1300mpa grade pressure containing equipment steel, manufacturing, forming and post heat treatment method

Abstract

The application provides a 1300MPa grade pressure-bearing equipment steel, a manufacturing method, a forming method and a post-heat treatment method, the steel has the following components in percentage by weight: C 0.18%-0.22%, Si 0.15%-0.35%, Mn 0.95%-1.30%, P≤0.010%, S≤0.003%, Cr 1.00%-1.50%, Mo 0.40%-0.60%, Ni 1.30%-1.55%, V 0.06%-0.09%, Alt 0.015%-0.045%, and the rest is Fe and inevitable inclusions. The manufacturing method comprises smelting, continuous casting, heating, rolling and tempering; after the forming heat treatment, the mechanical properties of the steel are 980MPa≤R p0.2 ≤1110MPa, 1300MPa≤R m ≤1430MP; at 400℃, 550MPa≤R p0.2 ≤630MPa; the impact energy at 0℃ is KV2≥120J; and the use requirements of high-strength pressure-bearing equipment are ensured.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal materials, and particularly relates to a 1300MPa-grade steel for pressure-bearing equipment, a manufacturing method, a forming method and a post-heat treatment method. BACKGROUND

[0002] Pressure-bearing equipment is widely used in the processing and preparation of bulk energy such as coal and chemical industry, and plays an important role in the whole energy production process. For example, the intense medium reaction process in a chemical plant produces a huge internal pressure, and the steam heat exchange process in a coal power plant produces gas pressure. The pressure-bearing equipment bears a huge pressure in the process, and for high-power equipment, the pressure can reach more than 100MPa. The special equipment industry defines this as extra-high pressure, and the steel used to manufacture such equipment needs to have a tensile strength of 1300MPa. In recent years, in order to meet the rapid development of the manufacturing industry of such pressure-bearing equipment, pressure-bearing equipment with high efficiency, high parameters and high reliability design requirements is proposed by design institutes, and the existing strength grade of pressure-bearing equipment cannot meet the design requirements, and ultra-high strength and toughness materials are needed to support the development of high-end equipment.

[0003] The disclosed patent "A steel for nuclear power pressure-bearing equipment and a manufacturing method thereof" (publication number CN103160732A) discloses a steel for pressure-bearing equipment applied in the field of nuclear power. The tensile strength of the steel plate is 560-625N / mm 2 , and the tensile strength of the simulated post-weld heat treatment state is reduced to 510-600N / mm 2 . When facing a higher pressure service environment, the product cannot provide higher strength support for equipment requirements, especially without providing a technical solution after forming and data support to have sufficient strength to meet the high pressure service requirements.

[0004] The disclosed patent "A hot-rolled weldable pressure-bearing equipment steel plate and a production method thereof" (publication number CN110983175A) discloses a steel plate with a tensile strength of 450-610MPa in the delivery state and the simulated post-weld heat treatment state. The microstructure is composed of low-strength ferrite and pearlite. When facing a higher pressure service environment, the product cannot provide higher strength support for equipment requirements, especially without providing a technical solution after forming and data support to have sufficient strength to meet the high pressure service requirements.

[0005] The disclosed invention patent "A hot-rolled automobile steel with tensile strength greater than 1300MPa and high surface quality and its manufacturing method" (publication number CN114262847A), from the disclosed composition, production method and beneficial effects, the patent product is used for automobile manufacturing, relates to ultra-thin specifications with a thickness of 2-4mm, and is not suitable for the manufacturing of pressure-bearing equipment. It also relates to the technical solutions and data after forming to support the manufacturing of pressure-bearing equipment. From the disclosed composition, production method and beneficial effects, the patent product is used for automobile manufacturing, relates to ultra-thin specifications with a thickness of 2-4mm, and is not suitable for the manufacturing of pressure-bearing equipment. It also relates to the technical solutions and data after forming to support the manufacturing of pressure-bearing equipment. SUMMARY

[0006] The purpose of the present application is to overcome the problems of the above-mentioned invention, which cannot provide a technical solution to improve the strength of high-strength pressure-bearing equipment after forming. The present application provides a steel plate with a thickness specification of 10-40mm and a pressure-bearing equipment steel product with a tensile strength of 1300MPa after forming, as well as a manufacturing process, forming and post-heat treatment process, to meet the manufacturing requirements of ultra-high-strength pressure-bearing equipment.

