Production method of steel plate for pressure vessel

Abstract

The present application discloses a production method for steel plates used in pressure vessels, including steelmaking, continuous casting, heating, rolling, and normalizing heat treatment; in terms of chemical composition, C: 0.13% - 0.16%, Si: 0.15% - 0.25%, Mn: 1.40% - 1.50%, Nb: 0.01% - 0.02%, V: 0.02% - 0.03%, Ti: 0.01% - 0.02%, Alt: 0.02% - 0.05%, P ≤ 0.015%, S ≤ 0.005%; during rolling, rolling is carried out in the austenite recrystallization zone, and the final rolling temperature ≥ 930°C; after rolling, water cooling is carried out, and the final cooling temperature is 700 ± 30°C; the normalizing temperature is 880 - 900°C, and the time in the furnace = a·t, where t is the thickness of the steel plate; after the steel plate is taken out of the furnace, it is cooled by water, and the return red temperature T fh = 700 - T s - 180×exp(-0.5×((t - 103) / 71) 2 ), T s is the water temperature.

Description

Technical Field

[0001] This application belongs to the technical field of steel material preparation, and relates to a production method of steel plates for pressure vessels. Background Art

[0002] Pressure vessels are widely used in industrial fields such as petrochemical industry and power station boilers, such as equipment like reaction kettles, storage tanks, and tower vessels. These application scenarios usually involve high temperature, high pressure, and corrosive media. Therefore, the materials used for pressure vessels need to have high strength, corrosion resistance, and good toughness, so that the pressure vessels can withstand large internal or external pressures under such harsh working conditions.

[0003] Nowadays, pressure vessels are continuously developing towards the direction of large-scale and high compressive performance. Corresponding to the steel plates for pressure vessels, it is required that the steel plates not only have excellent mechanical properties and low-temperature toughness, especially the impact toughness at -51°C, but also have relatively high requirements for the performance homogenization in the thickness direction. In addition, pressure vessels need to be subjected to post-weld heat treatment as a whole or partially for multiple times. Therefore, relatively high requirements are also put forward for the stability of the post-weld heat treatment performance of the steel plates for pressure vessels. Summary of the Invention

[0004] The purpose of this application is to provide a production method of steel plates for pressure vessels.

[0005] To achieve the above application purpose, an embodiment of this application provides a production method of steel plates for pressure vessels, which includes various processes of steelmaking, continuous casting, heating, rolling, and normalizing heat treatment in sequence;

[0006] In the steelmaking process, the chemical composition of the molten steel obtained by smelting includes, by mass percentage: C: 0.13% - 0.16%, Si: 0.15% - 0.25%, Mn: 1.40% - 1.50%, Nb: 0.01% - 0.02%, V: 0.02% - 0.03%, Ti: 0.01% - 0.02%, Alt: 0.02% - 0.05%, P ≤ 0.015%, S ≤ 0.005%, and the balance is iron and inevitable impurities;

[0007] In the rolling process, the continuously cast billet after heating is rolled in the austenite recrystallization zone to obtain a steel plate with a thickness of t, and the final rolling temperature ≥ 930°C; then water cooling is carried out, and the final cooling temperature is 700 ± 30°C; then air cooling is carried out;

[0008] In the normalizing heat treatment process, the normalizing temperature is 880 - 900°C, and the residence time in the furnace = a·t, where a is 1.6 - 1.7 min / mm and the unit of t is mm; after the steel plate is taken out of the furnace, it is cooled by water, and the return red temperature T fh = 700 - T s-180×exp(-0.5×((t - 103) / 71) 2 ), in degrees Celsius, and the allowable deviation range of the red - return temperature is ±20°C, where T s is the temperature of the cooling water, in degrees Celsius.

[0009] As a further improvement of an embodiment of the present application, in the heating process, a walking - beam reheating furnace is used for heating, the soaking temperature is 1150 - 1220°C, and the residence time in the furnace ≥ b·h, where b is 1.0 min / mm and h is the thickness of the continuous casting billet, in mm.

