A method for manufacturing a steel sheet having a reduced degree of performance degradation after multiple welds

Abstract

The application discloses a steel plate preparation method for reducing performance attenuation amplitude after multiple weldings, and relates to the technical field of steel plate preparation. The steel plate preparation method for reducing performance attenuation amplitude after multiple weldings has excellent resistance to multiple welding heat attenuation performance, outstanding resistance to welding heat cycle, controllable performance attenuation law, and high stability. After three weldings, the strength performance attenuation rate of the steel plate is not more than 15%, and the impact toughness attenuation rate at-40 DEG C is not more than 40%. After four weldings, the strength performance attenuation rate is not more than 20%, and the impact toughness attenuation rate at-40 DEG C is not more than 50%. After multiple weldings and repairings, the steel plate can still stably maintain qualified mechanical properties, effectively improves the fault tolerance of component welding construction, and avoids performance failure problems caused by multiple repair weldings.

Description

Technical Field

[0001] This application belongs to the field of steel plate preparation technology, and in particular relates to a method for preparing steel plates that reduces the performance degradation after multiple welding processes. Background Technology

[0002] Steel plates, as a core category of steel materials, have a wide range of market applications, suitable for many key fields such as shipbuilding, building steel structures, engineering machinery, and bridge engineering. Welding is the core processing step for forming steel plate components and realizing their structural functionality; in actual engineering projects, more than 85% of steel plate components need to be assembled through welding. Due to the influence of multiple factors such as welding technology, construction environment, and the condition of the base material, welding defects are difficult to completely avoid. Therefore, it is common in engineering projects to repair defects by welding, and in some cases, secondary, tertiary, or even multiple welding operations are required.

[0003] Existing conventional hot-rolled steel plates generally suffer from a severe technical defect: their mechanical properties degrade significantly after multiple welding thermal cycles, limiting their service safety. In terms of strength: conventional steel plates experience a strength reduction of approximately 10% after a single weld, and over 20% after a second weld, with reductions reaching up to 30%. After three or more welds, over 90% of conventional steel plates fail to meet engineering design requirements. The performance degradation is even more pronounced in terms of toughness: conventional steel plates experience a toughness reduction of approximately 20% and an increase in the ductile-brittle transition temperature of approximately 10°C after a single weld; a toughness reduction exceeding 50% and an increase in the ductile-brittle transition temperature of approximately 20°C after a second weld; and after multiple welds, the maximum toughness reduction can reach 90%, with the ductile-brittle transition temperature increasing by over 40°C, completely rendering the plates unusable.

[0004] Because existing steel plates suffer significant strength and toughness degradation and poor performance stability after multiple welding processes, current engineering specifications only allow for single-time repair welding and strictly prohibit multiple welding repairs. This restriction forces many components with localized welding defects to be scrapped entirely, resulting in wasted steel resources, increased construction costs, and project delays. Summary of the Invention

[0005] To address some or all of the technical problems existing in the prior art, this application provides a method for preparing steel plates that reduces the performance degradation after multiple welding processes.

[0006] This application provides a method for preparing steel plates that reduces the performance degradation after multiple welding processes, comprising the following steps: Step S1: Smelting and continuous casting to obtain a continuously cast billet. The chemical composition of the continuously cast billet, by mass percentage, is: C 0.13%~0.17%, Si 0.25%~0.35%, Mn 1.30%~1.60%, S≤0.007%, P≤0.010%, Nb 0.022%~0.032%, Ti 0.008%~0.020%, Cr 0.05%~0.25%, with the balance being Fe and unavoidable impurities; Step S2: Heat the 200-300mm thick continuous casting billet to 1130℃-1170℃, hold it at the set temperature for the set heating time, and then remove it from the furnace for rough rolling. The first intermediate billet is obtained after rough rolling. The thickness of the first intermediate billet is 2.9 times to 3.3 times the thickness of the finished steel plate. Step S3: The first intermediate billet is subjected to intermediate cooling in the range of 950℃~980℃. After cooling, it is air-cooled to 890℃~940℃ and the second stage rolling is carried out to obtain the second intermediate billet. The thickness of the second intermediate billet is 1.4 to 1.6 times the thickness of the finished steel plate. Step S4: Air cool the second intermediate billet to 830℃~870℃ and perform the final stage rolling to the set thickness of the finished steel plate. Step S5: Perform ACC accelerated water cooling treatment on the rolled steel plate, with an initial cooling temperature of 790℃~825℃ and a final cooling temperature of 580℃~630℃. Step S6: After accelerated cooling, the steel plates are removed from the production line and stacked for slow cooling. The initial slow cooling temperature is 485℃~535℃. After slow cooling until the overall temperature of the steel plates is ≤100℃, they are removed from the stack and cut.

