CTOD value of welded joint at -35℃ of 0.5 or more.

[0014] In some embodiments, the rare earth high-performance EH40 marine steel plate has an impact energy at -40℃ of ≥ 300 J at the head transverse, head longitudinal, tail transverse, and tail longitudinal.

[0015] In some embodiments, the rare earth high-performance EH40 marine steel plate has the following chemical composition in terms of mass percentage: C: 0.08-0.09%, Si: 0.24-0.27%, Mn: 1.53-1.58%, P ≤ 0.015%, S ≤ 0.005%, Nb: 0.042-0.046%, V: 0.039-0.041%, Ti: 0.013-0.015%, Als: 0.020-0.022%, rare earth Ce: 0.0010-0.0013%, and the balance being Fe and unavoidable impurities.

[0016] Another aspect of the present application provides a production method of a rare earth high-performance EH40 marine steel plate, which comprises the following processes: hot metal pretreatment, converter top and bottom combined blowing smelting, LF secondary refining, RH vacuum degassing, slab continuous casting (electromagnetic stirring, soft reduction), slab cold charging or hot charging heating, descaling, rough rolling, finish rolling, cooling, and straightening.

[0017] In the converter smelting, the hot metal and high-quality scrap steel pretreated by desulfurization are used as raw materials in the converter smelting stage, the hot metal temperature is ≥ 1260℃, the high-efficiency top and bottom combined blowing technology is used to reduce the phosphorus and carbon content, and the molten steel P ≤ 0.010% and S ≤ 0.004% are ensured.

[0018] In the LF secondary refining, the molten steel composition is accurately controlled in the secondary refining stage, and the deoxidizing alloying is performed to further reduce the non-metallic inclusions and harmful impurities in the molten steel, and S ≤ 0.004%.

[0019] In the RH vacuum treatment, the hydrogen, oxygen, and nitrogen gas content in the molten steel is greatly reduced by using the treatment mode, and the adverse effects of harmful gases on steel are reduced; the vacuum degree is less than 90 Pa, the vacuum time is maintained for more than 15 minutes, the pure degassing time is more than 15 minutes, and the soft blowing time is more than 15 minutes, so that the hydrogen content in the off-site molten steel is ≤ 1.6 ppm, the oxygen content is ≤ 30 ppm, and the nitrogen content is ≤ 50 ppm.

[0020] In the slab continuous casting, dynamic soft reduction is used during continuous casting, the soft reduction position is 8, 9, 10 section, and the total reduction amount is 7.5 mm; electromagnetic stirring is used during continuous casting, the electromagnetic stirring position is 3 section outlet and 4 section inlet, the electromagnetic stirring frequency is 5 Hz, and the current is 350 A; the water amount of the wide side of the crystallizer is 4500 L / min, the water amount of the narrow side is 370 L / min, the water temperature of the crystallizer is 36±2℃, the secondary cooling water temperature is 22-25℃, and the water quality index meets the process requirements; protective pouring is used, the sealing argon pressure of the long nozzle is greater than 0.3 MPa, and the flow is 130-160 L / min; the sealing argon pressure of the submerged nozzle of the tundish is greater than 0.2 MPa, and the flow is 15-20 L / min; the superheat during continuous casting is 20-30℃, the tundish liquid level during tundish changing is not less than 30 tons; constant speed is used, and the drawing speed is stabilized at 1.0 m / min; the straightening temperature of the cast blank is controlled to be 950-1000℃, and the temperature difference of the cast blank along the width direction is not more than 50℃; finally, the 250 mm thick continuous casting blank is produced, and the low multiple center segregation of the cast blank is controlled to be below C class 3.0 level;

[0021] In the heating, the slab is cold or hot charged and heated, the furnace atmosphere is strictly controlled, the slab heating temperature and heating time are ensured, the heating temperature is 1210℃-1250℃, the total furnace time is greater than 220 min, the heating section time is greater than 120 min, the soaking section time is greater than 30 min, the alloy elements are fully solid-solved, and the slab temperature is uniform;

