Steel plate for large heat input welding and its manufacturing method

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 production, and in particular to a steel plate for high heat input welding and a method for producing the same. [Background technology]

[0002] Large heat input welding steel can receive large energy during welding, and the low temperature toughness of the welded heat affected zone is stable, so that the welding efficiency can be improved. Crack resistance is an index that reflects the ability to resist crack propagation, and good crack resistance indicates that the ability to resist crack propagation is excellent, which can better prevent brittle fracture and ensure the safety of parts and components.

[0003] In recent years, with the increase in size of container ships, the shipping industry has been placing increasing demands on the performance of steel plates, particularly for crack resistance and high heat input welding. In the prior art, there are few reports on crack-resistant steels that can be welded with high heat input, and usually, steel materials have excellent crack resistance and crack resistance but cannot be welded with high heat input, or can be welded with high heat input but have insufficient crack resistance and crack resistance. Therefore, in order to meet the needs of container ships that are becoming larger, it is necessary to provide steel plates for large heat input welding that have excellent crack resistance and crack resistance. Summary of the Invention

[0004] The objective of the present invention is to provide a steel plate for large heat input welding, which can meet the welding needs of a welding heat input of 600 kJ / cm and has a crack resistance K ca ≧8500N / mm 1.5 This solves the problem in the prior art that the steel material cannot combine high heat input welding with excellent crack resistance.

[0005] In order to achieve the above object of the invention, one embodiment of the present invention provides a steel plate for large heat input welding, which 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.

[0006] As a further refinement of one embodiment of the present invention, the acicular ferrite content of said steel plate for welding is equal to or greater than 80% and the acicular ferrite size is equal to or less than 15 μm.

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

[0008] As a further improvement of one embodiment of the present invention, the welding steel plate has a tensile strength of the welded heat affected zone ≧540MPa and a −40° C. impact load of greater than 150J 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 K ca ≧8500N / mm 1.5 It is.

[0010] An embodiment of the present invention further provides a method for manufacturing a steel plate for high heat input welding, the method comprising the following steps: Smelting process: The steel is made in a converter, then in a LF furnace, and finally in a RH furnace. After the RH refining, the molten steel is continuously cast into a slab by a continuous casting machine. Calcium zirconium core wire is added during the RH refining. Rolling process: The slab is heated between 1050 and 1150 °C for at least 320 min. After the heating is completed, when the temperature reaches 900 to 1000 °C, recrystallized zone rolling is performed so that the one-pass reduction is greater than 15% and the cumulative reduction is greater than 50%. When the temperature drops to 860 °C or less, unrecrystallized zone rolling is performed so that the one-pass reduction is greater than 15% and the cumulative reduction of unrecrystallized zone rolling is greater than 60%. The steel sheet temperature obtained through recrystallized zone rolling and unrecrystallized zone rolling is measured by Ar. 3 The temperature should be within a range of 30 to 50 degrees Celsius higher than the Cooling step: After the rolling is completed, the steel plate is cooled to a temperature 20 to 40°C higher than the Bs temperature at a cooling rate of 10°C / s or more, and then the steel plate is air-cooled to 350°C or less.

[0011] In a further refinement of an embodiment of the present invention, the areal density of Ti, Mg, Zr or Ca oxides in the slab formed by continuous casting is 1500 particles / mm 2 Greater than.

[0012] In a further refinement of one embodiment of the present invention, the rolling step further comprises adding Ar 3 = 910-310C-80Mn-20Cu-15Cr-55Ni-80Mo-0.35 (H-8), where H is the target steel plate 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 said converter steelmaking, the mass ratio of molten iron to clean scrap is (7-8):1, and the temperature of molten iron is 1350-1450°C.

