Pressure vessel steel plate with good performance uniformity for low-temperature spherical tank and manufacturing method of pressure vessel steel plate

Abstract

The invention relates to the technical field of steel, in particular to a pressure vessel steel plate with good performance uniformity for a low-temperature spherical tank and a manufacturing method of the pressure vessel steel plate. The steel plate comprises the following chemical components in percentage by weight: 0.070% to 0.100% of C, 0.15% to 0.40% of Si, 1.45% to 1.60% of Mn, less than or equal to 0.015% of P, less than or equal to 0.003% of S, 0.030% to 0.050% of Nb, 0.015% to 0.025% of Ti, 0.030% to 0.040% of V, 0.20% to 0.25% of Ni, 0.06% to 0.11% of Mo, 0.10% to 0.18% of Cu, 0.015% to 0.045% of Alt and the balance of Fe and inevitable impurities. The process means of nickel molybdenum-niobium vanadium titanium microalloying, continuous casting billet smelting, controlled rolling and controlled cooling, differential temperature rolling and tempering treatment is adopted, so that the product has good obdurability and is matched with a flat and straight plate shape, the mechanical property difference in the thickness direction is large, and the phenomenon of core low-temperature impact dispersion is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of steel, and in particular to a pressure vessel steel plate for a cryogenic spherical tank with good performance uniformity and a manufacturing method thereof. Background Art

[0002] With the rapid development of modern industrial technology, pressure vessel equipment is constantly developing in the direction of large-scale, thick-walled and high-parameterized. As an indispensable key equipment in the field of cryogenic storage and transportation, the design thickness of cryogenic spherical tanks generally exceeds 40mm to meet the increasing storage needs and higher safety standards. This brings more stringent challenges to the manufacturing of cryogenic spherical tank steel plates, requiring the material to not only have excellent mechanical properties, but also to achieve efficient and low-cost production during the manufacturing process.

[0003] In order to shorten the process, improve production efficiency and reduce production costs, enterprises tend to adopt online controlled rolling and controlled cooling process to produce low-temperature spherical tank steel plates. However, when the thickness of the steel plate is large, especially when it exceeds 40mm, the traditional controlled rolling and controlled cooling process is difficult to achieve uniform deformation and cooling of the surface and core of the steel plate (i.e. 1 / 2 plate thickness position). The deformation conditions of the steel plate near the surface and the core are very different, and there is a large difference in mechanical properties in the thickness direction of the medium and thick plates. Although it can be improved by adjusting the subsequent heat treatment process, it is easy to cause the low-temperature impact toughness of the core to deteriorate. Summary of the invention

[0004] The object of the present invention is to overcome the above problems and shortcomings and to provide a pressure vessel steel plate for a cryogenic spherical tank having good uniformity of performance and a method for manufacturing the same.

[0005] The present invention adopts the process of nickel-molybdenum-niobium-vanadium-titanium microalloying + continuous casting billet smelting + controlled rolling and controlled cooling + differential temperature rolling + tempering treatment, so that the product has good strength and toughness matching and a flat plate shape, and the large difference in mechanical properties in the thickness direction and the phenomenon of low-temperature impact dispersion in the core are greatly improved.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] In one aspect, the present invention provides a pressure vessel steel plate for a cryogenic spherical tank having good uniformity of performance, wherein the chemical composition of the steel plate is as follows by weight percentage:

[0008] C: 0.070% ~ 0.100%, Si: 0.15% ~ 0.40%, Mn: 1.45% ~ 1.60%, P ≤ 0.015%, S ≤ 0.003%, Nb: 0.030% ~ 0.050%, Ti: 0.015% ~ 0.025%, V: 0.030% ~ 0.040%, Ni: 0.20% ~ 0.25%, Mo: 0.06% ~ 0.11%, Cu: 0.10% ~ 0.18%, Alt: 0.015 ~ 0.045%, the rest is Fe and unavoidable impurities.

