Production method of ultra-wide and ultra-thick high-toughness steel

Abstract

The invention relates to a production method of ultra-wide and ultra-thick high-toughness steel, the production process route of the steel comprises smelting, continuous casting, rolling and normalizing, and the steel comprises the following chemical components in percentage by mass: 0.08-0.12% of C, 0.10-0.40% of Si, 1.0-1.6% of Mn, less than or equal to 0.010% of P, less than or equal to 0.003% of S, 0.01-0.045% of Nb, 0.03-0.08% of V, 0.3-0.8% of Ni, 0.01-0.02% of Ti, 0.02-0.06% of Al and the balance of Fe and inevitable impurities. A 36kg-grade steel plate with the maximum thickness of 130mm and the maximum width of 4500mm is produced by adopting a continuous casting billet with the thickness of 450mm, the yield strength of the steel plate is greater than or equal to 355MPa, the tensile strength is greater than or equal to 490MPa, the ductility is greater than or equal to 26%, the percentage reduction of area stretched in the thickness direction is greater than or equal to 35%, and the impact at-60 DEG C is greater than or equal to 200J; and the requirements of large offshore work and wind power jackets are met.

Description

Technical Field

[0001] The invention belongs to the technical field of steel materials and relates to a production method of ultra-wide, ultra-thick and high-toughness steel. Background Art

[0002] Ultra-wide and ultra-thick plates can reduce the welds of large-scale marine engineering and wind power conductor frames, reduce welding processing costs, and shorten the operation cycle. With the enhancement of the rolling capacity of rolling equipment, the market demand for ultra-wide and ultra-thick plates has gradually increased, and the requirements for the width and thickness of steel plates have also become higher and higher. Wide and thick steel plates often mean that the unit weight of the steel plates is larger and the processing is more difficult, especially the toughness control of the steel plates. When the compression ratio is limited, the means of refining the grains through rolling compression are limited, and higher requirements are put forward for the production control of steel plates. In the past, steel ingots were mostly used for production, and the performance of steel plates was controlled by increasing the rolling compression ratio. However, ultra-wide and ultra-thick plates for conductor frames are often in large demand, with short processing cycles, fierce industry competition, and strong price sensitivity. The use of continuous casting billets, especially advanced ultra-thick continuous casting billets, can effectively increase production capacity, reduce costs and improve the uniformity of steel plate performance.

[0003] Chinese patent CN 110438396 "A low compression ratio, high performance Q345R ultra-wide and extra-thick container steel and its manufacturing method" discloses a method for producing wide and thick Q345R. However, it is mainly used in the container industry and needs to meet the requirements of not reducing strength after high-temperature stretching and thermal simulation at 450°C.

[0004] Chinese patent CN 109207854 "Super-wide specification high-strength and high-toughness marine engineering steel and its manufacturing method" discloses a production method for marine engineering steel with a maximum width of 4500mm and a maximum thickness of 90mm. However, it adopts the TMCP production process. The production process of TMCP steel plates is difficult to meet the performance uniformity requirements of ultra-thick steel plates above 100mm, especially the cooling intensity requirement of cooling speed ≥3℃ / s, which is also difficult to achieve during the rolling process of ultra-thick steel plates. Summary of the invention

[0005] The purpose of the present invention is to provide a method for producing ultra-wide and ultra-thick high-toughness steel to produce steel plates that meet the requirements of high core density and high toughness. 450mm thick continuous casting billets can be used to stably produce ultra-wide and ultra-thick steel plates with a maximum width of 130mm, and the maximum width of the steel plate can reach 4500mm. The normalizing production process is adopted, and the steel plate yield strength is ≥355MPa, the tensile strength is ≥490MPa, the elongation is ≥26%, the cross-sectional shrinkage rate of the thickness direction is ≥35%, and the -60℃ impact is ≥200J. The ultra-wide and ultra-thick high-toughness 36kg-grade steel plate is produced through the normalizing process.

