Extra-thick high-strength and high-toughness steel plate for high heat input welding and production method thereof

Abstract

The invention discloses an extra-thick high-strength and high-toughness steel plate for high heat input welding and a production method thereof, and belongs to the technical field of medium-thickness plates. The steel plate comprises the following chemical components in percentage by mass: 0.05 to 0.08 percent of C, 0.1 to 0.2 percent of Si, 1.5 to 1.6 percent of Mn, 1.2 to 1.5 percent of Ni, 0.08 to 0.15 percent of Mo, 0.015 to 0.025 percent of Nb, 0.03 to 0.05 percent of V, 0.008 to 0.015 percent of Ti, 0.0002 to 0.0007 percent of Mg, 0.0005 to 0.002 percent of Ca, less than or equal to 0.008 percent of P, less than or equal to 0.003 percent of S and the balance of iron and inevitable impurities. The production method comprises the procedures of LF refining, VD vacuum treatment, die casting, heating, rolling and heat treatment. When the maximum thickness of the steel plate is 150mm and the welding line energy is 200KJ / cm, the impact energy of a heat affected zone at 60 DEG C below zero is greater than or equal to 42J.

Description

Technical Field

[0001] The invention belongs to the technical field of medium and thick plates, and relates to a particularly thick, high-strength, high-toughness, and high-heat-input welding steel plate and a production method thereof. Background Art

[0002] With the increasing size and strength of components, the use of low-alloy, high-strength, extra-thick structural steel plates is becoming increasingly widespread, with thicknesses even exceeding 100mm. At the same time, the requirements for their strength, toughness, and weldability are becoming increasingly stringent. In order to improve construction efficiency and reduce costs, downstream companies using structural steel currently generally adopt high-heat input welding methods such as multi-wire submerged arc welding, multi-wire gas shielded welding, gas-electric vertical welding, and electroslag welding. Generally, welding with a heat input greater than 50KJ / cm is referred to as high-heat input welding. However, when the welding heat input of traditional steel plates is greater than 50KJ / cm, the mechanical properties of the welded joints will be severely reduced due to the excessive coarsening of the weld heat-affected zone structure, and may even be lower than the marked requirements of the parent steel plate.

[0003] Reports indicate that Japan's JFE has developed high-energy-input steel plate with a thickness of 40-100mm and a grade of EH36, achieving a welding heat input of 600kJ / cm. A domestic company has also developed 80mm-thick EH40 high-energy-input steel. However, reports of high-energy-input steel plates with a thickness of 120mm or greater and a yield strength of 420MPa or greater are rare. To meet market demands, such as the thicker offshore steel used in deepwater jackets for extreme environments, there is an urgent need to develop high-energy-input, high-strength, high-toughness, and extra-thick steel plates. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a super-thick, high-strength, high-toughness, high-wire energy welding steel plate and a production method thereof. The obtained steel plate has a thickness of 120 to 150 mm and a maximum welding wire energy of up to 200 kJ / cm.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is: A steel plate for ultra-thick, high-strength, toughness and high-heat-input welding, whose chemical composition and mass percentage are as follows: C: 0.05%-0.08%, Si: 0.1%-0.2%, Mn: 1.5%-1.6%, Ni: 1.2%-1.5%, Mo: 0.08%-0.15%, Nb: 0.015%-0.025%, V: 0.03%-0.05%, Ti: 0.008%-0.015%, Mg: 0.0002%-0.0007%, Ca: 0.0005%-0.002%, P≤0.008%, S≤0.003%, and the balance is Fe and unavoidable impurity elements.

[0006] Furthermore, the thickness of the steel plate is 120-150 mm, and the maximum welding line energy is 200 KJ / cm.

[0007] Furthermore, the steel plate has a yield strength of ≥420 MPa, a yield strength ratio of ≤0.8, an impact energy at -60°C of ≥100 J, and a fracture toughness CTOD characteristic value of -60°C >0.3 mm; when welded with a line energy of 200 KJ / cm, the impact energy at -60°C of the heat-affected zone is ≥42 J.

[0008] The present invention also provides a production method for the above-mentioned ultra-thick, high-strength and toughness steel plate for high-heat input welding, which includes LF refining, VD vacuum treatment, die casting, heating, rolling and heat treatment steps.

