Manufacturing method of high-performance Q345R end socket plate and simulated thermal forming process

Abstract

According to the manufacturing method and the simulated thermal forming process of the high-performance Q345R end socket plate, by means of strength and toughness matching component design and large-section continuous casting billet production, in combination with high-purity smelting process, two-stage rolling and narrow window heat treatment process process control, the thickness range of a manufactured steel plate is 120-150 mm, and the requirement for the mechanical properties of the steel plate can be met: the yield strength ReL is larger than or equal to 340 Mpa; the tensile strength Rm is 510-550 Mpa, the elongation A is larger than or equal to 25%, and the-20 DEG C low-temperature impact KV2 of the steel plate is larger than or equal to 120 J. Meanwhile, a simulated thermal forming and recovery performance heat treatment process of the economical high-performance Q345R end socket plate is provided, and it is ensured that the performance requirements can still be met after simulated postweld heat treatment at the temperature of 630 + / -10 DEG C.

Description

Technical Field

[0001] This invention belongs to the field of steel production technology and relates to a manufacturing method and simulated thermoforming process for a high-performance Q345R end plate. Background Technology

[0002] With the rapid development of industries such as petroleum, coal chemical, and energy, the market demand for cryogenic liquefied gas storage tanks is increasing daily, and the demand for container steel is growing year by year. Q345R steel has excellent comprehensive properties and is currently the most widely used and in-demand steel for cryogenic pressure vessels, widely used in the manufacture of cryogenic liquefied gas storage tanks. As cryogenic pressure vessel equipment becomes more high-end and larger, the wall thickness of the end plates is gradually increasing, and the technical requirements for them are becoming increasingly stringent. Compared to the body plates, the end plates require hot pressing and performance-restoring heat treatment during equipment manufacturing, making the process more complex and demanding higher requirements for the mechanical and weldability properties of the materials, thus increasing the technical difficulty of production.

[0003] Chinese patent CN116926424A discloses a production method and simulated hot forming process for thick steel plates used in high-temperature and high-pressure vessel heads. The steel plates produced by this process do not require heat treatment to restore performance after hot forming and still possess good toughness and high-temperature performance. However, the content of precious alloys Ni and Mo in the steel plate composition is 0.60%~1.0% and 0.20%~0.40%, respectively, resulting in high alloy costs. Chinese patent CN118497631A discloses a high-performance, thick-walled 16MnDR steel plate for vessel heads and its production method. The steel plate retains excellent mechanical properties in the rolled state and after hot forming, normalizing, tempering, and simulated stress-relieving heat treatment. However, the production process uses ingot casting, requiring pre-rolling into billets during the rolling process, leading to increased process costs and a longer production cycle. Furthermore, the yield rate of ingot production is lower than that of continuous casting due to the influence of risers, further increasing costs. Chinese patent CN108315539A discloses a method for producing extra-wide and extra-thick steel plates for container heads with excellent thermoformability. It is also produced from steel ingots, resulting in higher production costs.

[0004] Therefore, it is necessary to develop an economical, high-performance Q345R end plate with new components and new processes to meet the market demand for high-performance, thick end plates. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems and shortcomings of the existing technology and provide an economical and high-performance Q345R end plate manufacturing method. The manufactured steel plate thickness ranges from 120 to 150 mm, which can meet the mechanical property requirement of yield strength R. eL ≥340MPa, tensile strength R m=510~550Mpa, elongation A≥25%, steel plate -20℃ low temperature impact KV2≥120J. Another objective of this invention is to provide a simulated thermoforming and performance recovery heat treatment process for the above-mentioned economical high-performance Q345R end plate, ensuring that the above performance requirements can still be met after simulated post-weld heat treatment.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The manufacturing method of high-performance Q345R end plates, with the following chemical composition by mass percentage: C=0.17%~0.18%, Si=0.15%~0.20%, Mn=1.35%~1.40%, P≤0.010%, S≤0.003%, Alt=0.020%~0.050%, Nb=0.035%~0.04%, V=0.035%~0.040%, Ti≤0.008%, Ni=0.15%~0.20%, with the remainder being Fe and essential residual elements, includes the following process steps: (1) Converter smelting: Top and bottom blowing converter, the number of supplementary blowing times ≤ 2 times, deoxidizer and alloy are added during the tapping process for deoxidation and alloying, argon blowing is carried out throughout the process, slag is blocked during tapping, and the tapping P ≤ 0.007%; (2) Ladle refining: White slag formation and heating are carried out in the LF furnace, and the white slag holding time is ≥15min; ≥200m of pure Ca wire is fed in before leaving the LF furnace (adjusted appropriately according to the amount of charge and the change of the oxidizing property of the molten steel); after LF refining, VD vacuum treatment is adopted, the vacuum is drawn to below 0.5tor (67Pa), the vacuum holding time is ≥18min, and the molten steel is soft blown for ≥12min before leaving the VD furnace; (3) Continuous casting: adopt a cross section of 450mm2070mm, full-process protective casting, control the liquid level fluctuation in the crystallizer to ≤±5mm, continuous casting speed of 0.45-0.5m / min, and control the superheat to ≤15℃; (4) Heating and rolling: Furnace temperature ≤1250℃, soaking temperature 1190~1230℃, soaking time ≥120min, total time in furnace ≥480min; Stage I rolling temperature ≥1050℃, final rolling temperature ≥980℃, large reduction system adopted, the last two reductions ≥35mm, intermediate billet thickness ≥ finished plate thickness +50mm; Stage II rolling temperature ≤880℃, final rolling temperature 790~840℃, reddening temperature 680~720℃; (5) Heat treatment: normalizing heat treatment is adopted, with a normalizing temperature of 890±10℃ and a holding time of 70~90min, followed by air cooling.

