High-heat input steel plate for welding and method for manufacturing the same.

Abstract

The present invention provides a steel plate for large heat input welding and a method for producing the same. The steel plate for large heat input welding has a chemical composition of C≦0.1%, Si≦0.15%, S≦0.004%, Mn+Cr+Ni+Cu:1.5-4.5%, a Cr / Ni / Cu mass ratio of 1:2:1, Ti+Mg+Zr+Ca:0.03-0.3%, of which Ti+Mg:0.03-0.2%, the balance being Fe and unavoidable impurities, and a carbon equivalent Ceq:0.36-0.42, where Ceq=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15. In the production of the steel plate, calcium zirconium core wire is added during RH refining, and after RH tapping, the steel plate is continuously cast into a slab. The slab is rolled into a recrystallized zone and a non-recrystallized zone to promote the formation of acicular ferrite and improve the crack resistance of the steel plate.

Description

Technical Field

[0001] The present invention relates to the technical field of steel metallurgy manufacturing, and particularly to a steel plate for high-heat-input welding and a manufacturing method thereof.

Background Art

[0002] High-heat-input welding steel can receive a large amount of energy during welding, and the low-temperature toughness of the heat-affected zone of the weld is stable, so the welding efficiency can be improved. The crack resistance is an index reflecting the ability to resist crack propagation. Excellent crack resistance indicates that the ability to resist crack propagation is excellent, better preventing brittle fracture and ensuring the safety of parts and components.

[0003] In recent years, with the enlargement of container ships, the requirements for the performance of steel plates in the shipping industry have become increasingly high, especially the requirements for crack resistance and high-heat-input welding. In the prior art, there are few reports on crack-resistant steel that can be welded with high heat input. Usually, steel materials have excellent crack resistance and crack toughness but cannot be welded with high heat input, or can be welded with high heat input but have insufficient crack resistance and crack toughness. Therefore, in order to meet the needs of the enlarged container ships, it is required to provide a steel plate for high-heat-input welding with excellent crack resistance and crack toughness.

Summary of the Invention

[0004] The object of the present invention is to provide a steel plate for high-heat-input welding ,steel and solve the problem of the prior art that materials cannot combine high-heat-input welding and excellent crack toughness.

[0005] To achieve the above-mentioned objective of the invention, one embodiment of the present invention provides a steel sheet for high heat input welding. This welding steel sheet contains a chemical composition of C≦0.1%, Si≦0.15%, S≦0.004% by mass%, with Mn+Cr+Ni+Cu:1.5~4.5%, a Cr / Ni / Cu mass ratio of 1:2:1, Ti+Mg+Zr+Ca:0.03~0.3%, of which Ti+Mg:0.03~0.2%, the remainder being Fe and unavoidable impurities, and a carbon equivalent Ceq:0.36~0.42%, where Ceq = C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15.

[0006] As a further improvement of one embodiment of the present invention, the acicular ferrite content of the welding steel sheet is 80% or more, and the acicular ferrite size is 15 μm or less.

[0007] As a further improvement of one embodiment of the present invention, the welding steel plate has a yield strength of ≥430 MPa, a tensile strength of 550-620 MPa, an elongation of ≥25%, and a -40°C impact load of ≥300 J.

[0008] As a further improvement of one embodiment of the present invention, the welding steel plate has a tensile strength of ≥ 540 MPa in the heat-affected zone of the weld and a -40°C impact load greater than 150 J under the condition of a welding heat input of 600 kJ / cm.

[0009] As a further improvement of one embodiment of the present invention, the crack resistance characteristics K of the welding steel plate ca ≥8500N / mm 1.5 That is the case.

[0010] One embodiment of the present invention further provides a method for manufacturing steel sheets for high heat input welding. This manufacturing method includes the following steps. The smelting process involves sequentially going through converter steelmaking, LF furnace refining, and RH furnace refining, and after RH refining, the molten steel is continuously cast into slabs using a continuous casting machine, with calcium zirconium core wire added during RH refining. Rolling process: The slab is heated at 1050-1150°C for at least 320 minutes. After heating, when the temperature reaches 900-1000°C, recrystallized band rolling is performed so that the single-pass reduction ratio is greater than 15% and the cumulative reduction ratio is greater than 50%. When the temperature drops below 860°C, non-recrystallized band rolling is performed so that the single-pass reduction ratio is greater than 15% and the cumulative reduction ratio of the non-recrystallized band rolling is greater than 60%. The temperature of the steel sheet obtained through recrystallized band rolling and non-recrystallized band rolling is set to be within a range of 30-50°C higher than the Ar3 temperature. Cooling process: After rolling is complete, the steel sheet is cooled to a temperature 20-40°C higher than the Bs temperature at a cooling rate greater than 10°C / s, and then the steel sheet is air-cooled to a temperature of 350°C or lower.

[0011] As a further improvement of one embodiment of the present invention, the area density of Ti, Mg, Zr, or Ca oxides in a slab formed by continuous casting is 1500 particles / mm³. 2 It is larger than that.

[0012] As a further improvement of one embodiment of the present invention, in the rolling process, Ar3 = 910-310C-80Mn-20Cu-15Cr-55Ni-80Mo-0.35(H-8), where H is the target steel sheet thickness, and Bs temperature = 630-45Mn-40V-35Si-30Cr-25Mo-20Ni-15W.

