Forging piece for low-temperature pressure vessel and preparation method of forging piece

Abstract

The invention discloses a forge piece for a low-temperature pressure vessel and a preparation method of the forge piece, and the forge piece comprises the following chemical components in percentage by mass: 0.08%-0.15% of C, 0.20%-0.50% of Si, 0.80%-1.20% of Mn, 3.50%-5.00% of Ni, 0.02%-0.08% of Nb, 0.03%-0.09% of V, 0.40%-0.80% of Cr, 0.20%-0.50% of Mo, less than or equal to 0.005% of S, less than or equal to 0.005% of P, 0.02%-0.06% of Al and the balance of Fe and inevitable impurities. The alloy components are precisely designed, so that key elements such as C, Ni, Nb, V and the like generate a synergistic effect; wherein a proper amount of Ni element obviously reduces the ductile-brittle transition temperature of the material, and is a core for obtaining excellent low-temperature toughness; microalloy elements Nb and V are subjected to fine grain strengthening and precipitation strengthening mechanisms, so that the toughness reserve is further guaranteed while the strength is improved; by means of the component system, the forge piece can still keep Charpy V-shaped notch impact energy of 100 J or above at the low temperature of-50 DEG C while having high strength and high plasticity finally, and the harsh requirements for safety and reliability of a pressure container in the extreme environment are perfectly met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal material processing, in particular to a forged piece for low-temperature pressure vessels and a preparation method thereof. BACKGROUND

[0002] In many industrial fields, including petrochemical industry, natural gas treatment and low-temperature engineering, low-temperature pressure vessels are widely used for storing and transporting low-temperature media such as liquid natural gas, liquid nitrogen and liquid oxygen. Such vessels are long-term operated in extremely low-temperature environment, and therefore, the performance of the main structure material, especially the forged piece, is required to be extremely strict.

[0003] Under low-temperature conditions, the toughness of the material is usually significantly reduced, which is easy to induce brittle fracture. Therefore, the forged piece for low-temperature pressure vessels must have excellent low-temperature toughness to ensure safe operation under low-temperature, high-pressure and possible impact load. The traditional forged piece material often fails to meet this requirement, and the crack propagation sensitivity is enhanced under low-temperature, which seriously threatens the safety and reliability of the equipment.

[0004] In addition to low-temperature toughness, such forged pieces also need to have high strength and good plasticity. High strength ensures that the vessel can withstand internal pressure, and good plasticity ensures that it does not occur brittle failure or excessive deformation during manufacturing and use. However, in actual material development, it is challenging to achieve a good match between strength and plasticity. High-strength materials often have a sharp drop in plasticity under low-temperature, and high-plasticity materials often have insufficient strength, which is difficult to meet the design index.

[0005] In addition, the traditional forged piece manufacturing process itself has certain limitations. The conventional smelting process may result in low purity of molten steel, increase of non-metallic inclusions and other defects, and aggravation of the brittleness tendency of the material under low-temperature. A single forging method or inappropriate heat treatment system is easy to cause grain coarsening, non-uniform structure and other problems, thereby making it difficult to stably achieve the ideal combination of high strength and high low-temperature toughness. SUMMARY

[0006] The purpose of the present application is to provide a forged piece for low-temperature pressure vessels and a preparation method thereof. Through the whole-process collaborative design and precise control of composition, smelting, forging and heat treatment, a high-end forged piece for low-temperature pressure vessels with excellent comprehensive performance and stable and reliable quality is successfully prepared, which has good application prospect and market competitiveness.

[0007] To achieve the above object, the present application provides the following technical scheme: A forged piece for low-temperature pressure vessels, the chemical composition of the forged piece comprises, in percentage by mass: C: 0.08%-0.15%, Si: 0.20%-0.50%, Mn: 0.80%-1.20%, Ni: 3.50%-5.00%, Nb: 0.02%-0.08%, V: 0.03%-0.09%, Cr: 0.40%-0.80%, Mo: 0.20%-0.50%, S≤0.005%, P≤0.005%, Al: 0.02%-0.06%, and the balance is Fe and inevitable impurities.

[0008] As a preferred scheme, the tensile strength of the forged piece is ≥700MPa, the yield strength is ≥550MPa, the elongation is ≥18%, and the Charpy V-notch impact energy at-50℃ is ≥100J.