[0010] As a further improvement of an embodiment of the present application, the steel - making process includes the steps of hot metal pre - desulfurization, converter smelting, LF refining, and RH vacuum refining carried out in sequence;

[0011] In the converter smelting step, when 3 / 20 of the steel is tapped, ferrosilicon, ferromanganese, and aluminum are sequentially added to the molten steel, and then lime is added to the molten steel to form slag;

[0012] In the LF refining step, after the refining is completed, 0.60 - 0.75 m / ton of pure calcium wire is fed into the molten steel, the wire - feeding speed is 1.0 - 2.0 m / s, and soft stirring is carried out for 1 - 3 min after the wire - feeding is completed;

[0013] In the RH vacuum refining step, adding Al to the molten steel is prohibited, and soft stirring is carried out after breaking the vacuum, and the soft - stirring time ≥ 8 min.

[0014] As a further improvement of an embodiment of the present application, in the converter smelting step, the addition amount of aluminum is (15·[O]+0.65) kg / ton, where [O] is the mass percentage value of the O content in the molten steel detected before tapping.

[0015] As a further improvement of an embodiment of the present application, when the thickness t of the steel plate > 30 mm, the chemical composition of the molten steel obtained by smelting further includes Ni: 0.15% - 0.25% by mass percentage;

[0016] In the converter smelting step, scrap steel, nickel plates, and the hot metal obtained in the hot metal pre - desulfurization step are added to the converter for smelting.

[0017] As a further improvement of an embodiment of the present application, in the normalizing heat - treatment process, the steel plate is subjected to normalizing heat - treatment in a continuous roller - hearth non - oxidizing furnace.

[0018] As a further improvement of an embodiment of the present application, in the rolling process, a multi - functional intermittent cooling system is used for water cooling.

[0019] As a further improvement of an embodiment of the present application, the thickness t of the steel plate is 6 to 100 mm;

[0020] The Z-direction tensile section shrinkage of the steel plate is ≥65%, the yield strength of the steel plate at the 1 / 4 position and the 1 / 2 position along the thickness direction is ≥355MPa, the tensile strength is 540~620MPa, the elongation after fracture is ≥30%, and the -51°C low-temperature impact energy of the steel plate at the 1 / 4 position and the 1 / 2 position along the thickness direction is ≥100J.

[0021] As a further improvement of one embodiment of the present application, after the steel plate undergoes four simulated post-weld heat treatments, the Z-direction tensile section shrinkage of the steel plate is ≥65%, the yield strength of the steel plate at the 1 / 4 position and the 1 / 2 position along the thickness direction is ≥300 MPa, the tensile strength is 485~530 MPa, the elongation after fracture is ≥30%, and the -51°C low-temperature impact energy of the steel plate at the 1 / 4 position and the 1 / 2 position along the thickness direction is ≥100 J.

[0022] As a further improvement of an embodiment of the present application, the flaw detection grade of the steel plate complies with NB / T 47013.3 Level I;

[0023] The metallographic structure of the steel plate is ferrite+pearlite, the pearlite is dispersed, and there is no obvious banded structure.

[0024] Compared with the prior art, the advantages of this application include:

[0025] (1) Through the optimization design of chemical composition, the C+Si+Mn matrix combined with the Nb+V+Ti+Al composite microalloying composition system is adopted. Compared with the solution of adding Mo, Cr, and Cu alloys in the existing technology, the alloy cost is significantly reduced and the market competitiveness of the product is greatly improved; compared with the composition system in the existing technology that strictly limits the P and S content, the smelting difficulty is greatly reduced, which facilitates the efficient and stable production of the steelmaking process.

[0026] (2) Based on the chemical composition design scheme and combined with the control of the production process, this application can break through the thickness of the steel plate to 100mm, and the structure and strength of the steel plate can meet the requirements of steel plates for pressure vessels. It not only has excellent low-temperature toughness, but also can improve the performance uniformity of the steel plate along the thickness direction and the stability of the post-weld heat treatment performance. After the steel plate has undergone 4 simulated post-weld heat treatments, the steel plate still has excellent strength and toughness, and excellent performance uniformity along the thickness direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a metallographic image of the steel plate of Example 1 at the 1 / 2 position along the thickness direction;

[0028] Figure 2Metallographic structure picture at the 1 / 4 position along the thickness direction of the steel plate in Example 4;

[0029] Figure 3 Metallographic structure picture at the 1 / 2 position along the thickness direction of the steel plate in Example 4. Specific implementation manners

[0030] The following further introduces the present application in combination with specific implementation manners, but the scope of protection required is not limited to the description made.

[0031] One implementation manner of the present application provides a production method of a steel plate for pressure vessels, and further provides a steel plate for pressure vessels prepared by using this production method.

