Large-thickness steel plate suitable for superhigh-heat-input welding and production method therefor

Abstract

Disclosed in the present invention are a large-thickness steel plate suitable for superhigh-heat-input welding and a production method therefor. The steel plate comprises: C: 0.06-0.11%, Si: 0.15-0.35%, Mn: 1.4-1.8%, Cr: 0.1-0.5%, Ni: 0.3-0.8%, P<0.015%, S<0.015%, Ti: 0.02-0.05%, and Ti+Zr: 0.025-0.15%, with the balance being iron and impurities.

Description

Thick steel plate suitable for ultra-high heat input welding and production method thereof

[0001] This application is based on the Chinese patent application with application number CN202311084999.8 and application date August 28, 2023, and claims the priority of the Chinese patent application. The entire content of the above patent application is hereby introduced into this application as a reference. Technical Field

[0002] The present invention belongs to the technical field of iron and steel metallurgy, and relates to a production method of a thick steel plate suitable for ultra-large heat input welding, and a thick steel plate suitable for ultra-large heat input welding prepared by the production method. Background Art

[0003] With the emergence of transport trunk lines and container hub ports, as well as the rapid development of shipping technology, ships are continuously developing in the direction of large-scale. Container ships have developed from the first generation to the sixth generation, and the carrying capacity has increased to 7 times of the previous generation. This has brought about a strong demand for thick steel plates (i.e. steel plates with a thickness of ≥80mm). However, as the thickness of steel plates for ships has increased significantly, the production difficulty of thick steel plates has also continued to rise. In addition, the welding efficiency of thick steel plates is low, which easily leads to low production efficiency and high production costs of large ships.

[0004] In order to increase the thickness of steel plates in the steel industry, steel ingots are usually forged or rolled into blanks, and then heated and rolled into thick steel plates. However, the metallurgical quality of steel ingots is poor, and the performance of the rolled steel plates cannot meet the high requirements of shipbuilding steel plates. Therefore, the performance of the steel plates is usually improved through a heat treatment process after rolling, resulting in a long production process and great preparation difficulty.

[0005] Summary of the Invention

[0006] The object of the present invention is to provide a method for producing a low-yield-to-strength ratio steel plate suitable for high-heat-input welding, and a low-yield-to-strength ratio steel plate suitable for high-heat-input welding prepared by the production method.

[0007] To achieve the above-mentioned object of the invention, one embodiment of the present invention provides a method for producing a thick steel plate suitable for ultra-high heat input welding, wherein the chemical composition of the steel plate comprises, by mass percentage, the following: C 0.06-0.11%, Si 0.15-0.35%, Mn 1.4-1.8%, Cr 0.1-0.5%, Ni 0.3-0.8%, P < 0.015%, S < 0.015%, Ti 0.02-0.05%, Ti + Zr 0.025-0.15%, and the balance being iron and unavoidable impurities;

[0008] The production method comprises the steps of:

[0009] (1) molten steel is smelted by hot metal desulfurization, converter smelting, LF refining and RH vacuum refining, and the P content of the final molten steel is controlled to be less than 0.015% and the S content is less than 0.015% by mass. In the RH vacuum refining process, vacuum degassing and inclusion removal are completed and then the air is broken, and at least 800m of Zr-containing cored wire is fed at a speed of 4-5m / s;

[0010] (2) continuously casting the molten steel obtained in step (1) into a continuous casting billet;

[0011] (3) The continuous casting billet is sent to a heating furnace for heating at a temperature of 1050-1150°C, and the furnace time of each continuous casting billet is controlled to be ≥320 min;

[0012] (4) The heated continuous casting slab is sequentially subjected to recrystallization zone rolling and non-recrystallization zone rolling, wherein the final rolling temperature of the recrystallization zone rolling is 950-1050°C, the total reduction ratio is ≥43%, and the average reduction of each pass is ≥45 mm; the intermediate slab obtained by the recrystallization zone rolling is heated to below 800°C, and then subjected to non-recrystallization zone rolling to obtain a steel plate with a thickness of 80-120 mm;

[0013] (5) The rolled steel plate is transported to an accelerated cooling device at a speed of 1 to 2 m / s for cooling, with a cooling rate of ≥15°C / s and a final cooling temperature of ≤500°C;

[0014] (6) The steel plates produced in step (5) are straightened, stacked for slow cooling, and cut and finished to obtain finished steel plates.