[0013] As a further improvement of one embodiment of the present invention, during converter steelmaking, the ratio of molten iron to clean scrap mass is (7-8):1, and the molten iron temperature is 1350-1450°C.

[0014] As a further improvement of one embodiment of the present invention, the continuous casting temperature is controlled to 1540-1560°C and the drawing speed is controlled to 1.1-1.3 m / min in the smelting process.

[0015] One or more technical solutions provided by embodiments of this application have at least the following technical effects or advantages:

[0016] One embodiment of the present invention rationally designs the content of the Ti+Mg+Zr+Ca composition to refine the crystal grains, contribute to the formation of acicular ferrite, and does not reduce elemental yield or increase costs. By adding Mn to the Cr, Ni, and Cu system and rationally designing the content of the Mn+Cr+Ni+Cu composition, the toughness of the steel sheet is ensured while maintaining a certain strength. By controlling the Cr / Ni / Cu ratio to 1:2:1, the hardenability and low-temperature toughness of the steel sheet are further improved. Combined with the TMCP process, the temperature is controlled for rolling in the recrystallized and non-recrystallized zones, respectively, and the rolling reduction ratio is controlled at the same time, thereby improving the crack resistance of the steel sheet by making the acicular ferrite content of the steel sheet 80% or more and the acicular ferrite size 15 μm or less. [Modes for carrying out the invention]

[0017] The present invention will be described in detail below in relation to specific embodiments, but these embodiments are not limiting to the present invention, and any changes in reaction conditions, reactants, or raw material usage made in accordance with these embodiments by those skilled in the art will all be within the scope of protection of the present invention.

[0018] One embodiment of the present invention provides a steel sheet for high heat input welding. This welding steel sheet has a chemical composition of C ≤ 0.1%, Si ≤ 0.15%, S ≤ 0.004% by mass%, with Mn + Cr + Ni + Cu: 1.5 to 4.5%, a Cr / Ni / Cu mass ratio of 1:2:1, Ti + Mg + Zr + Ca: 0.03 to 0.3%, of which Ti + Mg: 0.03 to 0.2%, the remainder being Fe and unavoidable impurities, and a carbon equivalent Ceq: 0.36 to 0.42%, where Ceq = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15, where C, Mn, Cr, Mo, V, Cu, and Ni are the mass percentage content of each element contained in the steel, and 0 is substituted if the element is not present. The sum / comparison calculation of each element is performed based on the mass percentage content of each element contained in the steel.

[0019] The actions and usage amounts of the components included in this invention will be described selectively and specifically below.

[0020] Carbon (C) significantly affects the strength, low-temperature toughness, elongation, and weldability of steel sheets, especially high-heat-input weldability. Controlling the carbon content in the steel to a low level improves the low-temperature toughness, crack resistance, crack resistance characteristics, and high-heat-input weldability angle of the steel sheet. However, from the perspective of steel sheet strength, microstructure control during production, and manufacturing costs, the carbon content should not be controlled too low. Based on this, the carbon content should be ≤0.1%.

[0021] Si: While Si can promote deoxidation of molten steel during smelting and improve steel sheet strength, it significantly damages the low-temperature toughness, elongation, and weldability of the steel sheet. Furthermore, in steel sheets with high Mn content, under high heat input welding conditions, Si promotes the formation of MA islands. The resulting MA islands are coarser in size and have a non-uniform distribution, causing significant damage to the low-temperature toughness, crack resistance, and crack resistance properties of the heat-affected zone. Therefore, it is necessary to control the Si content in the steel to be as low as possible.

[0022] S: S has a very detrimental effect as an impurity that is harmful to the low-temperature toughness of steel sheets. More importantly, S combines with Mn in steel to form MnS impurities. When the Mn content in the steel is high, the number and size of the formed MnS are large. MnS is plastic, and during hot rolling, MnS stretches along the rolling direction, forming a MnS impurity band along the rolling direction. This seriously affects the low-temperature impact toughness of the steel sheet, especially crack resistance and crack resistance properties (MnS is not only a crack initiation point, but also reduces the energy required for crack propagation, significantly decreasing crack propagation resistance), elongation, Z-direction performance, and weldability (especially high heat input weldability). At the same time, S is the main element that generates thermal brittleness during hot rolling. Theoretically, lower levels are better, but from the viewpoint of steelmaking operability, the S content needs to be controlled to ≤0.0040%.

[0023] Mn, Cr, Ni, Cu: Mn, Cr, Ni, and Cu are important solid solution strengthening elements in steel. By appropriate addition, they can improve the low-temperature toughness of the steel plate and play an important role in the formation of acicular ferrite. By controlling the ratio of Cr / Ni / Cu to 1:2:1, the low-temperature toughness of the steel plate can be further improved. When the total of Mn+Cr+Ni+Cu (mass%) is less than 1.5%, the hardenability of the steel plate is low and the formation of acicular ferrite is not easy. When the total of Mn+Cr+Ni+Cu (mass%) is higher than 4.5%, the low-temperature toughness of the steel plate is low. Therefore, by controlling the total of Mn+Cr+Ni+Cu (mass%) to 1.5 - 4.5%, the steel plate has high low-temperature toughness and the formation of acicular ferrite is easy during phase transition. Furthermore, the single content of Mn, Cr, Ni, and Cu is not unique, and the content of Mn, Cr, Ni, and Cu elements can be adjusted respectively according to other different performances of the steel material.

