Production method of steel plate for pressure vessel

Abstract

The invention discloses a production method of a steel plate for a pressure vessel. The production method comprises the steps of steelmaking, continuous casting, heating, rolling and normalizing heat treatment. The chemical components comprise 0.13%-0.16% of C, 0.15%-0.25% of Si, 1.40%-1.50% of Mn, 0.01%-0.02% of Nb, 0.02%-0.03% of V, 0.01%-0.02% of Ti, 0.02%-0.05% of Alt, less than or equal to 0.015% of P and less than or equal to 0.005% of S; during rolling, austenite recrystallization zone rolling is carried out, and the final rolling temperature is larger than or equal to 930 DEG C; performing water cooling after rolling, wherein the final cooling temperature is 700 + / -30 DEG C; the normalizing temperature is 880-900 DEG C, the in-furnace time is equal to a.t, and t is the thickness of the steel plate; and after the steel plate is discharged out of the furnace, the steel plate enters water to be cooled, the self-tempering temperature Tfh is 700-Ts-180 * exp (-0.5 * ((t-103) / 71) 2), and Ts 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, the steel plates are required to 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 undergo post-weld heat treatment as a whole or locally for many 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 carried out in sequence; 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; In the rolling process, the continuously cast slab after heating is rolled in the austenite recrystallization zone to obtain a steel plate with a thickness of t, and the finish rolling temperature ≥ 930°C; then water cooling is carried out, and the finish cooling temperature is 700 ± 3°C; then air cooling; In the normalizing heat treatment process, the normalizing temperature is 880 - 900°C, and the 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 in water, and the return red temperature T fh = 700 - T s - 180 × exp(-0.5 × ((t - 103) / 71) 2), in °C, the allowable deviation range of the red-return temperature is ±20 °C, where T s is the temperature of the cooling water, in °C.

[0006] 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 slab, in mm.

[0007] As a further improvement of an embodiment of the present application, the steelmaking process includes the steps of hot metal pre-desulfurization, converter smelting, LF refining, and RH vacuum refining in sequence; 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; 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; 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.

[0008] 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.

[0009] 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; 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.

[0010] 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.

[0011] 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.

[0012] As a further improvement of an embodiment of the present application, the thickness t of the steel plate is 6 - 100 mm; The reduction of area of the steel plate in the Z-directional tensile test is ≥65%, the yield strength at the 1 / 4 and 1 / 2 positions along the thickness direction of the steel plate is ≥355 MPa, the tensile strength is 540 - 620 MPa, and the elongation after fracture is ≥30%. The low-temperature impact energy at -51 °C at the 1 / 4 and 1 / 2 positions along the thickness direction of the steel plate is ≥100 J.

[0013] As a further improvement of an embodiment of the present application, after the steel plate undergoes 4 times of simulated post-weld heat treatment, the reduction of area of the steel plate in the Z-directional tensile test is ≥65%, the yield strength at the 1 / 4 and 1 / 2 positions along the thickness direction of the steel plate is ≥300 MPa, the tensile strength is 485 - 530 MPa, and the elongation after fracture is ≥30%. The low-temperature impact energy at -51 °C at the 1 / 4 and 1 / 2 positions along the thickness direction of the steel plate is ≥100 J.

[0014] As a further improvement of an embodiment of the present application, the flaw detection grade of the steel plate conforms to Grade I of NB / T 47013.3; The metallographic structure of the steel plate is ferrite + pearlite, the pearlite is diffusely distributed, and there is no obvious banded structure.

[0015] Compared with the prior art, the beneficial effects of the present application include: (1) Through the optimized design of chemical composition, adopting a C + Si + Mn matrix combined with a Nb + V + Ti + Al complex microalloying composition system, compared with the prior art scheme of adding Mo, Cr, and Cu alloys, the alloy cost is significantly reduced, and the market competitiveness of the product is greatly improved; compared with the prior art composition system with strict restrictions on the P and S contents, the smelting difficulty is greatly reduced, facilitating the efficient and stable production of the steelmaking process.