[0007] Preferably, in step S2, the heating time of the continuously cast billet satisfies the formula t≥0.8h+25, where h is the thickness of the continuously cast billet in mm and t is the heating time in min; the furnace exit temperature of the continuously cast billet is controlled at 1135℃~1165℃.

[0008] Preferably, in step S2, the initial roughing temperature is 1105℃~1135℃, the final roughing temperature is 985℃~1015℃, and the total number of roughing passes is 3~6.

[0009] Preferably, step S2 is a rough rolling process. When the target finished product thickness is 30mm, a 250mm thick continuous casting billet is used. The rough rolling is set with 5 rolling passes. After rolling, a first intermediate billet with a thickness range of 91mm to 95mm is obtained, and the intermediate billet is cooled to 950℃ to 970℃. When the target finished product thickness specification is 40mm, a 300mm thick continuous casting billet is used, and the rough rolling is set with 6 rolling passes. After rolling, a first intermediate billet with a thickness range of 122mm to 126mm is obtained, and the intermediate billet is cooled to 960℃ to 980℃. When the target finished product thickness is 50mm, a 300mm thick continuous casting billet is used, and four rolling passes are set for rough rolling. After rolling, a first intermediate billet with a thickness range of 153mm to 157mm is obtained, and the intermediate billet is cooled to 960℃ to 980℃.

[0010] Preferably, step S3 is the second stage rolling process; When the target finished product thickness is 30mm, the intermediate billet is air-cooled to 920℃~940℃ after cooling and then rolled. A total of 3 rolling processes are set up. After rolling, a second intermediate billet with a thickness range of 44mm~46mm is obtained. When the target finished product thickness is 40mm, the intermediate billet is air-cooled to 900℃~920℃ after cooling and then rolled. A total of 5 rolling processes are set up. After rolling, a second intermediate billet with a thickness range of 59mm~61mm is obtained. When the target finished product thickness is 50mm, after the intermediate billet is cooled, it is air-cooled to 890℃~910℃ and then rolled. A total of 5 rolling processes are set up. After rolling, a second intermediate billet with a thickness range of 74mm~76mm is obtained.

[0011] Preferably, step S4 is the final rolling process, which uses 3 rolling passes; When the target finished product thickness is 30mm, the second intermediate billet is air-cooled to 850℃~870℃ before final rolling. When the target finished product thickness is 40mm, the second intermediate billet is air-cooled to 840℃~860℃ before final rolling. When the target finished product thickness is 50mm, the second intermediate billet is air-cooled to 830℃~850℃ before final rolling.

[0012] Preferably, step S5 is the ACC accelerated water cooling process; When the target finished product thickness is 30mm, the initial cooling temperature after steel plate rolling is 790℃~810℃, the final cooling temperature is 610℃~630℃, the roller conveyor running speed is 1.10m / s~2.10m / s, and the cooling rate is 6℃ / s~10℃ / s. When the target finished product thickness is 40mm, the initial cooling temperature after steel plate rolling is 800℃~820℃, the final cooling temperature is 600℃~620℃, the roller conveyor running speed is 0.85m / s~1.85m / s, and the cooling rate is 5℃ / s~9℃ / s. When the target finished product thickness is 50mm, the initial cooling temperature after steel plate rolling is 805℃~825℃, the final cooling temperature is 580℃~600℃, the roller conveyor running speed is 0.65m / s~1.65m / s, and the cooling rate is 4℃ / s~8℃ / s.

[0013] Preferably, step S6 is a stacking and slow cooling process, where the steel plates are slowly cooled until the overall temperature is ≤100℃ before being unstacked. When the target finished product thickness is 30mm, the initial temperature of slow cooling of steel plate stacking is controlled at 485℃~515℃. When the target finished product thickness is 40mm, the initial temperature of slow cooling of steel plate stacking is controlled between 495℃ and 525℃. When the target finished product thickness is 50mm, the initial temperature of slow cooling of the steel plate stack is controlled between 505℃ and 535℃.

[0014] This application provides a steel plate prepared by the above method that reduces the performance degradation after multiple welding processes. The steel plate has a yield strength ≥355MPa, tensile strength ≥490MPa, elongation after fracture ≥25%, and AKV impact toughness ≥200J at -40℃. After three welding processes, the strength performance degradation rate is ≤15%, and the impact toughness degradation rate at -40℃ is ≤40%. After four welding processes, the strength performance degradation rate is ≤20%, and the impact toughness degradation rate at -40℃ is ≤50%.

[0015] Preferably, the thickness of the finished steel plate ranges from 20mm to 50mm, and the width ranges from 1500mm to 4100mm.