[0024] Ti, Mg, Zr, Ca: Ti, Mg, Zr, and Ca are important elements in the formation of oxide inclusions. By adding an appropriate amount, they can refine crystal grains and play an important role in the formation of acicular ferrite. During the welding heat cycle of the steel, such oxide inclusions can be induced to promote the nucleation of intragranular ferrite, reduce the formation of ferrite at grain boundaries or upper bainite laths, and improve the low-temperature impact toughness of the heat-affected zone of the weld. Furthermore, similar to the Mn, Cr, Ni, and Cu elements, the single content of Ti, Mg, Zr, and Ca is not unique, and the content of Ti, Mg, Zr, and Ca elements can be adjusted respectively according to other different performances of the steel material.

[0025] As described above, compared with the prior art, in the design of the chemical composition in the present invention, by reasonably designing the total amount of Ti+Mg+Zr+Ca, Ti, Mg, Zr, and Ca oxides can effectively promote the formation of acicular ferrite. By reasonably designing the total amount of Mn+Cr+Ni+Cu and controlling the ratio of Cr / Ni / Cu, the hardenability and low-temperature toughness of the steel plate can be improved while maintaining a certain strength of the steel plate.

[0026] Specifically, in terms of mechanical properties, as proven by many experimental studies, the yield strength of the welding steel plate is ≧430 MPa, the tensile strength is between 550 and 620 MPa, the elongation rate is ≧25%, the -40°C impact load is ≧300 J, and the crack resistance property K ca ≧8500 N / mm 1.5 and, under the condition of a welding heat input of 600 kJ / cm, the tensile strength of the heat-affected zone of the weld is ≧540 MPa and the -40°C impact load is ≧150 J.

[0027] In one embodiment, a method for manufacturing a high heat input welding steel plate is further provided. This manufacturing method includes the following steps. (1) Steelmaking process: Through converter steelmaking, LF furnace refining, and RH furnace refining in sequence, after RH refining, the molten steel is continuously cast into slabs by a continuous caster. Here, during RH refining, a calcium zirconium cored wire is added. Hereinafter, preferred examples of each step of the steelmaking process will be described in detail.

[0028] a) Converter steelmaking: The ratio of molten iron amount to clean scrap is (7 - 8):1, the steelmaking temperature of the molten iron is 1350 - 1450°C, ferromanganese, ferrosilicon, and lime are sequentially added to the molten iron for steelmaking, and the steel material is discharged after steelmaking.

[0029] b) LF furnace refining: After discharging the steel material from the converter, elements such as Mn, Cr, Ni, Cu, Ti, and Mg are added to the molten steel, where Mn + Cr + Ni + Cu in the molten steel satisfies 1.5 - 4.5% by mass, the mass ratio of Cr / Ni / Cu is 1:2:1, and Ti + Mg satisfies 0.03 - 0.2%.

[0030] c) RH furnace refining: During RH refining, a calcium zirconium cored wire is added to the molten steel, and Ti + Mg + Zr + Ca in the molten steel satisfies 0.03 - 0.3% by mass.

[0031] d) Continuous casting: Control the continuous casting temperature at 1540 - 1560°C and the drawing speed at 1.1 - 1.3 m / min.

[0032] By controlling the total amount of Mn+Cr+Ni+Cu to 1.5-4.5% and the Cr / Ni / Cu ratio to 1:2:1, the hardenability of the steel sheet is effectively improved, low-temperature toughness is enhanced, and the strength of the steel sheet is maintained. Ti, Mg, Zr, and Ca oxides effectively prevent the growth of austenite grains in the heat-affected zone of the weld, while simultaneously promoting the nucleation of intragranular acicular ferrite, thereby improving the low-temperature toughness of the heat-affected zone during high-heat input welding. Adding Zr and Ca, as in core-spun yarn, diffuses oxide particles while refining their size, further promoting the formation of acicular ferrite. Among Ti, Mg, Zr, and Ca, a high ratio of Ti to Mg effectively reduces production costs.

[0033] (2) Rolling process: The slab is heated at 1050-1150°C for at least 320 minutes. After heating, when the temperature reaches 900-1000°C, recrystallized band rolling is performed so that the single-pass reduction ratio is greater than 15% and the cumulative reduction ratio is greater than 50%. When the temperature drops to 860°C or below, non-recrystallized band rolling is performed so that the single-pass reduction ratio is greater than 15% and the cumulative reduction ratio of the non-recrystallized band rolling is greater than 60%. The temperature of the steel sheet obtained through recrystallized band rolling and non-recrystallized band rolling is within a range of 30-50°C higher than the Ar3 temperature.