[0016] (2) Based on the chemical composition design scheme of the present application and combined with the control of the production process, the thickness of the steel plate can be increased to 100 mm, 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 along the thickness direction of the steel plate and the stability of the post-weld heat treatment performance. After the steel plate undergoes 4 times of simulated post-weld heat treatment, the steel plate still has excellent strength and toughness, and the performance uniformity along the thickness direction is excellent. Description of the Drawings

[0017] Figure 1 It is a metallographic structure picture of the 1 / 2 position along the thickness direction of the steel plate in Example 1; Figure 2 It is a metallographic structure picture of the 1 / 4 position along the thickness direction of the steel plate in Example 4; Figure 3 It is a metallographic structure picture of the 1 / 2 position along the thickness direction of the steel plate in Example 4. Detailed Embodiments

[0018] The following will further introduce the present application in combination with specific implementation manners, but the scope of protection required is not limited to the description made.

[0019] An embodiment of the present application provides a production method of a steel plate for a pressure vessel, and further provides a steel plate for a pressure vessel prepared by using the production method.

[0020] Specifically, the production method of the steel plate for a pressure vessel 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 the steel plate can be used to prepare a pressure vessel.

[0021] The following will describe the production method according to each process.

[0022] (1) Steelmaking process According to the chemical composition of the required steel plate, molten steel is smelted.

[0023] 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.

[0024] 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.

[0025] The following will explain the functions of each chemical composition and its content in the present application: C: It is a strengthening element. When the C content is low, the strength of the steel plate decreases significantly after long-time welding heat treatment, and it is difficult to meet the strength requirements of the pressure vessel; 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, not only can the strengthening effect on the steel plate be ensured, but also the low-temperature toughness of the steel plate can be improved.

[0026] Si: It is a deoxidizing element, a solid-solution strengthening element, and can also increase the carbon activity so that it does not dissolve 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.

[0027] 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.

[0028] 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.

[0029] V: It makes the area of pearlite clusters smaller, increases the number of breakpoints of cementite in pearlite lamellae and the degree of fragmentation, improves the strength and toughness of the steel plate, and plays a certain 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.

[0030] 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%.

[0031] Al: It is a deoxidizing and grain refinement element. Excessive aluminum is easy to increase the Al2O3 inclusions in the steel, affecting the low-temperature toughness of the steel. In this application, the Alt content is controlled to be 0.02% - 0.05%.

[0032] 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, significantly affecting 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.

[0033] 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, central segregation is effectively inhibited and the content of non-metallic inclusions is reduced, ensuring that the steel plate has excellent low-temperature toughness; on the other hand, the problems of increased production difficulty and rising production cost caused by overly strict control requirements for P and S content are avoided, achieving a balance between performance guarantee and economic benefits.

[0034] Through the optimized design of the above chemical composition, using a C + Si + Mn matrix combined with a Nb + V + Ti + Al complex microalloying 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.

[0035] When the thickness t of the steel plate is ≤ 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.

[0036] 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 unavoidable impurities.

[0037] Ni can make the edge of cementite smooth and disperse it, making dislocations easier to slip at low temperatures. It 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, both excellent low-temperature toughness of the steel plate can be ensured and the alloy cost can be reasonably controlled.

[0038] Specifically, the steelmaking process includes the steps of hot metal pre-desulfurization, converter smelting, LF refining, and RH vacuum refining in sequence.

[0039] s1. Hot metal pre-desulfurization The sulfur content in hot metal can be controlled at a relatively low level.

[0040] s2. Converter smelting The total charge of the converter is 200 tons ± 5 tons. When the thickness of the steel plate ≤ 30 mm, scrap steel 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 steel and hot metal obtained from the hot metal pre-desulfurization step are charged into the converter for smelting.

[0041] After the smelting is completed, tapping is carried out. 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.

[0042] 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.

[0043] In this way, the addition amount of aluminum can be accurately controlled according to the O content in the molten steel, and the generation of high-melting-point Al2O3 inclusions can be reduced.

[0044] s3. LF refining 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.

[0045] s4. RH vacuum refining After the molten steel obtained from the LF refining is transported to the RH treatment station by the ladle car, vacuum degassing is carried out; then deoxidation alloying is carried out. During the deoxidation alloying process, adding Al to the molten steel is prohibited; then breaking the vacuum and carrying out soft stirring, and the soft stirring time ≥ 8 min.