[0006] The present invention is achieved through the following technical solutions: A method for producing ultra-wide and ultra-thick high-toughness steel, wherein the chemical composition mass percentage of the steel is C=0.08-0.12, Si=0.10-0.40, Mn=1.0-1.6, P≤0.010, S≤0.003, Nb=0.01-0.045, V=0.03-0.08, Ni=0.3-0.8, Ti=0.01-0.02, Al=0.02-0.06, and the remainder is Fe and unavoidable impurities; a 450mm thick continuous casting billet is used to produce a 36kg grade steel plate with a maximum thickness of 130mm and a maximum width of 4500mm, wherein the yield strength of the steel plate is ≥355MPa, the tensile strength is ≥490MPa, the elongation is ≥26%, the cross-sectional shrinkage rate of the thickness direction tensile is ≥35%, and the -60°C impact is ≥200J; and the method comprises the following process steps: (1) Smelting: The BOF-LF-RH production process is adopted. The converter smelting controls P≤0.01%, the total oxygen content of the steel is 0.5%-0.8%, and the C content is 0.06%-0.08%. After steel is tapped, 1-2 tons of casting slag is used to wash the molten steel and quickly slag. The refining LF furnace enters the station to quickly heat up and make white slag. The reducibility of the molten steel is maintained by adding 40-80 kg of aluminum powder. The RH furnace production adopts a deep degassing process, and the total vacuum treatment time is ≥15 minutes. After the RH is broken, calcium treatment and soft blowing are ≥15 minutes; (2) Continuous casting: The ratio of the continuous casting billet thickness to the steel plate thickness is ≥3. The continuous casting adopts low temperature casting, and the superheat of the tundish is between 10 and 20 °C. (3) Rolling: Two-stage rolling technology is used during rolling. The first stage is high-temperature and large-reduction rolling, requiring an average pass reduction of 50-60 mm. Large intermediate billet and low-temperature two-stage rolling are used. The intermediate billet thickness is ≥ the finished product thickness + 60 mm. The second-stage rolling temperature is 740-780°C, and the final rolling temperature is between 740 and 760°C. After rolling, the steel plates are stacked and slowly cooled to room temperature. (4) Heat treatment: The steel plate is subjected to normalizing process and then air-cooled to room temperature.

[0007] Further, step (3) rolling: solid state reduction technology is used at the outlet of the casting machine to reduce the central looseness of the casting billet, and the total reduction amount in the last section of the casting machine outlet is 10 to 15 mm; Furthermore, in step (3) rolling, the temperature out of the heating furnace is 1280-1320°C, and the total time in the furnace is 600-800 minutes, so as to ensure that the ingot is fully heated; Furthermore, step (4) heat treatment: normalizing temperature is between 890 and 920°C, normalizing heating rate is 8 to 10°C / s, and holding time is 30 to 50 min.

[0008] Principle of the present invention: The main production difficulty of ultra-wide and ultra-thick steel plates lies in the matching of steel plate density and steel plate toughness, and the density problem of the core of the steel plate comes from the inherent central looseness of the continuous casting billet, which needs to be achieved through a larger rolling compression ratio. However, ultra-wide and ultra-thick plates lack the rolling conditions for a large compression ratio, and the rolling conditions also limit the realization of grain refinement.

[0009] The creativity and beneficial effects of the present invention improve the density of the core of the steel plate through a series of means. First, the tough-to-brittle transition temperature of the steel plate is reduced by appropriately reducing the C content and appropriately increasing the Ni content through composition design, and the grain size of the steel plate is controlled by matching appropriate amounts of microalloying elements. Secondly, in the smelting process, the purity of the steel plate is improved by the pure steel smelting technology. Then, in the continuous casting process, the solid-state reduction technology at the outlet of the caster is used to promote the deformation inside the continuous casting billet, thereby improving the density. Thirdly, in the rolling process, the slab is softened by ultra-high heating temperature, and an ultra-large reduction rate of ultra-wide plates is achieved, which promotes the closure of core defects; in the two-stage rolling process, low-temperature rolling is used to promote the deformation of austenite and refine the ferrite grain size of the steel plate. Finally, the grain size of the steel plate is further refined through a suitable normalizing process to improve the impact toughness of the steel plate, thereby achieving the common realization of the density and fine grains of the steel plate. The present invention can adopt 450mm thick continuous casting billets to stably produce ultra-wide and ultra-thick steel plates with a maximum width of 130mm. The maximum width of the obtained steel plates can reach 4500mm. The normalizing production process is adopted, and the yield strength of the steel plates is ≥355MPa, the tensile strength is ≥490MPa, the elongation is ≥26%, the cross-sectional shrinkage rate of the thickness direction is ≥35%, and the -60℃ impact is ≥200J. The ultra-wide and ultra-thick high-toughness 36kg-grade steel plates are produced, which are suitable for the needs of large-scale offshore engineering and wind power conductor frames. DETAILED DESCRIPTION