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

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

[0016] In one embodiment of the present invention, the content of Ti+Mg+Zr+Ca composition is rationally designed to refine crystal grains and contribute to the formation of acicular ferrite without reducing element yield and increasing costs; Mn element is added to Cr, Ni, Cu system, and the content of Mn+Cr+Ni+Cu composition is rationally designed to ensure the toughness of the steel plate and at the same time have a certain strength; the ratio of Cr / Ni / Cu is controlled to 1:2:1 to further improve the hardenability and low temperature toughness of the steel plate; and, in combination with the TMCP process, the steel plate is rolled at a controlled temperature in the recrystallized zone and the non-recrystallized zone, while controlling the rolling reduction rate at the same time, so that the acicular ferrite content of the steel plate is 80% or more and the acicular ferrite size is 15μm or less, thereby improving the crack resistance of the steel plate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention will be described in detail below with reference to specific embodiments, but these embodiments do not limit the present invention, and those skilled in the art will recognize that any changes in reaction conditions, amounts of reactants or raw materials used according to these embodiments are all within the scope of protection of the present invention.

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

[0019] The effects and amounts of the components contained in the present invention will now be selectively and specifically explained.

[0020] C: C has a great influence on the strength, low-temperature toughness, elongation and weldability of steel plate, especially large heat input weldability, and improves the low-temperature toughness, crack resistance and crack resistance properties and large heat input weldability angle of steel plate, so the C content in steel is controlled low. However, from the viewpoint of the strength of steel plate, microstructure control during production and manufacturing, and manufacturing cost, the C content should not be controlled too low. Based on this, the C content is ≦0.1%.

[0021] Si: Si can promote the deoxidation of molten steel during smelting and improve the strength of steel plate, but it can also significantly damage the low-temperature toughness, elongation and weldability of steel plate. When steel plate with a high Mn content is welded under high heat input conditions, Si promotes the formation of MA islands, which makes the size of the MA islands formed coarser and the distribution uneven, resulting in serious damage to the low-temperature toughness and crack resistance and crack resistance properties of the weld heat affected zone. Therefore, the Si content in steel should be controlled as low as possible.

[0022] S: As a harmful impurity to the low temperature toughness of steel plate, S has a very harmful effect. More importantly, S is combined with Mn in steel to form MnS impurities. When the Mn content in steel is high, the number of MnS formed is large and the size is huge. MnS has plasticity. During hot rolling, MnS elongates along the rolling direction, and a MnS impurity band along the rolling direction is formed, which has a serious effect on the low temperature impact toughness of steel plate, especially the crack resistance and crack resistance properties (MnS is not only the crack initiation point, but also reduces the energy required for crack propagation, greatly reducing the crack propagation resistance), elongation, Z direction performance, weldability (especially large heat input weldability), and at the same time, S is the main element that generates hot brittleness during hot rolling. In theory, the lower the better, but from the perspective of steelmaking operability, the S content should be controlled to ≦0.0040%.

[0023] Mn, Cr, Ni, Cu: Mn, Cr, Ni, and Cu are important solid solution strengthening elements of steel, and their appropriate addition improves the low-temperature toughness of steel plate and plays 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 steel plate can be further improved. When the sum (mass%) of Mn+Cr+Ni+Cu is less than 1.5%, the hardenability of steel plate is low and the formation of acicular ferrite is not easy, and when the sum (mass%) of Mn+Cr+Ni+Cu is higher than 4.5%, the low-temperature toughness of steel plate is low. Therefore, by controlling the sum (mass%) of Mn+Cr+Ni+Cu to 1.5-4.5%, the low-temperature toughness of steel plate is high 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 contents of Mn, Cr, Ni, and Cu elements can be adjusted respectively according to other different performances of steel material.

[0024] Ti, Mg, Zr, Ca: Ti, Mg, Zr, Ca are important elements in the formation of oxide inclusions, and the addition of appropriate amounts can refine the crystal grains and play an important role in the formation of acicular ferrite. During the welding heat cycle of steel, such oxide inclusions can be induced to promote the nucleation of intracrystalline ferrite, reduce the formation of ferrite at the grain boundary or the formation of upper bainite lath, and improve the low-temperature impact toughness of the weld heat affected zone. In addition, like Mn, Cr, Ni, Cu elements, the single content of Ti, Mg, Zr, Ca is not unique, and the contents of Ti, Mg, Zr, Ca elements can be adjusted respectively according to other different performances of steel materials.