[0022] In the rolling and cooling, two-stage controlled rolling is used for rolling, the first stage rolling temperature is above 1180℃, and the single pass relative reduction rate is controlled to be above 15% for at least two passes; the second stage strictly controls the deformation amount of each pass, the rolling temperature is ≤930℃, and the finish rolling temperature is ≤810℃; after the steel plate is rolled, laminar cooling is carried out, the water temperature is 17-20℃, the open cooling temperature is 750-780℃, the final cooling temperature is 635-655℃, the cooling speed is 7-9℃ / s, the head shielding is 0-2.0 m, the tail shielding is 0-2.5 m, the side shielding is 0-2.0 m, the overall temperature difference after the steel plate is red is controlled to be ≤50℃. The steel plate is slowly cooled for 12 hours after stacking, and sampling inspection is carried out.

[0023] The beneficial effects of the present application are:

[0024] The application is according to GB / T 712-2022 <Structural Steel for Ships and Ocean Engineering>, adopts low-carbon-niobium-vanadium-titanium alloying component design, and produces the thickness 10-50mm EH40 marine steel plate by adopting hot mechanical rolling technology, the yield strength of the steel plate is greater than or equal to 390MPa, the tensile strength is 510-660MPa, the elongation after fracture is greater than or equal to 20%, the impact energy at-40 DEG C is greater than or equal to 270J, the performance of the steel plate at the head, tail, transverse, longitudinal, 1 / 4 thickness and 1 / 2 thickness is uniform and stable, the tensile property after stress release is excellent, the CTOD value of the welded joint at-35 DEG C is greater than 0.5, has excellent crack arrest performance, and has the characteristics of easy welding and easy forming. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The steel plate of Example 3 is metallographic structure.

[0026] Figure 2 The steel plate of Example 3 is-40 DEG C impact fracture macro morphology.

[0027] Figure 3 The steel plate of Example 3 is-40 DEG C impact fracture micro morphology.

[0028] Figure 4 The steel plate of Example 1-2 is bent after morphology.

[0029] Figure 5 The steel plate of Example 4 is a welded joint CTOD sample. DETAILED DESCRIPTION

[0030] The chemical composition of the steel plate of the application is C: 0.06-0.09%, Si: 0.20-0.30%, Mn: 1.45-1.60%, P≤0.015%, S≤0.005%, Nb: 0.035-0.050%, V: 0.035-0.050%, Ti: 0.012-0.022%, Als: 0.020-0.035%, rare earth Ce: 0.0005-0.0020%, CEV≤0.40%, Pcm≤0.20%, and the balance is Fe and inevitable impurities.

[0031] In addition, the application also provides a manufacturing method of the steel plate, which comprises: hot metal pretreatment, converter top and bottom combined blowing smelting, LF furnace external refining, RH vacuum degassing, slab continuous casting (electromagnetic stirring, light pressing), slab cold charging or hot charging heating, descaling, rough rolling, finish rolling, cooling, straightening, quality inspection, sampling, inspection, and warehousing. The main steps and process parameters are as follows:

[0032] Converter smelting: The converter smelting stage uses desulfurized molten iron and high-quality scrap steel as raw materials, the molten iron temperature is ≥1260℃, and the high-efficiency top and bottom combined blowing technology is used to reduce the phosphorus and carbon content, to ensure that the molten steel P≤0.010%, S≤0.004%.

[0033] LF furnace refining: The LF furnace refining stage accurately controls the composition of the molten steel, deoxidizes and alloyizes, further reduces the non-metallic inclusions and harmful impurities in the molten steel, and S≤0.004%.