[0016] The steel plate preparation method of this application, which reduces the performance degradation after multiple welding processes, has the following advantages and positive effects: (1) The prepared steel plate has excellent resistance to repeated welding thermal decay, outstanding tolerance to welding thermal cycles, controllable performance decay law, and high stability. After three weldings, the strength performance decay rate of the steel plate does not exceed 15%, and the impact toughness decay rate at -40℃ does not exceed 40%; after four weldings, the strength performance decay rate does not exceed 20%, and the impact toughness decay rate at -40℃ does not exceed 50%. After multiple welding repairs, it can still stably maintain qualified mechanical properties, effectively improving the fault tolerance rate of component welding construction and avoiding performance failure problems caused by multiple welding repairs.

[0017] (2) The refined process of multi-stage segmented controlled rolling and cooling can achieve precise and coordinated control of parameters throughout the rolling and cooling process, effectively refine the matrix grains of the steel plate, optimize the distribution of fine precipitates, homogenize the internal structure, and release residual internal stress. The steel plate base material prepared by this process has excellent comprehensive mechanical properties, reasonable strength and toughness matching, and good microstructure uniformity. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0019] The method for preparing steel plates that reduces the performance degradation after multiple welding processes according to this application includes the following steps: Step S1: The continuously cast billet is obtained by smelting and casting. The chemical composition of the continuously cast billet, by mass percentage, is as follows: C 0.13%~0.17%; while ensuring the basic strength of the steel plate, avoid excessive carbon content leading to embrittlement of the weld heat-affected zone and a significant decrease in toughness.

[0020] Si 0.25%~0.35%; plays a role in deoxidation and solid solution strengthening, and improves the purity and uniformity of the steel structure.

[0021] Mn 1.30%~1.60%; solid solution strengthening refines austenite grains, improving the strength and low-temperature toughness of the steel plate.

[0022] S≤0.007%, P≤0.010%; Strictly controlling this content range can significantly reduce the proportion of harmful impurities, avoid structural defects, welding cracks and low-temperature brittleness caused by sulfur and phosphorus segregation, and improve the overall quality stability of steel plates.

[0023] Nb 0.022%~0.032%; fine carbonitrides can be precipitated during rolling, effectively pinning austenite grain boundaries, inhibiting high-temperature grain growth, and refining the matrix structure.

[0024] Ti 0.008%~0.020%; can preferentially combine with N element to form stable TiN particles, which are not easily decomposed at high temperature, can effectively inhibit abnormal grain coarsening during welding thermal cycling, and greatly improve the steel plate's resistance to repeated welding thermal damage.

[0025] Cr 0.05%~0.25%; can improve the hardenability and structural stability of steel, and slow down the structural deterioration caused by welding heat input.

[0026] The balance consists of Fe and unavoidable impurities. This compositional system works synergistically to lay the foundation for high-performance steel plates and low attenuation during repeated welding at the raw material level.

[0027] Step S2: Heat the 200-300mm thick continuous casting billet to 1130℃-1170℃, hold it at that temperature for the set heating time, and then remove it from the furnace. The billet exiting the furnace should be controlled at 1135℃-1165℃. This temperature range ensures sufficient solid solution of microalloying elements such as Nb and Ti, providing ample solute atoms for the formation of fine and dispersed precipitates during subsequent rolling and cooling. It also eliminates original defects such as casting segregation and porosity within the billet, resulting in a uniform internal structure. The heating time of the billet should satisfy the formula t≥0.8h+25, where h is the billet thickness in mm and t is the heating time in min. The holding time is adaptively matched to the billet thickness to address insufficient heating of the core and uneven internal and external structures in thick billets, ensuring uniform temperature and composition along the thickness direction. After exiting the furnace, rough rolling is performed. The initial rough rolling temperature is 1105℃-1135℃, and the final rough rolling temperature is... The initial rolling temperature is 985℃~1015℃, with a total of 3~6 passes. After rough rolling, the first intermediate billet is obtained. The preceding passes are in the complete recrystallization zone of austenite, and the final pass enters the critical recrystallization temperature range. Through 3~6 passes of continuous rolling with low reduction, the austenite can continuously undergo dynamic recrystallization in the high-temperature zone of the preceding passes, which fully breaks down and repeatedly refines the coarse original grains in the cast state. The final pass completes the finishing rolling in a lower temperature range, which not only avoids grain coarsening at high temperatures, but also prevents stress concentration and grain inhomogeneity, while providing reasonable temperature connection conditions for subsequent rolling stages. The thickness of the first intermediate billet is 2.9 to 3.3 times the thickness of the finished steel plate, which can reserve sufficient and matched deformation for subsequent intermediate cooling, second-stage rolling and final rolling, ensuring that each stage of rolling is within the design temperature range, realizing three-temperature gradient refinement, and ensuring that the final microstructure is uniform and the performance is stable.