[0025] As described above, compared with the prior art, in the design of the chemical composition in the present invention, by rationally designing the total amount of Ti+Mg+Zr+Ca, Ti, Mg, Zr, and Ca oxides can effectively promote the formation of acicular ferrite, and by rationally 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 performance, as proven by many experimental studies, the yield strength of the welding steel plate is ≥ 430MPa, the tensile strength is between 550-620MPa, the elongation rate is ≥ 25%, the -40℃ impact load is ≥ 300J, and the crack resistance property is K ca ≧8500N / mm 1.5 Under the condition of a welding heat input of 600 kJ / cm, the tensile strength of the welded heat-affected zone is ≧540 MPa, and the -40°C impact load is ≧150 J.

[0027] In one embodiment, there is further provided a method for manufacturing a steel plate for high heat input welding, the method comprising the steps of: (1) Smelting process: The steel is successively made through converter steelmaking, LF furnace refining, and RH furnace refining. After RH refining, the molten steel is continuously cast into a slab by a continuous casting machine. Here, calcium zirconium core wire is added during RH refining. Hereinafter, preferred embodiments of each step of the smelting process will be described in detail.

[0028] a) Converter smelting: The ratio of molten iron to clean scrap is (7~8):1, and the smelting temperature of molten iron is 1350~1450℃. Ferromanganese, ferrosilicon, and lime are added to the molten iron in sequence to smelt it, and the steel product is discharged after smelting.

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

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

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

[0032] By controlling the total amount of Mn+Cr+Ni+Cu to 1.5~4.5%, and controlling the ratio of Cr / Ni / Cu to 1:2:1, the steel plate hardenability can be effectively improved, and the low temperature toughness can be improved while maintaining a certain strength of the steel plate. Ti, Mg, Zr, Ca oxides can effectively prevent the growth of austenite grains in the heat affected zone of welding, while promoting the nucleation of intragranular acicular ferrite, and improve the low temperature toughness of the heat affected zone during large heat input welding. Zr and Ca are added as in core spun yarn, and on the other hand, the oxide particles can be diffused, while the size of the oxide particles can be refined, and the formation of acicular ferrite can be more promoted. Among Ti, Mg, Zr, Ca, the ratio of Ti and Mg is high, which can effectively reduce production costs.

[0033] (2) Rolling process: The slab is heated at a temperature between 1050 and 1150°C for at least 320 min. After the heating is completed, when the temperature reaches 900 to 1000°C, recrystallized zone rolling is performed so that the one-pass reduction is greater than 15% and the cumulative reduction is greater than 50%. When the temperature drops to 860°C or lower, unrecrystallized zone rolling is performed so that the one-pass reduction is greater than 15% and the cumulative reduction of unrecrystallized zone rolling is greater than 60%. The steel sheet temperature obtained through the recrystallized zone rolling and unrecrystallized zone rolling is measured using Ar. 3 The temperature should be within a range of 30 to 50 degrees Celsius higher than the

[0034] The slab is rolled in the recrystallization zone, and the grains are refined by the action of external forces at high temperatures. However, there is a certain limit to the refinement of the recrystallization zone grains, so non-recrystallization zone rolling is performed, and the austenite after refinement is compressed and continues to elongate, increasing the grain boundary area of ​​austenite in a unit volume, and increasing the nucleation site and nucleation rate of ferrite. By controlling the Cr / Ni / Cu ratio and the total amount of Ti, Mg, Zr, and Ca, combined with recrystallization zone rolling and non-recrystallization zone rolling, the ratio of acicular ferrite structure in the metal structure is made 80% or more, and the crack resistance of the steel plate is improved.

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

[0036] After rolling, the steel sheet is quenched to a temperature 20 to 40°C higher than the Bs temperature and then air-cooled. Quenching at the Bs temperature promotes the formation of bainite, reducing the strength of the steel sheet.

[0037] Here, in the rolling step, Ar 3 = 910-310C-80Mn-20Cu-15Cr-55Ni-80Mo-0.35 (H-8), where H is the target steel plate 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 contents (mass%) of each element contained in the steel.