[0034] RH vacuum treatment: The RH vacuum treatment mode greatly reduces the hydrogen, oxygen, and nitrogen gas content in the molten steel, reduces the adverse effects of harmful gases on steel. The vacuum degree is less than 90 Pa, the vacuum time is maintained for more than 15 minutes, the pure degassing time is greater than 15 minutes, the soft blowing time is greater than 15 minutes, to ensure that the off-site molten steel hydrogen content is ≤1.6 ppm, oxygen content is ≤30 ppm, and nitrogen content is ≤50 ppm.

[0035] Slab continuous casting: Dynamic soft reduction is used during continuous casting, the soft reduction position is 8, 9, and 10 segments, and the total soft reduction amount is 7.5 mm; electromagnetic stirring is used during continuous casting, the electromagnetic stirring position is the 3rd segment outlet and the 4th segment inlet, the electromagnetic stirring frequency is 5 Hz, and the current is 350 A; the mold wide side water flow is 4500 L / min, the narrow side water flow is 370 L / min, the mold water inlet temperature is 36±2℃, the secondary cooling water temperature is 22-25℃, and the water quality index meets the process requirements; protective casting is used, the long nozzle sealing argon pressure is greater than 0.3 MPa, and the flow is 130-160 L / min; the tundish submerged entry nozzle sealing argon pressure is greater than 0.2 MPa, and the flow is 15-20 L / min; the continuous casting superheat is 20-30℃, the tundish liquid level during tundish changing is not less than 30 tons; constant speed casting is used, and the casting speed is stabilized at 1.0 m / min; the casting billet straightening temperature is controlled at 950-1000℃, and the temperature difference of the casting billet along the width direction should not exceed 50℃. Finally, 250mm thick continuous casting billets are produced, and the low-multiple center segregation of the continuous casting billets is controlled below C class 3.0 level.

[0036] Heating: Slab cold charging or hot charging heating, strictly control the furnace atmosphere, ensure the slab heating temperature and heating time, heating temperature 1210℃-1250℃. The total time in the furnace is greater than 220 min, of which the heating section time is greater than 120 min, and the soaking section time is greater than 30 min, to ensure the full solid solution of alloy elements and the uniformity of slab temperature.

[0037] Rolling and cooling: the rolling adopts two-stage controlled rolling, the first stage is open rolling at a temperature of 1180℃ or above, and the relative reduction of single pass is controlled at 15% or above for two passes or more; the second stage strictly controls the deformation amount of each pass, the open rolling temperature is ≤930℃, and the finish rolling temperature is ≤810℃; after the steel plate is rolled, laminar cooling is performed, the water temperature is 17-20℃, the open cooling temperature is 750-780℃, the final cooling temperature is 635-655℃, the cooling speed is 7-9℃ / s, the head shielding is 0-2.0m, the tail shielding is 0-2.5m, the side shielding is 0-2.0m, and the overall temperature difference after the steel plate is red after the steel plate is red is controlled to be ≤50℃. The steel plate is stacked and slowly cooled for 12 hours, and then sampling inspection is performed.

[0038] The content of the present application is described in detail below through specific examples, and the examples are intended to help understand the present application, and are not intended to limit the content of the present application.

[0039] Table 1 lists the chemical compositions of the examples, and Table 2 lists the rolling process parameters of the examples.

[0040] Table 1: Chemical composition (wt%) of the examples of the present application

[0041] Examples C Si Mn P S Nb V Ti Als Ce 1 0.08 0.24 1.54 0.012 0.003 0.042 0.039 0.013 0.021 0.0012 2 0.08 0.24 1.53 0.013 0.002 0.045 0.040 0.015 0.021 0.0011 3 0.08 0.26 1.57 0.012 0.004 0.046 0.040 0.014 0.020 0.0010 4 0.09 0.25 1.58 0.011 0.002 0.042 0.040 0.013 0.022 0.0013 5 0.09 0.27 1.55 0.011 0.002 0.045 0.039 0.014 0.022 0.0010 6 0.09 0.25 1.58 0.012 0.003 0.044 0.041 0.013 0.022 0.0011

[0042] Table 2: Rolling process parameters of the examples of the present application

[0043]

[0044] The mechanical properties, low-temperature impact properties and cold bending properties of the steel plates produced by the examples of the present application are tested, and the results are shown in Tables 3-5.

