Pressure vessel carbon steel plate with excellent low-temperature impact toughness and production method thereof

Abstract

The invention discloses a carbon steel plate with excellent low-temperature impact toughness for a pressure vessel. The carbon steel plate comprises the following chemical components in percentage by mass: 0.13-0.16% of C, 0.20-0.40% of Si, 1.30-1.60% of Mn, less than or equal to 0.015% of P, less than or equal to 0.005% of S, 0.15-0.30% of Ni, 0.02-0.05% of Al, 0.01-0.03% of Nb and the balance of Fe and inevitable impurities. The steel plate for the pressure vessel has the advantages that the steel plate for the pressure vessel has excellent low-temperature impact toughness through reasonable component design, control of the internal quality of a continuous casting billet and optimization of a rolling process and a heat treatment process.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel rolling and heat treatment technology, and in particular relates to a carbon steel plate for pressure vessels with excellent low-temperature impact toughness and a production method thereof. Background Art

[0002] Pressure vessel steel plates are widely used in industries such as boilers and petrochemicals. Their fundamental requirements are primarily reflected in three key areas: excellent mechanical properties, excellent processability, and good corrosion and oxidation resistance. As pressure vessels become larger, higher pressure, and higher temperature, coupled with the corrosive and embrittlement effects of some media on metal materials, the operating conditions of these pressure vessels are becoming increasingly harsh. Consequently, higher performance requirements are placed on pressure vessel steel plates. Whether these plates possess high impact toughness under low-temperature operating conditions, while also maintaining a good balance of strength and toughness, has become a key performance criterion for measuring pressure vessel steel performance.

[0003] Domestically produced 610MPa-grade high-strength pressure vessel plates utilize a traditional quenching and tempering heat treatment process. This process is lengthy, energy-intensive, and costly, inconsistent with modern energy conservation and emission reduction principles. The microstructure of steel plates produced using traditional heat treatment is primarily tempered bainite, while steel plates produced using deformation effects are primarily bainite, a product of a medium-temperature transformation. Even after tempering, bainite remains the dominant structure, resulting in weaker overall mechanical properties. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems of poor low-temperature impact toughness, high production cost and high energy consumption of existing pressure vessel steel, and to provide a carbon steel plate for pressure vessels with excellent low-temperature impact toughness. Through reasonable composition design, control of the internal quality of the continuous casting billet, optimization of the rolling process and heat treatment process, the steel plate for pressure vessels has excellent low-temperature impact toughness performance.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A carbon steel plate for pressure vessels with excellent low-temperature impact toughness, the chemical composition and mass percentage of which include: C: 0.13-0.16%, Si: 0.20-0.40%, Mn: 1.30-1.60%, P≤0.015%, S≤0.005%, Ni: 0.15-0.30%, Al: 0.02-0.05%, Nb: 0.01-0.03%, and the balance being Fe and unavoidable impurities.

[0006] Furthermore, after heat treatment, the microstructure of 1 / 4 thickness of the steel plate is mainly ferrite + pearlite, and the grains are uniform and fine.

[0007] Furthermore, the chemical composition and mass percentage of the steel plate are as follows: C: 0.13%, Mn: 1.40%, P: 0.013%, S: 0.003%, Si: 0.28%, Ni: 0.17%, Nb: 0.025%, Al: 0.032%, and the balance is Fe and inevitable impurities.

[0008] Furthermore, the chemical composition and mass percentage of the steel plate are as follows: C: 0.14%, Mn: 1.45%, P: 0.011%, S: 0.003%, Si: 0.30%, Ni: 0.20%, Nb: 0.017%, Al: 0.031%, and the balance is Fe and inevitable impurities.

[0009] Furthermore, the chemical composition and mass percentage of the steel plate are as follows: C: 0.15%, Mn: 1.37%, P: 0.010%, S: 0.002%, Si: 0.31%, Ni: 0.24%, Nb: 0.013%, Al: 0.037%, and the balance is Fe and inevitable impurities.