[0038] Furthermore, the area density of Ti, Mg, Zr or Ca oxide in the slab formed by continuous casting is 1500 particles / mm 2 These oxides can effectively prevent the growth of austenite grains in the weld heat affected zone and promote the formation of acicular ferrite, so as to ensure the excellent performance of the heat affected zone during large heat input welding.

[0039] The technical solutions of the present application are further described below with reference to some specific examples.

[0040] Example 1 This Example 1 provides a steel plate for large heat input welding. The chemical composition of the steel plate is, 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: 0.0015%, Ca: 0.0015%, and the balance is Fe and unavoidable impurities.

[0041] The steps of the manufacturing method of the steel plate for large heat input welding 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℃. Ferromanganese, ferrosilicon, and lime are added to the molten iron in sequence to smelt it. After smelting is completed, the steel product is discharged.

[0042] b) LF furnace refining: After the steel material is discharged from the converter, Mn, Cr, Ni, Cu, Ti, Mg elements are added to the molten steel according to the chemical composition of the above welding steel plate, the temperature is measured, and sampling is performed. When the above elements meet the requirements of the chemical composition of the above welding steel plate, 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 contents in the molten steel are all 0.0015% by mass. Before discharging the steel, ultra-low carbonation rice husk is added to keep it warm.

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

[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 of the recrystallization zone rolling was 950°C, the reduction rate for one pass was 16%, and the rolling was performed four times with a final rolling temperature of 900°C. Unrecrystallization zone rolling was performed. The rolling start temperature of the unrecrystallization zone rolling was 850°C, the reduction rate for one pass was 16%, and the rolling was performed five times with a final rolling temperature of the unrecrystallization zone rolling of 770°C. A steel plate with a thickness of 66 mm was obtained.

[0046] (3) Cooling process: After rolling, the steel plate is transported to the ACC device at the maximum transport speed of the roller conveyor, where it is 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 Example 2 provides a steel plate for large heat input welding. The chemical composition of the steel plate is, 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: 0.0015%, Ca: 0.0015%, and the balance is Fe and unavoidable impurities.

[0048] The steps of the manufacturing method of the steel plate for large heat input welding are as follows. (1) Smelting process: a) Converter smelting: The ratio of molten iron to clean scrap is 8:1, and the molten iron smelting temperature is 1350-1450℃. Ferromanganese, ferrosilicon, and lime are added to the molten iron in sequence to smelt it. After smelting is completed, the steel product is discharged.

[0049] b) LF furnace refining: After the steel material is discharged from the converter, Mn, Cr, Ni, Cu, Ti, Mg elements are added to the molten steel according to the chemical composition of the above welding steel plate, the temperature is measured, and sampling is performed. When the above elements meet the requirements of the chemical composition of the above welding steel plate, 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 contents in the molten steel are all 0.0015% by mass. Before discharging the steel, ultra-low carbonation rice husk is added to keep it warm.

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

[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 rolling start temperature of the recrystallization zone rolling was 970°C, the reduction rate for one pass was 16%, and the rolling was performed four times with a final rolling temperature of 920°C. Unrecrystallization zone rolling was performed. The rolling start temperature of the unrecrystallization zone rolling was 840°C, the reduction rate for one pass was 16%, and the rolling was performed five times with a final rolling temperature of the unrecrystallization zone rolling of 760°C. A steel plate with a thickness of 66 mm was obtained.

[0053] (3) Cooling process: After rolling, the steel plate is transported to the ACC device at the maximum transport speed of the roller conveyor, where it is 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 Example 3 provides a steel plate for large heat input welding. The chemical composition of the steel plate is, by weight%, 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%, and the balance is Fe and unavoidable impurities.

[0055] The steps of the manufacturing method of the steel plate for large heat input welding 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℃. Ferromanganese, ferrosilicon, and lime are added to the molten iron in sequence to smelt it, and after smelting is completed, the steel product is discharged.