[0009] A preparation method of a forged piece for low-temperature pressure vessels, comprising the following steps: S1. Raw material preparation and smelting: high-quality carbon steel is selected as the base raw material, each element is accurately added according to the chemical composition ratio, and vacuum induction smelting plus electroslag remelting process is used for smelting and ingot casting to obtain a steel ingot with high purity and low segregation; S2. Steel ingot homogenization treatment: the steel ingot is heated to 1150-1200℃ and kept for 4-6h, and then slowly cooled to below 650℃ at a rate of ≤50℃ / h to fully eliminate dendritic segregation and solidification stress; S3. Multi-directional forging a. High-temperature rough forging: the homogenized steel ingot is heated to 1100-1200℃ for multi-directional free forging, the total forging ratio is ≥4, and the final forging temperature is not lower than 900℃; b. Low-temperature finish forging: the rough forged blank is reheated to 850-950℃ for near-net shape forging, the total forging ratio is controlled to be 1.5-2.5, and the final forging temperature is not lower than 800℃; S4. Performance heat treatment a. Normalizing: the forged piece after finish forging is heated to 910-930℃, the holding time is calculated according to the effective thickness of 1.5-2.0min / mm, and then cooled in static or weak circulating air to obtain uniform and refined grain structure; b. Quenching: the forged piece after normalizing is heated to 840-860℃, the holding time is calculated according to the effective thickness of 1.0-1.5min / mm, and then quenched and cooled in stirred polymer aqueous solution; c. Tempering: the forged piece after quenching is tempered at 600-630℃, the holding time is calculated according to the effective thickness of 2.0-3.0min / mm, and then furnace-cooled to below 300℃ and air-cooled after taking out of the furnace; S5. Quality detection and control: chemical composition analysis, mechanical property test and non-destructive test are carried out on the forgings.

[0010] As a preferred solution, in the step S1, the vacuum degree of vacuum induction melting is controlled to be ≤3Pa, the melting temperature is 1500-1550℃, and the time is 1.5-2.5h.

[0011] As a preferred solution, in the step S2, the temperature rising process of homogenization treatment adopts a stepwise temperature rising mode, and homogenization is carried out at 600-650℃ and 800-850℃ respectively, and the total temperature rising rate is controlled to be 5-8℃ / min.

[0012] As a preferred solution, in the step S3a, high-temperature rough forging adopts a process combination of multiple upsetting and elongation; and in the step S3b, the forging is immediately sent into a holding furnace at 600-650℃ for dehydrogenation annealing after finish forging, and the holding time is 4-6h.

[0013] As a preferred solution, in the step S4b, the quenching medium is PAG type water-based quenching liquid with a concentration of 8%-12%, and the medium temperature is controlled to be 20-40℃.

[0014] As a preferred solution, in the step S5, during the chemical composition analysis, the chemical composition of each batch of forgings is accurately detected by using a spectrum analysis method, so that the content of each element meets the design requirements.

[0015] As a preferred solution, in the step S5, during the mechanical property test, samples are cut from the forgings, and mechanical property tests such as tensile test and impact test are carried out, so that the tensile strength, yield strength, elongation and low-temperature impact toughness of the forgings meet the use standard of low-temperature pressure vessels.

[0016] As a preferred solution, in the step S5, during the non-destructive test, non-destructive test means such as ultrasonic flaw detection and magnetic particle flaw detection are used to detect defects in the forgings, so that no cracks, pores and other quality problems are ensured.

[0017] Compared with the prior art, the present application has the following beneficial effects: 1. The present application accurately designs the alloy composition, so that the key elements C, Ni, Nb and V produce a synergistic effect; the appropriate amount of Ni element significantly reduces the ductile-brittle transition temperature of the material, which is the core of obtaining excellent low-temperature toughness; the micro-alloy elements Nb and V further guarantee the toughness reserve while improving the strength through fine-grain strengthening and precipitation strengthening mechanism; the final composition system makes the forgings have high strength and high plasticity, and still have a Charpy V-type notch impact energy of more than 100J at-50℃ low temperature, which perfectly meets the harsh requirements of extreme environment on the safety and reliability of pressure vessels.

[0018] 2、The present application greatly improves the purity of the molten steel, effectively reduces the content of gas and harmful impurities by adopting the advanced melting process of vacuum induction melting combined with electroslag remelting, and precisely controlling the vacuum degree, temperature and time; the subsequent ingot homogenization treatment adopts stepped heating and long time holding, fully eliminates the dendritic segregation and internal stress, and obtains the ingot with highly uniform composition and structure, which ensures the consistency of subsequent processing and fundamentally improves the stability and reliability of the performance of the forged piece.