[0028] Step S3: The first intermediate billet is subjected to intermediate cooling in the range of 950℃~980℃. After cooling, it is air-cooled to 890℃~940℃ and the second stage rolling is carried out to obtain the second intermediate billet. This can quickly remove the excess heat of the billet, lock the fine austenite grains after rough rolling, and inhibit the spontaneous growth and coarsening of austenite at high temperature. The thickness of the second intermediate billet is 1.4 to 1.6 times the thickness of the finished steel plate, which can reserve sufficient and appropriate deformation allowance.

[0029] Step S4: Air cool the second intermediate billet to 830℃~870℃. Rolling deformation in this temperature range will not trigger austenite recrystallization, and can introduce high-density dislocations and a large number of deformation bands into the austenite grains. The final rolling stage is completed in three rolling passes, with the total reduction evenly distributed to avoid stress concentration caused by large reduction in a single pass, and the finished steel plate is rolled to the set thickness.

[0030] Step S5: Perform ACC accelerated water cooling treatment on the rolled steel plate. The initial cooling temperature is 790℃~825℃ and the final cooling temperature is 580℃~630℃. Accelerated cooling can quickly lock in the rolled and refined microstructure and inhibit the coarsening of austenite grains.

[0031] Step S6: After accelerated cooling, the steel plates are stacked and slowly cooled. The initial temperature of slow cooling is 485℃~535℃. Stacking and slow cooling can evenly release the residual stress in the steel plates, avoid deformation and cracking caused by uneven cooling, and further stabilize the structure. After slow cooling to an overall temperature of ≤100℃, the steel plate is removed from the stack and cut.

[0032] For different finished product thickness specifications, each process adopts differentiated and precise process control, as detailed below: (1) Finished product thickness 30mm specification: 250mm thick continuous casting billet is used; five rolling passes are set for rough rolling, and the first intermediate billet with a thickness range of 91mm to 95mm is obtained after rough rolling. The intermediate billet is cooled to 950℃ to 970℃. After intermediate cooling, it is air-cooled to 920℃ to 940℃ and then enters the second stage of rolling. A total of three rolling processes are set. After rolling, the second intermediate billet with a thickness range of 44mm to 46mm is obtained. The second intermediate billet is air-cooled to 850℃ to 870℃ and then the final stage of final rolling is carried out. In the ACC accelerated water cooling process, the starting cooling temperature is 790℃ to 810℃, the final cooling temperature is 610℃ to 630℃, the roller table running speed is 1.10m / s to 2.10m / s, and the cooling rate is 6℃ / s to 10℃ / s. The initial temperature of the stacked slow cooling is controlled at 485℃ to 515℃. After slow cooling, the steel plate is removed from the stack when the overall temperature is ≤100℃.

[0033] (2) Finished product thickness 40mm specification: 300mm thick continuous casting billet is used; 6 rolling passes are set for rough rolling, and the first intermediate billet with a thickness range of 122mm to 126mm is obtained after rough rolling. The intermediate billet is cooled to 960℃ to 980℃. After intermediate cooling, it is air-cooled to 900℃ to 920℃ and then enters the second stage of rolling. A total of 5 rolling processes are set. After rolling, the second intermediate billet with a thickness range of 59mm to 61mm is obtained. The second intermediate billet is air-cooled to 840℃ to 860℃ and then the final stage of final rolling is carried out. In the ACC accelerated water cooling process, the starting cooling temperature is 800℃ to 820℃, the final cooling temperature is 600℃ to 620℃, the roller table running speed is 0.85m / s to 1.85m / s, and the cooling rate is 5℃ / s to 9℃ / s. The initial temperature of the stacked slow cooling is controlled at 495℃ to 525℃. After slow cooling, the steel plate is removed from the stack when the overall temperature is ≤100℃.

[0034] (3) Finished product thickness 50mm specification: 300mm thick continuous casting billet is used; four rolling passes are set for rough rolling, and the first intermediate billet with a thickness range of 153mm to 157mm is obtained after rough rolling. The intermediate billet is cooled to 960℃ to 980℃. After intermediate cooling, it is air-cooled to 890℃ to 910℃ and then enters the second stage of rolling. A total of five rolling processes are set. After rolling, the second intermediate billet with a thickness range of 74mm to 76mm is obtained. The second intermediate billet is air-cooled to 830℃ to 850℃ and then the final stage of final rolling is carried out. In the ACC accelerated water cooling process, the starting cooling temperature is 805℃ to 825℃, the final cooling temperature is 580℃ to 600℃, the roller table running speed is 0.65m / s to 1.65m / s, and the cooling rate is 4℃ / s to 8℃ / s. The initial temperature of the stacked slow cooling is controlled at 505℃ to 535℃. After slow cooling, the steel plate is removed from the stack when the overall temperature is ≤100℃.