[0007] The purpose of the present application is achieved as follows:

[0008] A 1300MPa pressure-bearing equipment steel, the composition of the steel is as follows in terms of weight percentage: C 0.18%-0.22%, Si 0.15%-0.35%, Mn 0.95%-1.30%, P≤0.010%, S≤0.003%, Cr 1.00%-1.50%, Mo 0.40%-0.60%, Ni 1.30%-1.55%, V 0.06%-0.09%, Alt 0.015%-0.045%, and the balance is Fe and unavoidable inclusions.

[0009] The thickness of the pressure-bearing equipment steel is 10-40mm, and the mechanical properties are 950MPa≤R p0.2 ≤1080MPa, 1300MPa≤ Rm ≤1430MPa; and the impact energy at 0℃ is KV2≥100J.

[0010] The reasons for the composition design of the present application are as follows:

[0011] C is the most important element for improving the strength of steel. By adding C element, the hardenability of the steel is significantly improved. In addition, the combination of C and strong carbide alloying elements in the steel plays a role in precipitation strengthening, achieving secondary hardening effect and ensuring the high strength requirement of the steel. When the carbon content is less than 0.13%, the hardenability is low, and it is difficult to obtain uniform sorbite structure after subsequent tempering treatment, and the strength of the steel cannot meet the use requirements. However, too high carbon content will affect the machining performance of the steel, therefore, the C content range is limited to 0.18%-0.22% in the present application.

[0012] Si is used as a reducing agent and deoxidizer in the steelmaking process. Si has a certain effect on the martensite transformation during tempering. When the silicon content is higher than 0.5%, it will hinder the activity of C in the martensite during tempering, so that ε carbide is generated in the martensite steel instead of M3C type carbide, which reduces the hardness and toughness of the steel and increases the sensitivity of temper brittleness, therefore the Si content range is limited to 0.15% to 0.35% in the present application.

[0013] Mn is an element that strongly stabilizes austenite, can effectively reduce the decomposition rate of austenite, improve the hardenability of steel, and can strongly increase the strength and hardness of steel, but high Mn content will enhance the temper brittleness of steel, therefore the Mn content range is limited to 0.95% to 1.30% in the present application.

[0014] S and P are harmful elements in steel, and must be strictly controlled to ensure the purity and plasticity of the steel, therefore the present application limits S≤0.003% and P≤0.010%.

[0015] Adding a certain amount of Cr in steel significantly improves the hardenability of the steel, ensuring the strength of the steel matrix. In addition, Cr is a strong carbide-forming element that forms stable carbides with C in steel, improving the pressure-bearing capacity of pressure-bearing equipment. When the content of Cr is less than 0.3%, it has little effect on improving the hardenability and cannot generate lath martensite structure, which cannot meet the performance requirements of high-strength steel, therefore the Cr content range is limited to 1.00% to 1.50% in the present application.

[0016] Mo can improve the hardenability of steel, effectively refine the austenite grains, and also can strengthen the solid solution strengthening effect of ferrite. Adding a certain amount of Mo can improve the temper resistance of steel and inhibit temper embrittlement. At the same time, molybdenum is a strong carbide-forming element, and the Mo2C carbide formed during tempering has a secondary hardening effect, therefore the Mo content range is limited to 0.40% to 0.60% in the present application.

[0017] Ni is an alloying element that expands the austenite region, has the effect of refining ferrite grains, and does not reduce the plasticity and toughness of the steel, especially the low-temperature toughness, while ensuring the strength. However, since Ni is a noble metal element, therefore the Ni content is limited to 1.30% to 1.55% in the present application from the perspective of cost-effectiveness.

[0018] Adding an appropriate amount of V can form fine carbides (VC) with high stability, which are dispersedly distributed in the intracrystalline and grain boundary, and can significantly hinder the slip and climb of dislocations, thereby enhancing the matrix strength and hardness of the steel, but excessive content will increase the yield strength ratio of the steel, which is not conducive to forming and manufacturing, therefore the V content range is limited to 0.06% to 0.09% in the present application.

