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

Abstract

The present application discloses a large thickness steel plate suitable for ultra-high heat input welding and a production method thereof. In the steel plate, 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%, with the balance being iron and inevitable impurities.

Description

[0001] The present application is based on and claims priority to Chinese Patent Application Number CN202311084999.8 filed on August 28, 2023, the entire contents of which are incorporated herein by reference.TECHNICAL FIELD

[0002] The present application belongs to the field of iron and steel metallurgical technology, and relates to a production method for a large thickness steel plate suitable for ultra-high heat input welding, and a large thickness steel plate suitable for ultra-high heat input welding produced by the production method.BACKGROUND

[0003] With the emergence of transportation trunk lines and container hub ports, as well as the rapid development of shipping technology, ships have been continuously developing towards larger sizes. Container ships have evolved from the 1st generation to the 6th generation, with carrying capacity increased to 7 times that of previous generations. This has led to a strong demand for large thickness steel plates (i.e., steel plates with thickness ≥80 mm). However, as the thickness of steel plates for ships has increased significantly, the production difficulty of large thickness steel plates has also continuously escalated, and the welding efficiency of large thickness steel plates was low, which easily led to problems of low production efficiency and high production cost for large ships.

[0004] In the steel industry, to increase the thickness of steel plates, steel ingots were usually forged or rolled for billet preparation, and then heated and rolled into large thickness steel plates. However, steel ingots had poor metallurgical quality, and the performance of rolled steel plates could not meet the high requirements of steel plates for ships. Therefore, heat treatment processes were usually performed after rolling into steel plates to improve the performance of the steel plates, resulting in long production processes and great preparation difficulty.SUMMARY

[0005] An object of the present application is to provide a production method for a low yield-to-tensile ratio steel plate suitable for high heat input welding, and a low yield-to-tensile ratio steel plate suitable for high heat input welding produced by the production method.

[0006] To achieve the above object, an embodiment of the present application provides a production method for a large thickness steel plate suitable for ultra-high heat input welding, wherein the steel plate has a chemical composition comprising in percent by mass: 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%, with the balance being iron and inevitable impurities; the production method comprising the steps of: (1) performing molten steel refining using hot metal desulfurization, converter steelmaking, Ladle Furnace refining and RH Vacuum degassing refining, controlling the finally obtained molten steel with P<0.015% and S<0.015% in percent by mass, wherein in the RH Vacuum degassing refining process, after completing vacuum degassing and inclusions removal treatment, performing vacuum breaking, and feeding at least 800 m of Zr-containing cored wire at a speed of 4~5 m / s; (2) continuously casting the molten steel obtained in step (1) into a continuous casting slab; (3) feeding the continuous casting slab into a heating furnace for heating at a heating temperature of 1050~1150°C, and controlling the residence time of each continuous casting slab to be ≥320 min; (4) sequentially performing recrystallization zone rolling and non-recrystallization zone rolling on the heated continuous casting slab, wherein the recrystallization zone rolling has a finish rolling temperature of 950~1050°C, a total reduction ratio of ≥43%, and an average reduction amount per pass of ≥45 mm; performing temperature holding of the transfer bar obtained from the recrystallization zone rolling to below 800°C, and then performing non-recrystallization zone rolling to obtain a steel plate having a thickness of 80~120 mm; (5) conveying the rolled steel plate to accelerated cooling equipment for cooling at a speed of 1~2 m / s, with a cooling rate of ≥15°C / s and a final cooling temperature of ≤500°C; (6) subjecting the steel plate from step (5) to straightening, stack cooling and cutting and finishing to obtain a finished steel plate.

[0007] As a further improvement of an embodiment of the present application, the thickness of steel strip of the Zr-containing cored wire is 0.7~0.8 mm, and the size of Zr-containing alloy particles in the Zr-containing cored wire is 0.5~2 mm.

[0008] As a further improvement of an embodiment of the present application, the steel plate has an areal density of Ti-containing oxides and Zr-containing oxides of >800 particles / mm 2< .