[0034] The slab is rolled in the recrystallization zone, and the grains are refined by external forces at high temperatures. However, there is a certain limit to grain refinement in the recrystallization zone, so pre-recrystallization zone rolling is performed. This allows the refined austenite to continue to be compressed and elongated, increasing the grain boundary area of ​​austenite per unit volume and increasing the nucleation sites and nucleation rate of ferrite. By controlling the Cr / Ni / Cu ratio and the total amount of Ti, Mg, Zr, and Ca, in combination with recrystallization zone rolling and pre-recrystallization zone rolling, the ratio of acicular ferrite structure in the metal structure is made to 80% or more, improving the crack resistance of the steel sheet.

[0035] (3) Cooling process: After rolling is complete, the steel plates are transported to an ACC (accelerated cooling control) device at the maximum transport speed of the transport roller conveyor, and the steel plates are cooled in the ACC device at a cooling rate greater than 10°C / s to a range 20 to 40°C above the Bs temperature, and then the steel plates are air-cooled to below 350°C.

[0036] After rolling is complete, the steel is rapidly cooled to a temperature 20-40°C higher than the Bs temperature, followed by air cooling. Rapid cooling at the Bs temperature promotes bainite formation, reducing the strength of the steel sheet.

[0037] Here, in the rolling process, Ar3 = 910 - 310C - 80Mn - 20Cu - 15Cr - 55Ni - 80Mo - 0.35(H-8), where H is the target steel sheet thickness, and Bs = 630 - 45Mn - 40V - 35Si - 30Cr - 25Mo - 20Ni - 15W. In the above formula, C, Mn, Cu, Cr, Ni, Mo, V, Si, and W are the mass %) of each element contained in the steel.

[0038] Furthermore, the area density of Ti, Mg, Zr, or Ca oxides in the slab formed by continuous casting is 1500 particles / mm². 2 These oxides are larger than those found in other heat-affected zones (HATZs), and can effectively prevent the growth of austenite grains in the heat-affected zone and promote the formation of acicular ferrite, thereby ensuring excellent performance in the HATZs

[0039] The technical solutions of this application will be further described below in relation to several specific embodiments.

[0040] Example 1 This first embodiment provides a steel sheet for high heat input welding. The chemical composition of the steel sheet, in weight percent, is: C: 0.08%, Si: 0.15%, S: 0.002%, Mn: 1.55%, Cr: 0.15%, Ni: 0.3%, Cu: 0.15%, Ti: 0.03%, Mg: 0.0015%, Zr: 0.0015%, Ca: 0.0015%, with the remainder being Fe and unavoidable impurities.

[0041] The steps for manufacturing the high-heat-input steel plate described above are as follows: (1) Smelting process: a) Converter smelting: The ratio of molten iron to clean scrap is 7:1, the molten iron smelting temperature is 1350-1450°C, and ferromanganese, ferrosilicon, and lime are added sequentially to the molten iron during smelting. After smelting is complete, the steel material is discharged.

[0042] b) LF furnace refining: After discharging the steel material from the converter, elements Mn, Cr, Ni, Cu, Ti, and Mg are added to the molten steel according to the chemical composition of the welding steel sheet, the temperature is measured, and a sample is taken. When the elements satisfy the requirements of the chemical composition of the welding steel sheet, the steel material is discharged.

[0043] c) RH furnace refining: During RH refining, calcium zirconium core wire is added to the molten steel, and the Zr and Ca content in the molten steel is all 0.0015% by mass. Before discharge of the steel, ultra-low carbon dioxide rice husks are added to maintain the temperature.

[0044] d) Continuous casting: The casting temperature is controlled to 1550°C and the drawing speed is controlled to 1.2 m / min to produce a continuously cast slab with a thickness of 320 mm.

[0045] (2) Rolling process: The slab produced in the smelting process was heated at 1050°C for 330 minutes. After heating, recrystallization zone rolling was performed. The rolling start temperature for recrystallization zone rolling was 950°C, the reduction rate per pass was 16%, and it was rolled four times. The final rolling temperature for recrystallization zone rolling was 900°C. Non-recrystallization zone rolling was then performed. The rolling start temperature for non-recrystallization zone rolling was 850°C, the reduction rate per pass was 16%, and it was rolled five times. The final rolling temperature for non-recrystallization zone rolling was 770°C, resulting in a steel plate with a thickness of 66 mm.

[0046] (3) Cooling process: After rolling is complete, the steel plates are transported to the ACC device at the maximum conveying speed of the roller conveyor. In the ACC device, the steel plates are cooled to 580°C at a cooling rate of 10.5°C / s, and then air-cooled to below 350°C.

[0047] Example 2 This second embodiment provides a steel sheet for high heat input welding. The chemical composition of the steel sheet, in weight percent, is: C: 0.07%, Si: 0.15%, S: 0.002%, Mn: 1.6%, Cr: 0.2%, Ni: 0.4%, Cu: 0.2%, Ti: 0.03%, Mg: 0.0015%, Zr: 0.0015%, Ca: 0.0015%, with the remainder being Fe and unavoidable impurities.

[0048] The steps for manufacturing the high-heat-input steel plate described above are as follows: (1) Smelting process: a) Converter smelting: The ratio of molten iron to clean scrap is 8:1, the molten iron smelting temperature is 1350-1450°C, and ferromanganese, ferrosilicon, and lime are added sequentially to the molten iron during smelting. After smelting is complete, the steel material is discharged.