[0019] Alt is a common deoxidizer in steel, adding a small amount of aluminum can refine the grain, improve the strength and impact toughness of steel. Too high will affect the hot working properties, welding performance and cutting performance of steel, the Alt content range is limited to 0.015%~0.045% in the application.

[0020] The second technical scheme of the application is to provide a manufacturing method of 1300MPa grade pressure-bearing equipment steel, including smelting, continuous casting, heating, rolling, tempering;

[0021] Smelting: the molten steel smelting is carried out in a converter, high-quality scrap steel and molten iron are used as raw materials, the molten iron content is controlled at 75%~85%, at the same time, in order to effectively reduce the harmful element P content, the converter is used for separate smelting of dephosphorization and decarburization, the oxygen blowing time for dephosphorization is controlled at 7~10min, the oxygen blowing time for decarburization is controlled at 8~12min, and finally the phosphorus mass fraction is reduced to less than 0.006%; deep desulfurization treatment is carried out in an LF refining furnace, and the sulfur content is controlled to be less than 0.002%; degassing is completed in a VD furnace, the net circulation time is 10~15min, and the static time before pouring is 3~5min.

[0022] Continuous casting: after vacuum breaking, slab continuous casting machine is used for casting, the superheat degree is set to 20~30℃, and the casting speed is 1.0~1.4m / min. The cast blank is stacked and slowly cooled, the stacking and slow cooling time is 24~36h, and the unstacking is below 400℃ to prevent cracks and other defects caused by rapid cooling.

[0023] Heating: the heating temperature is controlled at 1180~1230℃, and the total heating time is 4.0~6.0 hours.

[0024] Rolling: two-stage controlled rolling method is used, the recrystallization zone rolling end temperature is greater than or equal to 1000℃, in order to fully fragment the core organization of the steel blank, the total deformation rate is greater than or equal to 50%. The starting rolling temperature in the unrecrystallized zone is 850~890℃, the final rolling temperature is 820~860℃, and the total deformation rate is greater than or equal to 60%. At this time, the austenite grains are further flattened and elongated, and with the increase of the grain boundary area, the ferrite nucleation rate increases in the subsequent phase transformation process, and the grains are fully refined, and the target thickness of the rolled piece is (10~40)mm.

[0025] Tempering: because of adding more C, Mn, Cr, Mo, Ni and other solid solution strengthening elements in the steel, the steel plate can obtain the lath martensite structure with super high strength and hardness after rolling. But the grain size of the steel plate is coarse, and there is stress and thermal stress concentration in the structure, so the delayed cracks are easy to occur during the flame cutting. Therefore, the heat treatment should be used in time to soften and eliminate the stress, the tempering heat treatment is used in the application to ensure that the strength of the pressure-bearing steel plate is not lost, and the steel plate has appropriate plasticity and toughness, which is beneficial to the forming processing of the steel plate. Therefore, the tempering heat treatment temperature of the steel is 650-700 DEG C, and the net holding time is 2.0-4.0 min / mm.

[0026] The third technical scheme of the application provides a forming process of the 1300 MPa pressure-bearing equipment steel. The hot forming is a necessary process for the steel plate to manufacture the pressure-bearing equipment. The forming process not only makes the steel plate obtain the shape required by the equipment, but also is an important means to improve the final strength of the pressure-bearing equipment. The optimal forming process of the steel is formulated in the application.

[0027] The setting parameters and reasons are as follows: in the forming process, the heating temperature is 900-930 DEG C, the net holding time is 1.0-2.0 min / mm, and after being discharged, the steel plate is cooled to room temperature in the salt water bath. In this process, the chemical elements C, Mn, Cr, Mo, Ni and the micro-alloy elements V enter the austenite zone, and after a period of holding, the alloy elements are dissolved in the austenite matrix, and then the steel plate is rapidly cooled at a cooling speed of 20-35 DEG C / s in the 0-5 DEG C salt water bath to obtain fine lath martensite structure. At this time, the steel has super high strength, which meets the requirements of the pressure-bearing equipment. However, the plasticity and toughness of the steel are poor, and the structure stress is high. Through the short-term tempering heat treatment with the heating temperature of 400-430 DEG C and the net holding time of 1.0-1.5 h, the quenching stress is eliminated in time, the structure is softened, the plasticity and toughness of the steel are improved, and the forming process of the steel is completed. At this time, the microstructure of the steel is sorbite.