[0009] As a further improvement of an embodiment of the present application, the converter steelmaking process uses a top and bottom combined blowing process, and adds alloys and slag-forming materials into 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 bottom argon blowing of the ladle during tapping is 0.5~0.6 MPa.

[0010] As a further improvement of an embodiment of the present application, the Ladle Furnace refining process performs argon blowing throughout; when adding slag-forming materials and alloys, the pressure of bottom argon blowing of the ladle is controlled to be 0.6~0.7 MPa; during heating, the pressure of bottom argon blowing of the ladle is 0.5 MPa.

[0011] As a further improvement of an embodiment of the present application, in the RH Vacuum degassing refining process, RH circulation degassing equipment is used to perform vacuum degassing and inclusions removal treatment, after feeding the Zr-containing cored wire, soft stirring is performed and the soft stirring time is controlled to be ≥8 min, and carbonized rice husk is added into the ladle for heat preservation before tapping.

[0012] As a further improvement of an embodiment of the present application, in step (2), during continuous casting, the casting temperature is controlled to be 1510~1580°C, the casting speed is controlled to be 1.0~1.3 m / min, the continuous casting process uses ladle long nozzle and argon sealing, basic tundish covering agent, and submerged entry nozzle for fully protected casting, the immersion depth of the submerged entry nozzle is 120~180 mm, and the mold level fluctuation is controlled within ±2 mm.

[0013] To achieve the above object, an embodiment of the present application further provides a large thickness steel plate suitable for ultra-high heat input welding, wherein the steel plate has a chemical composition comprising in percent by mass: 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%, with the balance being iron and inevitable impurities.

[0014] As a further improvement of an embodiment of the present application, the microstructure of the steel plate is a multiphase microstructure of acicular ferrite + polygonal ferrite + pearlite, wherein the content of acicular ferrite is ≥80%.

[0015] As a further improvement of an embodiment of the present application, the steel plate has a yield strength of ≥450 MPa, a tensile strength of 560~600 MPa, and an elongation of ≥25%; the heat affected zone formed by welding under conditions of heat input ≥600 kJ / cm has a tensile strength of ≥550 MPa and an impact energy at -40°C of ≥250 J.

[0016] Compared with the prior art, the beneficial effects of the present application include: (1) Through the above chemical composition design scheme, the addition of Cr can effectively improve the hardenability of the steel plate, and by controlling the content thereof, a microstructure with fine acicular ferrite as the matrix can be formed to improve the welding performance of the steel plate; Ni is an effective element for improving strength and low temperature toughness, and by controlling the content thereof, the surface quality of the steel plate can be improved and the cost can be controlled; the addition of Ti can form finely and dispersedly distributed Ti-containing oxides in the steel plate to improve the low temperature impact toughness of the steel plate; Zr is an important element for forming oxide inclusions, and the addition of Zr is favorable for promoting multidimensional nucleation of ferrite, making oxide particles dispersed and reducing oxide size. Thus, the chemical composition design scheme of the present application enables Ti-containing oxides and Zr-containing oxides to induce and promote intragranular ferrite nucleation during the welding thermal cycle process of the steel plate, reducing the formation of grain boundary ferrite or bainite laths, thereby improving the low temperature impact toughness of the heat affected zone of the steel plate. (2) The production method of the present application, through reasonable chemical composition design, adding microalloying elements of Cr, Ni, Ti, Zr, combined with process means of two-stage controlled rolling and controlled cooling, can form a microstructure with fine acicular ferrite as the matrix, improving strength and low temperature impact toughness, so that continuous casting slabs can be used to produce large thickness steel plates with thickness reaching 80 mm and above, and the maximum thickness of the steel plate can even reach 120 mm. Compared with using steel ingots with inferior metallurgical quality to continuous casting slabs to produce large thickness steel plates, the present application does not require heat treatment processes such as tempering, normalizing, quenching + tempering to improve the performance of the steel plate, and can realize the production of large thickness steel plates with thickness of 80~120 mm from continuous casting slabs with thickness of 320 mm, which not only saves processes, shortens production cycle, reduces production difficulty and cost, but also can use ultra-high heat input of ≥600 kJ / cm for welding with good welding quality and high welding efficiency, and the welded joints have excellent low temperature toughness, which can be applied to large ships such as container ships, which is beneficial to improving quality, manufacturing efficiency and use safety of ship. Specifically, the steel plate has a yield strength of ≥450 MPa, a tensile strength of 560~600 MPa, and an elongation of ≥25%; the heat affected zone formed by welding under conditions of heat input ≥600 kJ / cm has a tensile strength of ≥550 MPa and an impact energy at -40°C of ≥250 J. DETAILED DESCRIPTION