[0015] As a further improvement of one embodiment of the present invention, the thickness of the steel strip of the Zr-containing cored wire is 0.7-0.8 mm, and the size of the Zr-containing alloy particles in the Zr-containing cored wire is 0.5-2 mm.

[0016] As a further improvement of one embodiment of the present invention, the surface density of Ti oxides and Zr oxides in the steel plate is greater than 800 / mm 2 .

[0017] As a further improvement of one embodiment of the present invention, a top-bottom combined blowing process is adopted in the converter smelting process, and alloy and slag are added to the molten steel in the order of ferrosilicon, metallic manganese and lime. The target basicity of the slag is 3.5, and the pressure of the argon gas blown from the bottom of the ladle during tapping is 0.5-0.6 MPa.

[0018] As a further improvement of one embodiment of the present invention, argon is blown throughout the LF refining process; when adding slag and alloy, the pressure of the argon blown at the bottom of the ladle is controlled to be 0.6-0.7 MPa; during the heating period, the pressure of the argon blown at the bottom of the ladle is 0.5 MPa.

[0019] As a further improvement of one embodiment of the present invention, in the RH vacuum refining process, RH circulating degassing equipment is used for vacuum degassing and inclusion removal, soft stirring is performed after feeding the Zr-containing cored wire, and the soft stirring time is controlled to be ≥8 minutes, and carbonized rice husks are added to the ladle for heat preservation before tapping.

[0020] As a further improvement of one embodiment of the present invention, in step (2), the casting temperature during continuous casting is controlled to be 1510-1580°C, the casting speed is controlled to be 1.0-1.3 m / min, and the continuous casting process adopts a large ladle with a long water nozzle and argon seal, an alkaline tundish covering agent, and an immersion water nozzle for full protection casting. The immersion depth of the immersion water nozzle is 120-180 mm, and the liquid level fluctuation of the crystallizer is controlled to be within ±2 mm.

[0021] To achieve the above-mentioned purpose of the invention, one embodiment of the present invention further provides a thick steel plate suitable for ultra-high heat input welding, wherein the chemical composition of the steel plate comprises, by mass percentage, C 0.06-0.11%, Si 0.15-0.35%, Mn 1.4-1.8%, Cr 0.1-0.5%, Ni 0.3-0.8%, P < 0.015%, S < 0.015%, Ti 0.02-0.05%, Ti + Zr 0.025-0.15%, and the balance being iron and unavoidable impurities.

[0022] As a further improvement of one embodiment of the present invention, the structure of the steel plate is a multiphase structure of acicular ferrite+polygonal ferrite+pearlite, wherein the content of acicular ferrite is ≥80%.

[0023] As a further improvement of one embodiment of the present invention, the yield strength of the steel plate is ≥450 MPa, the tensile strength is 560-600 MPa, and the elongation is ≥25%; the tensile strength of the heat-affected zone formed by welding under the condition of heat input ≥600 kJ / cm is ≥550 MPa, and the impact energy at -40°C is ≥250 J.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) Through the above chemical composition design scheme, the addition of Cr can effectively improve the hardenability of the steel plate. By controlling its content, a microstructure with fine needle-shaped ferrite as the matrix can be formed, thereby improving the welding performance of the steel plate. Ni is an effective element for improving strength and low-temperature toughness. By controlling its content, the surface quality of the steel plate can be improved and the cost can be controlled. The addition of Ti can form fine and dispersed Ti-containing oxides in the steel plate, thereby improving the low-temperature impact toughness of the steel plate. Zr is an important element for forming oxide inclusions. The addition of Zr is beneficial to promoting the multidimensional nucleation of ferrite, dispersing oxide particles, and reducing oxide size. In this way, the chemical composition design scheme of the present application can enable the Ti-containing oxide and the Zr-containing oxide to induce the nucleation of intragranular ferrite during the welding heat cycle of the steel plate, reduce the formation of grain boundary ferrite or bainite laths, and thereby improve the low-temperature impact toughness of the weld heat affected zone of the steel plate.