[0035] The finished steel plates prepared by the above method, which reduce the performance degradation after multiple welding, have a thickness range of 20mm to 50mm and a width range of 1500mm to 4100mm.

[0036] The present application will be further described in detail below with reference to specific embodiments and comparative examples.

[0037] Example 1: 30mm thick steel plate for wind power Step S1: Smelting and continuous casting to obtain a 250mm thick continuous casting billet. The chemical composition (mass percentage) of the finished product is: C 0.16%, Si 0.28%, Mn 1.48%, S 0.005%, P 0.010%, Nb 0.026%, Ti 0.011%, Cr 0.25%, with the balance being Fe and unavoidable impurities.

[0038] Step S2: Heat the continuously cast billet to 1160℃ for 233 minutes, and the exit temperature is 1157℃. After exiting the furnace, perform rough rolling. The rough rolling start temperature is 1108℃, and a total of 5 passes are rolled. The temperature of the last rough rolling pass is 996℃. After rough rolling, a first intermediate billet with a thickness of 92.7mm is obtained.

[0039] Step S3: The first intermediate billet is cooled to 958°C; then air-cooled to 931°C for the second stage of rolling, which is carried out in 3 passes. The second intermediate billet with a thickness of 45.3 mm is obtained after rolling. The end temperature of the second stage of rolling is 897°C.

[0040] Step S4: Air-cool the second intermediate billet to 862°C, and complete the final stage of rolling in 3 rolling passes, with a final rolling temperature of 812°C, to a finished product thickness of 30mm.

[0041] Step S5: The rolled steel plate is subjected to ACC accelerated water cooling treatment, with an initial cooling temperature of 803℃, a final cooling temperature of 619℃, a roller conveyor running speed of 1.61m / s, and a cooling rate of 8.14℃ / s.

[0042] Step S6: After ACC cooling, the steel plate is hot straightened and cooled on a cooling bed. It is then stacked and slowly cooled. The initial temperature of the slow cooling is 503℃. After the overall temperature of the steel plate is ≤100℃, it is removed from the stack and cut, sampled, and cut to length.

[0043] Sampling and testing revealed the following basic mechanical properties of the steel plate: yield strength 452 MPa, tensile strength 545 MPa, elongation after fracture 29.4%, and AKV transverse impact toughness at -40℃ 233 J.

[0044] The properties and degradation of the steel plates after different welding cycles are shown in Table 1.

[0045] Table 1. Performance and degradation of 30mm steel plates after different welding cycles.

[0046] Example 2: 40mm thick marine steel plate Step S1: Smelting and continuous casting to obtain a 300mm thick continuous casting billet. The chemical composition (mass percentage) of the finished product is: C 0.14%, Si 0.31%, Mn 1.52%, S 0.006%, P 0.009%, Nb 0.031%, Ti 0.012%, Cr 0.18%, with the balance being Fe and unavoidable impurities.

[0047] Step S2: Heat the continuously cast billet to 1165℃ for 274 minutes, and the exit temperature is 1162℃. After exiting the furnace, rough rolling is carried out. The rough rolling start temperature is 1122℃, and a total of 6 passes are rolled. The temperature of the last rough rolling pass is 1003℃. After rough rolling, a first intermediate billet with a thickness of 124.6mm is obtained.

[0048] Step S3: The first intermediate billet is cooled to 977°C; then air-cooled to 909°C for the second stage of rolling, which is rolled in 5 passes to obtain a second intermediate billet with a thickness of 59.8 mm. The end temperature of the second stage of rolling is 894°C.

[0049] Step S4: Air-cool the second intermediate billet to 854°C, and complete the final stage of rolling in 3 rolling passes, with a final rolling temperature of 821°C, to a finished product thickness of 40mm.

[0050] Step S5: The rolled steel plate is subjected to ACC accelerated water cooling treatment, with an initial cooling temperature of 807℃, a final cooling temperature of 613℃, a roller conveyor running speed of 1.29m / s, and a cooling rate of 6.96℃ / s.

[0051] Step S6: After ACC cooling, the steel plate is hot straightened and cooled on a cooling bed. It is then stacked and slowly cooled. The initial temperature of the slow cooling is 515℃. After the overall temperature of the steel plate is ≤100℃, it is removed from the stack and cut, sampled, and cut to length.