[0019] 3、The present application adopts the multi-directional forging technology of "high-temperature rough forging + low-temperature precision forging", the high-temperature rough forging stage thoroughly crushes the as-cast structure and refines the grains through large forging ratio and multi-directional deformation; the low-temperature precision forging stage further homogenizes and densifies the microstructure while approaching the final forging shape; especially, the dehydrogenation annealing treatment immediately after precision forging can effectively diffuse and remove the dissolved hydrogen in the forged piece, fundamentally preventing the risk of hydrogen-induced delayed cracking, and significantly improving the intrinsic quality and long-term service safety of the product.

[0020] 4、The present application realizes the precise optimization of the microstructure of the forged piece by the complex heat treatment process of normalizing, quenching and tempering, and precisely regulating the temperature, time and cooling medium of each stage; the normalizing treatment obtains uniform and refined initial structure; the subsequent controllable quenching using PAG water-based quenching liquid ensures the smooth transformation of high-strength martensite / bainite structure; the final high-temperature tempering effectively eliminates internal stress, precipitates and stabilizes carbides, and finally realizes the best balance between high strength and high-low temperature impact toughness in the quenched and tempered microstructure.

[0021] 5、The present application establishes a quality detection and control system throughout the whole process, from spectral composition analysis of raw materials to mechanical property tests such as tensile and impact of finished products, to ultrasonic and magnetic powder non-destructive testing, which verifies the chemical composition, mechanical properties and internal quality of the forged piece in all directions and multiple levels, and this strict quality control system ensures that each product leaving the factory can meet the design requirements, guarantees the uniformity and high reliability of product quality under batch production conditions, and enhances the market competitiveness. DETAILED DESCRIPTION

[0022] The term "one embodiment" or "an embodiment" as may appear in various places of the specification is not necessarily to the same embodiment, and is not necessarily exclusive of other embodiments.

[0023] Embodiment one: the application provides a kind of low temperature pressure vessel forgings, according to mass percentage, the chemical composition of the forging includes: C:0.08%, Si:0.20%, Mn:0.80%, Ni:3.50%, Nb:0.02%, V:0.03%, Cr:0.40%, Mo:0.20%, S≤0.005%, P≤0.005%, Al:0.02%, the balance is Fe and inevitable impurities.

[0024] The tensile strength of the forging is greater than or equal to 700 MPa, the yield strength is greater than or equal to 550 MPa, the elongation is greater than or equal to 18%, and the Charpy V-notch impact energy at -50°C is greater than or equal to 100 J.

[0025] A method for preparing a low-temperature pressure vessel forging, comprising the following steps: S1. Raw material preparation and smelting: high-quality carbon steel is selected as the base raw material, each element is accurately added according to the chemical composition ratio, and vacuum induction smelting plus electroslag remelting process is used for smelting and ingot casting to obtain high-purity, low-segregation steel ingot; S2. Ingot homogenization treatment: heat the ingot to 1150°C and keep for 4h, then slowly cool to below 650°C at a rate of ≤50°C / h to fully eliminate dendritic segregation and solidification stress; S3. Multi-directional forging a. High-temperature rough forging: heat the homogenized ingot to 1100°C for multi-directional free forging, the total forging ratio is greater than or equal to 4, and the final forging temperature is not less than 900°C; b. Low-temperature precision forging: reheat the rough forged blank to 850°C for near-net shape forging, the total forging ratio is controlled to be 1.5, and the final forging temperature is not less than 800°C; S4. Performance heat treatment a. Normalizing: heat the precision forged forging to 910°C, the holding time is calculated according to the effective thickness of 1.5 min / mm, then cool in static or weak circulating air to obtain uniform and refined grain structure; b. Quenching: heat the normalized forging to 840°C, the holding time is calculated according to the effective thickness of 1.0 min / mm, then quench in stirred polymer water solution; c. Tempering: temper the quenched forging at 600°C, the holding time is calculated according to the effective thickness of 2.0 min / mm, then furnace cool to below 300°C and air cool after taking out of the furnace; S5. Quality detection and control: chemical composition analysis, mechanical property test and non-destructive testing are performed on the forging.

[0026] In step S1, the vacuum degree of vacuum induction smelting is controlled to be less than or equal to 3 Pa, the smelting temperature is 1500°C, and the time is 1.5h.

