Heat-resistant SA204GrB steel plate for container and manufacturing method of heat-resistant SA204GrB steel plate

Abstract

The invention relates to a heat-resistant SA204GrB steel plate for a container and a manufacturing method of the heat-resistant SA204GrB steel plate. The steel plate comprises the following chemical components in percentage by mass: 0.16-0.20% of C, 0.80-0.95% of Mn, 0.15-0.35% of Si, less than or equal to 0.010% of P, less than or equal to 0.010% of S, 0.45-0.55% of Mo and the balance of Fe and inevitable impurity elements. The production thickness of the steel plate is 6-50 mm, the tensile strength is 500-610 MPa, the yield strength is 290-500 MPa, the percentage elongation after fracture is larger than or equal to 23%, the average value of Charpy V-type impact absorption energy of the core part at the temperature of-20 DEG C is larger than or equal to 100 J, and the high-temperature yield strength Rp0.2 at the temperature of 500 DEG C is larger than or equal to 265 MPa. The metallographic structure mainly comprises pearlite. The manufacturing method of the steel plate comprises the steps of steelmaking, rolling and heat treatment, a normalizing process is adopted for heat treatment, and grains are refined, so that on one hand, the fine grain strengthening effect is achieved, and it is guaranteed that the steel plate has uniform and stable heat resistance; and on the other hand, the pearlite structure is refined, the proportion of ferrite and the small-spacing pearlite structure is increased, and the impact toughness of the material in the low-temperature environment is improved. The steel plate is suitable for manufacturing high-temperature equipment in industries such as petroleum, chemical engineering and boiler containers.

Description

Technical Field

[0001] The invention belongs to the field of iron-based alloys, and in particular relates to a medium-thickness SA204GrB steel plate for a container and a manufacturing method thereof. Background Art

[0002] SA204GrB is a heat-resistant steel containing molybdenum for pressure vessels. Since SA204GrB is a traditional carbon-manganese steel with molybdenum added, the steel has good high temperature resistance and long-lasting plasticity. It is often used in thermal power, solar thermal power generation, boiler containers and coal chemical projects. Its main equipment is desulfurization tanks, split deaerators, heat exchangers, etc. used in high temperature and high pressure environments.

[0003] In recent years, with the variability of the service environment of equipment, traditional steel plates only meet the standard requirements and can no longer meet the use requirements in special environments; traditional steel plates only meet the corresponding requirements of ASME SA204 / SA204M-2021, the impact temperature is room temperature, and the high-temperature tensile temperature is generally below 400°C; but with the needs of application projects, the impact temperature of the steel plate is reduced to 0°C, and the high-temperature service temperature is increased to 500°C. In order to further ensure the reliable use of materials, steel plate manufacturers optimize and improve the existing production processes.

[0004] By controlling the steelmaking and casting processes, improving and controlling the rolling process and heat treatment process, we develop steel plates with excellent comprehensive performance to meet the good match of strength and toughness and ensure that the steel plates can work at high temperatures in a low temperature environment.

[0005] The patent document with patent publication number CN103422023A discloses a method for producing heat-resistant container steel plates by adding more chromium alloys and molybdenum alloys and adopting quenching + tempering process. The production process is complicated, the production cost is high, and the production cycle is long; the patent document with patent publication number CN103320696A discloses a high-temperature container steel, which adds more chromium alloys and vanadium alloys and adds tempering process; the alloy cost is higher, and the production process and production cycle are longer. Summary of the invention

[0006] The present invention discloses a heat-resistant SA204GrB steel plate for containers and a manufacturing method thereof, which solves the problem of unstable impact toughness of heat-resistant steel produced by continuous casting process at service temperature of -20°C and above. The steel plate of the present invention has a good strength-to-toughness ratio, excellent low-temperature impact toughness, good high-temperature strength, and excellent welding performance, which meets the requirements of heat exchanger materials and can be used in the manufacture of main equipment such as desulfurization tanks, split deaerators, and heat exchangers.

[0007] The technical solution adopted by the present invention is: a heat-resistant SA204GrB steel plate for containers and a manufacturing method thereof, wherein the chemical composition and mass percentage of the steel plate are: C: 0.16-0.20%, Mn: 0.80-0.95%, Si: 0.15-0.35%, P≤0.010%, S≤0.010%, Mo: 0.45-0.55%, and the remainder is Fe and unavoidable impurity elements.

