Production method of high-toughness die-welding-resistant steel plate for pressure vessel

Abstract

The invention discloses a production method of a steel plate for a high-toughness die-welding-resistant pressure vessel. The steel comprises the following alloy components in percentage by mass: 0.16%-0.17% of C, 0.30%-0.40% of Si, 1.50%-1.55% of Mn, less than or equal to 0.010% of P, less than or equal to 0.002% of S, 0.02%-0.05% of Al, 0.040%-0.045% of Nb, 0.040%-0.045% of V, 0.015%-0.02% of Ti and the balance of Fe and inevitable impurities, and the carbon equivalent CEV is less than or equal to 0.45%. The thickness specification of the steel plate is 40-60 mm, the delivery state is a quenched and tempered state, the yield strength of 1 / 4 and 1 / 2 positions of the quenched and tempered and die welding state steel plate is larger than or equal to 350 MPa, the tensile strength is larger than or equal to 520 MPa, the ductility is larger than or equal to 23%, the-20 DEG C transverse KV2 impact unit value of the 1 / 4 and 1 / 2 positions of the quenched and tempered and die welding state steel plate is larger than or equal to 60 J, and the surface hardness of the quenched and tempered steel plate is smaller than or equal to 200 HB. According to the method, 260 / 300 mm casting blank section production is adopted, and the low-power C-type center segregation of the plate blank is not lower than the 2.0 level. And the high-toughness steel plate for the pressure vessel is prepared by adopting a quenched-tempered heat treatment process.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel production, and relates to a production method for a high-toughness and die-welding-resistant pressure vessel steel plate. Background Art

[0002] With the rapid development of industrial fields such as energy chemical industry and nuclear power equipment, pressure vessels are gradually developing towards large-scale, lightweight and high-parameter directions, and more stringent requirements are put forward for the comprehensive performance of steel plates for containers. When traditional pressure vessel steels pursue high strength indexes, there is often a shortage of reserves, and problems such as embrittlement in the heat-affected zone and strength mismatch of welded joints are likely to occur during the welding process. Especially in the die-welding composite manufacturing process, the material needs to withstand high strains during die forming and multi-pass welding heat cycles at the same time. Currently, the normalizing process is generally adopted in industrial production, and alloy design mostly relies on the addition of high Ni and Mo elements, resulting in rising costs and an increased tendency to cold crack during welding. Therefore, it is necessary to study how to achieve long-time die-welding heat treatment and excellent welding adaptability and forming processability through the coordinated innovation of composition and process while ensuring the strength-toughness matching of the material. Summary of the Invention

[0003] The purpose of the present invention is to provide a production method for a high-toughness and die-welding-resistant pressure vessel steel plate, which adopts a low-cost narrow composition design and a matching production process to meet the requirements of the current stage for the performance matching of high-toughness and die-welding-resistant steel plates for pressure vessels.

[0004] The technical solution of the present invention: A production method for a high-toughness and die-welding-resistant pressure vessel steel plate, the mass percentage of the alloy components of the steel is C = 0.16% - 0.17%, Si = 0.30% - 0.40%, Mn = 1.50% - 1.55%, P ≤ 0.010%, S ≤ 0.002%, Al = 0.02% - 0.05%, Nb = 0.040% - 0.045%, V = 0.040% - 0.045%, Ti = 0.015% - 0.02%, and the rest are Fe and inevitable impurities, and the carbon equivalent CEV = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15 ≤ 0.45%; the thickness specification of the steel plate is 40 - 60 mm, and the delivery state is tempered state. The yield strength at the 1 / 4 and 1 / 2 positions of the tempered state and die-welded state steel plates is ≥ 350 MPa, the tensile strength is ≥ 520 MPa, the elongation is ≥ 23%, the transverse KV2 impact single value at -20 °C at the 1 / 4 and 1 / 2 positions of the tempered state and die-welded state steel plates is ≥ 60 J, and the surface hardness of the tempered state steel plate is ≤ 200 HB; the key process steps include: (1) Converter control: the tapping C ≥ 0.06%, P ≤ 0.003%; (2)LF Control: The total argon blowing time for molten steel in the LF furnace is ≥ 40 min, and the white slag holding time is ≥ 20 min; Soft argon blowing operation is carried out before the molten steel exits the LF furnace, and the soft argon blowing time is ≥ 5 min; Calcium treatment operation is carried out at the end of refining, feeding pure calcium wire 100 - 200 m; (3)RH / VD Control: Argon is blown throughout the process when the molten steel enters the RH / VD furnace. The target vacuum for the VD furnace is below 67 Pa, and the holding time is ≥ 15 min; The vacuum for the RH furnace is below 67 Pa, and the holding time is ≥ 10 min; Soft argon blowing is carried out for more than 10 min before the molten steel exits the VD (RH) furnace; The hydrogen in the molten steel is determined when it leaves the station, and the requirement is [H] ≤ 2.0 ppm; (4)Continuous casting: The cross-section of the slab is 260 mm or 300 mm, and full-process protected casting is implemented. The casting speed is 0.8 - 1.0 m / min. The superheat of the tundish for the first casting furnace is ≤ 23 °C, and the superheat of the tundish for continuous casting furnaces is 8 - 15 °C. The dynamic soft reduction control technology is adopted, and the low magnification C-type center segregation of the slab is not lower than grade 2.0; (5)Slab heating: The slab is heated in a walking beam furnace, restricting the furnace temperature ≤ 1250 °C. The tapping temperature of the billet is controlled at 1180 - 1220 °C, and the total time of the slab in the furnace is 240 - 360 min; (6)Rolling: The starting rolling temperature in the first stage is 1080 - 1160 °C, and the finishing rolling temperature is ≥ 960 °C, ensuring that the reduction ratio in the last three passes is ≥ 18%; The starting rolling temperature in the second stage is 860 - 880 °C, the finishing rolling temperature is 790 - 830 °C, the recrystallization temperature after finishing cooling is 660 - 700 °C, and the cooling rate is 5 - 7 °C / S; (7)Heat treatment: The quenching process is 880 ± 10 °C, the time is ≥ 1.6 × slab thickness mm × min / mm, and the holding time is 20 - 30 min; The tempering process is 685 ± 10 °C, the time is ≥ 2.2 × slab thickness mm × min / mm, and the holding time is 30 - 40 min.