[0017] The technical solution of the present application will be further introduced below in combination with specific embodiments, but the scope of protection is not limited to the description made.

[0018] An embodiment of the present application provides a production method for a large thickness steel plate suitable for ultra-high heat input welding, and a large thickness steel plate suitable for ultra-high heat input welding produced by the production method. The so-called suitable for ultra-high heat input means that ultra-high heat input of ≥600 kJ / cm can be used for welding. The so-called large thickness steel plate means a steel plate with thickness ≥80 mm, and in the present embodiment, the thickness of the steel plate is 80~120 mm. The so-called large thickness steel plate suitable for ultra-high heat input welding means that the steel plate not only has a thickness that can reach 80 mm and above, but also can use ultra-high heat input of ≥600 kJ / cm for welding, thereby having good welding quality and high welding efficiency, and the welded joints have excellent low temperature toughness, so as to be applicable to large ships such as container ships, which is beneficial to improving quality, manufacturing efficiency and use safety of ship.

[0019] Specifically, in the production method, steelmaking is performed according to a predetermined chemical composition design scheme, and the obtained molten steel is cast into a continuous casting slab. Thus, the chemical composition of the molten steel at the steelmaking endpoint, the chemical composition of the continuous casting slab, and the chemical composition of the finally obtained steel plate all meet the predetermined chemical composition design scheme. The predetermined chemical composition design scheme is that the chemical composition comprises in percent by mass: 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%, with the balance being iron and inevitable impurities.

[0020] Through the above chemical composition design scheme, the addition of Cr can effectively improve the hardenability of the steel plate, and by controlling the content thereof, a microstructure with fine acicular ferrite as the matrix can be formed to improve the welding performance of the steel plate; Ni is an effective element for improving strength and low temperature toughness, and by controlling the content thereof, the surface quality of the steel plate can be improved and the cost can be controlled; the addition of Ti can form finely and dispersedly distributed Ti-containing oxides in the steel plate to improve the low temperature impact toughness of the steel plate; Zr is an important element for forming oxide inclusions, and the addition of Zr is favorable for promoting multidimensional nucleation of ferrite, making oxide particles dispersed and reducing oxide size. Thus, the chemical composition design scheme of the present application enables Ti-containing oxides and Zr-containing oxides to induce and promote intragranular ferrite nucleation during the welding thermal cycle process of the steel plate, reducing the formation of grain boundary ferrite or bainite laths, thereby improving the low temperature impact toughness of the heat affected zone of the steel plate.

[0021] In the large thickness steel plate suitable for ultra-high heat input welding, the areal density of Ti-containing oxides and Zr-containing oxides is >800 particles / mm 2< .

[0022] In terms of process flow, the production method comprises the following processes performed in sequence:(1) Molten steel refining

[0023] Molten steel refining is performed using hot metal desulfurization process, converter steelmaking process, Ladle Furnace refining process and RH Vacuum degassing refining process. During the entire molten steel refining 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 finally obtained molten steel with P<0.015% and S<0.015% in percent by mass.

[0024] In the RH Vacuum degassing refining process, after completing vacuum degassing and inclusions removal treatment, vacuum breaking is performed, and at least 800 m of Zr-containing cored wire is fed into the molten steel at a speed of 4~5 m / s. Zr is an important element for forming oxide inclusions, and the addition of Zr is favorable for promoting multidimensional nucleation of ferrite. Adding Zr in the form of cored wire can not only disperse oxide particles, but also refine oxide particles and reduce oxide size. Thus, when the steel plate undergoes the welding thermal cycle process, such oxide inclusions can induce and promote intragranular ferrite nucleation, thereby reducing the formation of grain boundary ferrite or bainite laths, and further improving the low temperature impact toughness of the heat affected zone.

