Heat-resistant sa204grb steel plate for a container and method for manufacturing the same

Abstract

The present application relates to a kind of heat-resistant SA204GrB steel plate for container and its manufacturing method, the chemical composition of steel plate and its mass percentage are as follows: 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%, the balance is Fe and inevitable impurity elements.The thickness of steel plate production is 6-50mm, tensile strength is 500~610MPa, yield strength is 290~500MPa, elongation after fracture is ≥23%, the average value of Charpy V-type impact energy in core is ≥100J at-20℃, high temperature yield strength Rp0.2 is ≥265MPa at 500℃.Metallographic structure is mainly pearlite.The manufacturing method of steel plate includes steelmaking, rolling and heat treatment, and normalizing process is used in heat treatment, which refines grain, on the one hand, it has the effect of fine-grain strengthening, to ensure that steel plate has uniform and stable hot strength, on the other hand, it refines pearlite structure, increases the proportion of ferrite and small pitch pearlite structure, and improves the problem of impact toughness of material in low temperature environment.The performance of steel plate is suitable for the manufacture of high temperature equipment in petroleum, chemical industry, boiler container and other industries.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of iron-based alloys, and particularly relates to a medium-thick SA204GrB steel plate for a container and a manufacturing method thereof. BACKGROUND

[0002] SA204GrB is a molybdenum-containing pressure vessel heat-resistant steel. Since SA204GrB is a traditional carbon-manganese steel to which molybdenum is added, the steel has good high-temperature resistance and durable plasticity, and is commonly used in thermal power, solar thermal power, boiler vessels and coal chemical projects, and the main equipment is a desulfurization tank, a split-type deaerator, a heat exchanger and the like used in a high-temperature and high-pressure environment.

[0003] In recent years, with the variability of the service environment of equipment, the traditional steel plate can only meet the standard requirements and cannot meet the use requirements in special environments. The traditional steel plate only meets the corresponding requirements of ASME SA204 / SA204M-2021, the impact temperature is room temperature, and the high-temperature tensile temperature is generally below 400 DEG C. However, with the needs of application projects, the impact temperature of the steel plate is reduced to 0 DEG C, and the high-temperature service temperature is increased to 500 DEG C, so as to further ensure the reliable use of the material, and the existing production process of the steel plate manufacturing plant is optimized and improved.

[0004] By controlling the steelmaking, casting blank process, improving the controlled rolling process and heat treatment process, a steel plate with excellent comprehensive performance is developed, the good matching of strength and toughness is met, and the demand of the steel plate for working at a high temperature in a low-temperature environment is ensured.

[0005] The patent document with the patent publication number CN103422023A discloses a heat-resistant container steel plate production method by adding more chromium alloy and molybdenum alloy and adopting quenching + tempering process, and the production process is complex, the production cost is high, and the production cycle is long. The patent document with the patent publication number CN103320696A discloses a high-temperature-resistant container steel by adding more chromium alloy and vanadium alloy and increasing the tempering process, and the alloy cost is higher, and the production process and production cycle are longer. SUMMARY

[0006] The application discloses a heat-resistant SA204GrB steel plate for a container and a manufacturing method thereof, and solves the problem of unstable impact toughness of the heat-resistant steel produced by a continuous casting blank process at a service temperature of-20 DEG C and above. The steel plate has a good strength-toughness ratio, excellent low-temperature impact toughness, good high-temperature strength and excellent welding performance, meets the requirements of a heat exchanger material, and can be applied to the manufacture of main equipment such as a desulfurization tank, a split-type deaerator and a heat exchanger.

[0007] The technical scheme adopted by the present application is: a heat-resistant SA204GrB steel plate for a container and a manufacturing method thereof, the chemical composition of the steel plate and the mass percentage thereof are as follows: 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 inevitable impurity elements.

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

[0009] The content of chemical elements in the steel determines the performance and service environment of the material, and the content of chemical elements in the present application is as follows:

[0010] Carbon (C): it is the most obvious element for solid solution strengthening in steel, it strengthens the structure of steel in the lattice, so that the material has good plasticity and toughness; with the increase of the content of carbon, the carbon phase at the grain boundary of the steel also increases, so that the grain boundary strength increases, but the plasticity and toughness decrease. In order to ensure excellent low-temperature toughness in low-temperature environment, the most economical way is to reduce the carbon content, but if the carbon content is too low, the strength of the steel will decrease sharply when used in high-temperature environment, so that the equipment fails. The C content in the present application is controlled to be 0.16-0.20%.