[0045] Table 3: Mechanical properties of the steel plates of the examples of the present application

[0046]

[0047] Table 4: Detailed properties of the steel plates of Example 5 of the present application

[0048]

[0049] Table 5: Detailed properties of the steel plates of Example 6 of the present application

[0050]

[0051] The steel plate of Example 4 is subjected to gas shielded welding, and the welded joint is subjected to a crack opening displacement (CTOD) test at -35℃ and a loading rate of 0.8mm / min, and the results are shown in Table 6.

[0052] Table 6: CTOD characteristic values of the welded joint of the steel plate of Example 4 of the present application

[0053]

[0054] From the results of the above examples, it can be seen that the present application produces a hot mechanical controlled rolling EH40 marine steel plate with a thickness of 10-50 mm by using reasonable chemical composition and specific process flow. The yield strength of the steel plate is ≥390 MPa, the tensile strength is 510-660 MPa, the elongation after fracture is ≥20%, the impact energy at -40 ℃ is ≥100 J, preferably ≥270 J, the properties at the head, tail, transverse, longitudinal, 1 / 4 thickness and 1 / 2 thickness of the steel plate are uniform and stable, the tensile properties after stress release are excellent, the CTOD value of the welded joint at -35 ℃ is above 0.5, and the steel plate has excellent crack arrest performance, and has the characteristics of easy welding and easy forming.

[0055] Finally, it should be noted that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A rare earth high-performance EH40 ship plate, characterized in that, The chemical composition of the rare earth high-performance EH40 marine steel plate is as follows in terms of mass percentage: C: 0.06-0.09%, Si: 0.20-0.30%, Mn: 1.45-1.60%, P≤0.015%, S≤0.005%, Nb: 0.035-0.050%, V: 0.035-0.050%, Ti: 0.012-0.022%, Als: 0.020-0.035%, rare earth Ce: 0.0005-0.0020%, CEV≤0.40%, Pcm≤0.20%, and the balance of Fe and inevitable impurities. The performance of the rare earth high-performance EH40 marine steel plate meets the following requirements: yield strength≥390MPa, tensile strength 510-660MPa, elongation after fracture≥20%, and impact energy at-40℃≥270J.

2. The high-performing EH40 naval steel plate according to claim 1, characterized in that, The performance of the rare earth high-performance EH40 marine steel plate meets the following requirements: yield strength≥460MPa, tensile strength 540-660MPa, elongation after fracture≥20%, and impact energy at-40℃≥270J.

3. The rare earth high-performance EH40 shipbuilding steel plate according to claim 1 or 2, characterized in that, The performance of the rare earth high-performance EH40 marine steel plate at the head, tail, transverse direction, longitudinal direction, 1 / 4 thickness and 1 / 2 thickness is uniform and stable, the tensile performance after stress release is excellent, and the CTOD value of the welded joint at-35℃ is above 0.

5.

4. The rare earth high-performance EH40 shipbuilding steel plate according to any one of claims 1-3, characterized in that, The impact energy at-40℃ of the rare earth high-performance EH40 marine steel plate at the head transverse direction, head longitudinal direction, tail transverse direction and tail longitudinal direction is≥300J.

5. The rare earth high-performance EH40 shipbuilding steel plate according to any one of claims 1-3, characterized in that, The chemical composition of the rare earth high-performance EH40 marine steel plate is as follows in terms of mass percentage: C: 0.08-0.09%, Si: 0.24-0.27%, Mn: 1.53-1.58%, P≤0.015%, S≤0.005%, Nb: 0.042-0.046%, V: 0.039-0.041%, Ti: 0.013-0.015%, Als: 0.020-0.022%, rare earth Ce: 0.0010-0.0013%, and the balance of Fe and inevitable impurities.