[0007] The simulated thermoforming process for the aforementioned high-performance Q345R end cap plate includes the following process steps: (1) Simulated hot forming: the holding temperature is 930±10℃, the holding time is 1.5~2.0 min / mm, and the steel plate is air-cooled after it comes out of the furnace; (2) Heat treatment to restore performance: Normalizing: holding temperature 900±10℃, heating coefficient 1.5~2.5 min / mm, holding time 50-70min, accelerated cooling; Tempering: holding temperature 660±10℃, heating coefficient 2.5~3.5 min / mm, holding time 70-90min, air cooling; (3) Simulated post-weld heat treatment: The steel plate is loaded into the furnace at a temperature below 400℃, with a heating rate of ≤55℃ / h, a holding temperature of 630±10℃, a holding time of 10~12h, and after holding, it is cooled down to 400℃ with the furnace at a rate of ≤55℃ / h, and then air-cooled after being taken out of the furnace.

[0008] The design principle of this invention is as follows: This invention employs a high-C, high-Mn composition system, combined with a normalizing process to ensure full solid solution of alloying elements, thereby fully utilizing the interstitial solid solution strengthening effect of C and the substitutional solid solution strengthening effect of Mn. The higher levels of Nb and V microalloying elements in this invention can form nanoscale precipitates with interstitial C in the steel, which can pin grain boundaries and refine the grains. This precipitation strengthening effect also contributes to strength, ensuring high strength even after simulated post-weld heat treatment. Simultaneously, the addition of 0.15%–0.20% Ni improves toughness. Ni is an austenite-forming element that can infinitely dissolve with Fe, expanding the austenite phase region and improving austenite stability, which is beneficial for improving low-temperature toughness. The use of low-Si, low-P, and low-S elements also contributes to improving the toughness of the steel plate. Excessive Si content reduces plasticity, toughness, and weldability, while lower impurity elements prevent grain boundary embrittlement during prolonged simulated post-weld heat treatment, improving the toughness of the matrix. By controlling the Ti content, the formation of sharp-angled TiN inclusions can be avoided. Sharp-angled TiN inclusions are prone to stress concentration under load, which leads to the initiation and propagation of cracks and significantly reduces the toughness of the steel plate.

[0009] The beneficial effects of this invention are: (1) It effectively reduces the cost of alloys. (2) Using a 450mm cross-section continuous casting billet can ensure the reduction rate during the rolling process, meeting the requirement of a compression ratio ≥3. At the same time, compared with steel ingot production, it can reduce process costs, shorten the production cycle, improve production and delivery efficiency, and is more conducive to market promotion. (3) Combining high-purity smelting process, two-stage rolling and narrow-window heat treatment process control, it can ensure that the mechanical properties of steel plates with a thickness range of 120~150mm meet the yield strength R. eL ≥340MPa, tensile strength R m =510~550Mpa, elongation A≥25%, steel plate -20℃ low temperature impact KV2≥120J. (4) By simulating hot forming and performance recovery heat treatment process, it can be ensured that the steel plate can still meet the above performance requirements after simulated welding heat treatment at 630±10℃. Attached Figure Description

[0010] Figure 1 This is a 200x magnified micrograph of the steel plate after normalizing heat treatment in Example 1. Detailed Implementation