[0025] Preferably, the thickness of steel strip of the Zr-containing cored wire is 0.7~0.8 mm, and the size of Zr-containing alloy particles in the Zr-containing cored wire is 0.5~2 mm. By controlling the larger thickness of steel strip and larger Zr-containing alloy particles of the Zr-containing cored wire, the melting speed of the Zr-containing cored wire in the molten steel can be delayed, the feeding depth of the cored wire into the molten steel can be increased, the residence time of the alloy in the molten steel can be improved, the burning loss of the alloy floating to the molten steel surface can be reduced, and the recovery rate can be improved.

[0026] Preferably, the converter steelmaking process is performed in a converter, and the converter steelmaking process uses a top and bottom combined blowing process, and adds alloys and slag-forming materials into 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 bottom argon blowing of the ladle during tapping is 0.5~0.6 MPa, so as to improve the purity of the molten steel and reduce impurities.

[0027] Preferably, the Ladle Furnace refining process performs chemical composition adjustment, temperature control, and inclusions control on the molten steel after converter steelmaking. The Ladle Furnace refining process performs argon blowing throughout; when adding slag-forming materials and alloys, the pressure of bottom argon blowing of the ladle is controlled to be 0.6~0.7 MPa; during heating, the pressure of bottom argon blowing of the ladle is 0.5 MPa.

[0028] Preferably, in the RH Vacuum degassing refining process, RH circulation degassing equipment is used to perform vacuum degassing and inclusions removal treatment, after feeding the Zr-containing cored wire, soft stirring is performed and the soft stirring time is controlled to be ≥8 min, and carbonized rice husk is added into the ladle for heat preservation before tapping, which can reduce production cost and reduce environmental pollution.

[0029] More preferably, in the RH Vacuum degassing refining process, the vacuum degassing time is >10 min, and after alloying, clean circulation treatment is performed, with the clean circulation treatment time being ≥5 min.(2) Continuous casting

[0030] The molten steel finally obtained from the molten steel refining process is continuously cast into a continuous casting slab on a continuous casting machine.

[0031] Preferably, during continuous casting, the casting temperature is controlled to be 1510~1580°C, and the casting speed is controlled to be 1.0~1.3 m / min. This can reduce center segregation of the continuous casting slab while preventing internal defects such as internal cracks and shrinkage cavities in the continuous casting slab.

[0032] The thickness of the continuous casting slab is 320 mm.

[0033] Preferably, the continuous casting process uses ladle long nozzle and argon sealing, basic tundish covering agent, and submerged entry nozzle for fully protected casting, the immersion depth of the submerged entry nozzle is 120~180 mm, and the mold level fluctuation is controlled within ±2 mm.(3) Billet heating

[0034] The continuous casting slab is fed into a heating furnace for heating at a heating temperature of 1050~1150°C, and the residence time of each continuous casting slab is controlled to be ≥320 min, so that the center of the continuous casting slab can be fully heated, the microstructure can be optimized, and segregation and defects can be reduced.(4) Two stage controlled rolling

[0035] The heated continuous casting slab is rolled in two stages.

[0036] The first stage is recrystallization zone rolling, wherein the continuous casting slab is rough rolled through multiple passes into a transfer bar whose thickness is 160~180 mm, with a finish rolling temperature of 950~1050°C, a total reduction ratio of ≥43%, and an average reduction amount per pass of ≥45 mm.

[0037] The second stage is non-recrystallization zone rolling, wherein after the recrystallization zone rolling is completed and before the non-recrystallization zone rolling begins, the transfer bar obtained from the recrystallization zone rolling is first subjected to temperature holding to below 800°C, and then multi-pass non-recrystallization zone rolling, i.e., finish rolling, is performed to obtain a steel plate having a thickness of 80~120 mm.