[0032] Specifically, the production method of the steel plate for pressure vessels includes a steelmaking process, a continuous casting process, a heating process, a rolling process, and a normalizing heat treatment process carried out in sequence, and thus a steel plate is obtained, and this steel plate can be used to prepare pressure vessels.

[0033] The following describes this production method in detail according to each process.

[0034] (1) Steelmaking process

[0035] According to the chemical composition of the required steel plate, molten steel is smelted.

[0036] The chemical composition of the molten steel obtained by smelting includes, by mass percentage: C: 0.13% - 0.16%, Si: 0.15% - 0.25%, Mn: 1.40% - 1.50%, Nb: 0.01% - 0.02%, V: 0.02% - 0.03%, Ti: 0.01% - 0.02%, Alt: 0.02% - 0.05%, P ≤ 0.015%, S ≤ 0.005%, and the balance is iron and unavoidable impurities.

[0037] It can be understood that the chemical composition of the finally obtained steel plate is obtained through the steelmaking process, that is, the chemical composition of the finally obtained steel plate is consistent with the chemical composition of the molten steel obtained by the steelmaking process.

[0038] The following explains the functions of each chemical composition and its content in the present application:

[0039] C: It is a strengthening element. When the C content is low, the strength of the steel plate decreases significantly after long-term welding heat treatment, and it is difficult to meet the strength requirements of pressure vessels; when the C content is high, the low-temperature toughness of the steel is poor. In the present application, the C content is controlled to be 0.13% - 0.16%. Combining with the overall design of other elements and processes, it can not only ensure the strengthening effect on the steel plate, but also improve the low-temperature toughness of the steel plate.

[0040] Si: It is a deoxidizing element, a solid solution strengthening element, and can also increase the carbon activity so that it is insoluble in carbides. Therefore, it can inhibit the coarsening of carbides and reduce the strength reduction of the steel plate after long-term welding heat treatment. However, when the Si content is relatively high, the surface quality of the steel plate is poor and the low-temperature toughness will be reduced. In this application, the Si content is controlled to be 0.15% - 0.25%. Combining with the overall design of other elements and processes, on the premise of not affecting the low-temperature toughness, the deoxidation effect is ensured, the oxide inclusions in the steel are reduced, and its strengthening effect is fully exerted.

[0041] Mn: It is a solid solution strengthening and grain refinement strengthening element. At the same time, it is an element that is prone to segregation and easy to form inclusions, which will affect the low-temperature impact toughness of the core of the steel plate. In this application, the Mn content is controlled to be 1.40% - 1.50%. On the one hand, it can ensure the strength of the steel plate, and on the other hand, it can reduce segregation and avoid the deterioration of the low-temperature impact toughness of the core of the steel plate caused by MnS inclusions.

[0042] Nb: It can reduce the overheating sensitivity and temper brittleness of the steel, and reduce the strength reduction of the steel plate after long-term welding heat treatment. However, when the Nb content is too high, the strengthening effect becomes weak. In this application, the Nb content is controlled to be 0.01% - 0.02% to ensure the strengthening and toughening effect.

[0043] V: It makes the area of pearlite clusters smaller, increases the number of breakpoints and the degree of fragmentation of cementite in pearlite lamellae, improves the strength and toughness of the steel plate, and at the same time plays a certain degree of precipitation strengthening role during long-term welding heat treatment. However, when the V content is too high, it is not conducive to the welding performance of the steel plate. In this application, the V content is controlled to be 0.02% - 0.03% to ensure the strengthening and toughening effect.

[0044] Ti: It is a nitrogen-fixing element and a deoxidizing element, but it is easy to form large particles of Ti(C, N), that is, the carbonitride of Ti, in the core of the steel plate, which affects the low-temperature impact toughness at 1 / 2 of the steel plate thickness. In this application, the Ti content is controlled to be 0.01% - 0.02%.

[0045] Al: It is a deoxidizing and grain refinement element. Excessive aluminum is easy to increase the Al2O3 inclusions in the steel, which affects the low-temperature toughness of the steel. In this application, the Alt content is controlled to be 0.02% - 0.05%.

[0046] P, S: They are inevitable impurity elements in the steel. P is easy to segregate in the center of the steel plate, and S is easy to combine with Mn to form MnS inclusions, which significantly affect the low-temperature impact toughness at 1 / 2 of the steel plate thickness. During the production process, the contents of P and S should be reduced as much as possible, but deep dephosphorization and desulfurization will greatly increase the difficulty and production cost of the steelmaking process.