[0046] 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 coking during the continuous casting process, making the steelmaking process proceed smoothly.

[0047] (2)Continuous casting process 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.

[0048] (3)Heating process 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 ≥ b·h, where b is 1.0 min / mm and h is taken in units of mm. For example, if h = 220 mm, then the residence time in the furnace ≥ 220 min.

[0049] Thus, by controlling the soaking temperature and the in-furnace time, the temperature uniformity of the continuous casting billet can be improved, laying a foundation for the rolling stability of the subsequent rolling process and facilitating the improvement of property uniformity and flatness.

[0050] (4) Rolling process 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 finish rolling temperature is ≥930°C; then it is water-cooled, and the finish cooling temperature is 700 ± 30°C; then it is air-cooled.

[0051] By adopting single-stage rolling, that is, only rolling in the austenite recrystallization zone and controlling the hot rolling, the original austenite structure can be fully recrystallized and refined. 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. Meanwhile, the rolling efficiency is improved, the rolling capacity requirement for the rolling mill is reduced, and the cost is greatly reduced. Water cooling can refine the as-rolled structure and provide a good tissue basis for the subsequent normalizing heat treatment.

[0052] Preferably, during water cooling, a multi-functional intermittent cooling system is used for water cooling to improve the cooling uniformity.

[0053] (5) Normalizing heat treatment process The steel plate is sent into a continuous roller hearth non-oxidizing furnace for normalizing heat treatment.

[0054] Among them, the normalizing temperature is 880 - 900°C, and the in-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 by water, and the return red temperature T fh = 700 - T s - 180×exp(-0.5×((t - 103) / 71) 2 ), with the unit of °C, and the allowable deviation range of the return red temperature is ±20°C, where T s is the temperature of the cooling water, with the unit of °C; and in the calculation formula of the return red temperature T fh , only the value in mm of t is taken for calculation, and only the value in °C of T s is taken for calculation. For example, if t = 100 mm and T s = 20°C, then in the calculation formula of the return red temperature T fh , t takes 100 and T s takes 20 for calculation.

[0055] By controlling the normalizing temperature and the holding 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 distribution, avoid the formation of pearlite banded structure, improve the strength and toughness of the steel plate, and ensure that the steel plate still has good strength and toughness after long-term simulated welding, still meeting the technical requirements, and having excellent performance uniformity in the thickness direction. By reasonably setting the temperature of the cooling water according to the thickness of the steel plate during cooling and strictly controlling the reheat 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 relatively small level during subsequent manufacturing processes such as cutting and welding.

[0056] Preferably, the temperature T of the cooling water s is 15 - 30 °C.

[0057] 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 diffusely distributed, and there is no obvious banded structure; The flaw detection grade of the steel plate meets Grade I of NB / T 47013.3; 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 is 540 - 620 MPa, the elongation after fracture A is ≥ 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.

[0058] 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 repeat this cycle 4 times. Control the heating rate ≤ 50 °C / h during heating and the cooling rate ≤ 50 °C / h during cooling.

[0059] 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 is 485 - 530 MPa, the elongation after fracture A is ≥ 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.

[0060] In summary, based on the chemical composition design scheme and combined with the control of the production process, the present application can break through the steel plate thickness to 100 mm, 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 undergoes 4 times of simulated post-weld heat treatment, the steel plate still has excellent strength and toughness, and the performance uniformity along the thickness direction is excellent.

[0061] Examples 1 to 4 are provided below to further introduce the present application. Of course, the 4 examples here are only a part, rather than all, of the numerous examples included in the present application, and these 4 examples do not constitute a limitation on the present application. For example, its steelmaking process, chemical composition of molten steel, etc. can also be implemented in other ways, not limited to those described below. Specifically, Examples 1 to 4 are implemented according to the following process: (1)Steelmaking process The molten steel is smelted by sequentially performing hot metal pre-desulfurization, converter smelting, LF refining, and RH vacuum refining to obtain molten steel. The chemical compositions of the molten steel in Examples 1 to 4 are shown in Table 1 by mass percentage, and the balance is iron and unavoidable impurities.