[0008] The present invention provides a heat-resistant SA204GrB steel plate for a container and a manufacturing method thereof. The steel plate has a thickness of 6 to 50 mm, a tensile strength of 500 to 610 MPa, a yield strength of 290 to 500 MPa, an elongation after fracture of ≥23%, an average value of -20°C Charpy (V-type) impact absorption energy of the core of ≥100 J, and a high-temperature yield strength Rp0.2 of ≥265 MPa at 500°C.

[0009] The content of chemical elements in steel determines the quality of material performance and service environment. The requirements for the content of chemical elements in the present invention are as follows:

[0010] Carbon (C): It is the element with the most obvious solid solution strengthening effect in steel. It strengthens the structure of steel in the lattice and makes the material have good plasticity and toughness. As the carbon content increases, the carbon figure phase at the grain boundary in the steel also increases, which increases the grain boundary strength, but the plasticity and toughness decrease. In order to ensure excellent low-temperature toughness in a low-temperature environment, the most economical way is to reduce the carbon content. However, if the carbon content is too low, the strength of the steel will drop sharply when used in a high-temperature environment, causing the equipment to fail. The C content of the present invention is controlled at 0.16-0.20%.

[0011] Silicon (Si): It is a beneficial element. It mainly deoxidizes carbon, manganese and other elements in steel to prevent the formation of pores and loose structures in steel. It can also improve the structure and performance by promoting spheroidization of coarse grains. Too much addition will reduce the plasticity and toughness of steel and increase the brittleness of steel. Too little addition will not improve the performance of steel. The Si content of the present invention is controlled at 0.15-0.35%.

[0012] Manganese (Mn): solid solution in ferrite and austenite, expanding the austenite region and raising the critical temperature. It forms MnS with a higher melting point with sulfur in steel, avoiding the formation of FeS film on the grain boundary and eliminating the hot brittleness of steel; it refines the pearlite size and significantly improves the strength of pearlite steel. Therefore, the Mn content of the present invention is controlled at 0.80-0.95%.

[0013] Phosphorus (P) and sulfur (S): reduce the toughness and plasticity of steel, thus affecting the strength of the material. If the content is too high, surface and internal cracks are likely to occur during processing, and brittle compounds are likely to form during welding, resulting in cracking of the welded joint and even brittle fracture during welding. Therefore, the P content of the present invention is controlled at ≤0.010%, and the S content is controlled at ≤0.010%.

[0014] Molybdenum (Mo): refines grains, reduces intergranular corrosion of steel, and improves oxidation resistance at high temperatures; reduces austenite phase area, dissolves in ferrite, austenite and carbide, improves carbide stability, inhibits intergranular brittleness, and maintains excellent plasticity and toughness of steel; forms MoC with carbon, has a secondary hardening effect, and improves the wear resistance and creep resistance of steel plates. Adding molybdenum in the present invention can not only improve the mechanical properties of the material, but also inhibit the brittleness caused by high-temperature tempering. The Mo content of the present invention is controlled at 0.45-0.55%.

[0015] The present invention provides a heat-resistant SA204GrB steel plate for a container and a manufacturing method thereof. The manufacturing method comprises steelmaking, rolling, heat treatment and other processes. The specific requirements are as follows:

[0016] (1) In the steelmaking process, preferably, oxygen converter + LF refining furnace + RH vacuum degassing furnace is used for smelting, the converter initial refining time is 35 to 48 minutes, and the tapping temperature after initial refining is ≥1550°C; oxygen converter is used for smelting and then LF refining furnace is used for refining, the refining time is ≥20 minutes, and when the molten steel temperature reaches 1550 to 1660°C, it is transferred to the RH vacuum degassing furnace for degassing treatment, the vacuum time is maintained for ≥15 minutes, and the tapping temperature is ≥1550°C; the molten steel is continuously cast in a non-oxidation protected water nozzle crystallizer, the superheat is controlled at 15 to 30°C, and the pulling speed is ≤1.4 m / min to obtain a continuous casting billet with a rectangular cross-section.