[0047] In this application, by controlling P and S within a reasonable range, that is: P ≤ 0.015% and S ≤ 0.005%, combined with an optimized alloy composition system and process control scheme, on the one hand, it effectively inhibits center segregation and reduces the content of non-metallic inclusions, ensuring that the steel plate has excellent low-temperature toughness; on the other hand, it avoids the problems of increased production difficulty and rising production cost caused by overly strict control requirements for P and S content, achieving a balance between performance guarantee and economic benefits.

[0048] Through the optimized design of the above chemical composition, adopting a C + Si + Mn matrix combined with a Nb + V + Ti + Al complex micro-alloying composition system, compared with the existing technology of adding Mo, Cr, Cu alloys, the alloy cost is significantly reduced, and the market competitiveness of the product is greatly improved; compared with the existing technology of strictly restricting the content of P and S, the smelting difficulty is greatly reduced, facilitating the efficient and stable production of the steelmaking process.

[0049] When the thickness t of the steel plate ≤ 30 mm, even without adding Ni, the low-temperature toughness of the steel plate can be ensured only by process control. However, when the thickness t of the steel plate > 30 mm, it is difficult to meet the requirements of the low-temperature toughness of the steel plate only by process control.

[0050] When the thickness t of the steel plate > 30 mm, the chemical composition of the molten steel obtained by smelting also includes Ni: 0.15% - 0.25% by mass percentage. That is, the chemical composition of the molten steel obtained by smelting and the final steel plate obtained includes: C: 0.13% - 0.16%, Si: 0.15% - 0.25%, Mn: 1.40% - 1.50%, Nb: 0.01% - 0.02%, V: 0.02% - 0.03%, Ti: 0.01% - 0.02%, Ni: 1.40% - 1.50%, Alt: 0.02% - 0.05%, P ≤ 0.015%, S ≤ 0.005%, and the balance is iron and inevitable impurities.

[0051] Ni can make the edge of cementite smooth and disperse it, making dislocations easier to slip under low-temperature conditions, which is an effective element to improve the low-temperature toughness of the steel plate, but the alloy cost is relatively high. By adding Ni and controlling the Ni content to 0.15% - 0.25%, combined with process control, it can not only ensure that the steel plate has excellent low-temperature toughness but also reasonably control the alloy cost.

[0052] Specifically, the steelmaking process includes the steps of hot metal pre-desulfurization, converter smelting, LF refining, and RH vacuum refining carried out in sequence.

[0053] s1. Hot metal pre-desulfurization

[0054] The sulfur content in the hot metal can be controlled at a relatively low level.

[0055] s2. Converter smelting

[0056] The total charge of the converter is 200 tons ± 5 tons. When the thickness of the steel plate ≤ 30 mm, scrap and hot metal obtained from the hot metal pre-desulfurization step are charged into the converter for smelting. When the thickness of the steel plate t > 30 mm, nickel plates, scrap and hot metal obtained from the hot metal pre-desulfurization step are charged into the converter for smelting.

[0057] After the smelting is completed, steel is tapped. When 3 / 20 of the steel is tapped, that is, when 30 tons of steel is tapped, ferrosilicon, ferromanganese and aluminum are sequentially added to the molten steel, and then lime is added to the molten steel to form slag.

[0058] Among them, the addition amount of aluminum is (15·[O] + 0.65) kg / ton, where [O] is the mass percentage value of the O content in the molten steel detected before tapping. For example, if the O content in the molten steel detected before tapping is 0.05%, then [O] is taken as 0.05.

[0059] In this way, accurately controlling the addition amount of aluminum according to the O content in the molten steel can reduce the generation of high-melting-point Al2O3 inclusions.

[0060] s3. LF refining

[0061] The molten steel obtained from the converter smelting and tapping is sent to the LF furnace for refining. After the refining is completed, 0.60 - 0.75 m / ton of pure calcium wire is fed into the molten steel, the wire feeding speed is 1.0 - 2.0 m / s, and soft stirring is carried out for 1 - 3 min after the wire feeding is completed.

[0062] s4. RH vacuum refining

[0063] After the molten steel obtained from the LF refining is transported to the RH treatment station by the steel ladle car, vacuum degassing is carried out; then deoxidation alloying is carried out, and during the deoxidation alloying process, adding Al to the molten steel is prohibited; then the vacuum is broken, and soft stirring is carried out, and the soft stirring time ≥ 8 min.