[0049] b) LF furnace refining: After discharging the steel material from the converter, elements Mn, Cr, Ni, Cu, Ti, and Mg are added to the molten steel according to the chemical composition of the welding steel sheet, the temperature is measured, and a sample is taken. When the elements satisfy the requirements of the chemical composition of the welding steel sheet, the steel material is discharged.

[0050] c) RH furnace refining: During RH refining, calcium zirconium core wire is added to the molten steel, and the Zr and Ca content in the molten steel is all 0.0015% by mass. Before discharge of the steel, ultra-low carbon dioxide rice husks are added to maintain the temperature.

[0051] d) Continuous casting: The casting temperature is controlled to 1540°C and the drawing speed is controlled to 1.1 m / min to produce a continuously cast slab with a thickness of 320 mm.

[0052] (2) Rolling process: The slab produced in the smelting process was heated at 1150°C for 335 minutes. After heating, recrystallization zone rolling was performed. The starting temperature for recrystallization zone rolling was 970°C, the reduction rate per pass was 16%, and it was rolled four times. The final rolling temperature for recrystallization zone rolling was 920°C. Non-recrystallization zone rolling was then performed. The starting temperature for non-recrystallization zone rolling was 840°C, the reduction rate per pass was 16%, and it was rolled five times. The final rolling temperature for non-recrystallization zone rolling was 760°C, resulting in a steel plate with a thickness of 66 mm.

[0053] (3) Cooling process: After rolling is complete, the steel plates are transported to the ACC device at the maximum conveying speed of the roller conveyor, where they are cooled to 575°C at a cooling rate of 10.3°C / s, and then air-cooled to below 350°C.

[0054] Example 3 This third example provides a steel sheet for high heat input welding. The chemical composition of the steel sheet, in weight percent, is: C: 0.08%, Si: 0.10%, S: 0.002%, Mn: 1.55%, Cr: 0.15%, Ni: 0.3%, Cu: 0.15%, Ti: 0.03%, Mg: 0.002%, Zr: 0.002%, Ca: 0.002%, with the remainder being Fe and unavoidable impurities.

[0055] The steps for manufacturing the high-heat-input steel plate described above are as follows: (1) Smelting process: a) Converter smelting: The ratio of molten iron to clean scrap is 7:1, and the molten iron smelting temperature is 1350-1450°C. Ferromanganese, ferrosilicon, and lime are added sequentially to the molten iron during smelting, and the steel material is discharged after smelting is complete.

[0056] b) LF furnace refining: After discharging the steel material from the converter, elements Mn, Cr, Ni, Cu, Ti, and Mg are added to the molten steel according to the chemical composition of the welding steel sheet, the temperature is measured, and a sample is taken. When the elements satisfy the requirements of the chemical composition of the welding steel sheet, the steel material is discharged.

[0057] c) RH furnace refining: During RH refining, calcium zirconium core wire is added to the molten steel, and the Zr and Ca content in the molten steel is all 0.002% by mass. Before discharge of the steel, ultra-low carbon dioxide rice husks are added to maintain the temperature.

[0058] d) Continuous casting: The casting temperature is controlled to 1560°C and the drawing speed is controlled to 1.3 m / min to produce a continuously cast slab with a thickness of 320 mm.

[0059] (2) Rolling process: The slab produced in the smelting process was heated at 1100°C for 332 minutes. After heating, recrystallization zone rolling was performed. The rolling start temperature for recrystallization zone rolling was 960°C, the reduction rate per pass was 16%, and it was rolled four times. The final rolling temperature for recrystallization zone rolling was 910°C. Non-recrystallization zone rolling was then performed. The rolling start temperature for non-recrystallization zone rolling was 855°C, the reduction rate per pass was 16%, and it was rolled five times. The final rolling temperature for non-recrystallization zone rolling was 770°C, resulting in a steel plate with a thickness of 66 mm.

[0060] (3) Cooling process: After rolling is complete, the steel plates are transported to the ACC device at the maximum conveying speed of the roller conveyor. In the ACC device, the steel plates are cooled to 580°C at a cooling rate of 10.2°C / s, and then air-cooled to below 350°C.

[0061] Example 4 This embodiment 4 provides a steel sheet for high heat input welding. The chemical composition of the steel sheet is as follows (by weight%): C: 0.08%, Si: 0.15%, S: 0.002%, Mn: 1.5%, Cr: 0.15%, Ni: 0.3%, Cu: 0.15%, Ti: 0.03%, Mg: 0.002%, Zr: 0.0015%, Ca: 0.0015%, with the remainder being Fe and unavoidable impurities.

[0062] The steps for manufacturing the high-heat-input steel plate described above are as follows: (1) Smelting process: a) Converter smelting: The ratio of molten iron to clean scrap is 7:1, the molten iron smelting temperature is 1350-1450°C, and ferromanganese, ferrosilicon, and lime are added sequentially to the molten iron during smelting. After smelting is complete, the steel material is discharged.

[0063] b) LF furnace refining: After discharging the steel material from the converter, elements Mn, Cr, Ni, Cu, Ti, and Mg are added to the molten steel according to the chemical composition of the welding steel sheet, the temperature is measured, and a sample is taken. When the elements satisfy the requirements of the chemical composition of the welding steel sheet, the steel material is discharged.

