A method for strengthening a postweld austenitic stainless steel tank and a tank

Abstract

The application discloses a cryogenic stepwise deformation strengthening method for post-welding austenitic stainless steel storage tanks. In view of the problems of easy weakening of the welding joint and inhibition of phase change by adiabatic heating in large deformation in the prior art, the application adopts a "welding first and then stepwise strengthening" path: the pre-assembled component after welding is placed in an ultra-low temperature environment of-150 DEG C to-269 DEG C, and a first deformation of 5% to 10% is applied to induce preliminary martensite phase change; then, inter-stage residence and stress relaxation are carried out in the ultra-low temperature for 10 to 30 minutes to dissipate deformation heat and promote redistribution of residual stress, so as to reduce the adverse effect of adiabatic heating on deformation-induced phase change; finally, a second deformation of 5% to 10% is applied, and the cumulative strain reaches 10% to 20%. The application controls the formation and distribution of deformation-induced martensite through inter-stage residence, promotes the formation of fine and dispersed deformation-induced martensite in the weld zone and the base material zone, improves the strength matching of the weld zone and the base material zone, and is beneficial to improving the dimensional stability of the component and the lightweight design margin.

Description

Technical Field

[0001] This invention relates to the field of manufacturing methods for aerospace structural components, specifically to a method for strengthening a welded austenitic stainless steel tank and the tank itself. Background Technology

[0002] With the rapid development of the aerospace industry, the demand for lightweight propellant tanks, as core structural components of launch vehicles, is becoming increasingly urgent. Metastable austenitic stainless steels (such as the 301 and 304 series) have become the preferred material for manufacturing cryogenic tanks due to their excellent cryogenic mechanical properties and weldability. Currently, the industry widely uses cryogenic strengthening technology to improve the strength of components. The basic principle is to subject stainless steel to large deformation stretching or bulging at liquid nitrogen temperature, utilizing deformation-induced martensitic phase transformation (γ→α) to significantly improve the yield strength of the material.

[0003] Although cryogenic strengthening technology has been applied in the manufacture of some pressure vessels, the following problems still need to be solved in the manufacturing process of high-performance aerospace tanks:

[0004] The heterogeneity of the weld zone is severely weakened: traditional manufacturing processes typically employ either "strengthening before welding" or "one-time integral bulging." In the former, the high temperature during welding causes the pre-strengthened martensite to undergo recovery or reverse transformation, making the weld and heat-affected zone (HAZ) a distinct "soft zone." In the latter, due to the mismatch between the hardening rates of the weld microstructure (cast state) and the base metal (rolled state), strain easily concentrates in the weld zone during a single large deformation, leading to premature necking or fracture of the joint.

[0005] Uneven microstructure evolution and adiabatic heating effect: During one-time strengthening with large deformation (e.g., 15% or more), intense exothermic phenomena occur within the material. Due to the limited heat transfer efficiency in a liquid nitrogen environment, localized adiabatic heating significantly inhibits the martensitic phase transformation kinetics, resulting in uneven distribution of martensite content within the final component and affecting the overall mechanical compatibility of the structure.

[0006] The main reason for this is that the strain-induced phase transformation of austenitic stainless steel in a cryogenic environment is a process that is extremely sensitive to the strain path and strain rate. Existing one-time strengthening processes ignore the nucleation and growth characteristics of phase transformation nuclei at different stages and fail to effectively coordinate the temporal contradiction between "welding thermal cycling" and "cold working strengthening". Summary of the Invention

[0007] The technical problem to be solved by this invention is: to address the shortcomings of existing technologies in the cryogenic deformation strengthening process of austenitic stainless steel aerospace tanks, such as poor strength matching of welded joints and suppression of phase transformation due to adiabatic heating caused by large deformation, and to provide a cryogenic stepwise deformation strengthening method for post-weld austenitic stainless steel tanks and the tank itself.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0009] A method for cryogenic stepwise deformation strengthening of austenitic stainless steel storage tanks after welding includes the following steps:

[0010] Step S1 Prefabrication and Welding: Austenitic stainless steel plates are welded together using welding technology to form prefabricated tank components with welded joints;

[0011] Step S2 Cryogenic Treatment: Place the prefabricated component in an ultra-low temperature environment or bring it into contact with an ultra-low temperature medium until it reaches thermal equilibrium. The temperature of the ultra-low temperature environment or medium is -150℃ to -269℃.