[0010] The following is a further description of the main contents of the present invention such as the component control range and the best mode of implementation in conjunction with the embodiments: Example 1: A method for producing ultra-wide and ultra-thick high-toughness steel, wherein the chemical composition of the steel is C=0.10, Si=0.25, Mn=1.55, P=0.008, S=0.003, Nb=0.035, V=0.045, Ni=0.42, Ti=0.015, Al=0.036 in weight percentage, and the remainder is Fe and unavoidable impurities; the total oxygen content of the steel tapped from the converter is 0.62%, the C content is 0.07, 1.5 tons of casting slag is used after tapping, and 40 kg of aluminum powder is added to the refining LF furnace; The total time of RH furnace vacuum treatment is 17min; RH is treated with calcium and soft blown for 20min after breaking the air; the continuous casting billet thickness is 350mm, the superheat of the continuous casting tundish is between 12 and 19℃, and the total reduction of the last section of the casting machine outlet is 10mm; the temperature of the rolling heating furnace is 1290℃, the total time in the furnace is 670min, the average pass reduction of the first stage is 58mm, the thickness of the intermediate billet is 180mm, the second stage rolling temperature is 760℃, the final rolling temperature is 750℃, the rolled steel plate is 110mm, and the width is 4250mm. The normalizing temperature is 900℃, the normalizing heating rate is 10℃ / s, the holding time is 40min, and the air cooling to room temperature is performed after normalizing.

[0011] Example 2: A method for producing ultra-wide and ultra-thick high-toughness steel, wherein the chemical composition of the steel is C=0.11, Si=0.28, Mn=1.52, P=0.007, S=0.003, Nb=0.037, V=0.048, Ni=0.46, Ti=0.017, Al=0.042 in weight percentage, and the remainder is Fe and unavoidable impurities; the total oxygen content of the steel tapped from the converter is 0.73%, the C content is 0.08, 1.7 tons of casting slag is used after tapping, and 60 kg of aluminum powder is added to the refining LF furnace; The total time of RH furnace vacuum treatment is 18min; RH is treated with calcium and soft blown for 23min after breaking the air; the continuous casting billet thickness is 400mm, the superheat of the continuous casting tundish is between 12 and 16℃, and the total reduction of the last section of the casting machine outlet is 12mm; the temperature of the rolling heating furnace is 1300℃, the total time in the furnace is 685min, the average pass reduction of the first stage is 56mm, the thickness of the intermediate billet is 190mm, the second stage rolling temperature is 753℃, the final rolling temperature is 732℃, the rolled steel plate is 120mm, and the width is 4300mm. The normalizing temperature is 910℃, the normalizing heating rate is (9 / plate thickness)℃ / s, the holding time is 46min, and the air cooling to room temperature after normalizing.

[0012] Example 3: A method for producing ultra-wide and ultra-thick high-toughness steel, wherein the chemical composition of the steel is C=0.12, Si=0.32, Mn=1.49, P=0.009, S=0.0018, Nb=0.042, V=0.056, Ni=0.56, Ti=0.015, Al=0.047 in weight percentage, and the balance is Fe and unavoidable impurities; the total oxygen content of the steel tapped from the converter is 0.56%, the C content is 0.06, 1.6t of casting slag is used after tapping, and 60kg of aluminum powder is added to the refining LF furnace ; The total time of RH furnace vacuum treatment is 19min; RH is treated with calcium and soft blown for 25min after breaking the air; the continuous casting billet thickness is 450mm, the continuous casting package overheating is between 17 and 20℃, and the total reduction of the last section of the casting machine outlet is 15mm; the temperature of the rolling heating furnace is 1310℃, the total time in the furnace is 733min, the average pass reduction of the first stage is 53mm, the thickness of the intermediate billet is 220mm, the second stage rolling temperature is 749℃, the final rolling temperature is 728℃, the rolled steel plate is 130mm, and the width is 4200mm. The normalizing temperature is 905℃, the normalizing heating rate is 8℃ / s, the holding time is 49min, and the air cooling to room temperature is performed after normalizing.