[0064] Through the coordination of converter smelting, LF refining and RH vacuum refining, inclusions can be fully modified and float up for removal, ensuring the cleanliness of the obtained molten steel, providing guarantee for the low-temperature toughness of the finished steel plate, and at the same time avoiding nozzle clogging during the continuous casting process, making the steelmaking process proceed smoothly.

[0065] (2) Continuous casting process

[0066] The molten steel obtained from the steelmaking process is made into a continuous casting billet with a thickness of h by a continuous caster, where h = 150 - 320 mm. Specifically, existing known continuous casting technologies can be used for implementation.

[0067] (3) Heating process

[0068] Heating is carried out using a walking beam reheating furnace. That is, the continuous casting billet is sent into the walking beam reheating furnace for heating. The soaking temperature is 1150 - 1220 °C, and the residence time in the furnace is ≥ b·h, where b is 1.0 min / mm and h is taken in mm. For example, if h = 220 mm, the residence time in the furnace is ≥ 220 min.

[0069] Thus, by controlling the soaking temperature and the residence time in the furnace, the temperature uniformity of the continuous casting billet can be improved, laying the foundation for the rolling stability of the subsequent rolling process and facilitating the improvement of property uniformity and plate shape.

[0070] (4)Rolling process

[0071] The heated continuous casting billet is rolled in the austenite recrystallization zone to obtain a steel plate with a thickness t of 6 - 100 mm, and the finishing rolling temperature is ≥ 930 °C; then it is water-cooled, and the finishing cooling temperature is 700 ± 30 °C; then it is air-cooled.

[0072] By adopting single-stage rolling, that is, only rolling in the austenite recrystallization zone and controlling the high-temperature rolling, the original austenite structure can be fully recrystallized and refined, and at the same time, the deformation can fully penetrate into the core of the steel plate, improving the tissue uniformity in the thickness direction of the steel plate, while improving the rolling efficiency, reducing the requirement for the rolling capacity of the rolling mill, and greatly reducing the cost. Water cooling can refine the as-rolled structure and provide a good tissue basis for the subsequent normalizing heat treatment.

[0073] Preferably, during water cooling, a multifunctional intermittent cooling system is used for water cooling to improve the cooling uniformity.

[0074] (5)Normalizing heat treatment process

[0075] The steel plate is sent into a continuous roller hearth non-oxidizing furnace for normalizing heat treatment.

[0076] Among them, the normalizing temperature is 880 - 900 °C, and the residence time in the furnace is = a·t, where a is 1.6 - 1.7 min / mm and t is in mm; after the steel plate is taken out of the furnace, it is water-cooled, and the return-to-red temperature T fh = 700 - T s - 180×exp(-0.5×((t - 103) / 71) 2 ), in °C, and the allowable deviation range of the return-to-red temperature is ± 20 °C, where T s is the temperature of the cooling water, in °C; and in the calculation formula of the return-to-red temperature T fh , only the value in mm is taken for t in the calculation, and only the value in °C is taken for T s in the calculation. For example, if t = 100 mm and T s = 20 °C, then in the calculation formula of the return-to-red temperature T fh , t takes 100 and Ts Take 20 for calculation.

[0077] By controlling the normalizing temperature and the time in the furnace, the structure of the steel plate can be fully austenitized without excessive growth, enabling the alloying elements to be fully dissolved. After normalizing, water cooling can refine the grains, disperse the pearlite, avoid the formation of pearlite banded structure, improve the strength and toughness of the steel plate. After long-term simulated welding, the steel plate still has good strength and toughness and can still meet the technical requirements, and the performance uniformity along the thickness direction is excellent. By reasonably setting the temperature of the cooling water according to the thickness of the steel plate during cooling and then strictly controlling the recalescence temperature, the structure type of the steel plate can be unchanged, the internal stress can be reduced, and the deformation of the steel plate can be reduced to a small level during subsequent manufacturing processes such as cutting and welding.

[0078] Preferably, the temperature T of the cooling water s is 15 - 30 °C.

[0079] After inspection, for the steel plate prepared by the above production method, the metallographic structure of the steel plate is ferrite + pearlite, the pearlite is dispersed, and there is no obvious banded structure;

[0080] The flaw detection grade of the steel plate meets Grade I of NB / T 47013.3;

[0081] The Z - direction tensile reduction of area of the steel plate is ≥ 65%, the yield strength Rt0.5 at the 1 / 4 and 1 / 2 positions along the thickness direction of the steel plate are both ≥ 355 MPa, the tensile strength Rm are both 540 - 620 MPa, the elongation after fracture A are both ≥ 30%, and the - 51 °C low - temperature impact energy at the 1 / 4 and 1 / 2 positions along the thickness direction of the steel plate are both ≥ 100 J.