[0062] Table 1

[0063] Among them, the total charge of the converter is 200 tons ± 5 tons. In Examples 1 to 2, scrap steel and the hot metal obtained from the hot metal pre-desulfurization step are charged into the converter for smelting. In Examples 3 to 4, nickel plates, scrap steel, and the hot metal obtained from the hot metal pre-desulfurization step are charged into the converter for smelting.

[0064] After the smelting is completed, tapping is carried out, and the O content in the molten steel is detected before tapping. 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 make slag.

[0065] The O content in the molten steel detected before tapping and the addition amount of aluminum are shown in Table 2. Among them, the addition amount of aluminum satisfies (15·[O] + 0.65) kg / ton, and [O] is the mass percentage value of the O content in the molten steel detected before tapping.

[0066] After the LF refining is completed, 0.60 - 0.75 m / ton of pure calcium wire is fed into the molten steel. After the wire feeding is completed, soft stirring is carried out. Among them, the feeding amount of the pure calcium wire, the wire feeding speed, and the soft stirring time are also shown in Table 2.

[0067] 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 carried out. 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.

[0068] Table 2

[0069] (2)Continuous casting process The molten steel obtained from the steelmaking process is made into a continuous casting billet with a thickness of h through a continuous caster. 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.

[0070] (3)Heating process 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.

[0071] Table 3

[0072] (4)Rolling process 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.

[0073] The thickness t of the steel plate, the finishing rolling temperature, and the final cooling temperature of water cooling are shown in Table 4.

[0074] (5)Normalizing heat treatment process 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 comes out of the furnace, it is cooled in water. The cooling water temperature and the re-reddening temperature are also shown in Table 4.

[0075] Table 4

[0076] The steel plates of Examples 1 - 4 are subjected to performance tests, specifically including: (1)Flaw detection test The obtained steel plates are subjected to flaw detection in accordance with NB / T 47013.3. 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.

[0077] (2)Metallographic structure test In accordance with the ASME SA-20 / SA-20M standard, a 15 cm × 15 cm sample is taken from the head of the steel plate along the rolling direction to make a metallographic sample. After mechanical grinding, polishing, and etching with nitric acid alcohol, it is placed under a metallographic microscope for microstructure observation.

[0078] The metallographic structures of the steel plates in Examples 1 to 4 were measured to be ferrite + pearlite structures, and the pearlite was diffusely distributed without obvious banded structures.

[0079] Here, the metallographic structure photos of the steel plates in Examples 1 and 4 are selected 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 in Examples 1 and 4 can represent the metallographic structure of the steel plates in this application as representatives.

[0080] Among them, Figure 1 is the metallographic structure picture at the 1 / 2 position along the thickness direction of the steel plate in Example 1, Figure 2 is the metallographic structure picture at the 1 / 4 position along the thickness direction of the steel plate in Example 4, Figure 3 is the metallographic structure picture at the 1 / 2 position along the thickness direction of the steel plate in Example 4.

[0081] (3) Mechanical property testing The tensile properties and impact properties of the steel plates in Examples 1 to 4 were tested with reference to ASTM A370 standard. 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 plates are shown in Table 5.

[0082] The Z-direction tensile properties of the steel plates in Examples 1 to 4 were tested with reference to ASTM A770 standard. The Z-direction tensile area reduction rate of the steel plates is shown in Table 5.

[0083] Table 5

[0084] Note: The thickness of the steel plate in Example 1 is only 10 mm, so the tensile test specimen of the steel plate is a full-thickness specimen; the impact energy is close at the 1 / 4 position and 1 / 2 position along the thickness direction; and the thickness is too thin to perform Z-direction tensile test.

[0085] (4) Simulated post-weld heat treatment The steel plates were placed in a box-type resistance furnace for 4 times of simulated post-weld heat treatment, that is, the steel plates were heated to 635 ± 15°C and held for 6 h, and then cooled to room temperature in the furnace. This cycle was repeated 4 times. During heating, the heating rate was controlled ≤ 50°C / h, and during cooling, the cooling rate was controlled ≤ 50°C / h.