[0064] c) RH furnace refining: During RH refining, calcium zirconium core wire is added to the molten steel, and the Zr and Ca content in the molten steel is all 0.0015% by mass. Before discharge of the steel, ultra-low carbon dioxide rice husks are added to maintain the temperature.

[0065] d) Continuous casting: The casting temperature is controlled to 1550°C and the drawing speed is controlled to 1.2 m / min to produce a continuously cast slab with a thickness of 320 mm.

[0066] (2) Rolling process: The slab produced in the smelting process was heated at 1050°C for 330 minutes. After heating, recrystallization zone rolling was performed. The rolling start temperature for recrystallization zone rolling was 950°C, the reduction rate per pass was 16%, and it was rolled four times. The final rolling temperature for recrystallization zone rolling was 900°C. Non-recrystallization zone rolling was then performed. The rolling start temperature for non-recrystallization zone rolling was 850°C, the reduction rate per pass was 16%, and it was rolled five times. The final rolling temperature for non-recrystallization zone rolling was 770°C, resulting in a steel plate with a thickness of 66 mm.

[0067] (3) Cooling process: After rolling is complete, the steel plates are transported to the ACC device at the maximum conveying speed of the roller conveyor. In the ACC device, the steel plates are cooled to 580°C at a cooling rate of 10.5°C / s, and then air-cooled to below 350°C.

[0068] Example 5 This Example 5 provides a steel sheet for high heat input welding. The chemical composition of the steel sheet, in weight percent, is: C: 0.07%, Si: 0.15%, S: 0.002%, Mn: 1.55%, Cr: 0.2%, Ni: 0.4%, Cu: 0.2%, Ti: 0.03%, Mg: 0.0015%, Zr: 0.0015%, Ca: 0.0015%, with the remainder being Fe and unavoidable impurities.

[0069] The steps for manufacturing the high-heat-input steel plate described above are as follows: (1) Smelting process: a) Converter smelting: The ratio of molten iron to clean scrap is 8:1, the molten iron smelting temperature is 1350-1450°C, and ferromanganese, ferrosilicon, and lime are added sequentially to the molten iron during smelting. After smelting is complete, the steel material is discharged.

[0070] b) LF furnace refining: After discharging the steel material from the converter, elements Mn, Cr, Ni, Cu, Ti, and Mg are added to the molten steel according to the chemical composition of the welding steel sheet, the temperature is measured, and a sample is taken. When the elements satisfy the requirements of the chemical composition of the welding steel sheet, the steel material is discharged.

[0071] c) RH furnace refining: During RH refining, calcium zirconium core wire is added to the molten steel, and the Zr and Ca content in the molten steel is all 0.0015% by mass. Before discharge of the steel, ultra-low carbon dioxide rice husks are added to maintain the temperature.

[0072] d) Continuous casting: The casting temperature is controlled to 1540°C and the drawing speed is controlled to 1.1 m / min to produce a continuously cast slab with a thickness of 320 mm.

[0073] (2) Rolling process: The slab produced in the smelting process was heated at 1150°C for 335 minutes. After heating, recrystallization zone rolling was performed. The starting temperature for recrystallization zone rolling was 970°C, the reduction rate per pass was 16%, and it was rolled four times. The final rolling temperature for recrystallization zone rolling was 925°C. Non-recrystallization zone rolling was then performed. The starting temperature for non-recrystallization zone rolling was 850°C, the reduction rate per pass was 16%, and it was rolled five times. The final rolling temperature for non-recrystallization zone rolling was 760°C, resulting in a steel plate with a thickness of 66 mm.

[0074] (3) Cooling process: After rolling is complete, the steel plates are transported to the ACC device at the maximum conveying speed of the roller conveyor. In the ACC device, the steel plates are cooled to 580°C at a cooling rate of 10.1°C / s, and then air-cooled to below 350°C.

[0075] Example 6 This embodiment 6 provides a steel sheet for high heat input welding. The chemical composition of the steel sheet is as follows (by weight%): C: 0.07%, Si: 0.10%, S: 0.002%, Mn: 1.55%, Cr: 0.18%, Ni: 0.36%, Cu: 0.18%, Ti: 0.03%, Mg: 0.002%, Zr: 0.002%, Ca: 0.002%, with the remainder being Fe and unavoidable impurities.

[0076] The steps for manufacturing the high-heat-input steel plate described above are as follows: (1) Smelting process: a) Converter smelting: The ratio of molten iron to clean scrap is 7:1, the molten iron smelting temperature is 1350-1450°C, and ferromanganese, ferrosilicon, and lime are added sequentially to the molten iron during smelting. After smelting is complete, the steel material is discharged.

[0077] b) LF furnace refining: After discharging the steel material from the converter, elements Mn, Cr, Ni, Cu, Ti, and Mg are added to the molten steel according to the chemical composition of the welding steel sheet, the temperature is measured, and a sample is taken. When the elements satisfy the requirements of the chemical composition of the welding steel sheet, the steel material is discharged.

[0078] c) RH furnace refining: During RH refining, calcium zirconium core wire is added to the molten steel, and the Zr and Ca content in the molten steel is all 0.002% by mass. Before discharge of the steel, ultra-low carbon dioxide rice husks are added to maintain the temperature.

