Production method of Q345R steel plate with excellent high-temperature PWHT resistance

Abstract

The invention discloses a production method of a Q345R steel plate with excellent high-temperature PWHT resistance. The steel comprises the following chemical components in percentage by mass: 0.15%-0.18% of C, 0.30%-0.40% of Si, 1.50%-1.60% of Mn, less than or equal to 0.010% of P, less than or equal to 0.003% of S, 0.020%-0.050% of Alt, 0.03%-0.05% of Nb, 0.02%-0.03% of V, 0.01%-0.02% of Ti, 0.15%-0.25% of Cr and the balance of Fe and essential residual elements. The production process comprises the technological steps of converter smelting, external refining, slab heating, two-stage controlled rolling and normalizing heat treatment. By replacing high-cost Ni and Cu alloys with low-cost Cr and V alloys, the production cost is reduced, the precipitation strengthening effect of the Cr and V alloys is utilized to ensure that Q345R has excellent high-temperature PWHT resistance, the mechanical property still meets the GB / T713.2-2023 requirement after high-temperature PWHT is kept at 700 + / -10 DEG C for 12 hours, and the low-temperature impact KV2 of a core part of the steel plate at-20 DEG C is greater than or equal to 150J.

Description

Technical Field

[0001] The invention belongs to the technical field of steel production, and in particular relates to a production method of a Q345R steel plate with excellent high-temperature PWHT resistance. Background Art

[0002] With the advancement of steel industry technology and the development of social economy, the demand for pressure vessel steel is gradually increasing. Among them, Q345R has the characteristics of excellent mechanical properties, high purity and good processing performance. It is a steel with high demand for boilers and pressure vessels. It is widely used in petroleum, chemical industry, nuclear power and other fields, and is used to manufacture key parts such as equipment cones and heads. After the equipment is welded, in order to eliminate the residual stress of the steel plate, the equipment needs to be subjected to post weld heat treatment (PWHT). Usually, the simulated post weld heat treatment temperature of Q345R steel plate is 560~630℃, and the mechanical properties of the simulated post weld heat treatment need to be guaranteed. In recent years, due to design requirements, the same equipment is required to use both carbon manganese steel and chromium-molybdenum steel. After the equipment is welded, it needs to be subjected to post weld heat treatment as a whole, and the simulated post weld heat treatment temperature of chromium-molybdenum steel is usually above 680℃. Therefore, Q345R is required to have excellent high temperature PWHT resistance to ensure that the steel plate still meets the performance requirements after high temperature simulated post weld heat treatment.

[0003] Chinese patent CN 110184528 discloses a Q345R steel plate with excellent performance under high temperature simulated post-weld heat treatment conditions and its manufacturing method. By increasing the compression ratio, improving the purity of molten steel, and matching the reasonable composition and rolling and heat treatment processes, excellent internal quality and PWHT state mechanical properties can be obtained. However, in order to achieve excellent PWHT resistance, the invention adds higher alloy elements, such as Ni = 0.10% ~ 0.30%, Cu = 0.10% ~ 0.30%, which increases production costs and reduces corporate profitability. Summary of the invention