[0011] Silicon (Si): it is a beneficial element, mainly for deoxidizing carbon, manganese and other elements in steel, preventing the formation of pores and loose structure in steel, and improving the structure and performance by promoting spheroidization and grain refinement, too much addition will reduce the plasticity and toughness of the steel, causing the increase of brittleness of the steel, and too little addition cannot improve the performance of the steel. The Si content in the present application is controlled to be 0.15-0.35%.

[0012] Manganese (Mn): it is dissolved in ferrite and austenite, expands the austenite zone, and increases the critical temperature. It forms MnS with sulfur in steel, which has a high melting point, avoids the formation of FeS film on the grain boundary, eliminates the thermal brittleness of the steel, refines the pearlite size, and significantly improves the strength of the pearlite steel. Therefore, the Mn content in the present application is controlled to be 0.80-0.95%.

[0013] Phosphorus (P), sulfur (S): reduce the toughness and plasticity of steel, thereby affecting the strength of the material. If the content is too high, it is easy to produce surface and internal cracks during processing, and it is easy to form brittle compounds during welding, which can cause the welded joint to crack or even brittle fracture during welding. Therefore, the P content of the present application is controlled to be ≤0.010%, and the S content is controlled to be ≤0.010%.

[0014] Molybdenum (Mo): refines the grain, reduces the grain boundary corrosion of steel, improves the oxidation resistance at high temperature; reduces the austenite phase region, dissolves in ferrite, austenite and carbide, improves the stability of carbide, inhibits the grain boundary brittleness, and maintains the excellent plasticity and toughness of the steel; MoC is formed with carbon, which has the effect of secondary hardening, and improves the wear resistance and creep resistance of the steel plate. In the present application, the addition of molybdenum not only improves the mechanical properties of the material, but also inhibits the brittleness caused by high temperature tempering. The Mo content of the present application is controlled to be 0.45-0.55%.

[0015] The present application provides a heat-resistant SA204GrB steel plate for containers and a manufacturing method thereof, which comprises steelmaking, rolling, heat treatment and the like processes, and the specific requirements are as follows:

[0016] (1) The steelmaking process preferably adopts oxygen converter + LF refining furnace + RH vacuum degassing furnace smelting, the initial smelting time of the converter is 35-48 minutes, and the tapping temperature after initial smelting is ≥1550℃; the oxygen converter is smelted and then refined in the LF refining furnace, the refining time is ≥20 minutes, the molten steel temperature reaches 1550-1660℃, then the RH vacuum degassing furnace is entered for degassing treatment, the vacuum time is ≥15 minutes, and the tapping temperature is ≥1550℃; the molten steel adopts the non-oxidizing protective nozzle crystallizer continuous casting mode, the superheat degree is controlled to be 15-30℃, and the drawing speed is ≤1.4 m / min, so as to obtain a rectangular section continuous casting blank.

[0017] (2) The rolling process adopts rough rolling + finish rolling rolling process, the surface of the blank is struck with high-pressure water descaling force ≥0.90 N / mm2 to effectively remove the iron scale, so as to avoid the surface defects such as surface pitting caused by the pressing of the primary iron scale during rolling. The rough rolling adopts uncontrolled rolling high-temperature large reduction mode, the opening rolling temperature is 1030-1080℃, the single pass reduction amount of 2-3 passes is ≥30 mm, and the cumulative deformation rate is ≥55%, so as to ensure sufficient deformation of the blank, on the one hand to break up large particle grains; on the other hand to fill the center porosity and other metallurgical defects of the continuous casting blank; the finish rolling stage adopts controlled rolling and controlled cooling mode, the opening rolling temperature is 900-950℃, the final cooling temperature is 600-680℃, the total reduction amount is ≥100 mm, and the cumulative reduction rate is ≥60%, which is mainly used to refine the original austenite grain size, reduce the proportion of banded structure, and at the same time ensure that the grain size after heat treatment is above grade 5 and the metallographic structure is a small amount of ferrite + pearlite.

[0018] (3) heat treatment process, using normalizing process, refining grain, on the one hand, the effect of fine grain strengthening, to ensure that the steel plate has uniform, stable thermal strength; On the other hand, the pearlite organization is refined, the proportion of ferrite and small pitch pearlite organization is increased, and the problem of improving the impact toughness of the material at low temperature environment. Normalizing furnace normalizing, normalizing temperature 850~900℃, in the furnace time 1.8~2.5min / mm, after the furnace is cooled in the static air, the required steel plate mainly with a small amount of ferrite + fine pearlite.