[0009] The reasons for adopting the above components are as follows:

[0010] (1) C: C is the main component element of steel. The strength of steel mainly depends on the content of C in the steel. Too high C content will lead to poor toughness, plasticity and welding performance of the steel; low C content will lead to low strength and performance after simulated stress relief treatment. In order to ensure that the steel plate has good low-temperature impact toughness, strength and welding performance during use, the C content in the steel of the present invention is controlled to be 0.070% to 0.100%.

[0011] (2) Si: Si is a common solid solution strengthening alloying element in steel. It is essential for the toughness and hardenability of steel and even for ensuring the deoxidation of steel. However, a high content of Si will also lead to a decrease in the toughness of the steel. Therefore, the Si content in the steel of the present invention is controlled at 0.15% to 0.40%.

[0012] (3) Mn: The Mn element can strengthen pearlite in steel by solid solution strengthening. C-Mn strengthening is also the main way to improve the strength of low carbon steel. However, if the Mn content is too high, the production cost will be increased. The Mn element is easy to combine with the S element to form MnS, which reduces the material's resistance to hydrogen-induced cracking. At the same time, too high a Mn content will reduce the activity of the carbon element. Therefore, the Mn content in the steel of the present invention is controlled at 1.45% to 1.60%.

[0013] (4) P: Phosphorus is a harmful element in steel. It increases the cold brittleness of steel, deteriorates welding performance, reduces plasticity, and deteriorates cold bending performance. In addition, P is particularly sensitive to radiation embrittlement. Therefore, the lower the P content in the steel of the present invention, the better, and it is controlled to be less than 0.015%.

[0014] (5) S: S is usually a harmful element. S is usually easy to form brittle sulfides with alloy elements in steel, making the steel hot brittle and reducing the ductility and toughness of the steel. At the same time, S also tends to accelerate radiation embrittlement. Therefore, the S content in the steel of the present invention is controlled to be less than 0.003%.

[0015] (6) V: V is a microalloying element. Microalloying of V in steel can form fine second phase particles, which play a role in pinning grain boundaries and precipitation strengthening, and can effectively refine grains, greatly improving the comprehensive mechanical properties of steel such as strength, toughness, ductility and thermal fatigue resistance. Therefore, the V content in the steel of the present invention is controlled at 0.030% to 0.040%.

[0016] (7) Nb: As a strong carbide-forming element, Nb forms a NbC phase with large dispersion and good high-temperature stability in steel, which plays a role in precipitation strengthening. Through multi-stage rolling, it can effectively refine the grains and improve the reduction of toughness caused by precipitation strengthening, so that the steel plate can obtain the comprehensive performance of high strength and high toughness. In addition, in the steel with Nb-Mo composite addition, Mo can also be segregated on the NbC matrix interface, preventing the coarsening of NbC particles, thereby greatly improving the high-temperature strength of the steel. Therefore, the Nb content of the present invention is controlled at 0.030% to 0.050%.

[0017] (8) Ti: Adding an appropriate amount of Ti can form a large number of dispersed fine TiN or Ti2O3 particles, which can serve as the heterogeneous nucleation core of needle-shaped pearlite during the solidification of the structure, thereby refining the structure. Ti also has a deoxidizing effect, ensuring that B is not oxidized and nitrided. B can reduce the transformation temperature from austenite to pearlite phase, promote the formation of needle-shaped pearlite in the grains, and play a role in refining the grains. However, when w(Ti) ≥ 0.09%, the needle-shaped pearlite content will be reduced, and the low-temperature toughness of the steel plate will deteriorate. Therefore, the Ti content in the steel of the present invention is controlled to be 0.015% to 0.025%.

[0018] (9) Alt: Adding a small amount of Al to steel can effectively refine austenite grains, thereby refining ferrite grains and structure, and improving the impact toughness of steel. However, Al has the disadvantage of affecting the hot working performance, welding performance and cutting performance of steel. Therefore, the Alt content in the steel of the present invention is controlled at 0.015% to 0.045%.