[0012] Step S3: First-stage cryogenic deformation strengthening: A deformation load is applied to the precast component under the ultra-low temperature environment to induce a first predetermined strain ε1 in the precast component, where ε1 is 5% to 10%, and the strain rate is controlled at 10. -5 s -1 ~10 -1 s -1 To induce austenite to martensite deformation-induced phase transformation;

[0013] Step S4 Interstage residence and stress relaxation: After the first predetermined strain is completed, the deformation load is unloaded or the displacement / load is kept constant, and interstage residence is performed in the ultra-low temperature environment for 10 to 30 minutes; the residence is used to dissipate the heat generated by the first stage deformation and relax the residual stress in the weld joint area, thereby suppressing the adiabatic heating from hindering the deformation-induced phase transformation and improving the deformation compatibility between the weld area and the base material area;

[0014] Step S5 Secondary cryogenic deformation strengthening and shaping: Deformation load is continued to be applied in the ultra-low temperature environment, so that the precast component generates a second predetermined strain ε2 on the basis of the first-level deformation, where ε2 is 5% to 10%, so that the cumulative strain reaches 10% to 20%, so as to achieve synchronous strengthening of the weld zone and the base material zone.

[0015] Furthermore, in step S2, the temperature of the ultra-low temperature environment or medium is preferably -180℃ to -196℃.

[0016] Furthermore, in step S4, the interstage is carried out in a fully unloaded state to promote deformation heat dissipation, local back stress reduction and residual stress redistribution; or it is carried out while keeping the displacement of the stretching machine constant or the internal pressurization pressure constant to prevent the component from springback deformation and maintain dimensional accuracy.

[0017] Furthermore, in steps S3 and S5, the deformation load is an axial tensile load or a circumferential expansion load; when a circumferential expansion load is applied, the direction of the load is perpendicular to the longitudinal weld of the tank prefabricated component, so that the weld area is subjected to the maximum circumferential tensile stress.

[0018] Furthermore, in step S1, the welding process is laser welding, friction stir welding, plasma welding, electron beam welding, or resistance seam welding.

[0019] Furthermore, the austenitic stainless steel sheet is a metastable austenitic stainless steel, including any one of 301, 304, 304L or 301L austenitic stainless steel.

[0020] Furthermore, the cryogenic stepwise deformation strengthening also includes three or more stages of cryogenic deformation strengthening steps, with the interstage dwell and stress relaxation steps performed between adjacent cryogenic deformation strengthening steps, in order to further improve the yield strength of the component and the strength matching between the weld zone and the base material zone.

[0021] Furthermore, the values ​​of the first predetermined strain ε1 and the second predetermined strain ε2 are not equal, and an asymmetric deformation ratio of "lighter at the beginning and heavier at the end" or "heavier at the beginning and lighter at the end" is adopted; and / or, the strain rate used in steps S3 and S5 is dynamically controlled according to the deformation stage.

[0022] Furthermore, during the deformation process in steps S3 and / or S5, local cryogenic spraying or local reinforcement tooling is used in conjunction with overall deformation loading to target weak areas of the welded joint, thereby achieving point-to-point reinforcement compensation for specific weak areas.

[0023] On the other hand, this application also provides an austenitic stainless steel storage tank, including a tank body welded from austenitic stainless steel plates and a welded joint located on the tank body. The internal microstructure of the tank body and the welded joint area includes an austenitic matrix and deformation-induced martensite dispersed in the austenitic matrix. The deformation-induced martensite is in the form of fine dots or short rods and is uniformly distributed in the austenitic matrix. The welded joint and the tank body achieve equal strength matching.

[0024] This invention presents a post-weld cryogenic step-by-step deformation strengthening method for austenitic stainless steel tanks, which involves "first welding and forming, followed by two stages of cryogenic deformation with interspersed ultra-low temperature stage residence." This method helps reduce the adverse effects of deformation heat accumulation during continuous large deformation on deformation-induced martensitic transformation and promotes the redistribution of residual stress between the weld zone and the base metal zone. By combining step-by-step loading with inter-stage residence, the risk of strain concentration and early necking in the heterogeneous zone of the weld can be reduced, promoting the formation of fine and dispersed deformation-induced martensite in both the weld zone and the base metal zone. This improves the strength matching between the weld zone and the base metal zone and enhances the dimensional stability and lightweight design margin of thin-walled tank components.

[0025] It should be understood that the above general description and the following specific embodiments are merely exemplary and illustrative, and do not limit the scope of the invention. Attached Figure Description

[0026] The accompanying drawings, which are part of the specification of this invention, illustrate exemplary embodiments of the invention. The drawings, together with the description in the specification, serve to illustrate the principles of the invention.