[0005] Innovation points of the present invention: 1) Adopt low-cost narrow composition control and composition design of Nb, V, Ti microalloys, without adding precious alloys such as Ni, Cr, Mo.

[0006] 2) Produce with a slab cross-section of 260 mm × 300 mm, implement full-process protection and low superheat casting, and use dynamic soft reduction control technology. The low magnification C-type center segregation of the slab is not lower than grade 2.0.

[0007] 3) The quenching and tempering heat treatment process is adopted to ensure that high-toughness steel plates for pressure vessels are prepared at the 1 / 4 and 1 / 2 positions of the steel plate under the long-term die welding process. In terms of mechanical properties: the yield strength of the steel plates at the 1 / 4 and 1 / 2 positions in the quenched and tempered state and die welding state is ≥ 350 MPa, the tensile strength is ≥ 520 MPa, the elongation is ≥ 23%, the transverse KV2 impact single value at -20 °C of the steel plates at the 1 / 4 and 1 / 2 positions in the quenched and tempered state and die welding state is ≥ 60 J, and the surface hardness of the quenched and tempered steel plate is ≤ 200 HB. Description of the Drawings

[0008] Figure 1 It is the microstructure morphology diagram of the 1 / 4 position of the 40-mm-thick 370-MPa-grade steel plate in Example 1.

[0009] Figure 2 It is the microstructure morphology diagram of the 1 / 2 position of the 40-mm-thick 370-MPa-grade steel plate in Example 1.

[0010] Figure 3 It is the microstructure morphology diagram of the 1 / 4 position of the 60-mm-thick 370-MPa-grade steel plate in Example 2.

[0011] Figure 4 It is the microstructure morphology diagram of the 1 / 2 position of the 60-mm-thick 370-MPa-grade steel plate in Example 2. Detailed Implementation Modes

[0012] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0013] Example 1 The production of 370-MPa-grade high-toughness die-welding-resistant pressure vessel steel plates with a steel plate thickness of 40 mm, and the chemical composition and carbon equivalent percentage are shown in Table 1. The production process includes smelting and casting, heating, rolling, controlled cooling, and heat treatment processes. The specific process steps and process parameters are as follows: Smelting and casting: Oxygen converter steelmaking - LF refining - VD refining - continuous casting, superheat 12 °C, H content 1.3 ppm, continuous casting billet cross-section thickness 260 mm, slab macro C-type center segregation grade 1.5; Heating, rolling, and cooling: The slab heating furnace outlet temperature is 1205 °C, and the residence time in the furnace is 270 min; Two-stage rolling is adopted, the rough rolling starting temperature is 1150 °C, the finish rolling starting temperature is 870 °C, the finish rolling temperature is 807 °C, water cooling after rolling, and the return red temperature is 685 °C; Heat treatment process: Quenching temperature 887 °C, quenching time 72 min, holding time 22 min, tempering temperature 691 °C, tempering time 95 min, holding time 33 min.

[0014] The microstructures at the 1 / 4 and 1 / 2 thicknesses of the high-toughness die-welding-resistant pressure vessel steel plates produced in this example in the quenched and tempered state are shown in Figure 1, and the mechanical property indexes are shown in Table 2.