6. The method of producing a rare earth high-performance EH40 shipbuilding steel plate according to any one of claims 1 to 5, characterized in that, The method comprises the following processes: hot metal pretreatment, converter top and bottom combined blowing smelting, LF external refining, RH vacuum degassing, slab continuous casting (electromagnetic stirring and light press-down), slab cold charging or hot charging heating, descaling, rough rolling, finish rolling, cooling and straightening; wherein: in the converter smelting, the hot metal and high-quality scrap steel after desulfurization pretreatment are used as raw materials in the converter smelting stage, the temperature of the hot metal is≥1260℃, the high-efficiency top and bottom combined blowing technology is used to reduce the phosphorus and carbon content, and the molten steel is ensured to meet the requirements of P≤0.010% and S≤0.004%; in the LF external refining, the molten steel composition is accurately controlled in the external refining stage, the deoxidizing alloying is performed, and the non-metallic inclusions and harmful impurities in the molten steel are further reduced, and S≤0.004%; In the RH vacuum treatment, the hydrogen, oxygen and nitrogen content in the molten steel is greatly reduced by using the treatment mode, and the adverse effects of harmful gases on the steel are reduced; the vacuum degree is less than 90 Pa, the vacuum time is maintained for more than 15 minutes, the pure degassing time is greater than 15 minutes, the soft blowing time is greater than 15 minutes, the hydrogen content of the off-line molten steel is ≤1.6 ppm, the oxygen content is ≤30 ppm, and the nitrogen content is ≤50 ppm; In the slab continuous casting, dynamic soft reduction is used during continuous casting, the soft reduction position is 8, 9 and 10 segments, and the total soft reduction amount is 7.5 mm; electromagnetic stirring is used during continuous casting, the electromagnetic stirring position is the outlet of the 3rd segment and the inlet of the 4th segment, the electromagnetic stirring frequency is 5 Hz, and the current is 350 A; the water quantity of the wide side of the crystallizer is 4500 L / min, the water quantity of the narrow side is 370 L / min, the water temperature of the crystallizer is 36±2℃, the secondary cooling water temperature is 22-25℃, and the water quality index meets the process requirements; protective pouring is used, the sealing argon pressure of the long nozzle is greater than 0.3 MPa, and the flow is 130-160 L / min; the sealing argon pressure of the submerged nozzle in the tundish is greater than 0.2 MPa, and the flow is 15-20 L / min; the superheat degree during continuous casting is 20-30℃, the tundish liquid level during tundish changing is not less than 30 tons; constant speed is used, and the drawing speed is stabilized at 1.0 m / min; the straightening temperature of the casting blank is controlled at 950-1000℃, and the temperature difference along the width direction of the casting blank should not exceed 50℃; finally, a 250 mm thick continuous casting blank is produced, and the macroscopic center segregation of the casting blank is controlled to be below C class 3.0 level; In the heating, the slab is cold or hot charged and heated, the furnace atmosphere is strictly controlled, the slab heating temperature and heating time are ensured, the heating temperature is 1210-1250℃, the total furnace time is greater than 220 min, the heating section time is greater than 120 min, the soaking section time is greater than 30 min, the alloy elements are fully solid-solved, and the slab temperature is uniform; In the rolling and cooling, two-stage controlled rolling is used, the first stage rolling temperature is above 1180℃, and the single pass relative reduction rate is controlled to be above 15% for at least two passes; the second stage strictly controls the deformation amount of each pass, the rolling temperature is ≤930℃, and the finish rolling temperature is ≤810℃; after the steel plate is rolled, laminar cooling is carried out, the water temperature is 17-20℃, the open cooling temperature is 750-780℃, the final cooling temperature is 635-655℃, the cooling speed is 7-9℃ / s, the head shielding is 0-2.0 m, the tail shielding is 0-2.5 m, the side shielding is 0-2.0 m, and the overall temperature difference after the steel plate is red is controlled to be ≤50℃.

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