[0026] (2) The production method of the present application, through reasonable chemical composition design, adds Cr, Ni, Ti, Zr microalloys, and combines the process means of two-stage controlled rolling and controlled cooling to form a structure with fine needle-shaped ferrite as the matrix, improve strength and low-temperature impact toughness, so that continuous casting billets can be used to prepare thick steel plates with a thickness of 80 mm or more, and the maximum thickness of the steel plates can even reach 120 mm. Compared with the use of steel ingots with metallurgical quality inferior to continuous casting billets to prepare thick steel plates, the present application does not require tempering, normalizing, quenching + tempering and other heat treatment processes to improve the performance of the steel plates, and can achieve the production of thick steel plates with a thickness of 80 to 120 mm from 320 mm thick continuous casting billets. This not only saves processes, shortens the production cycle, and reduces production difficulty and cost, but also can use ultra-large linear energy with a heat input of ≥600 kJ / cm for welding, and has good welding quality and high welding efficiency. The welded joints have excellent low-temperature toughness and can be applied to large ships such as container ships, which is beneficial to improving ship quality, manufacturing efficiency and safety of use. Specifically, the yield strength of the steel plate is ≥450MPa, the tensile strength is 560-600MPa, and the elongation is ≥25%; the tensile strength of the heat-affected zone formed by welding under the condition of heat input ≥600kJ / cm is ≥550MPa, and the impact energy at -40℃ is ≥250J. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described below in conjunction with specific implementation methods, but the scope of protection required is not limited to the description.

[0028] One embodiment of the present invention provides a method for producing a thick steel plate suitable for ultra-large heat input welding, and a thick steel plate suitable for ultra-large heat input welding prepared by the production method. The so-called suitability for ultra-large heat input means that ultra-large linear energy with a heat input of ≥600kJ / cm can be used for welding. The so-called thick steel plate means a steel plate with a thickness of ≥80mm. In this embodiment, the thickness of the steel plate is 80 to 120mm. The so-called thick steel plate suitable for ultra-large heat input welding means that the steel plate can not only have a thickness of 80mm or more, but also can be welded with ultra-large linear energy with a heat input of ≥600kJ / cm during welding, thereby having good welding quality and high welding efficiency. The welded joint has excellent low-temperature toughness, so that it is suitable for large ships such as container ships, etc., which is beneficial to improving ship quality, manufacturing efficiency and safety of use.

[0029] Specifically, in the production method, steel is smelted according to a predetermined chemical composition design scheme, and the resulting molten steel is cast into continuous casting ingots. Thus, the chemical composition of the molten steel at the end of steelmaking, the chemical composition of the continuous casting ingot, and the chemical composition of the resulting steel plate all meet the predetermined chemical composition design scheme. The predetermined chemical composition design scheme includes, by mass percentage, the following: C 0.06-0.11%, Si 0.15-0.35%, Mn 1.4-1.8%, Cr 0.1-0.5%, Ni 0.3-0.8%, P < 0.015%, S < 0.015%, Ti 0.02-0.05%, Ti + Zr 0.025-0.15%, and the balance being iron and unavoidable impurities.

[0030] Through the above chemical composition design scheme, the addition of Cr can effectively improve the hardenability of the steel plate. By controlling its content, a structure with fine needle-shaped ferrite as the matrix can be formed, thereby improving the welding performance of the steel plate. Ni is an effective element for improving strength and low-temperature toughness. By controlling its content, the surface quality of the steel plate can be improved and the cost can be controlled. The addition of Ti can form fine and dispersed Ti-containing oxides in the steel plate, thereby improving the low-temperature impact toughness of the steel plate. Zr is an important element for forming oxide inclusions. The addition of Zr is beneficial to promoting the multidimensional nucleation of ferrite, dispersing oxide particles, and reducing oxide size. In this way, the chemical composition design scheme of the present application can enable the steel plate to induce the nucleation of intragranular ferrite by Ti-containing oxides and Zr-containing oxides during the welding heat cycle, thereby reducing the formation of grain boundary ferrite or bainite laths, thereby improving the low-temperature impact toughness of the weld heat affected zone of the steel plate.

[0031] The surface density of the thick steel plate suitable for ultra-high heat input welding is greater than 800 pieces / mm2. 2 .