[0027] Figure 1 This is a schematic flowchart of a deep cryogenic stepwise deformation strengthening method for a post-weld austenitic stainless steel tank according to an embodiment of the present invention.

[0028] Figure 2 This is a comparison diagram of macroscopic load-time / strain relationship curves according to an embodiment of the present invention;

[0029] Figure 3 The diagram shows a comparison of the microstructure evolution of an embodiment of the present invention, where (a) is the undeformed microstructure, (b) is the microstructure with one-time deformation, and (c) is the microstructure with step-by-step deformation strengthening according to the present invention.

[0030] Figure 4 This is a comparison diagram of the microhardness distribution in the weld area according to an embodiment of the present invention;

[0031] Figure 5 This is a schematic diagram illustrating the step-by-step tensile strengthening of aerospace tank cylinder section according to an embodiment of the present invention. Detailed Implementation

[0032] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only configured to explain the present invention and to exemplify the principles of the present invention, and are not configured to limit the present invention. In addition, the structural components in the drawings are not necessarily drawn to scale. For example, the dimensions of some structural components or regions in the drawings may be enlarged for other structural components or regions to aid in the understanding of the embodiments of the present invention.

[0033] The directional terms used in the following description refer to the directions shown in the figures and are not intended to limit the specific structure of the embodiments of the present invention. In the description of the present invention, it should be noted that, unless otherwise stated, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0034] Furthermore, the terms "comprising," "including," "having," or any other variations thereof are intended to cover non-exclusive inclusion, such that a structure or component that includes a list of elements includes not only those elements but also other structural elements that are not expressly listed or inherent to the structure or component. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the article or apparatus that includes the element.

[0035] Spatial relation terms such as "below," "under," "under," "low," "above," "on," and "high" are used for descriptive convenience to explain the positioning of one element relative to a second element, indicating that these terms are intended to cover different orientations of the device, in addition to those different from those shown in the figure. Furthermore, phrases such as "one element on / below another element" can indicate that two elements are in direct contact, or that there are other elements between the two elements. In addition, terms such as "first" and "second" are also used to describe individual elements, areas, parts, etc., and should not be considered limiting. Similar terms are used throughout the description to refer to similar elements.

[0036] It will be apparent to those skilled in the art that the present invention can be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention.

[0037] This invention proposes a deep cryogenic stepwise deformation strengthening method for post-weld austenitic stainless steel tanks. Its core lies in overturning the traditional "strengthening before welding" or "one-time large-scale deformation" process, transforming the deformation-induced martensitic phase transformation process from "explosive and uncontrolled" to "controlled evolution." The following describes a preferred complete embodiment, such as... Figure 1 As shown, the five core steps of this method will be explained in detail.

[0038] Step S1: Pre-fabrication and welding:

[0039] This step aims to complete the structural connection first, avoiding strength loss caused by martensitic reversal in the weld heat-affected zone (HAZ) due to the strengthened material. In one embodiment, a 1.5mm thick 301 solution-treated metastable austenitic stainless steel plate is selected and cut into 800mm × 1200mm dimensions. After grinding and degreasing the edges to be welded, laser butt welding is used to weld the plates into a prefabricated tank section with a longitudinal welded joint. Post-weld X-ray non-destructive testing is performed to ensure that the weld is free of defects such as porosity and cracks.

[0040] It should be noted that the welding process in this step is not limited to laser welding. Depending on the plate thickness and structural requirements, friction stir welding (FSW), plasma welding (PAW), electron beam welding (EBW), or resistance seam welding can also be used. For resistance seam welding, subsequent step-by-step strengthening can effectively eliminate stress concentration at the joint indentation; for friction stir welding, the cryogenic environment can further refine the grains in the stirring pin region. Regarding materials, in addition to 301, austenitic stainless steels with metastable characteristics such as 304, 304L, or 301L are all suitable for this process.

[0041] Step S2: Cryogenic treatment:

[0042] The prefabricated tank components, assembled and welded as described above, were placed in a cryogenic environment chamber, and liquid nitrogen was introduced to bring them into direct contact with the ultra-low temperature medium. Real-time temperature monitoring was performed using thermocouples attached to the weld center and the base material area. Once the surface and core temperatures of the components reached thermal equilibrium and stabilized at -180℃ (within the preferred liquid nitrogen temperature range of -150℃ to -269℃), the temperature was maintained for 10 minutes. At this ultra-low temperature, the stacking fault energy of austenite was significantly reduced, providing a substantial thermodynamic driving force for subsequent deformation-induced martensitic phase transformation.