[0079] d) Continuous casting: The casting temperature is controlled to 1560°C and the drawing speed to 1.3 m / min to produce a continuously cast slab with a thickness of 320 mm.

[0080] (2) Rolling process: The slab produced in the smelting process was heated at 1100°C for 332 minutes. After heating, recrystallization zone rolling was performed. The rolling start temperature for recrystallization zone rolling was 960°C, the reduction rate per pass was 16%, and it was rolled four times. The final rolling temperature for recrystallization zone rolling was 910°C. Non-recrystallization zone rolling was then performed. The rolling start temperature for non-recrystallization zone rolling was 855°C, the reduction rate per pass was 16%, and it was rolled five times. The final rolling temperature for non-recrystallization zone rolling was 770°C, resulting in a steel plate with a thickness of 66 mm.

[0081] (3) Cooling process: After rolling is complete, the steel plates are transported to the ACC device at the maximum conveying speed of the roller conveyor. In the ACC device, the steel plates are cooled to 580°C at a cooling rate of 10.2°C / s, and then air-cooled to below 350°C.

[0082] Example 7 This embodiment 7 provides a steel sheet for high heat input welding. The chemical composition of the steel sheet is as follows (by weight%): C: 0.08%, Si: 0.15%, S: 0.002%, Mn: 1.55%, Cr: 0.15%, Ni: 0.3%, Cu: 0.15%, Ti: 0.03%, Mg: 0.0015%, Zr: 0.002%, Ca: 0.002%, with the remainder being Fe and unavoidable impurities.

[0083] The steps for manufacturing the high-heat-input steel plate described above are as follows: (1) Smelting process: a) Converter smelting: The ratio of molten iron to clean scrap is 7:1, the molten iron smelting temperature is 1350-1450°C, and ferromanganese, ferrosilicon, and lime are added sequentially to the molten iron during smelting. After smelting is complete, the steel material is discharged.

[0084] b) LF furnace refining: After discharging the steel material from the converter, elements Mn, Cr, Ni, Cu, Ti, and Mg are added to the molten steel according to the chemical composition of the welding steel sheet, the temperature is measured, and a sample is taken. When the elements satisfy the requirements of the chemical composition of the welding steel sheet, the steel material is discharged.

[0085] c) RH furnace refining: During RH refining, calcium zirconium core wire is added to the molten steel, and the Zr and Ca content in the molten steel is all 0.002% by mass. Before discharge of the steel, ultra-low carbon dioxide rice husks are added to maintain the temperature.

[0086] d) Continuous casting: The casting temperature is controlled to 1550°C and the drawing speed is controlled to 1.2 m / min to produce a continuously cast slab with a thickness of 320 mm.

[0087] (2) Rolling process: The slab produced in the smelting process was heated at 1050°C for 330 minutes. After heating, recrystallization zone rolling was performed. The rolling start temperature for recrystallization zone rolling was 950°C, the reduction rate per pass was 16%, and it was rolled four times. The final rolling temperature for recrystallization zone rolling was 900°C. Non-recrystallization zone rolling was then performed. The rolling start temperature for non-recrystallization zone rolling was 850°C, the reduction rate per pass was 16%, and it was rolled five times. The final rolling temperature for non-recrystallization zone rolling was 770°C, resulting in a steel plate with a thickness of 66 mm.

[0088] (3) Cooling process: After rolling is complete, the steel plates are transported to the ACC device at the maximum conveying speed of the roller conveyor. In the ACC device, the steel plates are cooled to 580°C at a cooling rate of 10.5°C / s, and then air-cooled to below 350°C.

[0089] Example 8 This embodiment 8 provides a steel sheet for high heat input welding. The chemical composition of the steel sheet is as follows (by weight%): C: 0.07%, Si: 0.15%, S: 0.002%, Mn: 1.6%, Cr: 0.2%, Ni: 0.4%, Cu: 0.2%, Ti: 0.03%, Mg: 0.0015%, Zr: 0.002%, Ca: 0.002%, with the remainder being Fe and unavoidable impurities.

[0090] The steps for manufacturing the high-heat-input steel plate described above are as follows: (1) Smelting process: a) Converter smelting: The ratio of molten iron to clean scrap is 8:1, the molten iron smelting temperature is 1350-1450°C, and ferromanganese, ferrosilicon, and lime are added sequentially to the molten iron during smelting. After smelting is complete, the steel material is discharged.

[0091] b) LF furnace refining: After discharging the steel material from the converter, elements Mn, Cr, Ni, Cu, Ti, and Mg are added to the molten steel according to the chemical composition of the welding steel sheet, the temperature is measured, and a sample is taken. When the elements satisfy the requirements of the chemical composition of the welding steel sheet, the steel material is discharged.

[0092] c) RH furnace refining: During RH refining, calcium zirconium core wire is added to the molten steel, and the Zr and Ca content in the molten steel is all 0.002% by mass. Before discharge of the steel, ultra-low carbon dioxide rice husks are added to maintain the temperature.

[0093] d) Continuous casting: The casting temperature is controlled to 1555°C and the drawing speed to 1.2 m / min to produce a continuously cast slab with a thickness of 320 mm.