[0032] In terms of process flow, the production method includes the following steps performed in sequence:

[0033] (1) Molten steel smelting

[0034] The molten steel is smelted using a molten iron desulfurization process, a converter smelting process, an LF refining process and an RH vacuum refining process. During the entire molten steel smelting process, the content of each chemical element in the molten steel is controlled according to the aforementioned predetermined chemical composition design scheme, including controlling the final molten steel to have P < 0.015% and S < 0.015% in terms of mass percentage.

[0035] During the RH vacuum refining process, after vacuum degassing and inclusion removal, the steel is broken open and fed with at least 800 m of Zr-containing cored wire at a speed of 4-5 m / s. Zr is a key element in the formation of oxide inclusions. Its addition promotes the multidimensional nucleation of ferrite. Adding Zr via cored wire not only disperses the oxide particles but also refines them, reducing their size. As the steel plate undergoes the welding thermal cycle, these oxide inclusions can induce intragranular ferrite nucleation, thereby reducing the formation of grain boundary ferrite or bainite laths and improving the low-temperature impact toughness of the weld heat-affected zone.

[0036] Preferably, the thickness of the steel strip of the Zr-containing cored wire is 0.7-0.8 mm, and the size of the Zr-containing alloy particles in the Zr-containing cored wire is 0.5-2 mm. By controlling the larger thickness of the steel strip of the Zr-containing cored wire and the larger Zr-containing alloy particles, the melting speed of the Zr-containing cored wire in the molten steel can be slowed down, the depth of the cored wire fed into the molten steel can be increased, the residence time of the alloy in the molten steel can be increased, the burning loss of the upper alloy floating to the surface of the molten steel can be reduced, and the yield can be improved.

[0037] Preferably, the converter smelting process is carried out in a converter, and the converter smelting process adopts a top-bottom combined blowing process, and alloys and slag are added to the molten steel in the order of ferrosilicon, metallic manganese, and lime. The target basicity of the slag is 3.5, and the pressure of argon gas blown from the bottom of the ladle during steel tapping is 0.5-0.6 MPa to improve the purity of the molten steel and reduce impurities.

[0038] Preferably, the LF refining process adjusts the chemical composition, controls the temperature, and controls the inclusions of the molten steel after converter smelting, and argon is blown throughout the LF refining process; when adding slag and alloy, the pressure of the argon gas blown at the bottom of the ladle is controlled to be 0.6-0.7 MPa; during the heating period, the pressure of the argon gas blown at the bottom of the ladle is 0.5 MPa.

[0039] Preferably, in the RH vacuum refining process, RH circulating degassing equipment is used for vacuum degassing and inclusion removal, soft stirring is performed after feeding the Zr-containing cored wire, and the soft stirring time is controlled to be ≥8 minutes, and carbonized rice husks are added to the ladle for heat preservation before tapping, which can reduce production costs and reduce environmental pollution.

[0040] More preferably, in the RH vacuum refining process, the vacuum degassing time is greater than 10 minutes, and a net circulation treatment is performed after alloying, and the net circulation treatment time is greater than or equal to 5 minutes.

[0041] (2) Continuous casting

[0042] The molten steel obtained from the smelting process is continuously cast into continuous casting billets on a continuous casting machine.

[0043] Preferably, the casting temperature during continuous casting is controlled at 1510-1580°C and the casting speed is controlled at 1.0-1.3 m / min. This can reduce the center segregation of the continuous casting billet and prevent internal defects such as internal cracks and shrinkage cavities in the continuous casting billet.

[0044] Among them, the thickness of the continuous casting billet is 320mm.

[0045] Preferably, the continuous casting process uses a large ladle with a long nozzle and argon seal, an alkaline tundish covering agent, and an immersion nozzle for full protection casting. The immersion depth of the immersion nozzle is 120 to 180 mm, and the liquid level fluctuation of the crystallizer is controlled within ±2 mm.

[0046] (3) Billet heating

[0047] The continuous casting billet is sent into the heating furnace for heating at a temperature of 1050-1150°C, and the time in the furnace for each continuous casting billet is controlled to be ≥320 minutes. This allows the center of the continuous casting billet to be fully heated, optimizes the structure, and reduces segregation and defects.

[0048] (4) Two-stage controlled rolling

[0049] The heated continuous casting slab is rolled in two stages.