[0009] LF refining process: Aluminum wire is added for deoxidation at the beginning of refining, followed by silicon manganese for deep deoxidation, with an oxygen content of 40-60ppm, magnesium wire is added, argon is stirred for 1-3 minutes, titanium iron is added, and calcium wire is added before vacuum; Heat treatment process: quenching + tempering process, quenching heating temperature 900±10℃, holding temperature 2~2.5min / mm, water cooling; tempering heating temperature 620~650℃, holding temperature 3~4min / mm, air cooling.

[0010] Furthermore, in the LF refining process, the amount of aluminum wire added is 50 to 100 meters, and the amount of magnesium wire added is 1 to 3 kg.

[0011] Furthermore, in the VD vacuum treatment process, the vacuum degree is less than 66pa, the vacuum holding time is 25 to 30 minutes, and the soft blowing after vacuum is 8 to 10 minutes.

[0012] Furthermore, in the die casting process, gas protection casting is used throughout the entire process, and the superheat of the molten steel is controlled at 35-45°C.

[0013] Furthermore, in the heating process, the charging temperature of the furnace is not higher than 600°C, the temperature is raised to 700±10°C and kept warm for 2.0 to 3.0 hours, then the temperature is raised to 930±10°C at a rate of ≤120°C / h and kept warm for 2.5 to 3.5 hours, and then the temperature is raised to 1240 to 1260°C and kept warm for 15 to 18 hours.

[0014] Furthermore, the rolling process adopts a temperature-controlled rolling process. The rolling temperature in stage I is 950-1200°C, the single-pass reduction is 10-20%, and the cumulative reduction rate is 30-60%. The steel is then aired and high-pressure water is used to remove the iron oxide scale on the surface of the steel plate. The rolling start temperature in stage II is 850-880°C, and the cumulative reduction rate is 30-50%.

[0015] The functions and contents of the key components in the steel plate of the present invention are described in detail as follows: C: is an element required to ensure the strength of the steel plate. However, in order to make the steel plate have good welding performance and good low-temperature impact toughness, the carbon content in the steel must be reduced. This is because carbon is a strong solid solution strengthening element and can significantly improve the strength of the steel plate, but at the same time it reduces the toughness and plasticity of the steel and deteriorates the welding performance of the steel plate. Therefore, in the present invention, the carbon content is controlled at 0.05% to 0.08%.

[0016] Mn: It is a major alloy strengthening element, which improves the strength and toughness of steel in the form of solid solution strengthening. It is inexpensive and can reduce the production cost of steel plates. The reasonable selection range of Mn in the present invention is 1.5% to 1.6%.

[0017] Ni: While slightly improving both the strength and ductility of the steel plate, it significantly increases low-temperature impact toughness. This is because Ni forms only a solid solution in the steel, increasing the lattice slip planes during plastic deformation, thereby increasing the material's plasticity. Ni also improves the steel's toughness at low temperatures, lowering the ductile-brittle transition temperature. The Ni content in this invention is preferably between 1.2% and 1.5%.

[0018] Mo: It significantly improves the strength, plasticity and low-temperature impact toughness of the steel plate. This is because when Mo is dissolved in ferrite and austenite, it can shift the C curve of the steel to the right, thereby significantly improving the hardenability of the steel. The Mo content of the present invention is selected to be within the range of 0.08% to 0.15%.

[0019] Nb: Niobium increases the yield strength of steel, improves the weldability of steel, refines grains, and increases the austenite recrystallization temperature. The Nb content of the present invention is selected to be in the range of 0.015% to 0.025%.

[0020] V: One of the primary functions of vanadium in steel is to increase its strength. This is primarily achieved by refining the steel's structure and grain size. Vanadium inhibits the deformation and recrystallization of austenite and prevents grain growth, thereby increasing the steel's yield strength and tensile strength. The V content in this invention is preferably within the range of 0.03% to 0.05%.

[0021] Ti, Ca, and Mg: Combined with O, they form fine, dispersed oxides. The pinning effect of these fine oxides significantly inhibits grain coarsening in the heat-affected zone (HAZ) under high-heat-input welding conditions, improving the low-temperature toughness of the HAZ. Furthermore, fine MgO particles can serve as nucleation sites for TiN, refining the TiN particles and mitigating the cracking effect of large TiN particles on the substrate.