[0082] Place the steel plate in a box - type resistance furnace and conduct 4 times of simulated post - weld heat treatment, that is, heat the steel plate to 635 ± 15 °C and hold for 6 h, then cool down to room temperature in the furnace, and cycle 4 times. Control the heating rate ≤ 50 °C / h during heating and the cooling rate ≤ 50 °C / h during cooling.

[0083] After inspection, after 4 times of simulated post - weld heat treatment, the Z - direction tensile reduction of area of the steel plate is ≥ 65%, the yield strength Rt0.5 at the 1 / 4 and 1 / 2 positions along the thickness direction of the steel plate are both ≥ 300 MPa, the tensile strength Rm are both 485 - 53 MPa, the elongation after fracture A are both ≥ 30%, and the - 51 °C low - temperature impact energy at the 1 / 4 and 1 / 2 positions along the thickness direction of the steel plate are both ≥ 100 J.

[0084] In summary, based on the chemical composition design scheme and combined with the control of the production process, this application can break through the steel plate thickness to 100mm, and the structure and strength of the steel plate can meet the requirements of steel plates for pressure vessels. It not only has excellent low-temperature toughness, but also can improve the performance uniformity of the steel plate along the thickness direction and the stability of the post-weld heat treatment performance. After the steel plate has undergone 4 simulated post-weld heat treatments, the steel plate still has excellent strength and toughness, and excellent performance uniformity along the thickness direction.

[0085] The following Examples 1 to 4 are provided to further illustrate the present application. These four examples are, of course, only a portion of the numerous examples included in the present application, and are not exhaustive. These four examples do not limit the present application. For example, the steelmaking process and chemical composition of the molten steel may also be implemented in other ways, and are not limited to those described below. Specifically, Examples 1 to 4 were implemented according to the following process:

[0086] (1) Steelmaking process

[0087] Molten steel was produced by sequentially performing molten iron pre-desulfurization, converter smelting, LF refining, and RH vacuum refining. The chemical compositions of the molten steels of Examples 1 to 4 are shown in Table 1 in terms of mass percentage, with the remainder being iron and unavoidable impurities.

[0088] Table 1

[0089]

[0090] The total charge of the converter is 200 tons ± 5 tons. In Examples 1 and 2, scrap steel and the molten iron obtained in the molten iron pre-desulfurization step are charged into the converter for smelting. In Examples 3 and 4, nickel plates, scrap steel, and the molten iron obtained in the molten iron pre-desulfurization step are charged into the converter for smelting.

[0091] After smelting, the steel is tapped and the oxygen content in the molten steel is tested before tapping. When 30 tons of steel has been tapped, ferrosilicon, metallic manganese, and aluminum are added to the molten steel in sequence, and lime is added to the molten steel to create slag.

[0092] The O content in the molten steel detected before tapping and the amount of aluminum added are shown in Table 2. The amount of aluminum added satisfies (15·[O]+0.65) kg / ton, where [O] is the mass percentage of the O content in the molten steel detected before tapping.

[0093] After LF refining, 0.60-0.75 m / ton of pure calcium wire was fed into the molten steel, followed by soft stirring. The pure calcium wire feed rate, feeding speed, and soft stirring time are shown in Table 2.

[0094] During RH vacuum refining, after the molten steel obtained from LF refining is transported to the RH treatment station by a ladle car, vacuum degassing is carried out; then deoxidation alloying is performed. During deoxidation alloying, adding Al to the molten steel is prohibited; then the vacuum is broken and soft stirring is carried out. The soft stirring time is also shown in Table 2.

[0095] Table 2

[0096]

[0097] (2)Continuous casting process

[0098] The molten steel obtained from the steelmaking process is made into a continuous casting billet with a thickness of h through a continuous casting machine. Specifically, it can be implemented by using existing known continuous casting technologies. The thickness h of the continuous casting billet is shown in Table 3.

[0099] (3)Heating process

[0100] A walking beam reheating furnace is used for heating. That is, the continuous casting billet is sent into the walking beam reheating furnace for heating. The soaking temperature is 1150 - 1220 °C, and the time in the furnace is shown in Table 3.