[0027] In step S2, the temperature rising process of the homogenization treatment adopts a stepwise temperature rising mode, and homogenization is carried out at 600 DEG C and 800 DEG C respectively, and the total temperature rising rate is controlled at 5 DEG C / min.

[0028] In step S3a, high-temperature rough forging adopts a process combination of multiple upsetting and elongation; in step S3b, after the finish forging, the forged piece is immediately sent into a 600 DEG C holding furnace for dehydrogenation annealing, and the holding time is 4h.

[0029] In step S4b, the quenching medium is a PAG type water-based quenching liquid with a concentration of 8%, and the medium temperature is controlled at 20 DEG C.

[0030] In step S5, during the chemical composition analysis, the chemical composition of each batch of forged pieces is accurately detected by using methods such as spectral analysis, so as to ensure that the content of each element meets the design requirements.

[0031] In step S5, during the mechanical property test, samples are cut from the forged pieces, and mechanical property tests such as tensile test and impact test are carried out, so as to ensure that the tensile strength, yield strength, elongation and low-temperature impact toughness and other indexes of the forged pieces meet the low-temperature pressure container use standard.

[0032] In step S5, during the nondestructive testing, nondestructive testing means such as ultrasonic flaw detection and magnetic particle flaw detection are used to detect defects in the forged pieces, so as to ensure that there are no cracks, pores and other quality problems.

[0033] Embodiment two: the application provides a forged piece for a low-temperature pressure container, and the chemical composition of the forged piece comprises, in percentage by mass: C: 0.115%, Si: 0.35%, Mn: 1%, Ni: 4.25%, Nb: 0.05%, V: 0.06%, Cr: 0.6%, Mo: 0.35%, S≤0.005%, P≤0.005%, Al: 0.04%, and the balance is Fe and unavoidable impurities.

[0034] The tensile strength of the forged piece is ≥700MPa, the yield strength is ≥550MPa, the elongation is ≥18%, and the Charpy V-notch impact energy at-50 DEG C is ≥100J.

[0035] A preparation method of a forged piece for a low-temperature pressure container, comprising the following steps: S1. raw material preparation and smelting: high-quality carbon steel is selected as the basic raw material, each element is accurately added according to the chemical composition ratio, and vacuum induction smelting plus electroslag remelting process is used for smelting and ingot casting, so as to obtain a steel ingot with high purity and low segregation; S2. steel ingot homogenization treatment: the steel ingot is heated to 1175 DEG C and kept for 5h, and then slowly cooled to below 650 DEG C at a rate of ≤50 DEG C / h, so as to fully eliminate dendritic segregation and solidification stress; S3. multi-directional forging a. High temperature rough forging: the homogenized ingot is heated to 1150℃ for multi-directional free forging, the total forging ratio is ≥4, and the final forging temperature is not lower than 900℃; b. Low temperature finish forging: the rough forged blank is reheated to 900℃ for near net shape forging, the total forging ratio is controlled at 2, and the final forging temperature is not lower than 800℃; S4. Performance heat treatment a. Normalizing: the finish forged workpiece is heated to 920℃, the holding time is calculated according to the effective thickness of 1.7min / mm, and then cooled in static or weak circulating air to obtain a uniform and refined grain structure; b. Quenching: the normalized workpiece is heated to 850℃, the holding time is calculated according to the effective thickness of 1.2min / mm, and then quenched and cooled in a stirred polymer water solution; c. Tempering: the quenched workpiece is tempered at 615℃, the holding time is calculated according to the effective thickness of 2.5min / mm, and then furnace cooled to below 300℃ and air cooled after taking out of the furnace; S5. Quality detection and control: the workpiece is subjected to chemical composition analysis, mechanical property testing and non-destructive testing.

[0036] In step S1, the vacuum degree of vacuum induction melting is controlled at ≤3Pa, the melting temperature is 1525℃, and the time is 2h.

[0037] In step S2, the temperature rising process of homogenization treatment adopts a stepwise heating mode, and homogenization is carried out at 625℃ and 825℃ respectively, and the total heating rate is controlled at 6.5℃ / min.

[0038] In step S3a, high temperature rough forging adopts a process combination of multiple upsetting and elongation; in step S3b, the workpiece is immediately sent into a holding furnace at 625℃ for hydrogen removal annealing after finish forging, and the holding time is 5h.

[0039] In step S4b, the quenching medium is a PAG type water-based quenching liquid with a concentration of 10%, and the medium temperature is controlled at 30℃.