[0022] P and S: In general, they are harmful elements in steel, which will increase the brittleness of steel. P will deteriorate the welding performance of steel and reduce plasticity. S will reduce the ductility and toughness of steel and cause cracks during rolling. Therefore, the content of P and S in steel should be reduced as much as possible.

[0023] The beneficial effects of the above technical solution are as follows: the addition of Ni and Mo elements to the chemical composition ensures uniform low-temperature impact toughness and performance at -60°C for steel layers of varying thickness. A small amount of aluminum wire is added early in LF refining for rapid deoxidation, ensuring the aluminum content in the steel is less than 0.007%. Silicon and manganese are then added for deep deoxidation, laying the foundation for metallurgy with oxides such as Mg and Ti. The addition of magnesium wire prior to ferrotitanium allows for fine MgO particles to serve as nucleation sites for TiN, thereby refining the TiN particles.

[0024] The thickness of the steel plate obtained by the present invention is 120 to 150 mm, and the maximum welding line energy can reach 200 kJ / cm; the yield strength of the steel plate is ≥420 MPa, the yield strength ratio is ≤0.8, the impact energy at -60°C is ≥100 J, and the -60°C fracture toughness CTOD characteristic value is greater than 0.3 mm; when welding with a line energy of 200 kJ / cm, the -60°C impact energy of the heat-affected zone is ≥42 J. DETAILED DESCRIPTION Example 1

[0025] The thickness of the ultra-thick, high-strength, high-toughness, high-heat-input welding steel plate in this embodiment is 120 mm, and its chemical composition and mass percentage are: C: 0.05%, Si: 0.1%, Mn: 1.5%, Ni: 1.2%, Mo: 0.08%, Nb: 0.015%, V: 0.03%, Ti: 0.009%, Mg: 0.0005%, Ca: 0.0015%, P: 0.007%, S: 0.0013%, and the balance is Fe and unavoidable impurity elements.

[0026] The production method of the ultra-thick, high-strength and high-toughness steel plate for high-heat input welding in this embodiment includes LF refining, VD vacuum treatment, die casting, heating, rolling, and heat treatment processes. The specific process steps are as follows: (1) LF refining process: 50 meters of aluminum wire was added for deoxidation at the beginning of refining, and then silicon manganese was added for deep deoxidation. The oxygen content was determined to be 55ppm by an oxygen meter. 2 kg of magnesium wire was added, and titanium iron was added after stirring with argon for 1 minute. 100 meters of Ca wire was added before vacuum; (2) Vacuum VD treatment process: vacuum degree 56 Pa, holding time 25 min, soft blowing for 8 minutes after vacuum; (3) Die casting process: full protection casting is adopted, the superheat of molten steel is controlled at 38℃, and the thickness of the steel ingot is 900mm; (4) Heating process: heating in a soaking furnace, charging the furnace temperature at 500°C, heating to 700°C and keeping it for 2 hours, then heating to 930°C at a rate of 100°C / h and keeping it for 3 hours, then heating to 1240°C and keeping it for 15 hours; (5) Rolling process: temperature-controlled rolling process is adopted. The rolling temperature of stage I is 950~1200℃, the single-pass reduction is 11%~15%, and the cumulative reduction rate is 40%. Then the steel is air-dried and the iron oxide scale on the surface of the steel plate is removed by high-pressure water. The starting rolling temperature of stage II is 850℃, and the cumulative reduction rate is 50%. (6) Heat treatment process: quenching heating temperature 890℃, holding temperature 2.5min / mm, water cooling; tempering heating temperature 650℃, holding temperature 4min / mm, air cooling.

[0027] The tensile and impact properties of the steel plate in this example are: yield strength 450 MPa, tensile strength 585 MPa, yield strength ratio 0.77, elongation 33%, average impact energy 280 J at -60°C, and fracture toughness CTOD characteristic value 1.3 mm at -60°C. The steel plate was welded with a heat input of 200 kJ / cm, and the average impact energy of the heat-affected zone at -60°C was 122 J. Example 2

[0028] The thickness of the ultra-thick, high-strength, high-toughness, high-heat-input welding steel plate in this embodiment is 135 mm, and its chemical composition and mass percentage are: C: 0.07%, Si: 0.15%, Mn: 1.55%, Ni: 1.3%, Mo: 0.1%, Nb: 0.02%, V: 0.04%, Ti: 0.012%, Mg: 0.0002%, Ca: 0.002%, P: 0.008%, S: 0.0015%, and the balance is Fe and unavoidable impurity elements.