[0010] In order to further achieve the object of the present invention, a production method of a carbon steel plate for pressure vessels with excellent low-temperature impact toughness is also provided, including smelting, continuous casting, high-temperature heating, rolling, and heat treatment processes, specifically: (1) In the smelting and continuous casting processes, it successively undergoes hot metal desulfurization pretreatment, converter smelting, LF refining, RH vacuum treatment, and continuous casting. Among them, the sulfur content after hot metal desulfurization treatment is controlled at ≤0.002%, and the slag is removed cleanly; the converter adopts the double slag method to strictly control the P content at ≤0.015%; LF refining uses white slag operation for desulfurization and deoxidation; the vacuum degree of RH vacuum treatment is ≤3.0 mbar, and the vacuum time is ≥15 min; calcium treatment is carried out after the vacuum ends; after the calcium treatment ends, static stirring is carried out, and the static stirring time is ≥12 min; in continuous casting, the tundish liquidus temperature is controlled, and the superheat is controlled within 15°C; the macrostructure rating of the billet is C1.0; (2) In the heating process, a continuous casting billet with a thickness of 370 mm is used, the total time in the furnace is 9 - 16 min / cm, the soaking time is ≥1.5 min / cm, and the tapping temperature is 1180 - 1240°C; (3) In the rolling process, a one-stage large reduction rolling and a two-stage low-temperature rolling process are adopted. After spreading, it is ensured that the single-pass reduction amount in ≥4 consecutive passes is >32 mm. The starting rolling temperature in the second stage is ≤840°C, the finishing rolling temperature is ≤810°C, and air cooling is carried out after rolling; (4) In the heat treatment process, the steel plate is heated to 610 - 640°C for tempering heat treatment. The tempering time is controlled at (2.0 - 2.5) min / mm × H + (20 - 40) min, where H is the thickness of the steel plate, and it is air-cooled to room temperature after being taken out of the furnace.

[0011] Furthermore, in step (2), for the continuous casting billet with a thickness of 370 mm, the soaking section is heat-insulated at a target temperature of 1200 ± 20 °C.

[0012] Furthermore, in step (3), the average reduction per pass in the four passes after the first-stage width spreading is 34.6 mm, 35.0 mm, 35.2 mm, and 33.1 mm in sequence, and the rolling start temperature in the second stage is 832 °C and the finishing rolling temperature is 805 °C.

[0013] Furthermore, in step (3), the average reduction per pass in the four passes after the first-stage width spreading is 35.4 mm, 35.4 mm, 35.4 mm, and 33.5 mm in sequence, and the rolling start temperature in the second stage is 824 °C and the finishing rolling temperature is 800 °C.

[0014] Furthermore, in step (3), the average reduction per pass in the four passes after the first-stage width spreading is 34.9 mm, 34.9 mm, 34.9 mm, and 33.4 mm in sequence, and the rolling start temperature in the second stage is 814 °C and the finishing rolling temperature is 795 °C.

[0015] Compared with the prior art, the advantages of the technical solution of the present invention are specifically as follows: (1) The present invention adopts a low-carbon, micro Nb+Ni alloy composition design, and combines the first-stage heavy reduction rolling, the second-stage low-temperature rolling process and the temper heat treatment to produce a carbon steel plate for pressure vessels with excellent low-temperature impact toughness that meets the delivery state and PWHT state, the transverse impact energy at 1 / 4 thickness and 1 / 2 thickness -45 °C ≥ 60 / 45 J, the yield strength ≥ 345 MPa, and the tensile strength 510-620 MPa, greatly improving the competitiveness of Nanjing Iron and Steel's pressure vessel steel plates in the market; (2) The present invention utilizes the advantages of a wide and heavy plate rolling mill, with high-temperature heavy reduction rolling after the first-stage width spreading, the reduction per pass > 32 mm, and low-temperature rolling in the second stage, improving the low-temperature impact toughness of the core; (3) Different from the traditional heat treatment process of normalizing followed by rapid cooling and then tempering, the present invention has successfully developed a low-temperature controlled rolling + temper heat treatment process through trial production, greatly reducing the production cost of the process. Description of the Drawings

[0016] Figure 1 It is the microstructure morphology at the 1 / 4 thickness of the 40 mm thick specification low-temperature container steel plate of the present invention; Figure 2 It is the microstructure morphology at the 1 / 2 thickness of the 40 mm thick specification low-temperature container steel plate of the present invention. Detailed Embodiments Example 1

[0017] To make the present invention more clear and understandable, the following further describes a carbon steel plate for pressure vessels with excellent low-temperature impact toughness and its production method. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0018] In this embodiment, a carbon steel plate for pressure vessels with excellent low-temperature impact toughness, its chemical composition and mass percentage content include: C: 0.13%, Mn: 1.40%, P: 0.013%, S: 0.003%, Si: 0.28%, Ni: 0.17%, Nb: 0.025%, Al: 0.032%, and the balance is Fe and unavoidable impurities.