[0094] (2) Rolling process: The slab produced in the smelting process was heated at 1150°C for 335 minutes. After heating, recrystallization zone rolling was performed. The starting temperature for recrystallization zone rolling was 970°C, the reduction rate per pass was 16%, and it was rolled four times. The final rolling temperature for recrystallization zone rolling was 920°C. Non-recrystallization zone rolling was then performed. The starting temperature for non-recrystallization zone rolling was 840°C, the reduction rate per pass was 16%, and it was rolled five times. The final rolling temperature for non-recrystallization zone rolling was 760°C, resulting in a steel plate with a thickness of 66 mm.

[0095] (3) Cooling process: After rolling is complete, the steel plates are transported to the ACC device at the maximum conveying speed of the roller conveyor. In the ACC device, the steel plates are cooled to 580°C at a cooling rate of 10.2°C / s, and then air-cooled to below 350°C.

[0096] [Table 1]

[0097] Table 1 shows the performance of the steel plates described in Examples 1 to 8. As can be seen from Table 1, the yield strength of the steel plate base material is greater than 430 MPa in all cases, the tensile strength is between 550 and 620 MPa, the elongation is 25% or more, the impact load at -40°C is 300 J or more, and under the condition of a welding heat input of 600 kJ / cm, the tensile strength of the heat-affected zone of the weld is 540 MPa or more, and the impact load at -40°C is 150 J or more. Crack resistance characteristic K ca It is 8500 N / mm 1.5 That's all.

[0098] Naturally, the above embodiments are merely illustrative for clarity and do not limit the embodiments. Those skilled in the art can make other different variations and modifications based on the above description. It is not possible to exhaustively list all embodiments in this specification. Any obvious variations and modifications derived therefrom are included within the scope of protection of the present invention.

Claims

1. A steel sheet for high heat input welding, characterized by a chemical composition of 0.07 ≤ C ≤ 0.1%, Si ≤ 0.15%, S ≤ 0.004%, 1.5% ≤ Mn ≤ 1.6%, and Mn + Cr + Ni + Cu: 2.1 to 2.4% by mass%, with a Cr / Ni / Cu mass ratio of 1:2:1, Ti + Mg + Zr + Ca: 0.03 to 0.3%, of which Ti + Mg: 0.03 to 0.2%, the remainder being Fe and unavoidable impurities, and a carbon equivalent Ceq: 0.36 to 0.42%, where Ceq = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15.

2. The steel sheet for welding with high heat input according to claim 1, characterized in that the acicular ferrite content of the welding steel sheet is 80% or more, and the acicular ferrite size is 15 μm or less.

3. The steel sheet for welding with high heat input according to claim 1, characterized in that the yield strength of the welding steel sheet is ≥ 430 MPa, the tensile strength is 550 to 620 MPa, the elongation is ≥ 25%, and the impact load at -40°C is ≥ 300 J.

4. Cracking resistance characteristics K of the aforementioned welded steel plate ｃａ ≥8500 N / mm １．５ The steel plate for high heat input welding according to feature 1.

5. A method for producing a steel plate for high heat input welding according to claim 1, A process in which molten steel is continuously cast into slabs using a continuous casting machine after sequentially going through converter steelmaking, LF furnace refining, and RH furnace refining, wherein a smelting step is performed in which calcium zirconium core wire is added during RH refining, The slab is heated to 1050-1150°C for at least 320 mins. After heating, when the temperature reaches 900-1000°C, recrystallized band rolling is performed so that the single-pass reduction ratio is greater than 15% and the cumulative reduction ratio is greater than 50%. When the temperature drops below 860°C, non-recrystallized band rolling is performed so that the single-pass reduction ratio is greater than 15% and the cumulative reduction ratio of the non-recrystallized band rolling is greater than 60%. The steel sheet temperature obtained after recrystallized band rolling and non-recrystallized band rolling is set to Ar ３ A rolling process in which the temperature is within a range of 30 to 50°C higher than the normal temperature, A method for producing steel sheets for high heat input welding, characterized by comprising a cooling step of cooling the steel sheet to a range 20 to 40°C higher than the Bs temperature at a cooling rate greater than 10°C / s after the completion of rolling, and then air-cooling the steel sheet to 350°C or below.

6. The area density of Ti, Mg, Zr, or Ca oxides in slabs formed by continuous casting is 1500 particles / mm². ２ A method for producing a large heat input welding steel plate according to claim 5, characterized in that it is larger than the specified size.

7. In the rolling process, Ar ３ The method for producing a steel sheet for high heat input welding according to claim 5, characterized in that = 910 - 310C - 80Mn - 20Cu - 15Cr - 55Ni - 80Mo - 0.35(H - 8), where H is the target steel sheet thickness, and Bs temperature = 630 - 45Mn - 40V - 35Si - 30Cr - 25Mo - 20Ni - 15W.

8. The method for producing steel plates for high heat input welding according to claim 5, characterized in that, during the converter steelmaking process, the mass ratio of molten iron to clean scrap is (7-8):1, and the molten iron temperature is 1350-1450°C.

9. The method for producing high-heat-input steel plates for welding according to claim 5, characterized in that the continuous casting temperature is controlled to 1540 to 1560°C and the drawing speed is controlled to 1.1 to 1.3 m / min in the smelting process.

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