[0029] The production method of the ultra-thick, high-strength and high-toughness steel plate for high-heat input welding in this embodiment includes LF refining, VD vacuum treatment, die casting, heating, rolling, and heat treatment processes. The specific process steps are as follows: (1) LF refining process: 100 meters of aluminum wire was added for deoxidation at the beginning of refining, and then silicon manganese was added for deep deoxidation. The oxygen content was determined to be 45ppm by an oxygen meter. 1.1 kg of magnesium wire was added, and titanium iron was added after stirring with argon for 2 minutes. 150 meters of Ca wire was added before vacuum; (2) Vacuum VD treatment process: vacuum degree 30pa, holding time 28min, soft blowing after vacuum for 9 minutes; (3) Mold casting process: full protection casting is adopted, the superheat of molten steel is controlled at 41°C, and the thickness of the steel ingot is 900mm; (4) Heating process: heating in a soaking furnace, charging the furnace temperature at 450 °C, heating to 695 °C and keeping it at that temperature for 2.2 hours, then heating to 935 °C at a rate of 80 °C / h and keeping it at that temperature for 2.8 hours, then heating to 1250 °C and keeping it at that temperature for 16 hours; (5) Rolling process: temperature-controlled rolling process is adopted. The rolling temperature of stage I is 950~1200℃, the single-pass reduction is 10%~20%, and the cumulative reduction rate is 45%. Then the steel is air-dried and the iron oxide scale on the surface of the steel plate is removed by high-pressure water. The starting rolling temperature of stage II is 860℃, and the cumulative reduction rate is 40%. (6) Heat treatment process: quenching heating temperature 900℃, holding temperature 2.2min / mm, water cooling; tempering heating temperature 640℃, holding temperature 3.5min / mm, air cooling.

[0030] The tensile and impact properties of the steel plate in this example are: yield strength 435 MPa, tensile strength 550 MPa, yield strength ratio 0.79, elongation 34%, average impact energy 260 J at -60°C, and fracture toughness CTOD characteristic value 1.7 mm at -60°C. The steel plate was welded at a heat input of 200 kJ / cm, and the average impact energy of the heat-affected zone at -60°C was 108 J. Example 3

[0031] The thickness of the ultra-thick, high-strength, high-toughness, high-heat-input welding steel plate of this embodiment is 150 mm, and its chemical composition and mass percentage are: C: 0.08%, Si: 0.2%, Mn: 1.6%, Ni: 1.5%, Mo: 0.15%, Nb: 0.025%, V: 0.05%, Ti: 0.015%, Mg: 0.0007%, Ca: 0.0005%, P: 0.006%, S: 0.0012%, and the balance is Fe and unavoidable impurity elements.

[0032] The production method of the ultra-thick, high-strength and high-toughness steel plate for high-heat input welding in this embodiment includes LF refining, VD vacuum treatment, die casting, heating, rolling, and heat treatment processes. The specific process steps are as follows: (1) LF refining process: 80 meters of aluminum wire was added for deoxidation at the beginning of refining, and then silicon manganese was added for deep deoxidation. The oxygen content was determined to be 50ppm by an oxygen meter, and 3 kg of magnesium wire was added. Titanium iron was added under argon stirring for 3 minutes, and 40 meters of Ca wire was added before vacuum; (2) Vacuum VD treatment process: vacuum degree 38pa, holding time 30min, soft blowing for 10 minutes after vacuum; (3) Die casting process: full protection casting is adopted, the superheat of molten steel is controlled at 45℃, and the thickness of the steel ingot is 900mm; (4) Heating process: heating in a soaking furnace, charging the furnace temperature at 580°C, heating to 700°C and keeping it for 2 hours, then heating to 930°C at a rate of 90°C / h and keeping it for 3 hours, then heating to 1260°C and keeping it for 18 hours; (5) Rolling process: temperature-controlled rolling process is adopted. The rolling temperature of stage I is 950~1200℃, the single-pass reduction is 10%~20%, and the cumulative reduction rate is 35%. Then the steel is air-dried and the iron oxide scale on the surface of the steel plate is removed by high-pressure water. The starting rolling temperature of stage II is 860℃, and the cumulative reduction rate is 50%. (6) Heat treatment process: quenching heating temperature 900℃, holding temperature 2.0min / mm, water cooling; tempering heating temperature 620℃, holding temperature 3.0min / mm, air cooling.