[0050] Among them, the first stage is recrystallization zone rolling, and the continuous casting billet is rough-rolled into an intermediate billet with a thickness of 160-180 mm through multiple passes. The final rolling temperature is 950-1050°C, the total reduction rate is ≥43%, and the average reduction per pass is ≥45 mm.

[0051] The second stage is non-recrystallization zone rolling. After the recrystallization zone rolling is completed and before the non-recrystallization zone rolling begins, the intermediate billet obtained by recrystallization zone rolling is first heated to below 800°C, and then multiple passes of non-recrystallization zone rolling, also known as finish rolling, are carried out to obtain steel plates with a thickness of 80 to 120 mm.

[0052] In this way, based on the aforementioned chemical composition design scheme, low compression ratio rolling can be achieved, and a continuous casting billet with a thickness of 320 mm can be rolled into a steel plate with a thickness of 80 to 120 mm. Through two-stage controlled rolling, first rolling is carried out in the recrystallization zone, and then rolling is carried out in the non-recrystallization zone, so as to fully refine the austenite grains. Further, by controlling the rolling temperature and the amount of reduction, the uniformity of the mechanical properties of the steel plate in the thickness direction is improved, the quality of the core is improved, and thus the low-temperature impact toughness and tensile strength are improved.

[0053] (5) Controlled cooling

[0054] The rolled steel plate is transported to a rapid cooling device at a speed of 1 to 2 m / s for cooling, with a cooling rate ≥ 15°C / s and a final cooling temperature ≤ 500°C. In other words, the steel plate after rolling is immediately transported to a rapid cooling device via a roller conveyor for rapid cooling. In this way, combining the aforementioned two-stage controlled rolling and the controlled cooling process, the nucleation rate of acicular ferrite during the post-rolling phase transformation can be increased, and the proportion of acicular ferrite in the structure can be greatly increased, thereby improving the low-temperature impact toughness and tensile strength.

[0055] In this embodiment, the accelerated cooling device is an ACC rapid cooling device.

[0056] (6) Finished product

[0057] The cooled steel plates are straightened, stacked for slow cooling and cut and finished to obtain finished steel plates.

[0058] In summary, the production method of this embodiment can form a structure with fine needle-shaped ferrite as the matrix through reasonable chemical composition design, addition of Cr, Ni, Ti, and Zr microalloys, combined with the process means of two-stage controlled rolling and controlled cooling, thereby improving strength and low-temperature impact toughness, so that continuous casting billets can be used to prepare large-thickness steel plates with a thickness of 80 mm or more, and the maximum thickness of the steel plates can even reach 120 mm. Compared with the use of steel ingots with metallurgical quality inferior to continuous casting billets to prepare large-thickness steel plates, this application does not require tempering, normalizing, quenching + tempering and other heat treatment processes to improve the performance of the steel plate, and can achieve the production of large-thickness steel plates with a thickness of 80 to 120 mm from 320 mm thick continuous casting billets. This not only saves processes, shortens the production cycle, and reduces production difficulty and cost, but also can use ultra-large linear energy with a heat input of ≥600 kJ / cm for welding, and has good welding quality and high welding efficiency. The welded joint has excellent low-temperature toughness and can be suitable for large ships such as container ships, which is beneficial to improving ship quality, manufacturing efficiency and safety of use. Specifically, the surface density of Ti oxides and Zr oxides in the steel plate is >800 pieces / mm 2The yield strength of the steel plate is ≥450MPa, the tensile strength is 560~600MPa, and the elongation is ≥25%; the tensile strength of the heat-affected zone formed by welding under the condition of heat input ≥600kJ / cm is ≥550MPa, and the impact energy at -40℃ is ≥250J.

[0059] One embodiment of the present invention also provides a thick steel plate suitable for ultra-high heat input welding, which is prepared using the production method of thick steel plates suitable for ultra-high heat input welding as described above. The chemical composition of the steel plate includes, by mass percentage, C 0.06-0.11%, Si 0.15-0.35%, Mn 1.4-1.8%, Cr 0.1-0.5%, Ni 0.3-0.8%, P <0.015%, S <0.015%, Ti 0.02-0.05%, Ti+Zr 0.025-0.15%, and the balance being iron and unavoidable impurities.

[0060] Among them, Ti+Zr is 0.025-0.15%, that is, the sum of the mass percentages of Ti and Zr is 0.025-0.15%.