[0052] Sampling and testing revealed the following basic mechanical properties of the steel plate: yield strength 423 MPa, tensile strength 539 MPa, elongation after fracture 30.7%, and AKV transverse impact toughness at -40℃ 242 J.

[0053] The performance and attenuation after different welding cycles are shown in Table 2.

[0054] Table 2. Performance and degradation of 40mm steel plates after different welding cycles.

[0055] Example 3: 50mm thick marine engineering steel plate Step S1: Smelting and continuous casting to obtain a 300mm thick continuous casting billet. The chemical composition (mass percentage) of the finished product is: C 0.14%, Si 0.27%, Mn 1.48%, S 0.003%, P 0.007%, Nb 0.029%, Ti 0.013%, Cr 0.16%, with the balance being Fe and unavoidable impurities.

[0056] Step S2: Heat the continuously cast billet to 1162℃ for 271 min, and the exit temperature is 1157℃. After exiting the furnace, rough rolling is performed. The initial rolling temperature is 1119℃, and a total of 4 passes are rolled. The temperature of the last pass of rough rolling is 996℃. After rough rolling, a first intermediate billet with a thickness of 153.8 mm is obtained.

[0057] Step S3: The first intermediate billet is cooled to 968°C; then air-cooled to 900°C for the second stage of rolling, which is rolled in 5 passes. The second intermediate billet with a thickness of 74.6 mm is obtained after rolling. The end temperature of the second stage of rolling is 871°C.

[0058] Step S4: Air-cool the second intermediate billet to 839°C, and complete the final stage of rolling in 3 rolling passes, with a final rolling temperature of 820°C, to a finished product thickness of 50mm.

[0059] Step S5: The rolled steel plate is subjected to ACC accelerated water cooling treatment, with an initial cooling temperature of 816℃, a final cooling temperature of 595℃, a roller conveyor running speed of 1.18m / s, and a cooling rate of 6.25℃ / s.

[0060] Step S6: After ACC cooling, the steel plate is hot straightened and cooled on a cooling bed, then stacked for slow cooling. The initial slow cooling temperature is 524℃. After slow cooling until the overall temperature of the steel plate is ≤100℃, it is removed from the stack for cutting, sampling, and length determination.

[0061] Sampling and testing revealed the following basic mechanical properties of the steel plate: yield strength 437 MPa, tensile strength 556 MPa, elongation after fracture 28.6%, and AKV transverse impact toughness at -40℃ 221 J.

[0062] The performance and attenuation after different welding cycles are shown in Table 3.

[0063] Table 3. Performance and degradation of 50mm steel plates after different welding cycles.

[0064] Comparative example: 30mm steel plate using conventional TMCP process Using the same 250mm thick continuously cast billet as in Example 1, the process flow is as follows: Step S1: Smelting and continuous casting to obtain a 250mm thick continuous casting billet. The chemical composition (mass percentage) of the finished product is: C 0.16%, Si 0.28%, Mn 1.48%, S 0.005%, P 0.010%, Nb 0.026%, Ti 0.011%, Cr 0.25%, with the balance being Fe and unavoidable impurities.

[0065] Step S2: Heat the continuously cast billet to 1180℃ for 216 minutes and exit the furnace at 1173℃. After exiting the furnace, perform rough rolling at 1151℃ for the first rolling pass and 7 passes for the second rolling pass. The temperature of the last rough rolling pass is 1087℃. After rough rolling, the first intermediate billet with a thickness of 89mm is obtained.

[0066] Step S3: The first intermediate billet is not subjected to special intermediate cooling, but is directly air-cooled to 910°C. No independent intermediate cooling and second-stage rolling control process is set up.

[0067] Step S4: The air-cooled intermediate billet is directly rolled in the final stage, with a total of 8 rolling passes. The finishing rolling temperature is 828℃, and the finished thickness is 30mm.

[0068] Step S5: Perform ACC water cooling on the rolled steel plate, with an initial cooling temperature of 815℃ and a final cooling temperature of 605℃.

[0069] Step S6: After ACC cooling, the steel plate is hot straightened and cooled on a cooling bed. It is then stacked and cooled within 20 minutes. Once the temperature of the steel plate drops below 100℃, it is removed from the stack and cut, sampled, and cut to length.

[0070] Sampling and testing revealed the following basic mechanical properties of the steel plate: yield strength 421 MPa, tensile strength 533 MPa, elongation after fracture 26.5%, and AKV transverse impact toughness at -40℃ 152 J.

[0071] The performance and attenuation after different welding cycles are shown in Table 4.