[0017] (2) Rolling process: rough rolling + finishing rolling is adopted. The surface impact force of high-pressure water descaling of the billet is ≥0.90N / mm2 to effectively remove the iron oxide scale and avoid surface defects such as roughness caused by the pressing of the iron oxide scale during rolling. The rough rolling adopts the high-temperature and large-reduction rolling method without controlled rolling. The starting rolling temperature is 1030-1080℃, and the single-pass reduction of 2-3 passes is ≥30mm, and the cumulative deformation rate is ≥55%, which ensures that the billet is fully deformed, on the one hand, the large grains are broken; on the other hand, the metallurgical defects such as the looseness of the center of the continuous casting billet are bridged; the finishing rolling stage adopts the controlled rolling and controlled cooling method, the starting rolling temperature is 900-950℃, the final cooling temperature is 600-680℃, the total reduction is ≥100mm, and the cumulative reduction rate is ≥60%, which is mainly used to refine the original austenite grain size and reduce the proportion of banded structure. At the same time, it can ensure that the grain size after heat treatment is above level 5 and the metallographic structure is a small amount of ferrite + pearlite.

[0018] (3) Heat treatment process, using normalizing process to refine grains, on the one hand, it has the effect of fine grain strengthening, ensuring that the steel plate has uniform and stable thermal strength; on the other hand, it refines the pearlite structure, increases the proportion of ferrite and small-spacing pearlite structure, and improves the impact toughness of the material under low temperature environment. Normalizing in normalizing furnace, normalizing temperature 850 ~ 900 ℃, furnace time 1.8 ~ 2.5min / mm, after being taken out of the furnace, cooling in still air, to obtain the required steel plate with a small amount of ferrite + fine pearlite as the main component.

[0019] The present invention adopts a low alloy component design system, cooperates with a controlled rolling and controlled cooling rolling method, and then performs normalizing treatment in a continuous non-oxidation heat treatment furnace to produce a steel plate with a thickness of 6 to 50 mm, and the comprehensive performance can reach: tensile strength 500 to 610 MPa, yield strength 290 to 500 MPa, elongation after fracture ≥ 23%, the average value of the core -20°C Charpy (V-type) impact absorption energy ≥ 100 J, and 500°C high temperature yield strength Rp0.2 ≥ 265 MPa. The production method provided by the present invention not only reduces the addition of alloy elements such as Mn, Si, and Mo, reduces energy consumption and saves resources, but also ensures the application of the obtained steel plate on high-temperature equipment in a -20°C low temperature environment, thereby improving the market competitiveness of the product.

[0020] Compared with the prior art, the advantages of the present invention are:

[0021] (1) The present invention provides a heat-resistant SA204GrB steel plate for containers and a method for manufacturing the same. Except for the alloy elements such as Mn, Si, and Mo required by the standard, no other alloy elements are added, and the production cost is the most economical.

[0022] (2) The present invention provides a heat-resistant SA204GrB steel plate for containers and a manufacturing method thereof. The steel plate with a thickness of 6 to 50 mm can achieve comprehensive properties: tensile strength of 500 to 610 MPa, yield strength of 290 to 500 MPa, elongation after fracture ≥ 23%, average value of -20°C Charpy (V-type) impact absorption energy of the core ≥ 100 J, and 500°C high temperature yield strength Rp0.2 ≥ 265 MPa. The steel plate has excellent low-temperature toughness, which solves the problem that such steel is prone to cracking in low-temperature environments. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with examples. The examples are exemplary and intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0024] Example 1

[0025] The thickness of the steel plate in this embodiment is 6 mm, and the chemical composition and mass percentage of the steel plate are: C: 0.20%, Mn: 0.85%, Si: 0.32%, P: 0.010%, S: 0.008%, Mo: 0.50%, and the remainder is Fe and unavoidable impurity elements.