[0061] Furthermore, the structure of the thick steel plate suitable for ultra-high heat input welding is a multiphase structure of acicular ferrite+polygonal ferrite+pearlite, wherein the content of acicular ferrite is ≥80%.

[0062] After testing, the yield strength of the thick steel plate suitable for ultra-large heat input welding is ≥450MPa, the tensile strength is 560-600MPa, and the elongation is ≥25%; the tensile strength of the heat-affected zone formed by welding under the condition of heat input ≥600kJ / cm is ≥550MPa, and the impact energy at -40℃ is ≥250J, showing excellent strength, welding performance and low-temperature impact toughness.

[0063] To further clarify the objectives, technical solutions, and advantages of one embodiment of the present invention, the following further describes this embodiment with reference to Examples 1 to 9 according to one embodiment of the present invention. Obviously, Examples 1 to 9 described herein are only a portion of the embodiments of the present invention, not all of them. Other embodiments based on the aforementioned embodiments do not depart from the technical spirit of the present invention.

[0064] Specifically, Examples 1 to 9 all provide a thick steel plate suitable for ultra-high heat input welding, the chemical composition of which is shown in Table 1, wherein P < 0.015%, S < 0.015%, and the rest is Fe and unavoidable impurities.

[0065] Table 1

[0066] The production method of each embodiment is described in detail below.

[0067] (1) Molten steel smelting

[0068] The molten steel was smelted using a molten iron desulfurization process, a converter smelting process, an LF refining process, and an RH vacuum refining process. During the entire molten steel smelting process, the content of each chemical element in the molten steel was controlled according to the chemical composition design scheme specified in Table 1, including controlling the mass percentage of P < 0.015% and S < 0.015% in the final molten steel.

[0069] The converter smelting process is carried out in the converter, and the converter smelting process adopts the top and bottom blowing process, and alloys and slag are added to the molten steel in the order of ferrosilicon, metallic manganese and lime. The target basicity of the slag is 3.5, and the pressure of argon gas blown from the bottom of the ladle during tapping is 0.5~0.6MPa.

[0070] The LF refining process adjusts the chemical composition, controls the temperature, and controls the inclusions of the molten steel after converter smelting. Argon is blown throughout the LF refining process. When adding slag and alloy, the pressure of the argon gas blown at the bottom of the ladle is controlled to be 0.6-0.7MPa; during the heating period, the pressure of the argon gas blown at the bottom of the ladle is 0.5MPa.

[0071] In the RH vacuum refining process, RH circulating degassing equipment is used for vacuum degassing and inclusion removal, with a vacuum degassing time of more than 10 minutes. After alloying, a net circulation treatment is performed, with a net circulation treatment time of ≥5 minutes. After completing the vacuum degassing and inclusion removal treatment, the air is broken, and Zr-containing cored wire is fed into the molten steel. The size of the Zr alloy particles in the Zr-containing cored wire is 0.5-2 mm. The feeding length, feeding speed, and steel strip thickness of the Zr-containing cored wire are shown in Table 2. After feeding the Zr-containing cored wire, soft stirring is performed and the soft stirring time is controlled to be ≥8 minutes. Carbonized rice husks are added to the ladle for insulation before tapping.

[0072] Table 2

[0073] (2) Continuous casting

[0074] The molten steel obtained from the smelting process is continuously cast into 320mm thick continuous casting billets on a continuous casting machine. The casting temperature is controlled at 1510-1580°C and the casting speed is controlled at 1.0-1.3m / min. The continuous casting process uses a large ladle with a long shroud, argon seal, alkaline tundish covering agent, and a submerged shroud for full protection. The immersion depth of the shroud is 120-180mm, and the liquid level fluctuation in the crystallizer is controlled within ±2mm.

[0075] (3) Billet heating

[0076] The continuous casting billet is sent into a heating furnace for heating at a temperature of 1050-1150°C, and the time each continuous casting billet spends in the furnace is controlled to be ≥320 minutes.

[0077] (4) Two-stage controlled rolling

[0078] The heated continuous casting slab is rolled in two stages.

[0079] Among them, the first stage is recrystallization zone rolling, and the continuous casting billet is rolled into an intermediate billet through multiple passes of rough rolling. The thickness of the intermediate billet, the final rolling temperature, the total reduction rate, and the average reduction per pass are shown in Table 3.