[0019] The present application adopts a low alloy component design system, cooperates with controlled rolling and controlled cooling rolling mode, and then normalizes in a continuous non-oxidizing heat treatment furnace. The produced steel plate with a thickness of 6~50mm has the following comprehensive performance: tensile strength 500~610MPa, yield strength 290~500MPa, elongation after fracture ≥23%, average value of Charpy (V-type) impact energy at-20℃ in the core ≥100J, and high temperature yield strength Rp0.2 at 500℃ ≥265MPa. The production method provided by the present application not only reduces the addition of alloy elements such as Mn, Si and Mo, saves energy and resources, but also guarantees the application of the obtained steel plate in high temperature equipment at-20℃ low temperature environment, and improves the product market competitiveness.

[0020] Compared with the prior art, the present application has the following advantages:

[0021] (1) The heat-resistant SA204GrB steel plate for containers and the manufacturing method thereof provided by the present application do not add other alloy elements except the standard required alloy elements such as Mn, Si and Mo, and the production cost is the most economical.

[0022] (2) The heat-resistant SA204GrB steel plate for containers and the manufacturing method thereof provided by the present application produce the steel plate with a thickness of 6~50mm, and the comprehensive performance can reach: tensile strength 500~610MPa, yield strength 290~500MPa, elongation after fracture ≥23%, average value of Charpy (V-type) impact energy at-20℃ in the core ≥100J, and high temperature yield strength Rp0.2 at 500℃ ≥265MPa. The steel plate has excellent low temperature toughness, and solves the problem that such steel material is easy to crack at low temperature environment. DETAILED DESCRIPTION

[0023] The present application will be further described in detail below in combination with examples, which are exemplary and intended to explain the present application, and cannot be understood as a limitation of the present application.

[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 as follows: C: 0.20%, Mn: 0.85%, Si: 0.32%, P: 0.010%, S: 0.008%, Mo: 0.50%, and the balance of Fe and inevitable impurity elements.

[0026] The manufacturing method of the heat-resistant SA204GrB steel plate for the container in this embodiment comprises the steps of steelmaking, rolling, heat treatment, etc., and the specific requirements are as follows:

[0027] (1) The steelmaking process adopts oxygen converter + LF refining furnace + RH vacuum degassing furnace smelting, the initial smelting time of the converter is 42 minutes, and the tapping temperature after initial smelting is 1580°C; the oxygen converter is used for smelting, and then the LF refining furnace is used for refining, the refining time is 23 minutes, the molten steel temperature reaches 1620°C, and then the RH vacuum degassing furnace is used for degassing treatment, the vacuum holding time is 18 minutes, and the tapping temperature is 1590°C; the molten steel is cast by the non-oxidizing protective nozzle crystallizer continuous casting mode, the superheat degree is controlled to be 18°C, and the pulling speed is 1.0 m / min, so as to obtain a rectangular section of the continuous casting blank.

[0028] (2) The rolling process adopts the rolling process of rough rolling + finish rolling, the surface impact intensity of the blank high-pressure water descaling is 1.1 N / mm 2 The scale is effectively removed, and surface defects such as surface pitting caused by the pressing of the primary scale during rolling are avoided. The rough rolling adopts the uncontrolled rolling high-temperature large reduction mode, wherein the single pass reduction amount of the three passes is 33 mm, 34 mm and 32 mm, and the cumulative reduction rate is 60%, so as to ensure sufficient deformation of the blank, break large particle grains on the one hand, and close the center porosity and other metallurgical defects of the continuous casting blank on the other hand; the finish rolling stage adopts the controlled rolling and controlled cooling mode, the starting rolling temperature is 925°C, the final cooling temperature is 665°C, the total reduction amount is 140 mm, and the cumulative reduction rate is 72%, which is mainly used for refining the original austenite grain size, reducing the proportion of banded structure, and the grain size after heat treatment is at level 6 and the metallographic structure is a small amount of ferrite + pearlite.

[0029] (3) The heat treatment process adopts the normalizing heat treatment process; the normalizing temperature of the normalizing furnace is 890°C, the furnace time is 2.2 min / mm, and the blank is cooled in the static air after being discharged from the furnace, so as to obtain the required steel plate mainly with pearlite.

[0030] The performance of the steel plate in this embodiment is shown in Table 1.