[0019] (10) Ni: Ni is a solid solution strengthening element in steel that can improve the strength of steel. Ni reduces the resistance to dislocation movement in steel, relaxes stress, and further changes the substructure of the matrix structure, thereby improving the toughness of steel, especially low-temperature toughness. However, excessive Ni content in medium carbon steel will increase the phase transition temperature. Therefore, the Ni content in the present invention is controlled at 0.20% to 0.25%.

[0020] (11) Mo: Mo mainly relies on solid solution strengthening and grain boundary strengthening to improve the strength of steel. Secondly, Mo increases the stability of supercooled austenite, shifts the austenite to pearlite transformation curve to the right, and obtains a finer pearlite structure after phase transformation. In addition, Ti and Mo are combined to precipitate a large amount of nano-sized Ti-Mo (CN) carbides in the steel. The refined carbides pin dislocations, greatly improving the strength and toughness of the steel. Therefore, the Mo content in the steel of the present invention is controlled at 0.06% to 0.11%.

[0021] (12) Cu: The prominent role of Cu in steel is to improve the corrosion resistance of ordinary carbon low alloy steel, and to increase the strength and yield strength ratio of steel, without adversely affecting the welding performance. At the same time, its role is similar to that of nickel, and it can play a certain role in saving nickel and reducing costs. However, when the content is high, it will cause copper brittleness during hot deformation processing. Therefore, the Cu content in the steel of the present invention is controlled at 0.10% to 0.18%.

[0022] In the above technical solution, further, the thickness of the finished steel plate is 40 to 60 mm.

[0023] In the above technical scheme, further, the transverse tensile strength of the finished steel plate at 1 / 4 and 1 / 2 of the thickness is 650-700MPa, the yield strength is 530-580MPa, the elongation after fracture is 19-24%, the impact energy at -50°C is 150-250J, the welding line energy is 140-150KJ / cm, and the impact energy of the heat affected zone at -50°C after welding is 100-200J.

[0024] Another aspect of the present invention provides a method for manufacturing the above steel plate, comprising the following steps:

[0025] (1) Continuous casting smelting:

[0026] RH inlet temperature is 1590~1620℃, RH oxygen blowing volume is 25~45m 3 / h, the circulating oxygen blowing time is 10-20min, which effectively prevents the secondary oxidation of molten steel. At the same time, a two-step aluminum addition method is used for deoxidation, that is, aluminum cake is added for pre-deoxidation during the converter steelmaking process + aluminum wire is added for deoxidation during the LF furnace refining process. The continuous casting adopts multi-stage argon protection pouring, and the continuous casting dynamic light pressure reduction process is adopted. The pressure reduction range is 4.0-7.0mm, the pressure reduction rate is 0.3-0.5mm / s, and the continuous casting billet thickness is 250-300mm;

[0027] (2) Controlled rolling and controlled cooling:

[0028] After heating, the continuous casting billet is rough rolled. The core temperature of the rough rolling billet is 1100-1130℃, and the core temperature of the rough rolling billet is 1050-1080℃. After rough rolling, it enters the laminar cooling device located between the rough rolling mill and the finishing mill. The billet is cooled by spraying high-pressure cooling water. The core temperature of the finishing rolling billet is 885-915℃, and the core temperature of the finishing rolling billet is 815-855℃. After finishing rolling, the steel is thrown at a speed of 4-5m / s to reduce the steel plate The temperature drop is followed by pre-straightening treatment. After pre-straightening, ACC laminar cooling is performed. The starting cooling temperature is 780-830℃ at the core of the steel plate, so that the austenite grains can retain more storage energy. The cooling rate is 30-50℃ / s water cooling. The red-return temperature of the steel plate is 480-580℃ at the core of the steel plate. At the same time, the head and tail of the pre-straightened steel plate are shielded during ACC laminar cooling, so that the red-return temperature difference between the head and tail of the steel plate is less than 20℃. After ACC laminar cooling, the unevenness of the steel plate is ≤8mm / m;

[0029] (3) Tempering heat treatment:

[0030] The tempering temperature is 620-640℃, the heating rate is 1.5-2.5min / mm, the net insulation time is 40-150min, and after the insulation is completed, it is air-cooled to room temperature;

[0031] (4) Straightening: The unevenness of the finished steel plate after straightening is ≤5mm / m.