[0033] The tensile and impact properties of the steel plate in this example are: yield strength 425 MPa, tensile strength 535 MPa, yield strength ratio 0.8, elongation 33%, average impact energy 240 J at -60°C, and fracture toughness CTOD characteristic value 0.7 mm at -60°C. The steel plate was welded with a heat input of 200 kJ / cm, and the average impact energy of the heat-affected zone at -60°C was 88 J. Example 4

[0034] The thickness of the extra-thick, high-strength, toughness, and high-heat-input welding steel plate of this embodiment is 130 mm, and its chemical composition and mass percentage are: C: 0.06%, Si: 0.12%, Mn: 1.53%, Ni: 1.28%, Mo: 0.10%, Nb: 0.018%, V: 0.04%, Ti: 0.009%, Mg: 0.0003%, Ca: 0.001%, P: 0.006%, S: 0.0015%, and the balance is Fe and unavoidable impurity elements.

[0035] The production method of the ultra-thick, high-strength and high-toughness steel plate for high-heat input welding in this embodiment includes LF refining, VD vacuum treatment, die casting, heating, rolling, and heat treatment processes. The specific process steps are as follows: (1) LF refining process: 95 meters of aluminum wire was added for deoxidation at the beginning of refining, and then silicon manganese was added for deep deoxidation. The oxygen content was determined to be 40ppm by an oxygen meter. 1.5 kg of magnesium wire was added, and titanium iron was added under argon stirring for 2 minutes. 120 meters of Ca wire was added before vacuum; (2) Vacuum VD treatment process: vacuum degree 25pa, holding time 28min, soft blowing after vacuum for 9min; (3) Die casting process: full protection casting is adopted, the superheat of molten steel is controlled at 42℃, and the thickness of the steel ingot is 900mm; (4) Heating process: heating in a soaking furnace, charging the furnace temperature at 530°C, heating to 690°C and keeping it for 2 hours, then heating to 940°C at a rate of 110°C / h and keeping it for 2.5 hours, then heating to 1240°C and keeping it for 18 hours; (5) Rolling process: temperature-controlled rolling process is adopted. The rolling temperature of stage I is 1150℃, the single-pass reduction is 10-20%, and the cumulative reduction rate is 52%. Then the steel is air-dried and the iron oxide scale on the surface of the steel plate is removed by high-pressure water. The starting rolling temperature of stage II is 870℃, and the cumulative reduction rate is 33%. (6) Heat treatment process: quenching heating temperature 890℃, holding temperature 2.5min / mm, water cooling; tempering heating temperature 640℃, holding temperature 3.8min / mm, air cooling.

[0036] The tensile and impact properties of the steel plate in this example are: yield strength 440 MPa, tensile strength 565 MPa, yield strength ratio 0.78, elongation 32%, average impact energy 268 J at -60°C, and fracture toughness CTOD characteristic value 1.2 mm at -60°C. The steel plate was welded with a heat input of 200 kJ / cm, and the average impact energy of the heat-affected zone at -60°C was 118 J. Example 5

[0037] The thickness of the extra-thick, high-strength, high-toughness, high-heat-input welding steel plate of this embodiment is 140 mm, and its chemical composition and mass percentage are: C: 0.07%, Si: 0.18%, Mn: 1.56%, Ni: 1.38%, Mo: 0.12%, Nb: 0.021%, V: 0.042%, Ti: 0.013%, Mg: 0.0005%, Ca: 0.0018%, P: 0.007%, S: 0.0012%, and the balance is Fe and unavoidable impurity elements.