[0072] Table 4. Performance and degradation of 30mm steel plates after different welding cycles (Comparative Example)

[0073] As shown in Tables 1 to 4, the finished steel plates produced by the process described in this application exhibit the following overall mechanical properties: yield strength ≥ 355 MPa, tensile strength ≥ 490 MPa, elongation after fracture ≥ 25%, and -40℃ AKV impact toughness ≥ 200 J. Regarding the base material properties, the 30mm, 40mm, and 50mm steel plates produced using the process described in this application demonstrate superior yield strength, tensile strength, and low-temperature impact toughness compared to steel plates produced using the conventional TMCP process. They exhibit a better balance of strength and toughness, more uniform internal quality, and higher overall mechanical properties.

[0074] Regarding the stability after multiple welding cycles, the performance of conventional TMCP process steel plates exhibits a precipitous decline after repeated welding thermal cycles. After three welding cycles, the impact toughness at -40℃ drops to only 20J, indicating complete performance failure and inability to meet engineering service requirements. The steel plates in the three embodiments of this application, however, possess excellent resistance to repeated welding degradation, fully meeting the preset performance control standards: after three welding cycles, the strength performance degradation rate is ≤15%, and the impact toughness degradation rate at -40℃ is ≤40%; after four welding cycles, the strength performance degradation rate is ≤20%, and the impact toughness degradation rate at -40℃ is ≤50%. Even after multiple welding cycles, the strength and toughness of the steel plate can still be stably maintained within the allowable range of engineering design, with a performance degradation rate far lower than that of steel plates produced by conventional processes. This solves the problem of performance degradation and component failure after multiple welding cycles of traditional steel plates.

[0075] This application utilizes a refined process route of "rough rolling + intermediate cooling + two-stage controlled rolling + ACC accelerated cooling + staged stacking slow cooling," breaking through the traditional mode of direct finishing rolling after rough rolling in conventional TMCP processes. This achieves precise, segmented control of rolling temperature, number of passes, and cooling rate throughout the entire process, effectively refining the steel plate matrix, optimizing the morphology and distribution of precipitated phases, and eliminating internal residual stress. The resulting steel plate base material exhibits excellent comprehensive mechanical properties; its yield strength, tensile strength, elongation after fracture, and low-temperature impact toughness all meet the requirements for high-end engineering materials, and its microstructure uniformity and performance stability are significantly superior to steel plates produced by conventional processes.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing steel plates that reduces the performance degradation after multiple welding processes, characterized in that, Includes the following steps: Step S1: Smelting and continuous casting to obtain a continuously cast billet. The chemical composition of the continuously cast billet, by mass percentage, is: C 0.13%~0.17%, Si 0.25%~0.35%, Mn 1.30%~1.60%, S≤0.007%, P≤0.010%, Nb 0.022%~0.032%, Ti 0.008%~0.020%, Cr 0.05%~0.25%, with the balance being Fe and unavoidable impurities. Step S2: Heat the 200-300mm thick continuous casting billet to 1130℃-1170℃, hold it at the set temperature for the set heating time, and then remove it from the furnace for rough rolling. The first intermediate billet is obtained after rough rolling. The thickness of the first intermediate billet is 2.9 times to 3.3 times the thickness of the finished steel plate. Step S3: The first intermediate billet is subjected to intermediate cooling in the range of 950℃~980℃. After cooling, it is air-cooled to 890℃~940℃ and the second stage rolling is carried out to obtain the second intermediate billet. The thickness of the second intermediate billet is 1.4 to 1.6 times the thickness of the finished steel plate. Step S4: Air cool the second intermediate billet to 830℃~870℃ and perform the final stage rolling to the set thickness of the finished steel plate. Step S5: Perform ACC accelerated water cooling treatment on the rolled steel plate, with an initial cooling temperature of 790℃~825℃ and a final cooling temperature of 580℃~630℃. Step S6: After accelerated cooling, the steel plates are stacked and slowly cooled. The initial temperature of the slow cooling is 485℃~535℃. After the overall temperature of the steel plates is ≤100℃, they are removed from the stack and cut.

2. The method for preparing steel plates to reduce the performance degradation after multiple welding operations according to claim 1, characterized in that, In step S2, the heating time of the continuously cast billet satisfies the formula t≥0.8h+25, where h is the thickness of the continuously cast billet in mm and t is the heating time in min; the temperature of the continuously cast billet exiting the furnace is controlled between 1135℃ and 1165℃.

3. The method for preparing steel plates to reduce the performance degradation after multiple welding operations according to claim 2, characterized in that, In step S2, the initial roughing temperature is 1105℃~1135℃, the final roughing temperature is 985℃~1015℃, and the total number of roughing passes is 3~6.