[0032] In the above technical solution, further, in step (1), during converter smelting, the charge block size is 50-100 mm, the charge hot charging temperature is 1150-1200° C., and the net insulation time is 3-6 min;

[0033] The amount of aluminum cake added is 5-10kg / ton, and the amount of aluminum wire added is 5-10kg / ton.

[0034] In the above technical scheme, further, in step (1), the mold protection slag is composed of the following components in weight percentage: CaO 35% to 50%, Al2O3 30% to 40%, MnO 0 to 10%, SiO2 5% to 10%, and the balance is inevitable impurities. The thickness of the slag film is 0.1 to 1.5 mm, which ensures that the inclusions are fully floated and removed to prevent the occurrence of linear defects in the ingot.

[0035] In the above technical solution, further, in step (1), the pouring temperature is 1530-1550°C, the pulling speed is 0.9-1.0 m·min -1 The billet is put into the slow cooling pit for slow cooling after coming off the line. The slow cooling temperature is 300-400℃ and the holding time is 12-24h.

[0036] In the above technical scheme, further, in step (1), the multi-stage argon protection pouring method is: argon is introduced from the ladle to the tundish for protection, the argon pressure is 0.1~0.3MPa, the argon flow rate is 2~5L / min, and the free O2 in the protective atmosphere is 0.1%~0.5%; argon is introduced from the tundish to the crystallizer for protection, the argon pressure is 0.3~0.5MPa, the argon flow rate is 1~3L / min, and the free O2 in the protective atmosphere is 0.5%~1%.

[0037] In the above technical solution, further, in step (2), the heating adopts a four-stage heating method, the heating stage I temperature is 600-650°C, the heating stage II temperature is 1000-1050°C, the heating stage III temperature is 1170-1210°C, the soaking stage temperature is 1150-1190°C, the soaking stage time is 30-40min, and the total heating time is H*(0.9-1.2)min·mm -1 , H is the continuous casting billet thickness, mm; the appropriate heating system effectively controls the original austenite grain size and ensures sufficient solid solution of alloy elements, ensuring good final performance of the product.

[0038] In the above technical solution, further, in step (2), rolling is carried out in a double-stand rolling mill, the reduction rate of each rough rolling pass is 15% to 25%, the thickness of the intermediate billet is 3 to 4 times the thickness of the finished steel plate, and the reduction rate of each finish rolling pass is 5% to 15%.

[0039] In the above technical solution, further, in step (2), the parameters of ACC laminar cooling are: number of headers 10 to 12 groups, roller speed 1.2 to 1.4 m / s, water volume 240 to 260 mm 3 / h, water temperature 14~20℃.

[0040] In the above technical solution, further, in step (2), according to the thickness of the finished steel plate, the roller gap setting parameters of the pre-straightening machine system are adjusted: the tilt correction range is 0 to +1.5 mm, the roller gap correction range is -1.5 to +0.5 mm and the load reduction range is +0.5 to +1.0 mm, so that the steel plate after pre-straightening is straight and can smoothly enter the ACC area, avoiding a series of problems such as uneven temperature and warping of the steel plate caused by local water accumulation, asymmetric cooling and uneven cooling during the water cooling process.

[0041] In the above technical solution, further, in step (2), according to the outlet plate shape of the online quenching steel plate, the head and tail of the steel plate are shielded and the shielding flow rate is controlled at 5% to 10%;

[0042] Shielding control principle: The temperature of the head and tail of the steel plate is close to that of the body, which reduces the number of cooling header groups for shielding control and shortens the flow adjustment time. Through the use of the ACC head and tail shielding function, the temperature uniformity of the steel plate is good, and the online quenching steel plate is straight, which meets the requirements of the tempering furnace for the steel plate entering the furnace.