[0038] The production method of the ultra-thick, high-strength and high-toughness steel plate for high-heat input welding in this embodiment includes LF refining, VD vacuum treatment, die casting, heating, rolling, and heat treatment processes. The specific process steps are as follows: (1) LF refining process: 60 meters of aluminum wire was added for deoxidation at the beginning of refining, and then silicon manganese was added for deep deoxidation. The oxygen content was determined to be 60 ppm by an oxygen meter. 2.8 kg of magnesium wire was added, and titanium iron was added under argon stirring for 3 minutes. 130 meters of Ca wire was added before vacuum; (2) Vacuum VD treatment process: vacuum degree 33pa, holding time 27min, soft blowing for 8 minutes after vacuum; (3) Mold casting process: full protection casting is adopted, the superheat of molten steel is controlled at 35℃, and the thickness of steel ingot is 900mm; (4) Heating process: heating in a soaking furnace, charging the furnace temperature at 580°C, heating to 710°C and keeping it at that temperature for 3 hours, then heating to 920°C at a rate of 105°C / h and keeping it at that temperature for 3.5 hours, then heating to 1260°C and keeping it at that temperature for 15 hours; (5) Rolling process: temperature-controlled rolling process is adopted. The rolling temperature of stage I is 1050℃, the single-pass reduction is 10-20%, and the cumulative reduction rate is 43%. Then the steel is air-dried and the iron oxide scale on the steel plate surface is removed with high-pressure water. The starting rolling temperature of stage II is 880℃, and the cumulative reduction rate is 50%. (6) Heat treatment process: quenching heating temperature 910℃, holding temperature 2min / mm, water cooling; tempering heating temperature 625℃, holding temperature 3.2min / mm, air cooling.

[0039] The tensile and impact properties of the steel plate in this example are: yield strength 435 MPa, tensile strength 550 MPa, yield strength ratio 0.79, elongation 33%, average impact energy 239 J at -60°C, and fracture toughness CTOD characteristic value 0.8 mm at -60°C. The steel plate was welded at a heat input of 200 kJ / cm, and the average impact energy of the heat-affected zone at -60°C was 107 J. Example 6

[0040] The thickness of the extra-thick, high-strength, toughness, and high-heat-input welding steel plate of this embodiment is 145 mm, and its chemical composition and mass percentage are: C: 0.08%, Si: 0.15%, Mn: 1.6%, Ni: 1.46%, Mo: 0.14%, Nb: 0.023%, V: 0.05%, Ti: 0.014%, Mg: 0.0007%, Ca: 0.0008%, P: 0.007%, S: 0.0013%, and the balance is Fe and unavoidable impurity elements.

[0041] The production method of the ultra-thick, high-strength and high-toughness steel plate for high-heat input welding in this embodiment includes LF refining, VD vacuum treatment, die casting, heating, rolling, and heat treatment processes. The specific process steps are as follows: (1) LF refining process: 60 meters of aluminum wire was added for deoxidation at the beginning of refining, and then silicon manganese was added for deep deoxidation. The oxygen content was determined to be 60 ppm by an oxygen meter. 1.8 kg of magnesium wire was added, and titanium iron was added under argon stirring for 2 minutes. 80 meters of Ca wire was added before vacuum; (2) Vacuum VD treatment process: vacuum degree 30pa, holding time 30min, soft blowing for 8 minutes after vacuum; (3) Die casting process: full protection casting is adopted, the superheat of molten steel is controlled at 45℃, and the thickness of the steel ingot is 900mm; (4) Heating process: heating in a soaking furnace, charging temperature 550℃, heating to 700℃ and keeping warm for 2.5 hours, then heating to 930℃ at a rate of 120℃ / h and keeping warm for 3 hours, then heating to 1250℃ and keeping warm for 16 hours; (5) Rolling process: temperature-controlled rolling process is adopted. The rolling temperature of stage I is 1200℃, the single-pass reduction is 10-20%, and the cumulative reduction rate is 45%. Then the steel is air-dried and the iron oxide scale on the surface of the steel plate is removed by high-pressure water. The rolling temperature of stage II is 860℃, and the cumulative reduction rate is 50%. (6) Heat treatment process: quenching heating temperature 905℃, holding time 2.2min / mm, water cooling; tempering heating temperature 620℃, holding time 3min / mm, air cooling.