[0015] Example 2 Production of 370 Mpa grade high toughness die welding resistant pressure vessel steel plate with a thickness of 60 mm. Its chemical composition and carbon equivalent percentage are shown in Table 1. The production process includes smelting and casting, heating, rolling, controlled cooling and heat treatment processes. The specific process steps and their process parameters are as follows: Smelting and casting: Oxygen converter steelmaking - LF refining - VD refining - continuous casting, superheat 10 °C, H content 1.1 ppm, cross-sectional thickness of continuous casting billet 300 mm, center segregation of type C in slab macrostructure 1.0 grade; Heating, rolling and cooling: The slab is discharged from the furnace at a temperature of 1210 °C and the residence time in the furnace is 320 min; Two-stage rolling is adopted, the rough rolling starting temperature is 1155 °C, the finishing rolling starting temperature is 860 °C, the finishing rolling temperature is 813 °C, water cooling is carried out after rolling, and the recrystallization temperature is 683 °C; Heat treatment process: Quenching temperature 885 °C, quenching time 110 min, holding time 28 min, tempering temperature 693 °C, tempering time 145 min, holding time 36 min.

[0016] Table 1 Chemical composition mass percentage (wt%) of the steel plate produced in the example 。

[0017] Table 2 Detection results of the mechanical properties of the steel plate produced in the example after heat treatment 。

[0018] The microstructure at 1 / 4 and 1 / 2 thickness of the high toughness die welding resistant pressure vessel steel plate produced in this example in the quenched and tempered state is shown in Figure 1 , and the mechanical property indexes are shown in Table 2.

[0019] In the example, the die welding process is 610 ± 15 °C * 11 h, the furnace is charged below 300 °C, the heating rate is 55 - 150 °C / h, after reaching the target temperature, it is held for 11 h, then cooled with the furnace to 300 °C, and taken out of the furnace and air-cooled to room temperature.

Claims

1. A production method of a steel plate for a high-toughness die-welding-resistant pressure vessel, characterized in that: The mass percentages of the alloying components of the steel are as follows: C = 0.16% - 0.17%, Si = 0.30% - 0.40%, Mn = 1.50% - 1.55%, P ≤ 0.010%, S ≤ 0.002%, Al = 0.02% - 0.05%, Nb = 0.040% - 0.045%, V = 0.040% - 0.045%, Ti = 0.015% - 0.02%, and the balance is Fe and inevitable impurities. The carbon equivalent CEV = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15 ≤ 0.45%; the thickness specification of the steel plate is 40 - 60 mm, and the delivery condition is quenched and tempered. The yield strength at the 1 / 4 and 1 / 2 positions of the quenched and tempered and die-welded steel plates ≥ 350 MPa, the tensile strength ≥ 520 MPa, the elongation ≥ 23%, the transverse KV2 impact single value at -20°C at the 1 / 4 and 1 / 2 positions of the quenched and tempered and die-welded steel plates ≥ 60 J, and the surface hardness of the quenched and tempered steel plate ≤ 200 HB; The key process steps include: (1) Converter control: The tapping C ≥ 0.06%, P ≤ 0.003%; (2) LF control: The total argon blowing time of the molten steel in the LF furnace ≥ 40 min, and the white slag holding time ≥ 20 min; Soft argon blowing operation is carried out before the molten steel exits the LF, and the soft argon blowing time ≥ 5 min; Calcium treatment operation is carried out at the end of refining, and 100 - 200 m of pure calcium wire is fed; (3) RH / VD control: The molten steel is blown with argon throughout the process when entering the RH / VD furnace. The target vacuum of the VD furnace is below 67 Pa, and the holding time ≥ 15 min; The vacuum of the RH furnace is below 67 Pa, and the holding time ≥ 10 min; Soft argon blowing is greater than 10 min before the molten steel exits the VD (RH) furnace; The molten steel is hydrogen-determined when leaving the station, and the requirement is [H] ≤ 2.0 ppm; (4) Continuous casting: The cross-section of the casting blank is 260 mm or 300 mm, and full protection casting is implemented. The casting speed is 0.8 - 1.0 m / min. The superheat of the tundish in the starting furnace ≤ 23°C, and the superheat of the tundish in the continuous casting furnace is 8 - 15°C. The dynamic soft reduction control technology is adopted, and the low magnification C-class center segregation of the slab is not lower than 2.0 grades; (5) Slab heating: The slab is heated in a walking beam furnace, and the furnace temperature is limited to ≤ 1250°C. The tapping temperature of the billet is controlled at 1180 - 1220°C, and the total time of the slab in the furnace is 240 - 360 min; (6) Rolling: The starting rolling temperature in the first stage is 1080 - 1160°C, the finishing rolling temperature ≥ 960°C, and the reduction rate in the last three passes is guaranteed to be ≥ 18%; The starting rolling temperature in the second stage is 860 - 880°C, the finishing rolling temperature is 790 - 830°C, the final cooling return red temperature is 660 - 700°C, and the cooling rate is 5 - 7°C / S; (7) Heat treatment: The quenching process is 880 ± 10°C, the time is ≥ 1.6 × plate thickness mm × min / mm, and the holding time is 20 - 30 min; The tempering process is 685 ± 10°C, the time ≥ 2.2 × plate thickness mm × min / mm, and the holding time is 30 - 40 min.

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