[0004] The object of the present invention is to provide a method for producing a Q345R steel plate with excellent high temperature PWHT resistance. The produced Q345R steel plate has excellent high temperature PWHT resistance, the steel plate thickness range is 10~70mm, the steel plate -20℃ core low temperature impact KV 2 ≥150J.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A production method of a Q345R steel plate with excellent high-temperature PWHT resistance, characterized in that: the chemical composition mass percentage of the steel plate is C=0.15%~0.18%, Si=0.30%~0.40%, Mn=1.50%~1.60%, P≤0.010%, S≤0.003%, Alt=0.020%~0.050%, Nb=0.03%~0.05%, V=0.02%~0.03%, Ti=0.01%~0.02%, Cr=0.15%~0.25%, and the others are Fe and essential residual elements; the steel plate thickness ranges from 10 to 70 mm, and the steel plate -20°C core low-temperature impact KV 2 ≥150J; the production process steps include: (1) Converter smelting: top and bottom double blowing converter, the number of re-blowing is ≤2 times, deoxidizer and alloy are added during the steelmaking process for deoxidation and alloying, and the steelmaking P is ≤0.007%; (2) Refining outside the furnace: After the molten steel arrives at the LF furnace, white slag is made and heated, and the white slag is kept for ≥15min; calcium treatment is carried out before the LF furnace leaves the station, and a pure Ca line of ≥150m is fed; after LF refining, VD vacuum treatment is adopted, and the vacuum is pumped to below 67Pa, and the holding time is ≥15min. Soft blowing is carried out before the molten steel leaves the VD furnace for ≥12min; protection casting is carried out throughout the process, and the superheat is controlled to ≤15℃; (3) Heating: The furnace temperature of the heating furnace is ≤1230℃, the soaking temperature is 1160~1200℃, and the soaking time is ≥50min; (4) Rolling: The starting rolling temperature of stage I is ≥1050℃, the final rolling temperature is ≥980℃, the reduction rate of the last three passes is ≥18%, and the thickness of the intermediate billet is 2~3 times the thickness of the finished plate; the starting rolling temperature of stage II is ≤880℃, the final rolling temperature is 780~820℃, and the steel is rapidly cooled at a cooling rate of 2~5℃ / s after rolling, and the red-returning temperature is 680~720℃; (5) Heat treatment: normalizing process is adopted, normalizing temperature is 880±10℃, holding time = steel plate thickness mm×1.0~1.5min / mm, and air cooling is carried out after leaving the furnace.

[0006] The obtained steel plate structure is uniform and fine ferrite + pearlite.

[0007] The innovative points and beneficial effects of the present invention: In terms of steel plate composition design, in order to ensure that the Q345R steel plate has excellent high-temperature PWHT resistance, and considering the cost issue, the high-cost Ni and Cu alloys are replaced by low-cost Cr and V alloys. During the rolling, heat treatment and PWHT process, the interaction between V, Nb, Cr and the interstitial element C forms a precipitate phase, especially promoting the precipitation of nano-scale (Nb, V) C precipitation phase. Its precipitation strengthening effect and pinning grain boundary refinement effect can effectively improve the strength and toughness, ensuring that the Q345R steel plate still has excellent mechanical properties after high-temperature PWHT. The thickness of the produced steel plate ranges from 10 to 70 mm. After high-temperature PWHT at 700±10℃ and insulation for 12h, the mechanical properties of the steel plate still meet the requirements of China's national standard GB / T713.2-2023, and the steel plate's -20℃ core low-temperature impact KV 2 ≥150J. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a 500-fold microstructure photograph of 1 / 2 the thickness of the steel plate in Example 3. DETAILED DESCRIPTION

[0009] The specific implementation modes of the present invention are described in detail below with reference to the embodiments. Example 1

[0010] A method for producing a Q345R steel plate with excellent high-temperature PWHT resistance. The Q345R steel plate produced in this embodiment has a thickness of 10 mm, and its chemical composition mass percentage is: C=0.17%, Si=0.34%, Mn=1.53%, P=0.008%, S=0.002%, Alt=0.034%, Nb=0.039%, V=0.024%, Ti=0.016%, Cr=0.19%, and the balance is Fe and unavoidable impurities. The production method includes the following key process steps: (1) Converter smelting: top and bottom double blowing converter, reblowing times 1, steel tapping P: 0.006%; (2) Refining outside the furnace: After the molten steel arrives at the LF furnace, white slag is made and heated, and the white slag is kept for 17 minutes; calcium treatment is carried out before the LF furnace leaves the station, and 150m of pure Ca line is fed; after LF refining, VD vacuum treatment is adopted, vacuuming to below 67Pa, and the holding time is 16 minutes. Soft blowing is carried out for 14 minutes before the molten steel leaves the VD furnace; protection casting is carried out throughout the process, and the superheat is controlled at 12~15℃; (3) Heating: The furnace temperature of the heating furnace is 1182~1199℃, the soaking temperature is 1164~1179℃, and the soaking time is 52min; (4) Rolling: The starting rolling temperature of stage I is 1061°C, the final rolling temperature is 987°C, the reduction rates of the last three passes are 21%, 20%, and 20% respectively, and the intermediate billet thickness is 30 mm; the starting rolling temperature of stage II is 878°C, the final rolling temperature is 808°C, and the red-returning temperature is 706°C; (5) Heat treatment: normalizing process, temperature 880℃, holding time 15min, air cooling after furnace exit.