[0080] The second stage is non-recrystallization zone rolling. After the recrystallization zone rolling is completed and before the non-recrystallization zone rolling begins, the intermediate billet obtained by the recrystallization zone rolling is first heated to below 800℃, and then multiple passes of non-recrystallization zone rolling, also known as finishing rolling, are carried out to obtain steel plates. The starting rolling temperature of the finishing rolling and the thickness of the steel plates are shown in Table 3.

[0081] (5) Controlled cooling

[0082] The rolled steel plates were transported to the ACC rapid cooling equipment for cooling, with the final cooling temperature ≤ 500°C. The transport speed and cooling speed of the steel plates to the ACC rapid cooling equipment are shown in Table 3.

[0083] (6) Finished product

[0084] The cooled steel plates are straightened, stacked for slow cooling and cut and finished to obtain finished steel plates.

[0085] Table 3

[0086] The finished steel plates of Examples 1 to 9 were sampled and subjected to metallographic structure testing, Ti oxide and Zr oxide density testing, mechanical property testing, and welding performance testing according to the same testing method. The test results are as follows:

[0087] (1) In terms of structure, the steel plates were observed using a metallographic microscope, and it was found that the structures of the steel plates of Examples 1 to 9 were all multiphase structures of acicular ferrite + polygonal ferrite + pearlite, and the content of acicular ferrite was ≥80%.

[0088] (2) The Ti-containing oxide and Zr-containing oxide inclusions in the steel plates of the above examples were counted using a scanning electron microscope, and the surface densities of the Ti-containing oxide and Zr-containing oxide inclusions were obtained as shown in Table 4.

[0089] (3) In terms of mechanical properties, the mechanical properties of the steel plates of the above embodiment were tested with reference to the GB / T 228.1-2021 standard. The details are as follows:

[0090] The yield strength, tensile strength and elongation of the steel plate were tested using a tensile testing machine. The test results are shown in Table 4.

[0091] (4) Welding performance: After welding the steel plates of the above embodiment, the mechanical properties of the heat-affected zone were tested with reference to GB / T 228.1-2021 and GB / T 229-2020 standards, where the welding heat input is shown in Table 4. The details are as follows:

[0092] The tensile strength of the heat affected zone of the weld was tested using a tensile testing machine, and the test results are shown in Table 4;

[0093] The impact energy of the heat affected zone of the weld was tested at -40°C using an impact testing machine. The test results are shown in Table 4.

[0094] Table 4

[0095] In summary, the present invention can use continuous casting billets to prepare large-thickness steel plates with a thickness of 80 mm or more, and the maximum thickness of the steel plates can even reach 120 mm. Compared with the use of steel ingots with metallurgical quality inferior to that of continuous casting billets to prepare large-thickness steel plates, the present application does not require tempering, normalizing, quenching + tempering and other heat treatment processes to improve the performance of the steel plates, and can achieve the production of large-thickness steel plates with a thickness of 80 to 120 mm from 320 mm thick continuous casting billets. It not only saves processes, shortens the production cycle, and reduces production difficulty and cost, but also can use ultra-large linear energy with a heat input of ≥600 kJ / cm for welding, and has good welding quality and high welding efficiency. The welded joints have excellent low-temperature toughness and can be suitable for large ships such as container ships, which is beneficial to improving ship quality, manufacturing efficiency and safety of use. Specifically, the yield strength of the steel plate is ≥450MPa, the tensile strength is 560-600MPa, and the elongation is ≥25%; the tensile strength of the heat-affected zone formed by welding under the condition of heat input ≥600kJ / cm is ≥550MPa, and the impact energy at -40℃ is ≥250J.