[0038] Thus, based on the aforementioned chemical composition design scheme, low compression ratio rolling can be realized to roll a continuous casting slab having a thickness of 320 mm into a steel plate with a thickness of 80~120 mm. Through two stage controlled rolling, rolling is first performed in the recrystallization zone, and then rolling is performed in the non-recrystallization zone, thereby fully refining austenite grains, and further through control of rolling temperature and reduction amount, the uniformity of mechanical properties of the steel plate in the thickness direction is improved, the center quality is improved, thereby enhancing low temperature impact toughness and tensile strength.(5) Controlled cooling

[0039] The rolled steel plate is conveyed to accelerated cooling equipment for cooling at a speed of 1~2 m / s, with a cooling rate of ≥15°C / s and a final cooling temperature of ≤500°C. That is to say, the steel plate after rolling completion is immediately conveyed rapidly to the accelerated cooling equipment through roller table for rapid cooling. Thus, combined with the aforementioned two-stage controlled rolling and the controlled cooling process means, the nucleation rate of acicular ferrite during the post-rolling phase transformation process can be improved, so that the proportion of acicular ferrite in the microstructure is greatly increased, thereby enhancing low temperature impact toughness and tensile strength.

[0040] In the present embodiment, the accelerated cooling equipment uses ACC accelerated cooling equipment.(6) Finished product

[0041] After the cooled steel plate is subjected to straightening, stack cooling and cutting and finishing, a finished steel plate is obtained.

[0042] In summary, the production method of the present embodiment, through reasonable chemical composition design, adding microalloying elements of Cr, Ni, Ti, Zr, combined with process means of two stage controlled rolling and controlled cooling, can form a microstructure with fine acicular ferrite as the matrix, improving strength and low temperature impact toughness, so that continuous casting slabs can be used to produce large thickness steel plates with thickness reaching 80 mm and above, and the maximum thickness of the steel plate can even reach 120 mm. Compared with using steel ingots with inferior metallurgical quality to continuous casting slabs to produce large thickness steel plates, the present application does not require heat treatment processes such as tempering, normalizing, quenching + tempering to improve the performance of the steel plate, and can realize the production of large thickness steel plates with thickness of 80~120 mm from continuous casting slabs with thickness of 320 mm, which not only saves processes, shortens production cycle, reduces production difficulty and cost, but also can use ultra-high heat input of ≥600 kJ / cm for welding with good welding quality and high welding efficiency, and the welded joints have excellent low temperature toughness, which can be applied to large ships such as container ships, which is beneficial to improving quality, manufacturing efficiency and use safety of ship. Specifically, the areal density of Ti-containing oxides and Zr-containing oxides in the steel plate is >800 particles / mm 2< , the steel plate has a yield strength of ≥450 MPa, a tensile strength of 560~600 MPa, and an elongation of ≥25%; the heat affected zone formed by welding under conditions of heat input ≥600 kJ / cm has a tensile strength of ≥550 MPa and an impact energy at - 40°C of ≥250 J.

[0043] An embodiment of the present application further provides a large thickness steel plate suitable for ultra-high heat input welding, produced by the production method for a large thickness steel plate suitable for ultra-high heat input welding as described above, wherein the steel plate has a chemical composition comprising in percent by mass: 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%, with the balance being iron and inevitable impurities.

[0044] Wherein, Ti+Zr is 0.025~0.15%, that is, the sum of mass percent of Ti and Zr is 0.025~0.15%.

[0045] Further, the microstructure of the large thickness steel plate suitable for ultra-high heat input welding is a multiphase microstructure of acicular ferrite + polygonal ferrite + pearlite, wherein the content of acicular ferrite is ≥80%.

[0046] Through testing, the large thickness steel plate suitable for ultra-high heat input welding has a yield strength of ≥450 MPa, a tensile strength of 560~600 MPa, and an elongation of ≥25%; the heat affected zone formed by welding under conditions of heat input ≥600 kJ / cm has a tensile strength of ≥550 MPa and an impact energy at -40°C of ≥250 J, having excellent strength, welding performance and low temperature impact toughness.