[0019] The production method of the above carbon steel plate is as follows, and it is characterized in that: In the smelting and continuous casting process, it successively undergoes hot metal desulfurization pretreatment, converter smelting, LF refining, RH vacuum treatment and continuous casting. Among them, the sulfur content after hot metal desulfurization treatment is controlled at ≤0.002%, and the slag is removed cleanly; the converter adopts the double slag method to strictly control the P content at ≤0.015%; LF refining adopts white slag operation for desulfurization and deoxidation; the vacuum degree of RH vacuum treatment is ≤3.0 mbar, and the vacuum time is ≥16 min; calcium treatment is carried out after the vacuum ends; after the calcium treatment ends, static stirring is carried out, and the static stirring time is ≥17 min; in continuous casting, the tundish liquidus temperature is controlled, and the superheat is controlled within 8°C; the macrostructure rating of the continuous casting billet is C1.0.

[0020] In the heating process, for a slab thickness of 370 mm, the soaking section is insulated at a target temperature of 1200 ± 20°C, the soaking section temperature is 1196°C, the soaking section time is 111 min, and the total time in the furnace is 439 min.

[0021] In the first-stage large reduction rolling and second-stage low-temperature rolling process, the finished thickness is 40 mm, and 370 mm continuous casting billets are used for rolling. The first-stage large reduction rolling and second-stage low-temperature rolling processes are adopted. After width spreading, it is ensured that the single-pass reduction amount in ≥4 consecutive passes is >32 mm. The rolling start temperature in the second stage is ≤840°C, and the finishing temperature is ≤810°C; air cooling is carried out after rolling. Specifically, the average reduction amount in the four passes after width spreading in the first stage is 34.6 mm, 35.0 mm, 35.2 mm, and 33.1 mm in sequence. The rolling start temperature in the second stage is 832°C, and the finishing temperature is 805°C.

[0022] In the heat treatment process, tempering heat treatment is adopted. The thickness specification is 40 mm, the heating temperature is set at 617°C, the time in the furnace is set at 126 min, and the cooling method is air cooling. Example 2

[0023] In this embodiment, a carbon steel plate for pressure vessels with excellent low-temperature impact toughness, its chemical composition and mass percentage content include: C: 0.14%, Mn: 1.45%, P: 0.011%, S: 0.003%, Si: 0.30%, Ni: 0.20%, Nb: 0.017%, Al: 0.031%, and the balance is Fe and unavoidable impurities.

[0024] The production method of the above carbon steel plate is as follows, and it is characterized in that: In the smelting and continuous casting process, it successively goes through hot metal desulfurization pretreatment, converter smelting, LF refining, RH vacuum treatment and continuous casting. Among them, the sulfur content after hot metal desulfurization treatment is controlled at ≤0.002%, and the slag is removed cleanly; the converter adopts the double slag method to strictly control the P content at ≤0.015%; LF refining adopts white slag operation for desulfurization and deoxidation; the vacuum degree of RH vacuum treatment is ≤3.0 mbar, and the vacuum time is ≥18 min; calcium treatment is carried out after the vacuum ends; after the calcium treatment ends, static stirring is carried out, and the static stirring time is ≥15 min; in continuous casting, the tundish liquidus temperature is controlled, and the superheat is controlled within 12°C; the low magnification rating of the slab is C1.0.

[0025] In the heating process, for a slab thickness of 370 mm, the soaking section is insulated at a target temperature of 1200 ± 20°C, the soaking section temperature is 1197°C, the soaking section time is 106 min, and the total time in the furnace is 452 min.

[0026] In the first-stage large reduction rolling and second-stage low-temperature rolling process, the finished product thickness is 40 mm, and 370 mm continuous casting billets are used for rolling. The first-stage large reduction rolling and second-stage low-temperature rolling process are adopted. After spreading, it is ensured that the single-pass reduction of ≥4 consecutive passes is >32 mm. The starting rolling temperature in the second stage is ≤840°C, and the finishing rolling temperature is ≤810°C; after rolling, it is air-cooled. Specifically, the average single-pass reduction of the four passes after spreading in the first stage is 35.4 mm, 35.4 mm, 35.4 mm, and 33.5 mm in sequence. The starting rolling temperature in the second stage is 824°C, and the finishing rolling temperature is 800°C.

[0027] In the heat treatment process, tempering heat treatment is adopted. The thickness specification is 40 mm, the heating temperature is set at 625°C, the time in the furnace is set at 120 min, and the cooling method is air-cooling. Example 3

[0028] In this embodiment, a carbon steel plate for pressure vessels with excellent low-temperature impact toughness, its chemical composition and mass percentage content include: C: 0.15%, Mn: 1.37%, P: 0.010%, S: 0.002%, Si: 0.31%, Ni: 0.24%, Nb: 0.013%, Al: 0.037%, and the balance is Fe and unavoidable impurities.