[0101] Table 3

[0102]

[0103] (4)Rolling process

[0104] The heated continuous casting billet is rolled in the austenite recrystallization zone to obtain a steel plate, and then it is sent into a multi-functional intermittent cooling system for water cooling and then air cooling.

[0105] The thickness t of the steel plate, the final rolling temperature, and the final cooling temperature of water cooling are shown in Table 4.

[0106] (5)Normalizing heat treatment process

[0107] The steel plate is sent into a continuous roller hearth non-oxidizing furnace for normalizing heat treatment. The normalizing temperature and the time in the furnace are shown in Table 4. After the steel plate is taken out of the furnace, it is cooled by water. The cooling water temperature and the re-reddening temperature are also shown in Table 4.

[0108] Table 4

[0109]

[0110] Performance tests are carried out on the steel plates of Examples 1 - 4, specifically including:

[0111] (1)Flaw detection test

[0112] The obtained steel plates are flaw detected in accordance with NB / T 47013.3, and it is measured that the flaw detection grades of the steel plates of Examples 1 - 4 all meet Grade I of NB / T 47013.3.

[0113] (2) Metallographic structure test

[0114] According to the ASME SA-20 / SA-20M standard, a 15 cm × 15 cm sample was taken from the head of the steel plate and made into a metallographic sample along the rolling direction. After mechanical grinding and nitric acid etching, the sample was placed under a metallographic microscope for tissue observation.

[0115] The metallographic structures of the steel plates of Examples 1 to 4 were all ferrite + pearlite structures, and the pearlite was diffusely distributed without obvious banded structures.

[0116] The metallographic structure photos of the steel plates of Examples 1 and 4 are selected here as examples. Example 1 is an example of the thinnest steel plate in this application, and Example 4 is an example of the thickest steel plate. The steel plates of Examples 1 and 4 are representative and can characterize the metallographic structure of the steel plates in this application.

[0117] in, Figure 1 This is the metallographic structure picture of the steel plate in Example 1 at the 1 / 2 position along the thickness direction. Figure 2 This is a metallographic image of the steel plate of Example 4 at the 1 / 4 position along the thickness direction. Figure 3 This is a metallographic image of the steel plate of Example 4 at the 1 / 2 position along the thickness direction.

[0118] (3) Mechanical properties test

[0119] The tensile and impact properties of the steel plates of Examples 1 to 4 were tested according to the ASTM A370 standard. The yield strength Rt0.5, tensile strength Rm, elongation after fracture A, and low-temperature impact energy at -51°C at the 1 / 4 and 1 / 2 positions along the thickness direction of the steel plates were measured and are shown in Table 5.

[0120] The Z-direction tensile properties of the steel plates of Examples 1 to 4 were tested with reference to the ASTM A770 standard. The measured Z-direction tensile section shrinkage of the steel plates are shown in Table 5.

[0121] Table 5

[0122]

[0123] Note: The thickness of the steel plate in Example 1 is only 10 mm, so the steel plate tensile specimen is a full-thickness specimen; the impact energy is close at the 1 / 4 position and the 1 / 2 position along the thickness direction; and the thickness is too thin and no Z-axis stretching is required.

[0124] (4) Simulation of post-weld heat treatment

[0125] Place the steel plate in a box-type resistance furnace and conduct 4 times of simulated post-weld heat treatment, that is, heat the steel plate to 635 ± 15 °C and hold for 6 hours, then cool it to room temperature in the furnace, and repeat this cycle 4 times. When heating, control the heating rate ≤ 50 °C / h, and when cooling, control the cooling rate ≤ 50 °C / h.

[0126] After 4 times of simulated post-weld heat treatment, refer to ASTM A370 standard to test the tensile properties and impact properties of the steel plates in Examples 1-4. The yield strength Rt0.5, tensile strength Rm, elongation after fracture A, and -51 °C low-temperature impact energy at the 1 / 4 position and 1 / 2 position along the thickness direction of the steel plate are shown in Table 6. Refer to ASTM A770 standard to test the Z-direction tensile properties of the steel plates in Examples 1-4. The Z-direction tensile area reduction rate of the steel plate is shown in Table 6.

[0127] Table 6

[0128]

[0129] The detailed descriptions listed above are only specific descriptions of the feasible implementation manners of this application, and they are not used to limit the protection scope of this application. Any equivalent implementation manners or changes made without departing from the technical spirit of this application should be included in the protection scope of this application.