[0026] The manufacturing method of the heat-resistant SA204GrB steel plate for containers in this embodiment includes steelmaking, rolling, heat treatment and other processes, and the specific requirements are as follows:

[0027] (1) Steelmaking process: oxygen converter + LF refining furnace + RH vacuum degassing furnace smelting, the converter initial refining time is 42 minutes, and the tapping temperature after initial refining is 1580°C; oxygen converter smelting and then LF refining furnace refining, refining time is 23 minutes, when the molten steel temperature reaches 1620°C, it is transferred to the RH vacuum degassing furnace for degassing treatment, the vacuum holding time is 18 minutes, and the tapping temperature is 1590°C; the molten steel adopts the non-oxidation protection water nozzle crystallizer continuous casting method, the superheat is controlled at 18°C, the pulling speed is 1.0 m / min, and a rectangular cross-section continuous casting billet is obtained.

[0028] (2) Rolling process: rough rolling + finishing rolling process is adopted, and the surface impact force of the billet high-pressure water descaling is 1.1N / mm 2 Effectively remove the scale and avoid surface defects such as pockmarks caused by the pressing of scale during rolling. The rough rolling adopts the high-temperature and large-reduction rolling method without controlled rolling, in which the single-pass reduction of 3 passes is 33mm, 34mm, and 32mm, and the cumulative reduction rate is 60%, to ensure the full deformation of the billet, on the one hand, to break the large grains; on the other hand, to bridge the metallurgical defects such as the looseness of the center of the continuous casting billet; the finishing rolling stage adopts the controlled rolling and controlled cooling method, the starting rolling temperature is 925℃, the final cooling temperature is 665℃, the total reduction is 140mm, and the cumulative reduction rate is 72%, which is mainly used to refine the original austenite grain size and reduce the proportion of banded structure. The grain size after heat treatment is at level 6 and the metallographic structure is a small amount of ferrite + pearlite.

[0029] (3) Heat treatment process: normalizing heat treatment process is adopted; normalizing in a normalizing furnace, normalizing temperature is 890°C, furnace time is 2.2 min / mm, and cooling in still air after being taken out of the furnace to obtain the desired steel plate mainly composed of pearlite.

[0030] The properties of the steel plate of this example are shown in Table 1.

[0031] Example 2

[0032] The thickness of the steel plate in this embodiment is 18 mm, and the chemical composition and mass percentage of the steel plate are: C: 0.18%, Mn: 0.90%, Si: 0.32%, P: 0.008%, S: 0.008%, Mo: 0.48%, and the remainder is Fe and unavoidable impurity elements.

[0033] The manufacturing method of the heat-resistant SA204GrB steel plate for containers in this embodiment includes steelmaking, rolling, heat treatment and other processes, and the specific requirements are as follows:

[0034] (1) Steelmaking process: oxygen converter + LF refining furnace + RH vacuum degassing furnace smelting, the initial refining time is 43 minutes, and the tapping temperature after initial refining is 1580°C; oxygen converter smelting and then LF refining furnace refining, the refining time is 25 minutes, when the molten steel temperature reaches 1590°C, it is transferred to the RH vacuum degassing furnace for degassing treatment, the vacuum holding time is 23 minutes, and the tapping temperature is 1620°C; the molten steel adopts the non-oxidation protection water nozzle crystallizer continuous casting method, the superheat is controlled at 22°C, the pulling speed is 1.2m / min, and a rectangular cross-section continuous casting billet is obtained.

[0035] (2) Rolling process: rough rolling + finishing rolling process is adopted, and the surface impact force of the billet high-pressure water descaling is 1.3N / mm 2 Effectively remove the scale and avoid surface defects such as pockmarks caused by the pressing of scale during rolling. The rough rolling adopts the high-temperature and large-reduction method without controlled rolling, in which the single-pass reduction of 3 passes is 32mm, 33mm, and 35mm, and the cumulative reduction rate is 62%, to ensure the full deformation of the billet, on the one hand, to break the large grains; on the other hand, to bridge the metallurgical defects such as the looseness of the center of the continuous casting billet; the finishing rolling stage adopts the controlled rolling and controlled cooling method, the starting rolling temperature is 920℃, the final cooling temperature is 630℃, the total reduction is 160mm, and the cumulative reduction rate is 70%, which is mainly used to refine the original austenite grain size and reduce the proportion of banded structure. The grain size after heat treatment is level 7 and the metallographic structure is a small amount of ferrite + pearlite.