[0043] The beneficial effects of the present invention are:

[0044] 1. The purpose of using niobium vanadium titanium-nickel molybdenum microalloying is to control the expected transformation of the organizational structure and lay the foundation for the strength and toughness of the steel plate.

[0045] 2. Through multi-stage Ar gas protection pouring and continuous casting dynamic light pressure reduction process, the inclusion level and gas element content in the ingot are greatly reduced, the center segregation and center looseness of the ingot are reduced, the internal quality of the ingot is improved, and thus the purity of the steel is improved;

[0046] 3. The differential temperature rolling process is adopted on the basis of controlled rolling and controlled cooling. The steel plate is cooled before rolling to form a gradient temperature difference along the thickness direction. The surface temperature is low and the deformation resistance is large. The temperature at 1 / 2 of the plate thickness is high and it is easy to deform. The deformation can be transmitted to the core of the steel plate, increasing the deformation amount of the core, refining the austenite grains in the core, eliminating the performance difference in the thickness direction of the steel plate, and making the core of the thick plate still have good strength and toughness matching.

[0047] 4. The tempered bainite + ferrite structure is obtained through tempering heat treatment, the second phase is dispersed, the structure is uniform, and the strength and toughness of the product are well matched. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a metallographic structure photograph of the steel plate in Example 1. DETAILED DESCRIPTION

[0049] The following examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0050] Examples 1-7

[0051] The chemical compositions of the steel plates of Examples 1-7 of the present invention are shown in Table 1.

[0052] Table 1 Chemical composition of steel plates of Examples 1-7 of the present invention (wt%)

[0053] Example C Si Mn P S V Nb Ti Ni Mo Cu Alt 1 0.096 0.16 1.49 0.010 0.003 0.035 0.036 0.017 0.20 0.07 0.11 0.027 2 0.092 0.29 1.47 0.012 0.002 0.031 0.031 0.022 0.21 0.10 0.13 0.033 3 0.074 0.24 1.54 0.011 0.003 0.033 0.043 0.025 0.23 0.11 0.16 0.045 4 0.088 0.25 1.45 0.005 0.001 0.035 0.040 0.020 0.20 0.10 0.15 0.035 5 0.088 0.26 1.52 0.008 0.002 0.039 0.048 0.018 0.24 0.08 0.14 0.039 6 0.098 0.30 1.51 0.006 0.001 0.036 0.034 0.019 0.22 0.06 0.17 0.026 7 0.100 0.35 1.56 0.007 0.001 0.040 0.040 0.020 0.21 0.09 0.15 0.030

[0054] Table 2 Main process parameters for continuous casting smelting of Examples 1-7 of the present invention

[0055]

[0056] Table 3 Chemical composition and slag film thickness of the mold protection slag of Examples 1-7 of the present invention

[0057]

[0058]

[0059] Table 4 Casting process parameters of Examples 1-7 of the present invention

[0060]

[0061] Table 5 Macroscopic evaluation grade of continuous casting slabs and gas element content of casting slabs in Examples 1-7 of the present invention

[0062]

[0063]

[0064] Table 6 Heating process parameters of continuous casting slabs in Examples 1-7 of the present invention

[0065]

[0066] Table 7 Steel plate rolling process parameters of Examples 1-7 of the present invention

[0067]

[0068]

[0069] Table 8 Pre-straightening process parameters of steel plates in Examples 1-7 of the present invention

[0070] Example Tilt correction / mm Roll gap correction / mm Depression with load / mm 1 0.9 -1.4 0.6 2 1.0 -1.0 0.7 3 1.1 -0.6 0.9 4 1.0 -0.9 0.8 5 1.2 0.1 0.8 6 1.4 0.4 0.9 7 1.3 0.2 0.6