4. The method for preparing steel plates to reduce the performance degradation after multiple welding operations according to claim 3, characterized in that, Step S2 is the rough rolling process. When the target finished product thickness is 30mm, a 250mm thick continuous casting billet is used. The rough rolling is set with 5 rolling passes. After rolling, a first intermediate billet with a thickness range of 91mm to 95mm is obtained, and the intermediate billet is cooled to 950℃ to 970℃. When the target finished product thickness specification is 40mm, a 300mm thick continuous casting billet is used, and the rough rolling is set with 6 rolling passes. After rolling, a first intermediate billet with a thickness range of 122mm to 126mm is obtained, and the intermediate billet is cooled to 960℃ to 980℃. When the target finished product thickness is 50mm, a 300mm thick continuous casting billet is used, and four rolling passes are set for rough rolling. After rolling, a first intermediate billet with a thickness range of 153mm to 157mm is obtained, and the intermediate billet is cooled to 960℃ to 980℃.

5. The method for preparing steel plates to reduce the performance degradation after multiple welding operations according to claim 1, characterized in that, Step S3 is the second stage of the rolling process; When the target finished product thickness is 30mm, the intermediate billet is air-cooled to 920℃~940℃ after cooling and then rolled. A total of 3 rolling processes are set up. After rolling, a second intermediate billet with a thickness range of 44mm~46mm is obtained. When the target finished product thickness is 40mm, the intermediate billet is air-cooled to 900℃~920℃ after cooling and then rolled. A total of 5 rolling processes are set up. After rolling, a second intermediate billet with a thickness range of 59mm~61mm is obtained. When the target finished product thickness is 50mm, after the intermediate billet is cooled, it is air-cooled to 890℃~910℃ and then rolled. A total of 5 rolling processes are set up. After rolling, a second intermediate billet with a thickness range of 74mm~76mm is obtained.

6. The method for preparing steel plates to reduce the performance degradation after multiple welding operations according to claim 1, characterized in that, Step S4 is the final rolling process, which uses 3 rolling passes; When the target finished product thickness is 30mm, the second intermediate billet is air-cooled to 850℃~870℃ before final rolling. When the target finished product thickness is 40mm, the second intermediate billet is air-cooled to 840℃~860℃ before final rolling. When the target finished product thickness is 50mm, the second intermediate billet is air-cooled to 830℃~850℃ before final rolling.

7. The method for preparing steel plates to reduce the performance degradation after multiple welding operations according to claim 1, characterized in that, Step S5 is the ACC accelerated water cooling process; When the target finished product thickness is 30mm, the initial cooling temperature after steel plate rolling is 790℃~810℃, the final cooling temperature is 610℃~630℃, the roller conveyor running speed is 1.10m / s~2.10m / s, and the cooling rate is 6℃ / s~10℃ / s. When the target finished product thickness is 40mm, the initial cooling temperature after steel plate rolling is 800℃~820℃, the final cooling temperature is 600℃~620℃, the roller conveyor running speed is 0.85m / s~1.85m / s, and the cooling rate is 5℃ / s~9℃ / s. When the target finished product thickness is 50mm, the initial cooling temperature after steel plate rolling is 805℃~825℃, the final cooling temperature is 580℃~600℃, the roller conveyor running speed is 0.65m / s~1.65m / s, and the cooling rate is 4℃ / s~8℃ / s.

8. The method for preparing steel plates to reduce the performance degradation after multiple welding operations according to claim 1, characterized in that, Step S6 is the stacking and slow cooling process, where the steel plates are slowly cooled until the overall temperature is ≤100℃ before being unstacked. When the target finished product thickness is 30mm, the initial temperature of slow cooling of steel plate stacking is controlled at 485℃~515℃. When the target finished product thickness is 40mm, the initial temperature of slow cooling of steel plate stacking is controlled between 495℃ and 525℃. When the target finished product thickness is 50mm, the initial temperature of slow cooling of the steel plate stack is controlled between 505℃ and 535℃.

9. A steel plate with reduced performance degradation after multiple welding processes, characterized in that, The steel plate is prepared by the method according to any one of claims 1 to 8, wherein the yield strength is ≥355MPa, the tensile strength is ≥490MPa, the elongation after fracture is ≥25%, and the AKV impact toughness at -40℃ is ≥200J; after three welding operations, the strength performance attenuation rate is ≤15%, and the impact toughness at -40℃ attenuation rate is ≤40%; after four welding operations, the strength performance attenuation rate is ≤20%, and the impact toughness at -40℃ attenuation rate is ≤50%.

10. The steel plate according to claim 9, characterized in that, The thickness of the finished steel plate ranges from 20mm to 50mm, and the width ranges from 1500mm to 4100mm.

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