[0029] The production method of the above carbon steel plate is as follows, characterized in that: In the smelting and continuous casting process, it successively goes through hot metal desulfurization pretreatment, converter smelting, LF refining, RH vacuum treatment and continuous casting. Among them, the sulfur content after hot metal desulfurization treatment is controlled at ≤0.002%, and the slag is removed cleanly; the converter uses the double slag method to strictly control the P content at ≤0.015%; LF refining uses white slag operation for desulfurization and deoxidation; the vacuum degree of RH vacuum treatment is ≤3.0 mbar, and the vacuum time is ≥20 min; calcium treatment is carried out after the vacuum ends; after the calcium treatment ends, static stirring is carried out, and the static stirring time is ≥18 min; in continuous casting, the liquidus temperature of the tundish is controlled, and the superheat is controlled within 10°C; the macrostructure rating of the slab is C1.0.

[0030] In the heating process, for a slab thickness of 370 mm, the soaking section is insulated at a target temperature of 1200 ± 20°C, the soaking section temperature is 1192°C, the soaking section time is 136 min, and the total time in the furnace is 480 min.

[0031] In the first-stage heavy reduction rolling and second-stage low-temperature rolling process, the finished product thickness is 40 mm, and 370 mm continuous casting billets are used for rolling. The first-stage heavy reduction rolling and second-stage low-temperature rolling processes are adopted. After spreading, it is ensured that the single-pass reduction amount in ≥4 consecutive passes is >32 mm. The starting rolling temperature in the second stage is ≤840°C, and the finishing rolling temperature is ≤810°C; after rolling, it is air-cooled. Specifically, the average reduction amounts in the four passes after spreading in the first stage are 34.9 mm, 34.9 mm, 34.9 mm, and 33.4 mm in sequence. The starting rolling temperature in the second stage is 814°C, and the finishing rolling temperature is 795°C.

[0032] In the heat treatment process, tempering heat treatment is adopted, the thickness specification is 40 mm, the heating temperature is set at 630°C, the time in the furnace is set at 118 min, and the cooling method is air-cooling.

[0033] In the above Examples 1 to 3, the mechanical properties of the produced carbon steel plates in the delivered state are as shown in Table 1 below:

[0034] After simulating the PWHT process with insulation at 620°C for 405 min, the tensile and impact performance results are as shown in Table 2 below:

[0035] The present invention develops a carbon steel plate for pressure vessels with technical indicators that can meet the requirements of -45°C transverse impact ≥ 60 / 45 J at 1 / 4 thickness and 1 / 2 thickness after delivery and PWHT, yield strength ≥ 345 MPa, and tensile strength 510 - 620 MPa by controlling smelting technology, rolling technology and heat treatment technology. See Figure 1 and Figure 2, which is the microstructure morphology at 1 / 4 and 1 / 2 thickness of the 40mm thick steel plate for low-temperature containers of the present invention. Calculated based on an annual production and sales volume of 10,000 tons and a gross profit of 300 yuan per ton of steel, the annual gross profit is expected to be 3 million yuan.

[0036] The present invention adopts a low-carbon, micro-Nb+Ni alloy composition design, and uses the large reduction in rough rolling of a wide and heavy plate mill, two-stage low-temperature controlled rolling, and an appropriate temper heat treatment process to greatly improve the low-temperature impact toughness at 1 / 2 of the steel plate thickness, making the carbon steel plate have excellent low-temperature impact toughness.

[0037] In addition to the above embodiments, the present invention may also have other embodiments. Any technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope required by the present invention.

Claims

1. A carbon steel plate for pressure vessels with excellent low-temperature impact toughness, characterized in that: The chemical composition and mass percentage of the steel plate include: C: 0.13 - 0.16%, Si: 0.20 - 0.40%, Mn: 1.30 - 1.60%, P ≤ 0.015%, S ≤ 0.005%, Ni: 0.15 - 0.30%, Al: 0.02 - 0.05%, Nb: 0.01 - 0.03%, and the balance is Fe and unavoidable impurities.

2. The carbon steel plate for pressure vessels with excellent low-temperature impact toughness according to claim 1, characterized in that: The microstructure of the 1 / 4 thickness of the steel plate after heat treatment is mainly ferrite + pearlite.