[0071] Table 9 ACC laminar cooling process parameters of steel plates in Examples 1-7 of the present invention

[0072]

[0073] Table 10 Heat treatment process parameters of steel in the embodiment of the present invention

[0074] Example Tempering temperature℃ Net insulation time min Unevenness after cold straightening mm / m 1 624 42 4.9 2 635 69 4.0 3 630 120 4.5 4 633 120 4.1 5 631 115 4.1 6 638 148 4.7 7 629 108 4.4

[0075] Table 11 Comprehensive mechanical properties of steel plates in Examples 1-7 of the present invention

[0076]

[0077]

[0078] The whole steel plate is ultrasonically tested according to the provisions of NB / T 47013.3. The scanning method is: the probe is scanned with parallel lines perpendicular to and parallel to the rolling direction of the steel plate and with a spacing of 190-200mm. 100% scanning should be done within 40-50mm on both sides of the predetermined line of the steel plate groove. The defect assessment is qualified according to the T1 level specified in NB / T 47013.3, and the qualified rate is 100%.

[0079] Table 12 Test results of flaw detection performance of steel plates in delivery state of Examples 1-7 of the present invention

[0080]

[0081] Table 13 Non-metallic inclusions in the steel plates of Examples 1-7 of the present invention as delivered

[0082]

[0083]

[0084] like Figure 1 As shown, the steel plate has a structure of 60%-70% tempered bainite + 30%-40% ferrite.

[0085] In order to describe the present invention, the present invention is appropriately and fully illustrated by the examples in the above. The above implementation modes are only used to illustrate the present invention, but not to limit the present invention. Ordinary technicians in the relevant technical field can make various changes and modifications without departing from the spirit and scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made should be included in the protection scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A pressure vessel steel plate for a cryogenic spherical tank with good performance uniformity, characterized in that: The chemical composition of the steel plate is as follows by weight percentage: C: 0.070% ~ 0.100%, Si: 0.15% ~ 0.40%, Mn: 1.45% ~ 1.60%, P ≤ 0.015%, S ≤ 0.003%, Nb: 0.030 ~ 0.050%, Ti: 0.015% ~ 0.025%, V: 0.030% ~ 0.040%, Ni: 0.20% ~ 0.25%, Mo: 0.06% ~ 0.11%, Cu: 0.10% ~ 0.18%, Alt: 0.015 ~ 0.045%, the rest is Fe and unavoidable impurities.

2. The pressure vessel steel plate for cryogenic spherical tank with good performance uniformity according to claim 1, characterized in that: The thickness of the finished steel plate is 40 to 60 mm.

3. The pressure vessel steel plate for cryogenic spherical tank with good performance uniformity according to claim 1, characterized in that: The finished steel plate has a transverse tensile strength of 650-700MPa at 1 / 4 and 1 / 2 of the thickness, a yield strength of 530-580MPa, an elongation of 19-24%, an impact energy of 150-250J at -50℃, a welding line energy of 140-150KJ / cm, and an impact energy of 100-200J at -50℃ in the heat affected zone after welding.