[0047] To make the objects, technical schemes and advantages of an embodiment of the present application clearer, the present embodiment will be further described below in combination with Examples 1~9 according to an embodiment of the present application. Obviously, the described Examples 1~9 are part of the embodiments of the present application, not all of the embodiments. Other embodiments based on the aforementioned embodiments do not deviate from the technical spirit of the present application.

[0048] Specifically, Examples 1~9 all provide a large thickness steel plate suitable for ultra-high heat input welding, the chemical compositions of which are shown in Table 1, wherein P<0.015%, S<0.015%, and the balance is Fe and inevitable impurities. Table 1ExampleChemical composition in percent by mass (wt, %)CSiMnCrNiTiZr10.090.251.600.360.690.0360.03220.090.251.600.360.720.0350.03330.090.251.600.330.740.0370.03140.090.201.600.210.380.0340.03050.090.201.600.210.410.0340.03460.090.201.600.220.420.0330.03270.080.251.550.330.710.0260.02280.080.251.550.340.690.0220.02190.080.251.550.360.730.0240.023

[0049] The production methods of each example are described in detail below.(1) Molten steel refining

[0050] Molten steel refining is performed using hot metal desulfurization process, converter steelmaking process, Ladle Furnace refining process and RH Vacuum degassing refining process. During the entire molten steel refining process, the content of each chemical element in the molten steel is controlled according to the predetermined chemical composition design scheme of Table 1, including controlling the finally obtained molten steel with P<0.015% and S<0.015% in percent by mass.

[0051] The converter steelmaking process is performed in a converter, and the converter steelmaking process uses a top and bottom combined blowing process, and adds alloys and slag-forming materials into 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 bottom argon blowing of the ladle during tapping is 0.5~0.6 MPa.

[0052] The Ladle Furnace refining process performs chemical composition adjustment, temperature control, and inclusions control on the molten steel after converter steelmaking. The Ladle Furnace refining process performs argon blowing throughout; when adding slag-forming materials and alloys, the pressure of bottom argon blowing of the ladle is controlled to be 0.6~0.7 MPa; during heating, the pressure of bottom argon blowing of the ladle is 0.5 MPa.

[0053] In the RH Vacuum degassing refining process, RH circulation degassing equipment is used to perform vacuum degassing and inclusions removal treatment, the vacuum degassing time is >10 min, and after alloying, clean circulation treatment is performed with the clean circulation treatment time being ≥5 min; after completing vacuum degassing and inclusions removal treatment, vacuum breaking is performed, and Zr-containing cored wire is fed into the molten steel, the size of the Zr-containing alloy particles in the Zr-containing cored wire is 0.5~2 mm, wherein the feeding length, feeding speed and thickness of steel strip 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 min, and carbonized rice husk is added into the ladle for heat preservation before tapping. Table 2ExampleFeeding length / mFeeding speed / m / sThickness of steel strip / mm110004.50.80210004.50.80310004.50.80490050.75590050.75690050.75780040.70880040.70980040.70 (2) Continuous casting

[0054] The molten steel finally obtained from the molten steel refining process is continuously cast into a continuous casting slab having a thickness of 320 mm on a continuous casting machine, the casting temperature during continuous casting is controlled to be 1510~1580°C, and the casting speed is controlled to be 1.0~1.3 m / min. The continuous casting process uses ladle long nozzle and argon sealing, basic tundish covering agent, and submerged entry nozzle for fully protected casting, the immersion depth of the submerged entry nozzle is 120~180 mm, and the mold level fluctuation is controlled within ±2 mm.(3) Billet heating

[0055] The continuous casting slab is fed into a heating furnace for heating at a heating temperature of 1050~1150°C, and the residence time of each continuous casting slab is controlled to be ≥320 min.(4) Two stage controlled rolling

[0056] The heated continuous casting slab is rolled in two stages.

[0057] The first stage is recrystallization zone rolling, wherein the continuous casting slab is rough rolled through multiple passes into a transfer bar, and the thickness of the transfer bar, finish rolling temperature, total reduction ratio, and average reduction amount per pass are shown in Table 3.