[0056] b) LF furnace refining: After the steel material is discharged from the converter, Mn, Cr, Ni, Cu, Ti, Mg elements are added to the molten steel according to the chemical composition of the above welding steel plate, the temperature is measured, and sampling is performed. When the above elements meet the requirements of the chemical composition of the above welding steel plate, 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 contents in the molten steel are all 0.002% by mass. Before discharging the steel, ultra-low carbonation rice husk is added to keep it warm.

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

[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 of the recrystallization zone rolling was 960°C, the reduction rate for one pass was 16%, and the rolling was performed four times with a final rolling temperature of 910°C. Unrecrystallization zone rolling was performed. The rolling start temperature of the unrecrystallization zone rolling was 855°C, the reduction rate for one pass was 16%, and the rolling was performed five times with a final rolling temperature of the unrecrystallization zone rolling of 770°C. A steel plate with a thickness of 66 mm was obtained.

[0060] (3) Cooling process: After rolling, the steel plate is transported to the ACC device at the maximum transport speed of the roller conveyor, where it is 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 Example 4 provides a steel plate for large heat input welding. The chemical composition of the steel plate is, 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%, and the balance is Fe and unavoidable impurities.

[0062] The steps of the manufacturing method of the steel plate for large heat input welding 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℃. Ferromanganese, ferrosilicon, and lime are added to the molten iron in sequence to smelt it. After smelting is completed, the steel product is discharged.

[0063] b) LF furnace refining: After the steel material is discharged from the converter, Mn, Cr, Ni, Cu, Ti, Mg elements are added to the molten steel according to the chemical composition of the above welding steel plate, the temperature is measured, and sampling is performed. When the above elements meet the requirements of the chemical composition of the above welding steel plate, 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 contents in the molten steel are all 0.0015% by mass. Before discharging the steel, ultra-low carbonation rice husk is added to keep it warm.

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

[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 of the recrystallization zone rolling was 950°C, the reduction rate for one pass was 16%, and the rolling was performed four times with a final rolling temperature of 900°C. Unrecrystallization zone rolling was performed. The rolling start temperature of the unrecrystallization zone rolling was 850°C, the reduction rate for one pass was 16%, and the rolling was performed five times with a final rolling temperature of the unrecrystallization zone rolling of 770°C. A steel plate with a thickness of 66 mm was obtained.

[0067] (3) Cooling process: After rolling, the steel plate is transported to the ACC device at the maximum transport speed of the roller conveyor, where it is 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 plate for large heat input welding. The chemical composition of the steel plate is, by weight%, 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%, and the balance is Fe and unavoidable impurities.

[0069] The steps of the manufacturing method of the steel plate for large heat input welding are as follows. (1) Smelting process: a) Converter smelting: The ratio of molten iron to clean scrap is 8:1, and the molten iron smelting temperature is 1350-1450℃. Ferromanganese, ferrosilicon, and lime are added to the molten iron in sequence to smelt it. After smelting is completed, the steel product is discharged.

[0070] b) LF furnace refining: After the steel material is discharged from the converter, Mn, Cr, Ni, Cu, Ti, Mg elements are added to the molten steel according to the chemical composition of the above welding steel plate, the temperature is measured, and sampling is performed. When the above elements meet the requirements of the chemical composition of the above welding steel plate, 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 contents in the molten steel are all 0.0015% by mass. Before discharging the steel, ultra-low carbonation rice husk is added to keep it warm.

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

[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 rolling start temperature of the recrystallization zone rolling was 970°C, the reduction rate for one pass was 16%, and the rolling was performed four times with a final rolling temperature of 925°C. Unrecrystallization zone rolling was performed. The rolling start temperature of the unrecrystallization zone rolling was 850°C, the reduction rate for one pass was 16%, and the rolling was performed five times with a final rolling temperature of the unrecrystallization zone rolling of 760°C. A steel plate with a thickness of 66 mm was obtained.

[0074] (3) Cooling process: After rolling, the steel plate is transported to the ACC device at the maximum transport speed of the roller conveyor, where it is 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 Example 6 provides a steel plate for large heat input welding. The chemical composition of the steel plate is, 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%, and the balance is Fe and unavoidable impurities.