[0086] After 4 times of simulated post-weld heat treatment, the tensile properties and impact properties of the steel plates of Examples 1 to 4 were tested with reference to 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 position and 1 / 2 position along the thickness direction of the steel plates are shown in Table 6. The Z-direction tensile properties of the steel plates of Examples 1 to 4 were tested with reference to ASTM A770 standard. The Z-direction tensile area reduction rate of the steel plates is shown in Table 6.

[0087] Table 6

[0088] The detailed descriptions listed above are only specific descriptions of the feasible implementation manners of this application, and they are not intended to limit the protection scope of this application. Any equivalent implementation manners or modifications made without departing from the technical spirit of this application should be included in the protection scope of this application.

Claims

1. A production method of a steel plate for a pressure vessel, characterized in that, It includes each process of steelmaking, continuous casting, heating, rolling, and normalizing heat treatment carried out in sequence; 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 unavoidable impurities; 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 finish rolling temperature ≥ 930°C; then water cooling is carried out, and the finish cooling temperature is 700 ± 30°C; then air cooling is carried out; 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 in water, and the red - return temperature T fh = 700 - T s - 180×exp(-0.5×((t - 103) / 71) 2 ), with the unit of °C. The allowable deviation range of the red - return temperature is ±20 °C, where T s is the temperature of the cooling water, with the unit of °C.

2. The production method of the steel plate for pressure vessels according to claim 1, characterized in that, In the heating process, a walking beam reheating furnace is used for heating, the soaking temperature is 1150 - 1220°C, and the time in the furnace ≥ b·h, where b is 1.0 min / mm and h is the thickness of the continuously cast billet in mm.

3. The production method of the steel plate for pressure vessels according to claim 1, characterized in that, The steelmaking process includes the steps of hot metal pretreatment desulfurization, converter smelting, LF refining, and RH vacuum refining carried out in sequence; 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 make 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, 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; 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.

4. The production method of the steel plate for pressure vessels according to claim 3, characterized in that, 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.

5. The production method of the steel plate for pressure vessels according to claim 3, characterized in that, When the thickness t of the steel plate > 30 mm, the chemical composition of the molten steel obtained by smelting further includes, by mass percentage: Ni: 0.15% - 0.25%; In the converter smelting step, scrap steel, nickel plates, and the hot metal obtained in the hot metal pretreatment desulfurization step are added to the converter for smelting.

6. The production method of the steel plate for pressure vessels according to claim 1, characterized in that, In the normalizing heat treatment process, the steel plate is subjected to normalizing heat treatment in a continuous roller hearth non-oxidizing furnace.

7. The production method of the steel plate for pressure vessels according to claim 1, characterized in that, In the rolling process, a multi-functional intermittent cooling system is used for water cooling.

8. The production method of the steel plate for pressure vessels according to claim 1, characterized in that, The thickness t of the steel plate is 6 - 100 mm; The Z-direction tensile reduction of area of the steel plate ≥ 65%, the yield strength at the 1 / 4 position and 1 / 2 position along the thickness direction of the steel plate are both ≥ 355 MPa, the tensile strength is 540 - 620 MPa, the elongation after fracture is both ≥ 30%, and the -51°C low-temperature impact energy at the 1 / 4 position and 1 / 2 position along the thickness direction of the steel plate are both ≥ 100 J.

9. The production method of the steel plate for pressure vessels according to claim 1, characterized in that, After the steel plate has undergone post-weld heat treatment through 4 simulations, the Z-direction tensile area reduction rate of the steel plate is ≥65%, the yield strength at the 1 / 4 position and the 1 / 2 position along the thickness direction of the steel plate are both ≥300 MPa, the tensile strength is 485 - 530 MPa, the elongation after fracture is both ≥30%, and the -51°C low-temperature impact energy at the 1 / 4 position and the 1 / 2 position along the thickness direction of the steel plate is both ≥100 J.

10. The production method of the steel plate for pressure vessels according to claim 1, characterized in that, The flaw detection grade of the steel plate conforms to Grade I of NB / T 47013.3; The metallographic structure of the steel plate is ferrite + pearlite, the pearlite is diffusely distributed, and there is no obvious banded structure.

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