[0011] The mechanical properties test results of the 10 mm thick Q345R steel plate in this embodiment after high-temperature PWHT at 700±10°C and insulation for 12 hours are: yield strength 369 MPa, tensile strength 559 MPa, elongation 31.5%, and low-temperature impact energy of -20°C at the 1 / 2 position of the plate thickness 212 J, 231 J, and 219 J. Example 2

[0012] A method for producing a Q345R steel plate with excellent high-temperature PWHT resistance. The Q345R steel plate produced in this embodiment has a thickness of 40 mm, and the chemical composition of the steel is C=0.16%, Si=0.37%, Mn=1.56%, P=0.009%, S=0.002%, Alt=0.031%, Nb=0.034%, V=0.026%, Ti=0.013%, Cr=0.20%, and the balance is Fe and unavoidable impurities. The production method includes the following key process steps: (1) Converter smelting: top and bottom double blowing converter, reblowing times 1, steel tapping P: 0.007%; (2) Refining outside the furnace: After the molten steel arrives at the LF furnace, white slag is made and heated, and the white slag is kept for 18 minutes; calcium treatment is carried out before the LF furnace leaves the station, and 150m of pure Ca line is fed; after LF refining, VD vacuum treatment is adopted, vacuuming to below 67Pa, and the holding time is 15 minutes. Soft blowing is carried out for 13 minutes before the molten steel leaves the VD furnace; protection casting is carried out throughout the process, and the superheat is controlled at 11~15℃; (3) Heating: The furnace temperature of the heating furnace is 1187~1211℃, the soaking temperature is 1171~1190℃, and the soaking time is 59 minutes; (4) Rolling: The starting rolling temperature of stage I is 1059°C, the final rolling temperature is 984°C, the reduction rates of the last three passes are 19%, 20%, and 19% respectively, and the intermediate billet thickness is 90 mm; the starting rolling temperature of stage II is 867°C, the final rolling temperature is 801°C, and the red-returning temperature is 696°C; (5) Heat treatment: normalizing process, temperature 880℃, holding time 49min, air cooling after furnace exit.

[0013] The mechanical properties test results of the 40 mm thick Q345R steel plate in this embodiment after high-temperature PWHT at 700±10°C and insulation for 12 hours are: yield strength 344 MPa, tensile strength 547 MPa, elongation 33%, and low-temperature impact energy of -20°C at the 1 / 2 position of the plate thickness 209 J, 211 J, and 228 J. Example 3