[0036] (3) Heat treatment process: normalizing heat treatment process is adopted; normalizing in a normalizing furnace, normalizing temperature is 880°C, furnace time is 2.1 min / mm, and cooling in still air after being taken out of the furnace to obtain the desired steel plate mainly composed of pearlite.

[0037] The properties of the steel plate of this example are shown in Table 1.

[0038] Example 3

[0039] The thickness of the steel plate in this embodiment is 36 mm, and the chemical composition and mass percentage of the steel plate are: C: 0.19%, Mn: 0.88%, Si: 0.28%, P: 0.008%, S: 0.005%, Mo: 0.55%, and the remainder is Fe and unavoidable impurity elements.

[0040] The manufacturing method of the heat-resistant SA204GrB steel plate for containers in this embodiment includes steelmaking, rolling, heat treatment and other processes, and the specific requirements are as follows:

[0041] (1) Steelmaking process: oxygen converter + LF refining furnace + RH vacuum degassing furnace smelting, the initial refining time is 45 minutes, and the tapping temperature after initial refining is 1580°C; oxygen converter smelting and then LF refining furnace refining, the refining time is 26 minutes, when the molten steel temperature reaches 1620°C, it is transferred to the RH vacuum degassing furnace for degassing treatment, the vacuum is maintained for 20 minutes, and the tapping temperature is 1610°C; the molten steel is continuously cast in a non-oxidation protection water nozzle crystallizer, the superheat is controlled at 18°C, the pulling speed is 1.2 m / min, and a rectangular cross-section continuous casting billet is obtained.

[0042] (2) Rolling process: rough rolling + finishing rolling is adopted. The surface impact force of high-pressure water descaling of the billet is 1.30N / mm2 to effectively remove the iron oxide scale and avoid surface defects such as roughness caused by the pressing of the iron oxide scale during rolling. The rough rolling adopts the high-temperature and large reduction method without controlled rolling. The reduction of the three passes is 33mm, 32mm, and 34mm, and the cumulative reduction rate is 61%, which ensures that the billet is fully deformed. On the one hand, it breaks the large grains; on the other hand, it bridges the metallurgical defects such as the looseness of the center of the continuous casting billet. The finishing rolling stage adopts the controlled rolling and controlled cooling method, with the starting rolling temperature of 930℃, the final cooling temperature of 640℃, the total reduction of 130mm, and the cumulative reduction rate of 67%, which is mainly used to refine the original austenite grain size and reduce the proportion of banded structure. The grain size after heat treatment is level 6 and the metallographic structure is a small amount of ferrite + pearlite.

[0043] (3) Heat treatment process: normalizing heat treatment process is adopted; normalizing in a normalizing furnace, normalizing temperature is 890°C, furnace time is 1.90 min / mm, and cooling in still air after being taken out of the furnace to obtain the desired steel plate mainly composed of pearlite.

[0044] The properties of the steel plate of this example are shown in Table 1.

[0045] Example 4

[0046] The thickness of the steel plate in this embodiment is 50 mm, and the chemical composition and mass percentage of the steel plate are: C: 0.17%, Mn: 0.83%, Si: 0.30%, P: 0.008%, S: 0.005%, Mo: 0.60%, and the remainder is Fe and unavoidable impurity elements.

[0047] The manufacturing method of the heat-resistant SA204GrB steel plate for containers in this embodiment includes steelmaking, rolling, heat treatment and other processes, and the specific requirements are as follows:

[0048] (1) Steelmaking process: oxygen converter + LF refining furnace + RH vacuum degassing furnace smelting, the initial refining time is 43 minutes, and the tapping temperature after initial refining is 1590°C; oxygen converter smelting and then LF refining furnace refining, the refining time is 30 minutes, when the molten steel temperature reaches 1630°C, it is transferred to the RH vacuum degassing furnace for degassing treatment, the vacuum holding time is 24 minutes, and the tapping temperature is 1570°C; the molten steel adopts the non-oxidation protection water nozzle crystallizer continuous casting method, the superheat is controlled at 22°C, the pulling speed is 1.10m / min, and a rectangular cross-section continuous casting billet is obtained.