[0043] Step S3: Primary Cryogenic Deformation Strengthening

[0044] While maintaining an ultra-low temperature environment of -180℃, the tensile loading system was activated to apply axial tensile deformation load to the precast component. The strain rate was controlled at 1×10⁻⁶. -3 s -1 (belonging to 10) -5 s -1 ~10 -1 s -1 The preferred range is to induce a first predetermined strain ε1=8% (within the range of 5% to 10%) in the component to induce an initial deformation-induced phase transformation from austenite to martensite.

[0045] The choice of a lower strain rate in this step is to avoid the instantaneous conversion of plastic work into heat. Controlling the initial strain to below 10% ensures the safe induction of the initial phase transformation before the difference in deformation capacity between the weld zone (cast state) and the base metal zone (rolled state) becomes apparent. At this point, high-density shear bands and dislocation cells begin to form within the austenite grains of both the weld zone and the base metal zone. These defect locations become preferred nucleation sites for subsequent martensitic phase transformation. The initially formed fine martensite nuclei lay the foundation for subsequent strengthening, rather than directly causing strain-concentrated fracture in the weld zone as in a single large deformation.

[0046] Regarding the method of applying the deformation load in this step, as follows: Figure 5As shown in the schematic diagram of the step-by-step tensile strengthening implementation of the aerospace tank section, in addition to directly applying axial tensile load using a tensile machine, another implementation method for the integral tank section 5 is to apply a circumferential expansion load 7 (e.g., to achieve bulging by internal liquid filling and pressurization). When applying this circumferential expansion load 7, the direction of the load must be controlled to be perpendicular to the longitudinal weld joint 6 on the tank prefabricated component. The circumferential tensile stress (Hoop Stress) generated by the internal pressure in this method is twice that of the axial tensile stress. Applying the direction of the maximum principal stress perpendicular to the longitudinal joint 6 ensures that the weld and heat-affected zone receive the maximum deformation driving force, thereby achieving the most direct and effective targeted strengthening of the weak link of the longitudinal weld and avoiding insufficient deformation of the weld area due to the force direction being parallel to the weld. Choosing a lower strain rate and controlling the initial strain to within 10% is to safely complete the initial phase deformation nucleus before the difference in deformation capacity between the weld area and the base material area becomes apparent, so as not to directly lead to strain concentration fracture in the weld area.

[0047] Step S4: Interstage residence and stress relaxation:

[0048] After achieving the first predetermined strain of 8%, the deformation load of the tensile machine is completely unloaded to zero, and the component is held in an ultra-low temperature environment of -180℃ for 20 minutes (within the range of 10 to 30 minutes).

[0049] This step is in traditional one-time continuous cryogenic stretching (such as...) Figure 2 (Curve 1) Due to the lack of heat dissipation gaps, a significant adiabatic heating effect occurs within the material. In particular, the weld heat-affected zone (HAZ) exhibits initial residual tensile stress and grain coarsening. The localized temperature increase significantly raises the stacking fault energy, inhibiting martensite nucleation and resulting in insufficient strengthening in this region, as shown in the hardness distribution diagram (…). Figure 4 The curve 4) forms a "depression zone" that improves mechanical properties.

[0050] At the same time, corresponding Figure 3 'a' represents the baseline state of the weld heat-affected zone. The original 301 / 304 solution-treated stainless steel sheet consists of a single austenitic phase with regular polygonal grains and typical straight annealed twins. At this point, the dislocation density is extremely low, and there is no martensite phase, exhibiting high plasticity but low yield strength. Under traditional one-time continuous deformation, due to the rapid strain rate and lack of heat dissipation gaps, a significant adiabatic heating effect occurs within the material. Local temperature increases reduce the driving force for the transformation of austenite to martensite and may cause uneven distribution and local coarsening of the already formed martensite structure. The deformation ultimately resulting from this traditional one-time continuous deformation induces the martensite to exhibit a coarse, blocky morphology (such as...). Figure 3 b), and is mainly distributed in a banded pattern along grain boundaries or slip zones. Figure 3The coarse, hard, and brittle phase shown in b is prone to causing stress concentration at the phase boundary, increasing the risk of microcrack initiation and leading to a significant decrease in the material's low-temperature toughness.