[0011] The specific embodiments of the present invention will be described in detail below with reference to examples. Example 1

[0012] The manufacturing method of high-performance Q345R end plates involves producing steel plates with a thickness of 122mm. The chemical composition (mass percentage) is as follows: C=0.17%, Si=0.17%, Mn=1.38%, P=0.009%, S=0.002%, Alt=0.032%, Nb=0.038%, V=0.037%, Ti=0.003%, Ni=0.19%, with the remainder being Fe and essential residual elements. Key steps in the production process include: (1) Converter smelting: Top and bottom blowing converter, 0 times of supplementary blowing, deoxidizer and alloy are added during the tapping process for deoxidation and alloying, argon blowing throughout the process, slag blocking during tapping, and tapping P=0.006%; (2) Ladle refining: White slag making and heating operations are carried out in the LF furnace, and the white slag is held for 16 minutes; 200m of pure Ca wire is fed in before leaving the LF furnace; after LF refining, VD vacuum treatment is adopted, and the vacuum is drawn to below 0.5tor (67Pa) and held for 18 minutes. The molten steel is soft blown for 14 minutes before leaving the VD furnace. (3) Continuous casting: The cross section is 450mm×2070mm, the whole process is protected during casting, the liquid level fluctuation in the crystallizer is controlled to be ≤±5mm, the continuous casting speed is 0.46m / min, and the superheat is controlled to be 11~14℃; (4) Heating and rolling: Furnace temperature 1221~1247℃, soaking temperature 1196~1224℃, soaking time 132min, total furnace time 483min; Stage I rolling temperature 1052℃, final rolling temperature 985℃, large reduction system is adopted, the last two reductions are 36mm and 35mm respectively, and the intermediate billet thickness is 175mm; Stage II rolling temperature 864℃, final rolling temperature 826℃, reddening temperature 709℃; (5) Heat treatment: normalizing heat treatment is adopted, with a normalizing temperature of 890±10℃, a holding time of 76 min, and air cooling.

[0013] The simulated thermoforming process of the 122mm high-performance Q345R end plate in this embodiment includes the following process steps: (1) Simulated hot forming: The holding temperature is 930±10℃ and the holding time is 196 min. The steel plate is then air-cooled after being taken out of the furnace. (2) Heat treatment to restore performance: normalizing, holding temperature 900±10℃, heating coefficient 1.7 min / mm, holding time 55 min, accelerated cooling; tempering, holding temperature 660±10℃, heating coefficient 2.8 min / mm, holding time 78 min, air cooling; (3) Simulated post-weld heat treatment: The steel plate is loaded into the furnace at a temperature below 400℃, with a heating rate of ≤55℃ / h, a holding temperature of 630±10℃, a holding time of 11h, and after holding, it is cooled down to 400℃ with the furnace at a rate of ≤55℃ / h, and then air-cooled after being taken out of the furnace.

[0014] The performance test results of the 122mm thick Q345R steel plate in the delivery state of this embodiment are as follows: yield strength 363MPa, tensile strength 542MPa, elongation 31%, and impact energy at -20℃ 177J, 185J, and 189J. After simulated hot forming + performance recovery heat treatment + simulated post-weld heat treatment, the performance test results are as follows: yield strength 356MPa, tensile strength 539MPa, elongation 30%, and impact energy at -20℃ 184J, 181J, and 195J. The microstructure after normalizing heat treatment is as follows. Figure 1 As shown, the microstructure of the steel plate is ferrite + pearlite. Example 2

[0015] The manufacturing method of high-performance Q345R end plates involves producing 135mm thick steel plates with the following chemical composition by mass percentage: C=0.18%, Si=0.19%, Mn=1.38%, P=0.008%, S=0.002%, Alt=0.027%, Nb=0.036%, V=0.039%, Ti=0.002%, Ni=0.16%, with the remainder being Fe and essential residual elements. The production method includes the following key process steps: (1) Converter smelting: Top and bottom blowing converter, with one additional blowing cycle. Deoxidizer and alloy are added during the tapping process for deoxidation and alloying. Argon is blown throughout the process, and slag is blocked during tapping. The tapping P=0.005%; (2) Ladle refining: White slag making and heating operations are carried out in the LF furnace, and the white slag is held for 18 minutes; 200m of pure Ca wire is fed in before leaving the LF furnace; after LF refining, VD vacuum treatment is adopted, the vacuum is drawn to below 0.5tor (67Pa), the vacuum time is held for 20 minutes, and the molten steel is soft blown for 13 minutes before leaving the VD furnace. (3) Continuous casting: The cross section is 450mm2070mm, the whole process is protected during casting, the fluctuation of the liquid level in the crystallizer is controlled to be ≤±5mm, the continuous casting speed is 0.48m / min, and the superheat is controlled to be 9~13℃; (4) Heating and rolling: Furnace temperature 1217~1245℃, soaking temperature 1193~1221℃, soaking time 144min, total furnace time 494min; Stage I rolling temperature 1058℃, final rolling temperature 986℃, large reduction system is adopted, the last two reductions are 35mm and 36mm respectively, and the intermediate billet thickness is 185mm; Stage II rolling temperature 870℃, final rolling temperature 819℃, reddening temperature 706℃; (5) Heat treatment: normalizing heat treatment is adopted, with a normalizing temperature of 890±10℃, a holding time of 82 min, and air cooling.