[0013] Example 4: A production method for ultra-wide and ultra-thick high-toughness steel, wherein the chemical composition of the steel is C=0.11, Si=0.35, Mn=1.57, P=0.010, S=0.0026, Nb=0.045, V=0.062, Ni=0.78, Ti=0.019, Al=0.027, and the remainder is Fe and unavoidable impurities; the total oxygen content of the steel tapped from the converter is 0.61%, the C content is 0.08, 1.8t of casting slag is used after tapping, and 60kg of aluminum powder is added to the refining LF furnace ; The total time of RH furnace vacuum treatment is 20min; RH is treated with calcium and soft blown for 20min after breaking the air; the continuous casting billet thickness is 450mm, the continuous casting package overheating is between 11 and 14℃, and the total reduction of the last section of the casting machine outlet is 15mm; the temperature of the rolling heating furnace is 1320℃, the total time in the furnace is 783min, the average pass reduction of the first stage is 56mm, the thickness of the intermediate billet is 230mm, the second stage rolling temperature is 742℃, the final rolling temperature is 721℃, the rolled steel plate is 130mm, and the width is 4500mm. The normalizing temperature is 907℃, the normalizing heating rate is 8℃ / s, the holding time is 46min, and the air cooling to room temperature after normalizing.

[0014] Table 1 Performance test results of each example (impact temperature -60℃, impact test thickness 1 / 2)

[0015] As can be seen from Table 1, the strength and core impact toughness of the material of the present invention meet the requirements of steel grades such as F36, S355NL and Q355F, and the core impact of the steel plate is stable, with an average value of more than 200 J. It is suitable for the production of offshore jackets with special thickness and width requirements. The steel plate has simple composition, excellent performance, strong resistance to lamellar tearing, and has excellent development prospects.

Claims

1. A method for producing ultra-wide, ultra-thick and high-toughness steel, characterized in that: The chemical composition of the steel is C=0.08-0.12, Si=0.10-0.40, Mn=1.0-1.6, P≤0.010, S≤0.003, Nb=0.01-0.045, V=0.03-0.08, Ni=0.3-0.8, Ti=0.01-0.02, Al=0.02-0.06, and the balance is Fe and unavoidable impurities; 450mm thick continuous casting billet is used to produce a 36kg grade steel plate with a maximum thickness of 130mm and a maximum width of 4500mm, the steel plate has a yield strength of ≥355MPa, a tensile strength of ≥490MPa, an elongation of ≥26%, a cross-sectional shrinkage rate of tensile in the thickness direction of ≥35%, and an impact of -60℃ of ≥200J; the process steps are as follows: (1) Smelting: The BOF-LF-RH production process is adopted. The converter smelting controls P≤0.01%, the total oxygen content of the steel is 0.5%-0.8%, and the C content is 0.06%-0.08%. After steel is tapped, 1-2 tons of casting slag is used to wash the molten steel and quickly slag. The refining LF furnace enters the station to quickly heat up and make white slag. The reducibility of the molten steel is maintained by adding 40-80 kg of aluminum powder. The RH furnace production adopts a deep degassing process, and the total vacuum treatment time is ≥15 minutes. After the RH is broken, calcium treatment and soft blowing are ≥15 minutes; (2) Continuous casting: The ratio of the continuous casting billet thickness to the steel plate thickness is ≥3. The continuous casting adopts low temperature casting, and the superheat of the tundish is between 10 and 20 °C; (3) Rolling: Two-stage rolling technology is used during rolling. The first stage is high-temperature and large-reduction rolling, requiring an average pass reduction of 50-60 mm. Large intermediate billet and low-temperature two-stage rolling are used. The intermediate billet thickness is ≥ the finished product thickness + 60 mm. The second-stage rolling temperature is 740-780°C, and the final rolling temperature is between 740 and 760°C. After rolling, the steel plates are stacked and slowly cooled to room temperature. (4) Heat treatment: The steel plate is subjected to normalizing process and then air-cooled to room temperature.

2. The method for producing ultra-wide, ultra-thick, high-toughness steel according to claim 1, characterized in that Step (3) Rolling: Solid state reduction technology is used at the outlet of the casting machine to reduce the central looseness of the ingot. The total reduction in the last section of the casting machine outlet is 10 to 15 mm.

3. The method for producing ultra-wide, ultra-thick and high-toughness steel according to claim 1, characterized in that Step (3) rolling: the temperature out of the heating furnace is 1280-1320°C, and the total time in the furnace is 600-800 min to ensure that the ingot is fully heated.

4. The method for producing ultra-wide, ultra-thick and high-toughness steel according to claim 1, characterized in that Step (4) heat treatment: normalizing temperature is between 890 and 920°C, normalizing heating rate is 8 to 10°C / s, and holding time is 30 to 50 min.

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