[0031] Embodiment 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 as follows: C: 0.18%, Mn: 0.90%, Si: 0.32%, P: 0.008%, S: 0.008%, Mo: 0.48%, and the balance of Fe and inevitable impurity elements.

[0033] The manufacturing method of the heat-resistant SA204GrB steel plate for the container of the present embodiment comprises the processes of steelmaking, rolling, heat treatment, etc., and the specific requirements are as follows:

[0034] (1) The steelmaking process adopts oxygen converter + LF refining furnace + RH vacuum degassing furnace smelting, the initial smelting time is 43 minutes, and the steel tapping temperature after initial smelting is 1580℃; the oxygen converter smelting is followed by LF refining furnace refining, the refining time is 25 minutes, the molten steel temperature reaches 1590℃, then the RH vacuum degassing furnace is used for degassing treatment, the vacuum holding time is 23 minutes, and the steel tapping temperature is 1620℃; the molten steel adopts the non-oxidizing protective nozzle crystallizer continuous casting mode, the superheat degree is controlled to be 22℃, and the drawing speed is 1.2m / min, so as to obtain a rectangular section of continuous casting blank.

[0035] (2) The rolling process adopts the rolling process of rough rolling + finish rolling, the surface impact intensity of the blank high-pressure water descaling is 1.3N / mm 2 The iron oxide scale is effectively removed to avoid surface defects such as rough surface caused by the pressing of primary iron oxide scale during rolling. The rough rolling adopts the uncontrolled rolling high-temperature large reduction mode, wherein the single pass reduction amount of the 3 passes is 32mm, 33mm and 35mm, and the cumulative reduction rate is 62%, so as to ensure sufficient deformation of the blank, which on the one hand breaks large particle grains, and on the other hand fills the metallurgical defects such as the center porosity of the continuous casting blank; the finish rolling stage adopts the controlled rolling and controlled cooling mode, the opening rolling temperature is 920℃, the final cooling temperature is 630℃, the total reduction amount is 160mm, and the cumulative reduction rate is 70%, which is mainly used for refining the original austenite grain size and reducing the proportion of banded structure, and the grain size after heat treatment is at the 7th level and the metallographic structure is a small amount of ferrite + pearlite.

[0036] (3) The heat treatment process adopts the normalizing heat treatment process; the normalizing temperature of the normalizing furnace is 880℃, the furnace time is 2.1min / mm, and the steel plate is cooled in the static air after being discharged from the furnace, so as to obtain the required steel plate mainly with pearlite.

[0037] The performance of the steel plate of the present embodiment is shown in Table 1.

[0038] Example 3

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

[0040] The manufacturing method of the heat-resistant SA204GrB steel plate for the container of the present embodiment comprises the processes of steelmaking, rolling, heat treatment, etc., and the specific requirements are as follows:

[0041] (1) Steelmaking process, using oxygen converter + LF refining furnace + RH vacuum degassing furnace smelting, initial smelting time 45 minutes, after initial smelting the tapping temperature 1580°C; using oxygen converter smelting then LF refining furnace refining, refining time 26 minutes, the molten steel temperature reaches 1620°C into the RH vacuum degassing furnace for degassing treatment, vacuum holding time 20 minutes, the tapping temperature 1610°C; the molten steel using non-oxidizing protective nozzle crystallizer continuous casting mode, the superheat control at 18°C, the drawing speed 1.2 m / min, to get the rectangular section of continuous casting billet.

[0042] (2) Rolling process, using rough rolling + finishing rolling rolling process, billet high pressure water descaling surface impact 1.30 N / mm2effective removal of iron oxide scale, to avoid the surface of the rolling once the oxide scale pressure into the defects such as surface. Rough rolling using uncontrolled rolling high temperature large reduction mode, of which 3 passes single pass reduction 33 mm, 32 mm, 34 mm, cumulative reduction 61%, to ensure that the billet is fully deformed, on the one hand to break the large particle size; on the other hand to fill the center of the continuous casting billet porosity and other metallurgical defects; finishing rolling stage to take the way of controlled rolling and controlled cooling, the opening temperature 930°C, the final cooling temperature 640°C, the total reduction 130 mm, the cumulative reduction 67%, mainly used to refine the original austenite grain size, reduce the proportion of banded structure, the grain size after heat treatment at 6 level and the metallographic structure is a small amount of ferrite + pearlite.

[0043] (3) Heat treatment process, using normalizing heat treatment process; normalizing furnace normalizing, normalizing temperature 890°C, in the furnace time 1.90 min / mm, after the furnace cooling in the static air, to get the required steel plate with pearlite as the main.