[0076] The steps of the manufacturing method of the steel plate for large heat input welding 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℃. Ferromanganese, ferrosilicon, and lime are added to the molten iron in sequence to smelt it. After smelting is completed, the steel product is discharged.

[0077] b) LF furnace refining: After the steel material is discharged from the converter, Mn, Cr, Ni, Cu, Ti, Mg elements are added to the molten steel according to the chemical composition of the above welding steel plate, the temperature is measured, and sampling is performed. When the above elements meet the requirements of the chemical composition of the above welding steel plate, 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 contents in the molten steel are all 0.002% by mass. Before discharging the steel, ultra-low carbonation rice husk is added to keep it warm.

[0079] 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 of 320 mm thickness.

[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 of the recrystallization zone rolling was 960°C, the reduction rate for one pass was 16%, and the rolling was performed four times with a final rolling temperature of 910°C. Unrecrystallization zone rolling was performed. The rolling start temperature of the unrecrystallization zone rolling was 855°C, the reduction rate for one pass was 16%, and the rolling was performed five times with a final rolling temperature of the unrecrystallization zone rolling of 770°C. A steel plate with a thickness of 66 mm was obtained.

[0081] (3) Cooling process: After rolling, the steel plate is transported to the ACC device at the maximum transport speed of the roller conveyor, where it is 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 Example 7 provides a steel plate for large heat input welding. The chemical composition of the steel plate is, 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%, and the balance is Fe and unavoidable impurities.

[0083] The steps of the manufacturing method of the steel plate for large heat input welding 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℃. Ferromanganese, ferrosilicon, and lime are added to the molten iron in sequence to smelt it. After smelting is completed, the steel product is discharged.

[0084] b) LF furnace refining: After the steel material is discharged from the converter, Mn, Cr, Ni, Cu, Ti, Mg elements are added to the molten steel according to the chemical composition of the above welding steel plate, the temperature is measured, and sampling is performed. When the above elements meet the requirements of the chemical composition of the above welding steel plate, 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 contents in the molten steel are all 0.002% by mass. Before discharging the steel, ultra-low carbonation rice husk is added to keep it warm.

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

[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 of the recrystallization zone rolling was 950°C, the reduction rate for one pass was 16%, and the rolling was performed four times with a final rolling temperature of 900°C. Unrecrystallization zone rolling was performed. The rolling start temperature of the unrecrystallization zone rolling was 850°C, the reduction rate for one pass was 16%, and the rolling was performed five times with a final rolling temperature of the unrecrystallization zone rolling of 770°C. A steel plate with a thickness of 66 mm was obtained.

[0088] (3) Cooling process: After rolling, the steel plate is transported to the ACC device at the maximum transport speed of the roller conveyor, where it is 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 Example 8 provides a steel plate for large heat input welding. The chemical composition of the steel plate is, 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%, and the balance is Fe and unavoidable impurities.

[0090] The steps of the manufacturing method of the steel plate for large heat input welding are as follows. (1) Smelting process: a) Converter smelting: The ratio of molten iron to clean scrap is 8:1, and the molten iron smelting temperature is 1350-1450℃. Ferromanganese, ferrosilicon, and lime are added to the molten iron in sequence to smelt it. After smelting is completed, the steel product is discharged.

[0091] b) LF furnace refining: After the steel material is discharged from the converter, Mn, Cr, Ni, Cu, Ti, Mg elements are added to the molten steel according to the chemical composition of the above welding steel plate, the temperature is measured, and sampling is performed. When the above elements meet the requirements of the chemical composition of the above welding steel plate, 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 contents in the molten steel are all 0.002% by mass. Before discharging the steel, ultra-low carbonation rice husk is added to keep it warm.

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

[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 rolling start temperature of the recrystallization zone rolling was 970°C, the reduction rate for one pass was 16%, and the rolling was performed four times with a final rolling temperature of 920°C. Unrecrystallization zone rolling was performed. The rolling start temperature of the unrecrystallization zone rolling was 840°C, the reduction rate for one pass was 16%, and the rolling was performed five times with a final rolling temperature of the unrecrystallization zone rolling of 760°C. A steel plate with a thickness of 66 mm was obtained.