[0051] This invention achieves "heat dissipation and stress redistribution" by introducing an ultra-low temperature interstage residence in step S4: First, heat dissipation, transferring the localized adiabatic temperature rise generated in stage S3 to the ultra-low temperature medium, allowing the weld zone temperature to return to the -180℃ temperature range, which is conducive to deformation-induced phase transformation; second, stress redistribution, by unloading or maintaining residence under constant displacement / load conditions, reducing the localized back stress caused by dislocation pile-up, and promoting the redistribution of residual stress in the weld zone and base metal zone. The interstage residence employed in this invention is beneficial for improving the deformation compatibility between the weld zone and the base metal zone.

[0052] In other embodiments, the interstage dwell time can also be carried out in a state of "keeping the displacement of the stretching machine constant or the internal pressurization pressure constant", which can prevent springback deformation of thin-walled cylinder sections and is more conducive to maintaining dimensional accuracy.

[0053] Step S5: Secondary Cryogenic Deformation Strengthening and Shaping

[0054] After completing a 20-minute interstage dwell period, under the same -180°C cryogenic environment, the loading system is restarted to continue applying axial tensile deformation loads or circumferential expansion loads (such as...). Figure 2 (Curve 2). The precast component is subjected to a second predetermined strain ε2=7% (within the range of 5% to 10%) based on the first-level deformation. At this point, the cumulative strain reaches 15% (within the range of 10% to 20%), and then it is unloaded and shaped.

[0055] Since step S4 achieves deformation heat dissipation and local stress state control, secondary deformation can be carried out under relatively stable temperature and stress conditions. At this point, the hardening modulus of the weld zone has been significantly improved by primary strengthening, and the deformation coordination between the weld zone and the base metal zone is improved during secondary loading. Strain no longer concentrates in the weak areas of the weld. Under the action of secondary deformation, the martensite nuclei formed in step S3 grow uniformly and induce new deformation to induce the formation of fine and dispersed martensite.

[0056] After adopting the ultra-low temperature stepwise deformation strengthening process of the present invention, the microstructure evolution path has been fundamentally changed.

[0057] First-order deformation (S3): At low temperature, a high density of shear bands and dislocation cells are induced in the austenite grain boundaries and within the grains through appropriate deformation. These defect sites become preferred nucleation points for subsequent martensitic phase transformation.

[0058] Interstage residence (S4): This key step, through the thermodynamic equilibrium process at ultra-low temperature, dissipates deformation heat in a timely manner, allowing the material to return to the temperature range conducive to phase transformation; on the other hand, it promotes the relaxation and rearrangement of dislocation pile-ups, eliminates local high stress state, and thus effectively inhibits the explosive coarsening growth of martensite.

[0059] Secondary deformation (S5): Under stable thermo-mechanical conditions, the already formed martensite nuclei grow uniformly, and new deformation is induced to form fine, dispersed martensite. In the final microstructure, the deformation-induced martensite exhibits fine, dispersed dot-like or short rod-like features, uniformly embedded in the austenite matrix (corresponding to...). Figure 3 c).

[0060] This microstructure, composed of an austenitic matrix and deformation-induced martensite, is conducive to achieving a balance between transformation strengthening and plasticity retention. Testing showed that the yield strength σ of the component prepared in this embodiment... 0.2 The hardness can be increased from approximately 300 MPa in the solution-treated state to over 850 MPa, reducing the hardness difference between the weld zone and the base metal zone. Figure 4 As shown in curve 3, it can improve the strength matching of welded joints and provide a process basis for the lightweight design of thin-walled tank structures.

[0061] This application utilizes a process path of "welding first, followed by step-by-step cryogenic stretching" to fully leverage the difference in strain hardening rates between the weld zone and the base material at ultra-low temperatures. Step-by-step strengthening provides a buffer and evolutionary space for dislocation proliferation and martensite nucleation in the weld zone, which helps reduce the weakening effect of the weld in traditional processes and improves the strength matching between the weld zone and the base material. Using "step-by-step deformation" instead of "one-time large deformation" helps reduce the adiabatic heating effect caused by severe deformation. Physical retention during the step-by-step process facilitates stress relaxation, resulting in a finer and more uniform induced martensite structure, reducing the risk of increased brittleness due to microstructure coarsening. Step-by-step loading reduces the peak load of a single forming operation, mitigating the risk of stress concentration in complex structures. The process of this application, through inter-stage adjustments, helps reduce the influence of residual stress and improves the dimensional stability and manufacturing consistency of thin-walled tank components.