[0016] The simulated thermoforming process of the 135mm high-performance Q345R end plate in this embodiment includes the following process steps: (1) Simulated hot forming: the holding temperature is 930±10℃, the holding time is 245min, and the steel plate is air-cooled after it is taken out of the furnace; (2) Heat treatment to restore performance: normalizing, holding temperature 900±10℃, heating coefficient 1.9 min / mm, holding time 62min, accelerated cooling; tempering, holding temperature 660±10℃, heating coefficient 2.9 min / mm, holding time 82min, air cooling; (3) Simulated post-weld heat treatment: The steel plate is loaded into the furnace at a temperature below 400℃, the heating rate is ≤55℃ / h, the holding temperature is 630±10℃, the holding time is 12h, and after holding, it is cooled down to 400℃ with the furnace at a rate of ≤55℃ / h, and then air-cooled after being taken out of the furnace.

[0017] The performance test results of the 135mm thick Q345R steel plate in the delivery state of this embodiment are as follows: yield strength 359MPa, tensile strength 540MPa, elongation 32%, and low-temperature impact energy at -20℃ 194J, 192J, and 183J. After simulated hot forming + performance recovery heat treatment + simulated post-weld heat treatment, the performance test results are as follows: yield strength 353MPa, tensile strength 536MPa, elongation 30%, and low-temperature impact energy at -20℃ 177J, 174J, and 185J. Example 3

[0018] The manufacturing method of high-performance Q345R end plates involves producing steel plates with a thickness of 150mm. The chemical composition of the steel (by mass percentage) is as follows: C=0.18%, Si=0.17%, Mn=1.36%, P=0.009%, S=0.003%, Alt=0.041%, Nb=0.037%, V=0.038%, Ti=0.003%, Ni=0.19%, with the remainder being Fe and essential residual elements. The production method includes the following key process steps: (1) Converter smelting: Top and bottom blowing converter, 0 times of supplementary blowing, deoxidizer and alloy are added during the tapping process for deoxidation and alloying, argon blowing throughout the process, slag blocking during tapping, and tapping P=0.006%; (2) Ladle refining: White slag making and heating operations are carried out in the LF furnace, and the white slag is held for 17 minutes; pure Ca wire ≥200m is fed in before leaving the LF furnace; after LF refining, VD vacuum treatment is adopted, and the vacuum is drawn to below 0.5tor (67Pa) and held for 19 minutes. The molten steel is soft blown for 13 minutes before leaving the VD furnace. (3) Continuous casting: The cross section is 450mm2070mm, the whole process is protected during casting, the liquid level fluctuation in the crystallizer is controlled to be ≤±5mm, the continuous casting speed is 0.47m / min, and the superheat is controlled to be 10~14℃; (4) Heating and rolling: Furnace temperature 1220~1247℃, soaking temperature 1199~1225℃, soaking time 148min, total furnace time 498min; Stage I rolling temperature 1057℃, final rolling temperature 990℃, large reduction system adopted, the last two reductions are 37mm and 36mm respectively, intermediate billet thickness 202mm; Stage II rolling temperature 875℃, final rolling temperature 825℃, reddening temperature 699℃; (5) Heat treatment: normalizing heat treatment is adopted, with a normalizing temperature of 890±10℃, a holding time of 84min, and air cooling.