[0028] The fourth technical scheme of the application provides a forming heat treatment process of the 1300 MPa pressure-bearing equipment steel. In order to ensure the super high strength and excellent plasticity and toughness of the pressure-bearing equipment steel, the size and type of the second phase particles in the steel need to be further adjusted, that is, the secondary hardening heat treatment is carried out. The process is 430-460 DEG C, and the net holding time is 2.0-4.0 h. At this time, the stable (10-30) nm level (Fe, Mn, Cr, Mo) 23 C6, Mo2C and VC second phase particles, the volume percentage content is 18%-23%, which interacts with the high density dislocations in the sorbite to improve the strength and plasticity of the matrix. After the forming heat treatment, the mechanical properties of the steel are 980 MPa<=R p0.2 <=1110 MPa, 1300 MPa<=R m <=1430 MP; at 400 DEG C, 550 MPa<=R p0.2≤630MPa; impact energy at 0℃ is KV2≥120J; and the use requirement of high-strength pressure-bearing equipment is ensured.

[0029] The beneficial effects of the present application are:

[0030] (1) By adding Cr, Mo, Ni and Cu alloy elements on the basis of C, Si and Mn strengthening elements, and strictly controlling the content of harmful elements P and S, and combining with the manufacturing process, the steel plate of the present application obtains high-density tempered sorbite structure.

[0031] (2) The pressure-bearing equipment steel obtained by the specific production process has mechanical properties of 950MPa≤R p0.2 ≤1080MPa, 1300MPa≤R m ≤1430MPa, elongation A≥19%, and impact energy at 0℃ is KV2≥100J.

[0032] (3) The steel plate of the present application obtains high-density tempered martensite structure complex phase structure after forming and secondary hardening heat treatment, and a large amount of (10-30) nm grade (Fe, Mn, Cr, Mo) 23 C 6、 Mo2C and VC second phase particles are dispersedly precipitated in the steel, and the structure proportion is 18-23%, which ensures that the steel plate still has 1300MPa grade strength and good plasticity and toughness after forming.

[0033] (4) The mechanical properties of the pressure-bearing equipment steel of the present application after forming heat treatment are 980MPa≤R p0.2 ≤1110MPa, 1300MPa≤R m ≤1430MPa, 400℃, 550MPa≤R p0.2 ≤630MPa, impact energy at 0℃ is KV2≥120J.

[0034] (5) The present application obtains 1300MPa grade high-strength steel plate for pressure-bearing equipment with a thickness of (10-40) mm. DETAILED DESCRIPTION

[0035] The present application will be further described below by examples.

[0036] The examples of the present application are smelted, continuously cast, heated, rolled, tempered, formed and heat treated according to the component proportion of the technical scheme.

[0037] Manufacturing method of 1300MPa grade pressure-bearing equipment steel:

[0038] Heating: the heating temperature is controlled at 1180-1230℃, and the total heating time is 4.0-6.0 hours;

[0039] Rolling: the rolling adopts two-stage controlled rolling method, the recrystallization zone rolling end temperature is ≥1000℃, the total deformation rate is ≥50%; the non-recrystallization zone starting rolling temperature is 850-890℃, the finish rolling temperature is 820-860℃, and the total deformation rate is ≥60%;

[0040] Tempering: the tempering temperature is 650-700℃, and the holding time is 2.0-4.0min / mm.

[0041] Further; smelting: the molten steel is smelted in a converter, high-quality scrap steel and molten iron are used as raw materials, the molten iron content is controlled to be 75-85%, and the converter is used for separate smelting of dephosphorization and decarburization; the dephosphorization oxygen blowing is controlled to be 7-10min, the decarburization oxygen blowing is controlled to be 8-12min, the final phosphorus mass fraction is reduced to be less than 0.006%, deep desulfurization treatment is carried out in an LF refining furnace, the sulfur content is controlled to be less than 0.002%, and degassing is completed in a VD furnace, the net circulation time is 10-15min, and the static time before pouring is 3-5min.