[0040] In step S5, during the chemical composition analysis, the chemical composition of each batch of workpiece is accurately detected by methods such as spectral analysis, to ensure that the content of each element meets the design requirements.

[0041] In step S5, during the mechanical property testing, samples are cut from the workpiece for mechanical property testing such as tensile test and impact test, to ensure that the tensile strength, yield strength, elongation and low temperature impact toughness of the workpiece meet the low temperature pressure vessel use standard.

[0042] In step S5, the internal defects of the forging are detected by means of ultrasonic flaw detection, magnetic particle flaw detection and other non-destructive testing methods during non-destructive testing to ensure that there are no cracks, pores and other quality problems.

[0043] Embodiment three: the present application provides a kind of low temperature pressure vessel forgings, according to mass percentage, the chemical composition of the forging includes: C:0.15%, Si:0.50%, Mn:1.20%, Ni:5.00%, Nb:0.08%, V:0.09%, Cr:0.80%, Mo:0.50%, S≤0.005%, P≤0.005%, Al:0.06%, the balance is Fe and inevitable impurities.

[0044] The tensile strength of the forging is greater than or equal to 700 MPa, the yield strength is greater than or equal to 550 MPa, the elongation is greater than or equal to 18%, and the Charpy V-notch impact energy at -50℃ is greater than or equal to 100 J.

[0045] A method for preparing a low temperature pressure vessel forging, comprising the following steps: S1. Raw material preparation and smelting: high-quality carbon steel is selected as the base raw material, each element is accurately added according to the chemical composition ratio, and vacuum induction smelting plus electroslag remelting process is used for smelting and ingot casting to obtain high-purity, low-segregation steel ingot; S2. Steel ingot homogenization treatment: heat the steel ingot to 1200℃ and keep for 6h, then slowly cool to below 650℃ at a rate of ≤50℃ / h to fully eliminate dendritic segregation and solidification stress; S3. Multi-directional forging a. High-temperature rough forging: multi-directional free forging of the homogenized steel ingot at 1200℃, total forging ratio ≥4, and final forging temperature not less than 900℃; b. Low-temperature precision forging: reheat the rough-forged blank to 950℃ for near-net shape forging, total forging ratio controlled at 2.5, and final forging temperature not less than 800℃; S4. Performance heat treatment a. Normalizing: heat the precision-forged forging to 930℃, the holding time is calculated according to the effective thickness of 2.0min / mm, then cool in static or weak circulating air to obtain uniform and refined grain structure; b. Quenching: heat the normalized forging to 860℃, the holding time is calculated according to the effective thickness of 1.5min / mm, then quench in stirred polymer water solution; c. Tempering: temper the quenched forging at 630℃, the holding time is calculated according to the effective thickness of 3.0min / mm, then furnace cool to below 300℃ and air cool after taking out of the furnace; S5. Quality detection and control: chemical composition analysis, mechanical property test and non-destructive testing are performed on the forging.

[0046] In step S1, the vacuum degree of vacuum induction melting is controlled to be ≤3 Pa, the melting temperature is 1550℃, and the time is 2.5 h.

[0047] In step S2, the temperature rising process of homogenization treatment adopts a stepwise heating mode, and homogenization is carried out at 650℃ and 850℃ respectively, and the total heating rate is controlled to be 8℃ / min.

[0048] In step S3a, high-temperature rough forging adopts a process combination of multiple upsetting and elongation; and in step S3b, the forged piece is immediately sent into a holding furnace at 650℃ for dehydrogenation annealing after finish forging, and the holding time is 6 h.

[0049] In step S4b, the quenching medium is a PAG type water-based quenching liquid with a concentration of 12%, and the medium temperature is controlled to be 40℃.

[0050] In step S5, during chemical composition analysis, the chemical composition of each batch of forged pieces is accurately detected by using methods such as spectral analysis, so as to ensure that the content of each element meets the design requirements.

[0051] In step S5, during mechanical property testing, samples are cut from the forged pieces, and mechanical property tests such as tensile test and impact test are carried out, so as to ensure that the tensile strength, yield strength, elongation and low-temperature impact toughness and other indexes of the forged pieces meet the use standard of low-temperature pressure vessels.