[0014] A method for producing a Q345R steel plate with excellent high-temperature PWHT resistance. The Q345R steel plate produced in this embodiment has a thickness of 70 mm, and its chemical composition mass percentage is C=0.18%, Si=0.33%, Mn=1.52%, P=0.008%, S=0.003%, Alt=0.029%, Nb=0.038%, V=0.023%, Ti=0.014%, Cr=0.21%, and the balance is Fe and unavoidable impurities. The production method includes the following key process steps: (1) Converter smelting: top and bottom double blowing converter, 2 times of supplementary blowing, steel tapping P = 0.005%; (2) Refining outside the furnace: After the molten steel arrives at the LF furnace, white slag is made and heated, and the white slag is kept for 15 minutes; calcium treatment is carried out before the LF furnace leaves the station, and 150m of pure Ca line is fed; after LF refining, VD vacuum treatment is adopted, vacuuming to below 67Pa, and the holding time is 17 minutes. Soft blowing is carried out for 14 minutes before the molten steel leaves the VD furnace; protection casting is carried out throughout the process, and the superheat is controlled at 10~14℃; (3) Heating: The furnace temperature of the heating furnace is 1191~1214℃, the soaking temperature is 1177~1194℃, and the soaking time is 76min; (4) Rolling: The starting rolling temperature of stage I is 1064°C, the final rolling temperature is 988°C, the reduction rates of the last three passes are 19%, 18%, and 18% respectively, and the intermediate billet thickness is 160 mm; the starting rolling temperature of stage II is 855°C, the final rolling temperature is 797°C, and the red-returning temperature is 685°C; (5) Heat treatment: normalizing process, temperature 880℃, holding time 90min, air cooling after furnace exit.

[0015] The mechanical properties of the 70mm thick Q345R steel plate in this embodiment after high temperature PWHT at 700±10℃ and 12h insulation are as follows: yield strength 338MPa, tensile strength 544MPa, elongation 30%, and low temperature impact energy of -20℃ at 1 / 2 thickness position 225J, 216J, 218J. Figure 1 As shown, the metallographic structure at the 1 / 2 position of the steel plate is ferrite + pearlite.

Claims

1. A method for producing a Q345R steel plate with excellent high temperature PWHT resistance, characterized in that: The chemical composition of the steel plate is C=0.15%~0.18%, Si=0.30%~0.40%, Mn=1.50%~1.60%, P≤0.010%, S≤0.003%, Alt=0.020%~0.050%, Nb=0.03%~0.05%, V=0.02%~0.03%, Ti=0.01%~0.02%, Cr=0.15%~0.25%, and the others are Fe and essential residual elements; the thickness range of the steel plate is 10~70mm, and the low-temperature impact KV2 of the steel plate at -20℃ core is ≥150J; The production process steps include: (1) Converter smelting: top and bottom double blowing converter, the number of re-blowing is ≤2 times, deoxidizer and alloy are added during the steelmaking process for deoxidation and alloying, and the steelmaking P is ≤0.007%; (2) Refining outside the furnace: After the molten steel arrives at the LF furnace, white slag is made and heated, and the white slag is kept for ≥15min; calcium treatment is carried out before the LF furnace leaves the station, and a pure Ca line of ≥150m is fed; after LF refining, VD vacuum treatment is adopted, and the vacuum is pumped to below 67Pa, and the holding time is ≥15min. Soft blowing is carried out before the molten steel leaves the VD furnace for ≥12min; protection casting is carried out throughout the process, and the superheat is controlled to ≤15℃; (3) Heating: The furnace temperature of the heating furnace is ≤1230℃, the soaking temperature is 1160~1200℃, and the soaking time is ≥50min; (4) Rolling: The starting rolling temperature of stage I is ≥1050℃, the final rolling temperature is ≥980℃, the reduction rate of the last three passes is ≥18%, and the thickness of the intermediate billet is 2~3 times the thickness of the finished plate; the starting rolling temperature of stage II is ≤880℃, the final rolling temperature is 780~820℃, and the steel is rapidly cooled at a cooling rate of 2~5℃ / s after rolling, and the red-returning temperature is 680~720℃; (5) Heat treatment: normalizing process is adopted, normalizing temperature is 880±10℃, holding time = steel plate thickness mm×1.0~1.5min / mm, and air cooling is carried out after leaving the furnace.

2. The Q345R steel plate according to claim 1, characterized in that: The steel plate structure is uniform and fine ferrite+pearlite.

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