[0019] The simulated thermoforming process of the 150mm high-performance Q345R end plate in this embodiment includes the following steps: (1) Simulated hot forming: the holding temperature is 930±10℃, the holding time is 280 min, and the steel plate is air cooled after it is taken out of the furnace; (2) Heat treatment to restore performance: Normalizing: holding temperature 900±10℃, heating coefficient 2.0 min / mm, holding time 63min, accelerated cooling; Tempering: holding temperature 660±10℃, heating coefficient 2.9 min / mm, holding time 84min, air cooling; (3) Simulated post-weld heat treatment: The steel plate is loaded into the furnace at a temperature below 400℃, with a heating rate of ≤55℃ / h, a holding temperature of 630±10℃, a holding time of 11h, and after holding, it is cooled down to 400℃ with the furnace at a rate of ≤55℃ / h, and then air-cooled after being taken out of the furnace.

[0020] The performance test results of the 150mm thick Q345R steel plate in the delivery state of this embodiment are as follows: yield strength 355MPa, tensile strength 536MPa, elongation 31%, and low-temperature impact energy at -20℃ 188J, 172J, and 171J. After simulated hot forming + performance recovery heat treatment + simulated post-weld heat treatment, the performance test results are as follows: yield strength 349MPa, tensile strength 532MPa, elongation 31%, and low-temperature impact energy at -20℃ 184J, 180J, and 174J.

Claims

1. A method for manufacturing a high-performance Q345R end plate, characterized in that: The chemical composition of the steel plate, by mass percentage, is C=0.17%~0.18%, Si=0.15%~0.20%, Mn=1.35%~1.40%, P≤0.010%, S≤0.003%, Alt=0.020%~0.050%, Nb=0.035%~0.04%, V=0.035%~0.040%, Ti≤0.008%, Ni=0.15%~0.20%, with the remainder being Fe and essential residual elements; Steel plates with a thickness of 120~150mm are produced. The steel plates are shown in their delivery condition and after simulated hot forming + performance recovery heat treatment + simulated post-weld heat treatment, including their mechanical properties, yield strength R. eL ≥340MPa, tensile strength R m =510~550Mpa, elongation A≥25%, steel plate -20℃ low temperature impact KV2≥120J; The production process steps include: (1) Converter smelting: Top and bottom blowing converter, the number of supplementary blowing times ≤ 2 times, deoxidizer and alloy are added during the tapping process for deoxidation and alloying, argon blowing is carried out throughout the process, slag is blocked during tapping, and the tapping P ≤ 0.007%; (2) Ladle refining: white slag making and heating operations are carried out in the LF furnace, and the white slag holding time is ≥15min; 200~250m of pure Ca wire is fed in before leaving the LF furnace; after LF refining, VD vacuum treatment is adopted, the vacuum is drawn to below 67Pa, the vacuum holding time is ≥18min, and the molten steel is soft blown for ≥12min before leaving the VD furnace. (3) Continuous casting: The cross section is 450mm×2070mm, the whole process is protected during casting, the fluctuation of the liquid level in the crystallizer is controlled to be ≤±5mm, the continuous casting speed is 0.45~0.5m / min, and the superheat is controlled to be ≤15℃; (4) Heating and rolling: Furnace temperature ≤1250℃, soaking temperature 1190~1230℃, soaking time ≥120min, total time in furnace ≥480min; Stage I rolling temperature ≥1050℃, final rolling temperature ≥980℃, large reduction system adopted, the last two reductions ≥35mm, intermediate billet thickness ≥ finished plate thickness +50mm; Stage II rolling temperature ≤880℃, final rolling temperature 790~840℃, reddening temperature 680~720℃; (5) Heat treatment: normalizing heat treatment is adopted, with a normalizing temperature of 890±10℃ and a holding time of 70~90min, followed by air cooling.

2. The manufacturing method of a high-performance Q345R end plate according to claim 1, characterized in that: The microstructure of the steel plate is ferrite + pearlite.

3. A simulated thermoforming process for a high-performance Q345R end plate, characterized in that... The process includes the following steps: (1) Simulated hot forming: the holding temperature is 930±10℃, the holding time is 1.5~2.0 min / mm, and the steel plate is air-cooled after it comes out of the furnace; (2) Heat treatment to restore performance: normalizing, holding temperature 900±10℃, heating coefficient 1.5~2.5 min / mm, holding time 50~70min, accelerated cooling; tempering, holding temperature 660±10℃, heating coefficient 2.5~3.5 min / mm, holding time 70~90min, air cooling; (3) Simulated post-weld heat treatment: The steel plate is loaded into the furnace at a temperature below 400℃, with a heating rate of ≤55℃ / h, a holding temperature of 630±10℃, a holding time of 10~12h, and after holding, it is cooled down to 400℃ with the furnace at a rate of ≤55℃ / h, and then air-cooled after being taken out of the furnace.

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