[0058] The second stage is non-recrystallization zone rolling, wherein after the recrystallization zone rolling is completed and before the non-recrystallization zone rolling begins, the transfer bar obtained from the recrystallization zone rolling is first subjected to temperature holding to below 800°C, and then multi-pass non-recrystallization zone rolling, i.e., finish rolling, is performed to obtain a steel plate, and the start rolling temperature of finish rolling and the thickness of the steel plate are shown in Table 3.(5) Controlled cooling

[0059] The rolled steel plate is conveyed to ACC accelerated cooling equipment for cooling with a final cooling temperature of ≤500°C, and the conveying speed of the steel plate to the ACC accelerated cooling equipment and the cooling rate are shown in Table 3.(6) Finished product

[0060] After the cooled steel plate is subjected to straightening, stack cooling and cutting and finishing, a finished steel plate is obtained. Table 3ExampleRecrystallization zone rollingNon-recrystallization zone rollingControlled coolingThicknes s of the transfer bar / mmFinish rolling temperatu re / °CTotal reduction ratio / %Average reductio n amount per pass / mmStart rolling temperatur e / °CThickness of the steel plate / mmConveying speed / m / sCooling rate / °C / s117098047507701201.815.5217396046497751201.816.8317996044477801201.816.0416798048517701201.816.5517097047507751201.816.0617697045487601201.816.5716796048517701201.816.0817097047507651201.815.6917998044477801201.815.5

[0061] For the finished steel plates of Examples 1~9, sampling and metallographic microstructure detection, Ti-containing oxides and Zr-containing oxides density detection, mechanical property detection and welding performance testing are performed according to the same test methods, and the test results are as follows: (1) In terms of microstructure, the steel plates are observed using a metallographic microscope, and it is found that the microstructures of the steel plates of Examples 1~9 are all multiphase microstructures of acicular ferrite + polygonal ferrite + pearlite, and the content of acicular ferrite is all ≥80%. (2) Scanning electron microscopy is used to count the Ti-containing oxides and Zr-containing oxide inclusions in the steel plates of the above examples, and the areal density of Ti-containing oxides and Zr-containing oxide inclusions is obtained as shown in Table 4. (3) In terms of mechanical properties, the mechanical properties of the steel plates of the above examples are tested according to the GB / T 228.1-2021 standard. Specifically as follows: A tensile testing machine is used to test the yield strength, tensile strength, and elongation of the steel plates, and the test results are shown in Table 4; (4) In terms of welding performance: after welding the steel plates of the above examples, the mechanical properties of the heat affected zone are tested according to GB / T 228.1-2021 and GB / T 229-2020 standards, wherein the welding heat input is shown in Table 4. Specifically as follows: A tensile testing machine is used to test the tensile strength of the heat affected zone, and the test results are shown in Table 4; An impact testing machine is used to test the impact energy at -40°C of the heat affected zone, and the test results are shown in Table 4. Table 4 ExampleTi-containing oxides and Zr-containing oxide inclusionsSteel plateHeat affected zoneAreal density / particles / mm 2< Yield strength / MPaTensile strength / MPaElongation / %Welding heat input / kJ / cmTensile strength / MPaImpact energy at - 40°C / J1129645359126600583312,325,3392135146559026600585315,326,3153132046858327600578329,311,3394128846357126700555285,276,2755126947557027700563281,263,2716132547456127700550279,260,286790747358425650574255,276,265893246857826650561268,251,260994546357726650563255,274,266

[0062] In summary, the present application can use continuous casting slabs to produce large thickness steel plates with thickness reaching 80 mm and above, and the maximum thickness of the steel plate can even reach 120 mm. Compared with using steel ingots with inferior metallurgical quality to continuous casting slabs to produce large thickness steel plates, the present application does not require heat treatment processes such as tempering, normalizing, quenching + tempering to improve the performance of the steel plate, and can realize the production of large thickness steel plates with thickness of 80~120 mm from continuous casting slabs with thickness of 320 mm, which not only saves processes, shortens production cycle, reduces production difficulty and cost, but also can use ultra-high heat input of ≥600 kJ / cm for welding with good welding quality and high welding efficiency, and the welded joints have excellent low temperature toughness, which can be applied to large ships such as container ships, which is beneficial to improving quality, manufacturing efficiency and use safety of ship. Specifically, the steel plate has a yield strength of ≥450 MPa, a tensile strength of 560~600 MPa, and an elongation of ≥25%; the heat affected zone formed by welding under conditions of heat input ≥600 kJ / cm has a tensile strength of ≥550 MPa and an impact energy at -40°C of ≥250 J.