[0042] The tensile and impact properties of the steel plate in this example are: yield strength 425 MPa, tensile strength 545 MPa, yield strength ratio 0.78, elongation 32%, average impact energy 232 J at -60°C, and fracture toughness CTOD characteristic value 0.63 mm at -60°C. The steel plate was welded at a heat input of 200 kJ / cm, and the average impact energy of the heat-affected zone at -60°C was 102 J.

Claims

1. A steel plate with extra-thickness, high strength and toughness for high heat input welding, characterized in that: The chemical composition of the steel plate and its mass percentage are: C: 0.05%-0.08%, Si: 0.1%-0.2%, Mn: 1.5%-1.6%, Ni: 1.2%-1.5%, Mo: 0.08%-0.15%, Nb: 0.015%-0.025%, V: 0.03%-0.05%, Ti: 0.008%-0.015%, Mg: 0.0002%-0.0007%, Ca: 0.0005%-0.002%, P≤0.008%, S≤0.003%, and the balance is Fe and unavoidable impurity elements.

2. The ultra-thick, high-strength, high-toughness, high-heat input welding steel plate according to claim 1, characterized in that: The thickness of the steel plate is 120-150 mm, and the maximum welding line energy is 200 KJ / cm.

3. The extra-thick, high-strength, high-toughness, high-heat input welding steel plate according to claim 2, characterized in that: The steel plate has a yield strength of ≥420MPa, a yield strength ratio of ≤0.8, an impact energy at -60°C of ≥100J, and a fracture toughness CTOD characteristic value of -60°C of >0.3mm; when welded with a line energy of 200KJ / cm, the impact energy of the heat-affected zone at -60°C is ≥42J.

4. The method for producing a super thick high strength and toughness high heat input welding steel plate according to any one of claims 1 to 3, characterized in that: Including LF refining, VD vacuum treatment, die casting, heating, rolling and heat treatment processes; LF refining process: Aluminum wire is added for deoxidation at the beginning of refining, followed by silicon manganese for deep deoxidation, with an oxygen content of 40-60ppm, magnesium wire is added, argon is stirred for 1-3 minutes, titanium iron is added, and calcium wire is added before vacuum; Heat treatment process: quenching + tempering process, quenching heating temperature 900±10℃, holding temperature 2~2.5min / mm, water cooling; tempering heating temperature 620~650℃, holding temperature 3~4min / mm, air cooling.

5. The method for producing a super thick high strength and toughness high heat input welding steel plate according to claim 4, characterized in that: In the LF refining process, the amount of aluminum wire added is 50 to 100 meters, and the amount of magnesium wire added is 1 to 3 kg.

6. The method for producing a super thick high strength and toughness high heat input welding steel plate according to claim 5, characterized in that: VD vacuum treatment process, vacuum degree <66pa, vacuum holding time 25~30min, soft blowing after vacuum for 8~10min.

7. The method for producing a super thick high strength and toughness high heat input welding steel plate according to claim 6, characterized in that: In the die casting process, the whole process is gas-protected casting, and the superheat of the molten steel is controlled at 35-45℃.

8. The method for producing a super thick high strength and toughness high heat input welding steel plate according to claim 7, characterized in that: In the heating process, the charging temperature of the furnace shall not be higher than 600℃, and the temperature shall be raised to 700±10℃ and kept at this temperature for 2.0~3.0h, then raised to 930±10℃ at a rate of ≤120℃ / h and kept at this temperature for 2.5~3.5h, then raised to 1240~1260℃ and kept at this temperature for 15~18h.

9. The method for producing a super thick high strength and toughness high heat input welding steel plate according to claim 8, characterized in that: The rolling process adopts a temperature-controlled rolling process. The rolling temperature in stage I is 950-1200℃, the single-pass reduction is 10-20%, and the cumulative reduction rate is 30-60%. The steel is then air-dried and the iron oxide scale on the surface of the steel plate is removed with high-pressure water.

10. The method for producing a super thick high strength and toughness high heat input welding steel plate according to any one of claims 4 to 9, characterized in that: In the rolling process, the starting rolling temperature of the II stage is 850-880°C, and the cumulative reduction rate is 30-50%.