[0042] Further; continuous casting: the superheating degree is 20-30℃, and the casting speed is 1.0-1.4m / min when pouring; the cast blank is discharged into a stacking and slow cooling device, the stacking and slow cooling time is 24-36h, and the stacking is removed below 400℃.

[0043] A forming process of a pressure-bearing equipment steel, in the forming process, the heating temperature is 900-930℃, the holding time is 1.0-2.0min / mm, after discharging, the steel is rapidly cooled in a 0-5℃ salt water bath at a cooling speed of 20-35℃ / s, and the phase change is a lath martensite structure.

[0044] Further; after the salt water bath rapid cooling, the steel is subjected to short-time tempering heat treatment, the short-time tempering heat treatment temperature is 400-430℃, the holding time is 1.0-1.5h, and the microstructure of the steel after the short-time tempering heat treatment is sorbite.

[0045] A post-forming heat treatment process of a pressure-bearing equipment steel, the heat treatment is secondary hardening heat treatment, and the specific process parameters are that the heating temperature is 430-460℃, and the holding time is 2.0-4.0h.

[0046] Further; after the secondary hardening heat treatment, (Fe, Mn, Cr, Mo) 23 C6, Mo2C and VC second phase particles, the volume percentage content is 18%-23%.

[0047] Further; the mechanical properties of the steel after the forming heat treatment are 980MPa≤R p0.2 ≤1110MPa, 1300MPa≤R m ≤1430MP; at 400℃, 550MPa≤R p0.2(400℃)≤630MPa; at 0℃, impact energy KV2≥120J.

[0048] The component of the steel of the embodiment of the present application is shown in Table 1. The main process parameters of the steel of the embodiment of the present application are shown in Table 2. The mechanical properties and microstructure of the steel of the embodiment of the present application are shown in Table 3. The forming of the steel of the embodiment of the present application and the mechanical properties and microstructure after heat treatment are shown in Table 4.

[0049] Table 1 Component of the steel of the embodiment of the present application (wt%)

[0050] Embodiments C Si Mn P S Cr Mo Ni V Alt 1 0.18 0.17 0.95 0.006 0.001 1.42 0.43 1.45 0.08 0.039 2 0.20 0.18 1.14 0.006 0.002 1.47 0.50 1.35 0.07 0.022 3 0.19 0.30 1.20 0.008 0.003 1.17 0.58 1.44 0.06 0.033 4 0.19 0.18 1.28 0.010 0.001 1.23 0.40 1.47 0.09 0.028 5 0.20 0.25 1.05 0.005 0.002 1.29 0.49 1.43 0.08 0.045 6 0.18 0.35 1.00 0.009 0.001 1.00 0.60 1.49 0.07 0.031 7 0.21 0.33 1.30 0.006 0.001 1.08 0.56 1.55 0.06 0.028 8 0.18 0.24 1.06 0.007 0.002 1.13 0.57 1.48 0.07 0.015 9 0.22 0.15 1.17 0.009 0.003 1.35 0.44 1.55 0.09 0.023 10 0.22 0.17 0.98 0.006 0.001 1.50 0.43 1.30 0.09 0.040

[0051] Table 2 Main process parameters of the steel of the embodiment of the present application

[0052]

[0053]

[0054] Table 3 Mechanical properties and microstructure of the steel of the embodiment of the present application

[0055]

[0056] Table 4 Forming of the steel plate of the embodiment of the present application and the mechanical properties and microstructure after heat treatment

[0057]

[0058] According to the above results, it can be concluded that the 1300MPa grade pressure-bearing equipment steel plate provided by the present application has very low content of harmful elements P and S, and the mechanical properties are as follows: at normal temperature, 950MPa≤R p0.2 ≤1080MPa, 1300MPa≤R m ≤1430MPa, at 0℃, impact energy KV2≥100J. The mechanical properties after forming and heat treatment are as follows: at normal temperature, 980MPa≤R p0.2 ≤1110MPa, 1300MPa≤R m ≤1430MPa, A≥20%; at 400℃, 550MPa≤R p0.2 ≤630MPa; at 0℃, impact energy KV2≥120J.