[0044] The performance of the steel plate of this example is shown in Table 1.

[0045] Example 4

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

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

[0048] (1) Steelmaking process, using oxygen converter + LF refining furnace + RH vacuum degassing furnace smelting, initial smelting time 43 minutes, after initial smelting the tapping temperature 1590 °C; using oxygen converter smelting then LF refining furnace refining, refining time 30 minutes, the molten steel temperature reaches 1630 °C into the RH vacuum degassing furnace for degassing treatment, vacuum holding time 24 minutes, the tapping temperature 1570 °C; molten steel using non-oxidizing protective nozzle crystallizer continuous casting mode, the superheat control for 22 °C, the drawing speed 1.10 m / min, get the rectangular section of continuous casting billet.

[0049] (2) Rolling process, using rough rolling + finishing rolling rolling process, billet high pressure water descaling surface impact 1.30 N / mm2effective removal of iron oxide scale, avoid in rolling once iron oxide scale pressure into the surface of the defects such as pitting. Rough rolling using uncontrolled rolling high temperature large reduction way rolling, which 3 pass single pass reduction 30 mm, 30 mm, 30 mm, cumulative reduction 55%, to ensure that the billet deformation, on the one hand to break the large particle size grains; on the other hand to fill the center of continuous casting billet porosity and other metallurgical defects; finishing rolling stage take the way of controlled rolling and controlled cooling, open rolling temperature 920 °C, final cooling temperature 610 °C, total reduction 105 mm, cumulative reduction 64%, mainly used to refine the original austenite grain size, reduce the proportion of banded structure, after heat treatment of the grain size at 7 level and the metallographic structure for a small amount of ferrite + pearlite.

[0050] (3) Heat treatment process, using normalizing heat treatment process; normalizing furnace normalizing, normalizing temperature 880 °C, in the furnace time 2.4 min / mm, after the furnace cooling in the static air, get the required steel plate with pearlite as the main.

[0051] The performance of the steel plate of the example is shown in Table 1.

[0052] Table 1

[0053]

Claims

1. A method of manufacturing a heat-resistant SA204GrB steel plate for a container, characterized by: The chemical composition of the steel plate and its mass percentage are as follows: 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 of Fe and inevitable impurity elements; the production thickness is 6-50 mm, the tensile strength is 500-610 MPa, the yield strength is 290-500 MPa, the elongation after fracture is ≥23%, the average Charpy V-type impact energy at -20°C is ≥100 J, and the high-temperature yield strength Rp0.2 at 500°C is ≥265 MPa; the method comprises the following steps: 1) steelmaking: smelting molten steel according to the chemical composition design, adopting converter initial smelting+LF refining+vacuum degassing smelting, the initial smelting time is 35-48 minutes, and the initial smelting temperature is ≥1550°C; after converter smelting, LF refining is carried out, the refining time is ≥20 minutes, the molten steel temperature reaches 1550-1660°C, and then the vacuum degassing furnace is entered for degassing treatment, the vacuum holding time is ≥15 minutes, and the tapping temperature is ≥1550°C; the molten steel is cast by using the non-oxidizing protective nozzle crystallizer, the continuous casting overheat degree is 15-30°C, the drawing speed is ≤1.4 m / min, and the rectangular section continuous casting blank is obtained; 2) rolling: adopting the rolling process of rough rolling and finish rolling, wherein the rough rolling adopts uncontrolled rolling, the rough rolling temperature is 1030-1080°C, the single pass reduction of 2-3 passes in the rough rolling pass is ≥30 mm, and the cumulative deformation rate of rough rolling is ≥55%; the finish rolling adopts controlled rolling and controlled cooling, the finish rolling temperature is 900-950°C, the final cooling temperature is 600-680°C, the total reduction is ≥100 mm, and the cumulative reduction is ≥60%, so that the grain size is 5 or more, and a small amount of ferrite+pearlite structure is obtained; 3) heat treatment: adopting normalizing process to refine the grain, the normalizing temperature is 850-900°C, the furnace time is 1.8-2.5 min / mm*steel plate thickness / mm, and after being discharged from the furnace, the steel plate is cooled in the static air, so that the required steel plate with a small amount of ferrite+fine pearlite is obtained.

2. The method of claim 1, wherein the method further comprises: In step 2), the blank is heated to complete austenitization before rolling, and the blank is descaled, and the surface impact of high-pressure water descaling is greater than or equal to 0.90 N / mm 2 . ​

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