[0062] In one embodiment, asymmetric strain is employed. When performing steps S1-S5 above, a "lighter at the beginning, heavier at the end" ratio is used: ε1=5% is applied in step S3, and the pressure is maintained for 30 minutes in S4 (to maintain constant internal pressure and prevent rebound), and ε2=10% is applied in step S5. This variant is particularly suitable for tank head-type components with complex radius angles.

[0063] In one embodiment, multi-level strengthening and local compensation are employed. For extremely high strength requirements, steps S1-S5 are extended to three or more levels. Specifically, after executing steps S1 and S2, steps S3 (5% strain) → S4 (15-minute dwell) → S5 (5% strain) are executed → S4 (15-minute dwell) is executed again → S5 (5%~10% strain) is executed again. Furthermore, during the final execution of step S5, a "localized deep-cryogenic liquid nitrogen spraying fixture" is used for targeted temperature compensation in the extremely weak area where the cross welds intersect, to prevent localized adiabatic heating in the later stages of high strain.

[0064] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for strengthening a post-weld austenitic stainless steel storage tank, characterized in that, Includes the following steps: S1: Austenitic stainless steel plates are welded together using welding technology to form prefabricated tank components with welded joints; S2: Place the prefabricated component in an ultra-low temperature environment or bring it into contact with an ultra-low temperature medium until it reaches thermal equilibrium. The temperature of the ultra-low temperature environment or medium is -150℃ to -269℃. S3: Apply a deformation load to the precast component under the ultra-low temperature environment to induce a first predetermined strain ε1 in the precast component, where ε1 is 5% to 10%, and control the strain rate to be 10. -5 s -1 ~10 -1 s -1 To induce austenite to martensite deformation-induced phase transformation; S4: After completing the first predetermined strain, the deformation load is unloaded or the displacement / load is kept constant, and the stage dwell time is 10 to 30 minutes in the ultra-low temperature environment; S5: Continue to apply deformation load under the ultra-low temperature environment to generate a second predetermined strain ε2 on the basis of the first-level deformation of the precast component, wherein ε2 is 5% to 10%, so that the cumulative strain reaches 10% to 20% to achieve synchronous strengthening of the weld zone and the base material zone.

2. The method according to claim 1, characterized in that, In step S2, the temperature of the ultra-low temperature environment or medium is -180℃ to -196℃.

3. The method according to claim 1, characterized in that, In step S4, the interstage is carried out in a fully unloaded state to promote deformation heat dissipation, local back stress reduction and residual stress redistribution; or it is carried out while keeping the displacement of the stretching machine constant or the internal pressurization pressure constant to prevent the component from springback deformation and maintain dimensional accuracy.

4. The method according to claim 1, characterized in that, In steps S3 and S5, the deformation load is an axial tensile load or a circumferential expansion load; When a circumferential expansion load is applied, the direction of the load is perpendicular to the longitudinal weld of the tank prefabricated component, so that the weld area is subjected to the maximum circumferential tensile stress.

5. The method according to claim 1, characterized in that, In step S1, the welding process is laser welding, friction stir welding, plasma welding, electron beam welding, or resistance seam welding.

6. The method according to claim 1, characterized in that, The austenitic stainless steel sheet is a metastable austenitic stainless steel, including any one of 301, 304, 304L or 301L austenitic stainless steel.

7. The method according to claim 1, characterized in that, The cryogenic stepwise deformation strengthening also includes three or more stages of cryogenic deformation strengthening steps, with the interstage residence and stress relaxation steps performed between adjacent cryogenic deformation strengthening steps.

8. The method according to claim 1, characterized in that, The values ​​of the first predetermined strain ε1 and the second predetermined strain ε2 are not equal, and an asymmetric deformation ratio of "lighter at the beginning and heavier at the end" or "heavier at the beginning and lighter at the end" is adopted; and / or, the strain rate used in steps S3 and S5 is dynamically controlled according to the deformation stage.

9. The method according to claim 1, characterized in that, During the deformation process in steps S3 and / or S5, local cryogenic spraying or local reinforcement fixtures are used in conjunction with overall deformation loading to target the weak areas of the welded joint.

10. An austenitic stainless steel storage tank, characterized in that, The enclosure includes a box body welded from austenitic stainless steel plates and a welded joint located on the box body. The internal microstructure of the box body and the welded joint area includes an austenitic matrix and deformation-induced martensite dispersed in the austenitic matrix. The deformation-induced martensite is in the form of fine dots or short rods and is uniformly distributed in the austenitic matrix. The welded joint and the box body achieve equal strength matching.

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