[0096] It should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each implementation method can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0097] The detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for producing a steel plate, characterized in that: The chemical composition of the steel plate includes, by mass percentage, C 0.06-0.11%, Si 0.15-0.35%, Mn 1.4-1.8%, Cr 0.1-0.5%, Ni 0.3-0.8%, P < 0.015%, S < 0.015%, Ti 0.02-0.05%, Ti+Zr 0.025-0.15%, and the balance is iron and unavoidable impurities; The production method comprises the steps of: (1) molten steel is smelted by hot metal desulfurization, converter smelting, LF refining and RH vacuum refining, and the P content and S content of the final molten steel are controlled to be less than 0.015% and 0.015% by mass percentage, wherein in the RH vacuum refining process, vacuum degassing and inclusion removal are completed and then the vacuum is broken, and at least 800m of Zr-containing core wire is fed at a speed of 4-5m / s; (2) continuously casting the molten steel obtained in step (1) into a continuous casting billet; (3) The continuous casting billet is sent into a heating furnace for heating at a temperature of 1050-1150°C, and the furnace time of each continuous casting billet is controlled to be ≥320 min; (4) the heated continuous casting slab is sequentially subjected to recrystallization zone rolling and non-recrystallization zone rolling, the final rolling temperature of the recrystallization zone rolling is 950-1050°C, the total reduction ratio is ≥43%, and the average reduction amount of each pass is ≥45 mm; the intermediate slab obtained by the recrystallization zone rolling is heated to below 800°C, and then non-recrystallization zone rolling is performed to obtain a steel plate with a thickness of 80-120 mm; (5) conveying the rolled steel plate to an accelerated cooling device at a speed of 1 to 2 m / s for cooling, with a cooling rate of ≥15°C / s and a final cooling temperature of ≤500°C; (6) The steel plate produced in step (5) is straightened, stacked, slowly cooled, and cut and finished to obtain a finished steel plate.

2. The method for producing a steel plate according to claim 1, characterized in that: The thickness of the steel strip of the Zr-containing cored wire is 0.7-0.8 mm, and the size of the Zr-containing alloy particles in the Zr-containing cored wire is 0.5-2 mm.

3. The method for producing a steel plate according to claim 1, characterized in that: The surface density of Ti oxide and Zr oxide in the steel plate is > 800 pieces / mm 2 .

4. The method for producing a steel plate according to claim 1, characterized in that: The converter smelting process adopts a top-bottom combined blowing process, and alloys and slag are added to the molten steel in the order of ferrosilicon, metallic manganese and lime. The target basicity of the slag is 3.5, and the pressure of argon gas blown from the bottom of the ladle during steel tapping is 0.5-0.6 MPa.

5. The method for producing a steel plate according to claim 1, characterized in that: Argon is blown throughout the LF refining process; when adding slag and alloy, the pressure of the argon gas blown at the bottom of the ladle is controlled to be 0.6-0.7MPa; during the heating period, the pressure of the argon gas blown at the bottom of the ladle is 0.5MPa.

6. The method for producing a steel plate according to claim 1, characterized in that: In the RH vacuum refining process, RH circulating degassing equipment is used for vacuum degassing and inclusion removal, Zr-containing cored wire is fed and soft stirring is performed, and the soft stirring time is controlled to be ≥8 minutes, and carbonized rice husk is added to the ladle for heat preservation before steel tapping.

7. The method for producing a steel plate according to claim 1, characterized in that: In step (2), the casting temperature during continuous casting is controlled at 1510-1580°C, the pulling speed is controlled at 1.0-1.3 m / min, and the continuous casting process adopts a large ladle long water nozzle and argon seal, an alkaline tundish covering agent, and an immersion water nozzle for full protection casting. The immersion depth of the immersion water nozzle is 120-180 mm, and the liquid level fluctuation of the crystallizer is controlled within ±2 mm.

8. A steel plate, characterized in that: The chemical composition of the steel plate includes, by mass percentage, C 0.06-0.11%, Si 0.15-0.35%, Mn 1.4-1.8%, Cr 0.1-0.5%, Ni 0.3-0.8%, P < 0.015%, S < 0.015%, Ti 0.02-0.05%, Ti+Zr 0.025-0.15%, and the balance is iron and unavoidable impurities.

9. The steel plate according to claim 8, characterized in that: The structure is a multiphase structure of acicular ferrite + polygonal ferrite + pearlite, wherein the content of acicular ferrite is ≥80%.

10. The steel plate according to claim 8, characterized in that The yield strength of the steel plate is ≥450MPa, the tensile strength is 560-600MPa, and the elongation is ≥25%; the tensile strength of the welding heat affected zone formed by welding under the condition of heat input ≥600kJ / cm is ≥550MPa, and the impact energy at -40°C is ≥250J.

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