4. A method for manufacturing a pressure vessel steel plate for a cryogenic spherical tank having good uniformity of performance as claimed in any one of claims 1 to 3, characterized in that: The method comprises the following steps: (1) Continuous casting smelting: RH inlet temperature is 1590~1620℃, RH oxygen blowing volume is 25~45m 3 / h, the circulating oxygen blowing time is 10-20min, and a two-step aluminum addition method is used for deoxidation, that is, aluminum cake is added for pre-deoxidation during the converter steelmaking process and aluminum wire is added for deoxidation during the LF furnace refining process. The continuous casting adopts multi-stage argon protection pouring, and the continuous casting dynamic light pressure reduction process is adopted. The pressure reduction range is 4.0-7.0mm, the pressure reduction rate is 0.3-0.5mm / s, and the continuous casting billet thickness is 250-300mm; (2) Controlled rolling and controlled cooling: After heating, the continuous casting billet is rough rolled. The core temperature of the rough rolling billet is 1100-1130℃, and the core temperature of the rough rolling billet is 1050-1080℃. After rough rolling, it enters the laminar cooling device located between the rough rolling mill and the finishing mill. The billet is cooled by spraying high-pressure cooling water. The core temperature of the finishing rolling billet is 885-915℃, and the core temperature of the finishing rolling billet is 815-855℃. After finishing rolling, the steel is thrown at a speed of 4-5m / s. After pre-straightening, ACC laminar cooling is performed. The starting cooling temperature is 780-830℃ at the core of the steel plate, so that the austenite grains can retain more storage energy. The cooling rate is 30-50℃ / s water cooling. The red-return temperature of the steel plate is 480-580℃ at the core of the steel plate. At the same time, the head and tail of the pre-straightened steel plate are shielded during ACC laminar cooling, so that the red-return temperature difference between the head and tail of the steel plate is less than 20℃. After ACC laminar cooling, the unevenness of the steel plate is ≤8mm / m. (3) Tempering heat treatment: The tempering temperature is 620-640℃, the heating rate is 1.5-2.5min / mm, the net insulation time is 40-150min, and after the insulation is completed, it is air-cooled to room temperature; (4) Straightening; The unevenness of the finished steel plate after straightening is ≤5mm / m.

5. The manufacturing method according to claim 4, characterized in that: In step (1), during converter smelting, the charge block size is 50-100 mm, the charge hot charging temperature is 1150-1200° C., and the net insulation time is 3-6 min; The amount of aluminum cake added is 5-10kg / ton, and the amount of aluminum wire added is 5-10kg / ton.

6. The manufacturing method according to claim 4, characterized in that: In step (1), the pouring temperature is 1530-1550°C and the pulling speed is 0.9-1.0 m·min -1 The billet is put into the slow cooling pit for slow cooling after it comes off the production line. The slow cooling temperature is 300-400℃ and the holding time is 12-24h. The crystallizer protection slag is composed of the following components in weight percentage: CaO 35%-50%, Al2O3 30%-40%, MnO 0-10%, SiO2 5%-10%, and the balance is inevitable impurities. The thickness of the slag film is 0.1-1.5 mm.

7. The manufacturing method according to claim 4, characterized in that: In step (2), the heating adopts a four-stage heating method, with the temperature of heating stage I being 600-650°C, the temperature of heating stage II being 1000-1050°C, the temperature of heating stage III being 1170-1210°C, the temperature of the soaking stage being 1150-1190°C, the soaking stage time being 30-40 min, and the total heating time being H*(0.9-1.2) min·mm -1 , H is the thickness of the continuous casting billet, mm.

8. The manufacturing method according to claim 4, characterized in that: In step (2), rolling is carried out in a double-stand rolling mill, with a reduction rate of 15% to 25% in each rough rolling pass, the thickness of the intermediate billet being 3 to 4 times the thickness of the finished steel plate, and a reduction rate of 5% to 15% in each finish rolling pass.

9. The manufacturing method according to claim 4, characterized in that: In step (1), the multi-stage argon protection casting method is: argon is introduced from the ladle to the tundish for protection, the argon pressure is 0.1-0.3 MPa, the argon flow rate is 2-5 L / min, and the free O2 in the protective atmosphere is 0.1%-0.5%; argon is introduced from the tundish to the crystallizer for protection, the argon pressure is 0.3-0.5 MPa, the argon flow rate is 1-3 L / min, and the free O2 in the protective atmosphere is between 0.5% and 1%.

10. The manufacturing method according to claim 4, characterized in that: In step (2), in ACC laminar cooling, the number of headers is 10 to 12 groups, the roller speed is 1.2 to 1.4 m / s, and the water volume is 240 to 260 mm 3 / h, water temperature 14~20℃.

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