[0052] In step S5, during non-destructive testing, non-destructive testing means such as ultrasonic flaw detection and magnetic particle flaw detection are used to detect defects in the forged pieces, so as to ensure that there are no quality problems such as cracks and pores.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A forged product for a cryogenic pressure vessel, characterized by, The chemical composition of the forging by mass percentage comprises: C: 0.08%-0.15%, Si: 0.20%-0.50%, Mn: 0.80%-1.20%, Ni: 3.50%-5.00%, Nb: 0.02%-0.08%, V: 0.03%-0.09%, Cr: 0.40%-0.80%, Mo: 0.20%-0.50%, S≤0.005%, P≤0.005%, Al: 0.02%-0.06%, and the balance of Fe and inevitable impurities.

2. A forged product for cryogenic pressure vessels according to claim 1, characterized in that: The tensile strength of the forging is ≥700 MPa, the yield strength is ≥550 MPa, the elongation is ≥18%, and the Charpy V-notch impact energy at -50℃ is ≥100 J.

3. A method for producing a forged product for a cryogenic pressure vessel, for producing the forged product for a cryogenic pressure vessel according to any one of claims 1 to 2, characterized by, The method comprises the following steps: S1. Raw material preparation and smelting: high-quality carbon steel is selected as the base raw material, each element is accurately added according to the chemical composition ratio, and vacuum induction smelting plus electroslag remelting process is used for smelting and ingot casting to obtain a steel ingot with high purity and low segregation; S2. Ingot homogenization treatment: the ingot is heated to 1150-1200℃ and kept for 4-6h, and then slowly cooled to below 650℃ at a rate of ≤50℃ / h to fully eliminate dendritic segregation and solidification stress; S3. Multi-directional forging a. High-temperature rough forging: the homogenized ingot is heated to 1100-1200℃ for multi-directional free forging, the total forging ratio is ≥4, and the final forging temperature is not lower than 900℃; b. Low-temperature finish forging: the rough forged blank is reheated to 850-950℃ for near-net shape forging, the total forging ratio is controlled to be 1.5-2.5, and the final forging temperature is not lower than 800℃; S4. Performance heat treatment a. Normalizing: the finish forged forging is heated to 910-930℃, the holding time is calculated according to the effective thickness of 1.5-2.0min / mm, and then cooled in static or weak circulating air to obtain uniform and refined grain structure; b. Quenching: the normalized forging is heated to 840-860℃, the holding time is calculated according to the effective thickness of 1.0-1.5min / mm, and then quenched in stirred polymer water solution; c. Tempering: the quenched forging is tempered at 600-630℃, the holding time is calculated according to the effective thickness of 2.0-3.0min / mm, and then furnace cooled to below 300℃ and air cooled after taking out of the furnace; S5. Quality detection and control: the forging is subjected to chemical composition analysis, mechanical property test and non-destructive testing.

4. A method of producing a forged product for cryogenic pressure vessels according to claim 3, characterized in that: In the step S1, the vacuum degree of the vacuum induction smelting is controlled to be ≤3Pa, the smelting temperature is 1500-1550℃, and the time is 1.5-2.5h.

5. The method of claim 3, wherein: In the step S2, the temperature rising process of the homogenization treatment adopts stepwise heating, and the homogenization is kept at 600-650℃ and 800-850℃ respectively, and the total heating rate is controlled to be 5-8℃ / min.

6. A method of producing a forged product for cryogenic pressure vessels according to claim 3, characterized in that: In the step S3a, the high-temperature rough forging adopts the process combination of multiple upsetting and elongation; in the step S3b, the forging is immediately sent into a holding furnace at 600-650℃ for hydrogen removal annealing after finish forging, and the holding time is 4-6h.

7. The method of claim 3, wherein: In the step S4b, the quenching medium is PAG water-based quenching liquid with a concentration of 8%-12%, and the medium temperature is controlled at 20-40℃.

8. The method of claim 3, wherein: In the step S5, the chemical composition of each batch of forgings is accurately detected by using spectral analysis and other methods during chemical composition analysis, so as to ensure that the content of each element meets the design requirements.

9. The method of claim 3, wherein: In the step S5, the samples are cut from the forgings during the mechanical property test, and the mechanical property test such as tensile test and impact test is carried out, so as to ensure that the tensile strength, yield strength, elongation and low-temperature impact toughness and other indexes of the forgings meet the use standard of low-temperature pressure vessels.

10. The method of claim 3, wherein: In the step S5, the non-destructive testing means such as ultrasonic flaw detection and magnetic particle flaw detection are used during the non-destructive testing, so as to detect the defects inside the forgings, and ensure that there are no quality problems such as cracks and pores.