[0063] It should be understood that although the present specification is described according to embodiments, not every embodiment contains only one independent technical solution. This narrative manner of the specification is merely for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in the various embodiments may also be appropriately combined to form other embodiments understandable to those skilled in the art.

[0064] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present application, and are not intended to limit the scope of protection of the present application. All equivalent embodiments or changes made without departing from the technical spirit of the present application shall be included within the scope of protection of the present application.

Claims

1. A production method for a steel plate, wherein the steel plate has a chemical composition comprising in percent by mass: 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%, with the balance being iron and inevitable impurities; the production method comprising the steps of: (1) performing molten steel refining using hot metal desulfurization, converter steelmaking, Ladle Furnace refining and RH Vacuum degassing refining, controlling the finally obtained molten steel with P<0.015% and S<0.015% in percent by mass, wherein in the RH Vacuum degassing refining process, after completing vacuum degassing and inclusions removal treatment, performing vacuum breaking, and feeding at least 800 m of Zr-containing cored wire at a speed of 4~5 m / s; (2) continuously casting the molten steel obtained in step (1) into a continuous casting slab; (3) feeding the continuous casting slab into a heating furnace for heating at a heating temperature of 1050~1150°C, and controlling the residence time of each continuous casting slab to be ≥320 min; (4) sequentially performing recrystallization zone rolling and non-recrystallization zone rolling on the heated continuous casting slab, wherein the recrystallization zone rolling has a finish rolling temperature of 950~1050°C, a total reduction ratio of ≥43%, and an average reduction amount per pass of ≥45 mm; performing temperature holding of the transfer bar obtained from the recrystallization zone rolling to below 800°C, and then performing non-recrystallization zone rolling to obtain a steel plate having a thickness of 80~120 mm; (5) conveying the rolled steel plate to accelerated cooling equipment for cooling at a speed of 1~2 m / s, with a cooling rate of ≥15°C / s and a final cooling temperature of ≤500°C; (6) subjecting the steel plate from step (5) to straightening, stack cooling and cutting and finishing to obtain a finished steel plate.

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

3. The production method for a steel plate according to claim 1, wherein the steel plate has an areal density of Ti-containing oxides and Zr-containing oxides of >800 particles / mm2.

4. The production method for a steel plate according to claim 1, wherein the converter steelmaking process uses a top and bottom combined blowing process, and adds alloys and slag-forming materials into 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 bottom argon blowing of the ladle during tapping is 0.5~0.6 MPa.

5. The production method for a steel plate according to claim 1, wherein the Ladle Furnace refining process performs argon blowing throughout; when adding slag-forming materials and alloys, the pressure of bottom argon blowing of the ladle is controlled to be 0.6~0.7 MPa; during heating, the pressure of bottom argon blowing of the ladle is 0.5 MPa.

6. The production method for a steel plate according to claim 1, wherein in the RH Vacuum degassing refining process, RH circulation degassing equipment is used to perform vacuum degassing and inclusions removal treatment, after feeding the Zr-containing cored wire, soft stirring is performed and the soft stirring time is controlled to be ≥8 min, and carbonized rice husk is added into the ladle for heat preservation before tapping.

7. The production method for a steel plate according to claim 1, wherein in step (2), during continuous casting, the casting temperature is controlled to be 1510~1580°C, the casting speed is controlled to be 1.0~1.3 m / min, the continuous casting process uses ladle long nozzle and argon sealing, basic tundish covering agent, and submerged entry nozzle for fully protected casting, the immersion depth of the submerged entry nozzle is 120~180 mm, and the mold level fluctuation is controlled within ±2 mm.

8. A steel plate, wherein the steel plate has a chemical composition comprising in percent by mass: 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%, with the balance being iron and inevitable impurities.

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

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

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