[0059] For the purpose of illustrating the present application, the best mode for the same will be described in the above embodiments with reference to the accompanying drawings. The embodiments are presented herein for purposes of illustration and description and are not intended to limit the scope of the present application. The skilled person in the art, without departing from the spirit and scope of the present application, can make various changes and modifications, and any modification, equivalent replacement, improvement, etc. made should be included in the protection scope of the present application. The patent protection scope of the present application should be defined by the claims.

Claims

1. A 1300 MPa grade pressure containing equipment steel characterized in that, The components of the steel are as follows in percentage by weight: C 0.18%~0.22%, Si 0.15%~0.35%, Mn 0.95%~1.30%, P ≤0.010%, S ≤0.003%, Cr 1.00%~1.50%, Mo 0.40%~0.60%, Ni 1.30%~1.55%, V 0.06%~0.09%, Alt 0.015%~0.045%, and the balance of Fe and inevitable inclusions; In the forming process of the steel for pressure equipment, the heating temperature is 900~930℃, the net holding time is 1.0~2.0min / mm, after discharging, the steel is rapidly cooled in a salt bath at a cooling speed of 20~35℃ / s, and fine lath martensite structure is obtained; after the rapid cooling in the salt bath, the steel is subjected to short-term tempering heat treatment, the short-term tempering heat treatment temperature is 400~430℃, the net holding time is 1.0~1.5h, and the microstructure of the steel after the short-term tempering heat treatment is sorbite; the heat treatment after the forming of the steel for pressure equipment is secondary hardening heat treatment, and the specific process parameters are as follows: the heating temperature is 430~460℃, and the net holding time is 2.0~4.0h.

2. The 1300 MPa grade pressure equipment steel in accordance with claim 1 characterized in that, The thickness of the steel for pressure equipment is 10-40 mm, and the mechanical properties are 950 MPa≤ R p0.2 1080 MPa, 1300 MPa≤ R m 1430 MPa; the impact energy at 0℃ is KV 2≥100 J.

3. The 1300 MPa grade pressure equipment steel in accordance with claim 1 characterized in that: 10-30 nm-sized (Fe, Mn, Cr, Mo) precipitates in the steel after the secondary hardening heat treatment 23 C6, Mo2C and VC second phase particles in a volume percentage content of 18-23%.

4. The 1300 MPa grade pressure equipment steel in accordance with claim 1 characterized by: mechanical properties of the steel after the shaped heat treatment are 980 MPa ≤ R p0.2 ≤1110 MPa, 1300 MPa ≤ R m ≤1430 MP; at 400°C, 550 MPa ≤ R p0.2 ≤630 MPa; at 0°C, impact energy is KV 2≥120 J.

5. A manufacturing method of the 1300MPa-grade steel for pressure equipment according to any one of claims 1-4, comprising smelting, continuous casting, heating, rolling, and tempering; characterized in that: the heating is controlled at a temperature of 1180~1230℃, and the total heating time is 4.0~6.0 hours; the rolling adopts a two-stage controlled rolling method, the recrystallization zone rolling ends at a temperature of ≥1000℃, and the total deformation rate is ≥50%; the non-recrystallization zone starts rolling at a temperature of 850~890℃, the final rolling temperature is 820~860℃, and the total deformation rate is ≥60%; the tempering is at a temperature of 650~700℃, and the net holding time is 2.0~4.0 min / mm.

6. The manufacturing method of the 1300MPa-grade steel for pressure equipment according to claim 5, characterized in that: the smelting is performed in a converter, high-quality scrap steel and molten iron are used as raw materials, the content of molten iron is controlled at 75%~85%, and the converter is used for separate smelting for dephosphorization and decarburization, the oxygen blowing time for dephosphorization is controlled at 7~10min, the oxygen blowing time for decarburization is controlled at 8~12min, and the final mass fraction of phosphorus is reduced to within 0.006%; deep desulfurization treatment is performed in an LF refining furnace, and the sulfur content is controlled to be below 0.002%; and degassing is completed in a VD furnace, the net circulation time is 10~15min, and the static time before pouring is 3~5min.

7. The method of manufacturing a 1300 MPa grade pressure equipment steel according to claim 5, characterized in that: the continuous casting is at a superheat of 20~30℃, and the casting speed is 1.0~1.4m / min; the cast blank is discharged into a stack for slow cooling, the stack slow cooling time is 24~36h, and the stack is disassembled below 400℃.

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