[0049] (2) Rolling process: rough rolling + finishing rolling is adopted. The high-pressure water descaling force of the billet is 1.30N / mm2 to effectively remove the iron oxide scale and avoid surface defects such as roughness caused by the pressing of the iron oxide scale during rolling. The rough rolling adopts the high-temperature and large reduction method without controlled rolling. The reduction of the three passes is 30mm, 30mm, and 30mm, and the cumulative reduction rate is 55%, which ensures that the billet is fully deformed. On the one hand, it breaks the large grains; on the other hand, it bridges the metallurgical defects such as the looseness of the center of the continuous casting billet. The finishing rolling stage adopts the controlled rolling and controlled cooling method, with the starting rolling temperature of 920℃, the final cooling temperature of 610℃, the total reduction of 105mm, and the cumulative reduction rate of 64%, which is mainly used to refine the original austenite grain size and reduce the proportion of banded structure. The grain size after heat treatment is level 7 and the metallographic structure is a small amount of ferrite + pearlite.

[0050] (3) Heat treatment process: normalizing heat treatment process is adopted; normalizing in a normalizing furnace, normalizing temperature is 880°C, furnace time is 2.4 min / mm, and cooling in still air after being taken out of the furnace to obtain the desired steel plate mainly composed of pearlite.

[0051] The properties of the steel plate of this example are shown in Table 1.

[0052] Table 1

[0053]

Claims

1. A heat-resistant SA204GrB steel plate for containers, characterized in that: The chemical composition of the steel plate and its mass percentage are: C: 0.16-0.20%, Mn: 0.80-0.95%, Si: 0.15-0.35%, P≤0.010%, S≤0.010%, Mo: 0.45-0.55%, and the balance is Fe and unavoidable impurity elements.

2. The heat-resistant SA204GrB steel plate for container according to claim 1, characterized in that: The production thickness is 6-50mm, the tensile strength is 500-610MPa, the yield strength is 290-500MPa, the elongation after break is ≥23%, the average value of the -20℃ Charpy V-type impact absorption energy of the core is ≥100J, and the high temperature yield strength Rp0.2 at 500℃ is ≥265MPa.

3. The heat-resistant SA204GrB steel plate for container according to claim 1, characterized in that: The metallographic structure of the steel plate is mainly pearlite.

4. A method for manufacturing the heat-resistant SA204GrB steel plate for container according to claim 1, characterized in that: Includes steps: 1) Steelmaking: Molten steel is smelted according to the chemical composition and cast into billets using continuous casting process; 2) Rolling: adopting rough rolling and finishing rolling process, wherein the rough rolling adopts uncontrolled rolling, the starting rolling temperature is 1030-1080°C, the single pass reduction of 2-3 passes in the rough rolling pass is ≥30mm, and the cumulative deformation rate of rough rolling is ≥55%; the finishing rolling adopts controlled rolling and controlled cooling method, the starting rolling temperature is 900-950°C, the final cooling temperature is 600-680°C, the total reduction is ≥100mm, the cumulative reduction rate is ≥60%, and a small amount of ferrite + pearlite structure with a grain size of more than 5 levels is obtained; 3) Heat treatment: The normalizing process is used to refine the grains. The normalizing temperature is 850-900°C, and the furnace time is 1.8-2.5min / mm*steel plate thickness / mm. After being taken out of the furnace, it is cooled in still air to obtain the required steel plate composed mainly of a small amount of ferrite + fine pearlite.

5. The method according to claim 4, characterized in that: In step 1), converter primary refining + LF refining + vacuum degassing smelting is adopted, the primary refining time is 35 to 48 minutes, and the tapping temperature after primary refining is ≥1550°C; LF refining is carried out after converter smelting, the refining time is ≥20 minutes, and when the molten steel temperature reaches 1550 to 1660°C, it is transferred to a vacuum degassing furnace for degassing treatment, the vacuum holding time is ≥15 minutes, and the tapping temperature is ≥1550°C; the molten steel is continuously cast in a non-oxidation protected water nozzle crystallizer, the continuous casting superheat is 15 to 30°C, and the pulling speed is ≤1.4m / min to obtain a continuous casting billet with a rectangular cross-section.

6. The method according to claim 4, characterized in that: In step 2), the billet is heated before rolling until the structure is completely austenitized, and the billet is descaled. The impact force of high-pressure water descaling surface is ≥ 0.90N / mm 2 .

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