[0095] (3) Cooling process: After rolling, the steel plate is transported to the ACC device at the maximum transport speed of the roller conveyor, where it is 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 each steel plate described in Examples 1 to 8. As can be seen from Table 1, the yield strength of the steel plate base material is all greater than 430 MPa, the tensile strength is in the range of 550 to 620 MPa, the elongation is 25% or more, the -40°C impact load is 300 J or more, and under the condition of a welding heat input of 600 kJ / cm, the tensile strength of the welded heat affected zone is 540 MPa or more, and the -40°C impact load is 150 J or more. Crack resistance K ca is 8500N / mm 1.5 That's all.

[0098] Of course, the above examples are merely illustrative for clear explanation, and do not limit the embodiments. Those skilled in the art can make other different changes and modifications based on the above description. It is not possible to comprehensively list all the embodiments in this specification. Any obvious changes or modifications derived therefrom shall be included within the protection scope of the present invention.

Claims

1. 1. A steel plate for large heat input welding comprising, in mass%, C≦0.1%, Si≦0.15%, S≦0.004%, and 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%, with 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.

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

3. The steel plate for large heat input welding according to claim 1, characterized in that the steel plate for welding has a yield strength of ≧430 MPa, a tensile strength of 550 to 620 MPa, an elongation of ≧25%, and a −40° C. impact load of ≧300 J.

4. The steel plate for welding according to claim 1, characterized in that, under conditions of a welding heat input of 600 kJ / cm, the weld heat affected zone tensile strength is ≧540 MPa and the −40° C. impact load is greater than 150 J.

5. The crack resistance characteristic K of the welding steel plate ｃａ ≧8500N / mm １．５ The steel plate for large heat input welding according to claim 1,

6. A method for producing a steel plate for large heat input welding according to claim 1, A process in which the molten steel is successively subjected to converter steelmaking, LF furnace refining, and RH furnace refining, and after RH refining, the molten steel is continuously cast into a slab by a continuous casting machine, and a smelting process in which calcium zirconium core wire is added during RH refining; The slab is heated between 1050 and 1150°C for at least 320 min. After the heating is completed, when the temperature reaches 900 to 1000°C, recrystallization zone rolling is performed so that the one-pass reduction is greater than 15% and the cumulative reduction is greater than 50%. When the temperature drops to 860°C or less, unrecrystallized zone rolling is performed so that the one-pass reduction is greater than 15% and the cumulative reduction of the unrecrystallized zone rolling is greater than 60%. The steel sheet temperature obtained through the recrystallization zone rolling and the unrecrystallized zone rolling is Ar. ３ a rolling step in which the temperature is within a range of 30 to 50° C. higher than the temperature of the rolling step; and a cooling step of cooling the steel plate to a temperature range of 20 to 40°C higher than the Bs temperature at a cooling rate of more than 10°C / s after completion of rolling, and then air-cooling the steel plate to 350°C or lower.

7. The area density of Ti, Mg, Zr or Ca oxide in the slab formed by continuous casting is 1500 pieces / mm ２ The method for producing a steel plate for high heat input welding according to claim 6, characterized in that

8. In the rolling step, Ar ３ 7. The method for producing a steel plate for large heat input welding according to claim 6, characterized in that: Bs temperature=910-310C-80Mn-20Cu-15Cr-55Ni-80Mo-0.35(H-8), where H is the target steel plate thickness, and Bs temperature=630-45Mn-40V-35Si-30Cr-25Mo-20Ni-15W.

9. 7. The method for producing a steel plate for large heat input welding according to claim 6, wherein, during the converter steelmaking, a mass ratio of the amount of molten iron to the amount of clean scrap is (7-8):1, and a temperature of the molten iron is 1350-1450°C.

10. 7. The method for producing a steel plate for large heat input welding according to claim 6, wherein in the smelting process, 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.

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