3. The carbon steel plate for pressure vessels with excellent low-temperature impact toughness according to claim 1 or 2, characterized in that: The chemical composition and mass percentage of the steel plate include: C: 0.13%, Mn: 1.40%, P: 0.013%, S: 0.003%, Si: 0.28%, Ni: 0.17%, Nb: 0.025%, Al: 0.032%, and the balance is Fe and unavoidable impurities.

4. The carbon steel plate for pressure vessels with excellent low-temperature impact toughness according to claim 1 or 2, characterized in that: The chemical composition and mass percentage of the steel plate include: C: 0.14%, Mn: 1.45%, P: 0.011%, S: 0.003%, Si: 0.30%, Ni: 0.20%, Nb: 0.017%, Al: 0.031%, and the balance is Fe and unavoidable impurities.

5. The carbon steel plate for pressure vessels with excellent low-temperature impact toughness according to claim 1 or 2, characterized in that: The chemical composition and mass percentage of the steel plate include: C: 0.15%, Mn: 1.37%, P: 0.010%, S: 0.002%, Si: 0.31%, Ni: 0.24%, Nb: 0.013%, Al: 0.037%, and the balance is Fe and unavoidable impurities.

6. A production method of the carbon steel plate for pressure vessels with excellent low-temperature impact toughness as claimed in claim 1, including smelting, continuous casting, high-temperature heating, rolling, and heat treatment processes, characterized in that: (1) In the smelting and continuous casting processes, successively pass through hot metal desulfurization pretreatment, converter smelting, LF refining, RH vacuum treatment, and continuous casting. Among them, the sulfur content after hot metal desulfurization treatment is controlled at ≤ 0.002%, and the slag is removed cleanly; the converter adopts the double slag method to strictly control the P content ≤ 0.015%; LF refining adopts white slag operation for desulfurization and deoxidation; the vacuum degree of RH vacuum treatment is ≤ 3.0 mbar, and the vacuum time is ≥ 15 min; calcium treatment is carried out after the vacuum ends; after the calcium treatment ends, static stirring is carried out, and the static stirring time is ≥ 12 min; in continuous casting, the tundish liquidus temperature is controlled, and the superheat is controlled within 15°C; the low magnification rating of the billet is C1.

0. (2) In the heating process, a continuous casting billet with a thickness of 370 mm is used. The total time in the furnace is 9 - 16 min / cm, the soaking time is ≥1.5 min / cm, and the tapping temperature is 1180 - 1240 °C; (3) In the rolling process, a one-stage large reduction rolling and a two-stage low-temperature rolling process are adopted. After width spreading, it is ensured that the reduction per pass in at least 4 consecutive passes is > 32 mm. The starting rolling temperature in the second stage is ≤840 °C, the finishing rolling temperature is ≤810 °C, and air cooling is carried out after rolling; (4) In the heat treatment process, the steel plate is heated to 610 - 640 °C for tempering heat treatment. The tempering time is controlled at (2.0 - 2.5) min / mm × H + (20 - 40) min, where H is the thickness of the steel plate, and it is air cooled to room temperature after leaving the furnace.

7. The production method of a carbon steel plate for pressure vessels with excellent low-temperature impact toughness according to claim 6, characterized in that: In the step (2), for the continuous casting billet with a thickness of 370 mm, the soaking section is heat-insulated at a target temperature of 1200 ± 20 °C.

8. The production method of a carbon steel plate for pressure vessels with excellent low-temperature impact toughness according to claim 6, characterized in that: In the step (3), the average reduction per pass in the four passes after width spreading in the first stage is 34.6 mm, 35.0 mm, 35.2 mm, and 33.1 mm in sequence. The starting rolling temperature in the second stage is 832 °C, and the finishing rolling temperature is 805 °C.

9. The production method of a carbon steel plate for pressure vessels with excellent low-temperature impact toughness according to claim 6, characterized in that: In the step (3), the average reduction per pass in the four passes after width spreading in the first stage is 35.4 mm, 35.4 mm, 35.4 mm, and 33.5 mm in sequence. The starting rolling temperature in the second stage is 824 °C, and the finishing rolling temperature is 800 °C.

10. The production method of a carbon steel plate for pressure vessels with excellent low-temperature impact toughness according to claim 6, characterized in that: In the step (3), the average reduction per pass in the four passes after width spreading in the first stage is 34.9 mm, 34.9 mm, 34.9 mm, and 33.4 mm in sequence. The starting rolling temperature in the second stage is 814 °C, and the finishing rolling temperature is 795 °C.

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