Claims

1. A method for producing a steel plate for a pressure vessel, characterized in that: It includes the processes of steelmaking, continuous casting, heating, rolling, and normalizing heat treatment in sequence; The steelmaking process includes the steps of molten iron pre-desulfurization, converter smelting, LF refining, and RH vacuum refining, which are performed in sequence. In the converter smelting step, scrap steel, nickel plate, and molten iron obtained in the molten iron pre-desulfurization step are added to the converter for smelting. When 3 / 20 of the steel is tapped, ferrosilicon, metallic manganese, and aluminum are added to the molten steel in sequence, and the amount of aluminum added is (15·[O]+0.65) kg / ton, where [O] is the mass percentage value of the O content in the molten steel detected before tapping. Lime is then added to the molten steel to form slag. In the LF refining step, after the refining is completed, 0.60-0.75 m / ton of pure calcium wire is fed into the molten steel at a wire feeding speed of 1.0-2.0 m / s, and soft stirring is performed for 1-3 minutes after the wire feeding is completed. In the RH vacuum refining step, the addition of Al to the molten steel is prohibited, and soft stirring is performed after breaking the air, and the soft stirring time is ≥8 minutes. In the steelmaking process, the chemical composition of the molten steel obtained by smelting, in percentage by mass, includes: C: 0.13%-0.16%, Si: 0.15%-0.25%, Mn: 1.40%-1.50%, Nb: 0.01%-0.02%, V: 0.02%-0.03%, Ti: 0.01%-0.02%, Alt: 0.02%-0.05%, Ni: 0.15%-0.25%, P≤0.015%, S≤0.005%, and the balance is iron and unavoidable impurities; In the rolling process, the heated continuous casting billet is rolled in the austenite recrystallization zone to obtain a steel plate with a thickness of t, t>30mm, and a final rolling temperature of ≥930°C; then water-cooled, with a final cooling temperature of 700±30°C; and then air-cooled; In the normalizing heat treatment process, the normalizing temperature is 880-900°C, the furnace time = a·t, where a is 1.6-1.7 min / mm and the unit of t is mm; after the steel plate is taken out of the furnace, it is cooled in water and the red-return temperature T fh =700-T s -180×exp(-0.5×((t-103) / 71) 2 ), the unit is ℃, the allowable deviation range of the red-return temperature is ±20℃, where T s is the temperature of cooling water in °C.

2. The method for producing a steel plate for a pressure vessel according to claim 1, wherein: In the heating process, a walking beam heating furnace is used for heating, the soaking temperature is 1150-1220° C., and the furnace time is ≥b·h, where b is 1.0 min / mm and h is the thickness of the continuous casting billet in mm.

3. The method for producing a steel plate for a pressure vessel according to claim 1, wherein: In the normalizing heat treatment process, the steel plate is subjected to normalizing heat treatment in a continuous roller hearth non-oxidizing furnace.

4. The method for producing a steel plate for a pressure vessel according to claim 1, wherein: In the rolling process, a multifunctional intermittent cooling system is used for water cooling.

5. The method for producing a steel plate for a pressure vessel according to claim 1, wherein: The thickness t of the steel plate is 6 to 100 mm; The Z-direction tensile section shrinkage of the steel plate is ≥65%, the yield strength of the steel plate at the 1 / 4 position and the 1 / 2 position along the thickness direction is ≥355MPa, the tensile strength is 540~620MPa, the elongation after fracture is ≥30%, and the -51°C low-temperature impact energy of the steel plate at the 1 / 4 position and the 1 / 2 position along the thickness direction is ≥100J.

6. The method for producing a steel plate for a pressure vessel according to claim 1, wherein: After four simulated post-weld heat treatments, the steel plate has a Z-direction tensile section shrinkage rate of ≥65%, a yield strength of ≥300 MPa at the 1 / 4 position and the 1 / 2 position along the thickness direction, a tensile strength of 485-530 MPa, an elongation after fracture of ≥30%, and a -51°C low-temperature impact energy of ≥100 J at the 1 / 4 position and the 1 / 2 position along the thickness direction.

7. The method for producing a steel plate for a pressure vessel according to claim 1, wherein: The flaw detection grade of the steel plate complies with NB / T 47013.3 Level I; The metallographic structure of the steel plate is ferrite+pearlite, the pearlite is dispersed, and there is no obvious banded structure.

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