A method for additive manufacturing valve housing connection and heat treatment

Abstract

A kind of suitable for additive manufacturing valve shell connection and heat treatment method meets the manufacture requirement of large-thrust liquid rocket engine, suitable for additive manufacturing valve shell, by setting connection form, welding process parameters, heat treatment method, the beam welding tooling of anti-welding leakage, manufacture a kind of low temperature, high pressure service environment under additive manufacturing shell.The shell matrix and welded joint performance obtained by the present application meet the requirements of room temperature tensile strength greater than 1200MPa, yield strength greater than 1100MPa, elongation not less than 10%, reduction of area not less than 40%, room temperature impact energy not less than 80J, low temperature impact energy at-196℃ not less than 50J, the internal quality of welded joint, surface quality are qualified, meet GJB1718A-2005 I level weld standard.

Description

Technical Field

[0001] This invention relates to the field of welding, and more particularly to a method for connecting and heat-treating valve bodies in additive manufacturing. Background Technology

[0002] Liquid rocket engines are core components of launch vehicles and missile weapons. To meet the power requirements of my country's large-scale space activities, such as manned lunar landings, deep space exploration, and the launch of heavy space stations, and to enhance my country's space access capabilities, higher requirements are placed on the performance indicators of liquid rocket engines, such as thrust-to-mass ratio and specific impulse. Key components are characterized by complexity, thin walls, integration, and lightweight design. To adapt to high-pressure (90MPa), low-temperature (-207℃~-150℃), and high-flow-rate (864.1kg / s) operation requirements, the liquid oxygen main valve of a certain type of high-thrust liquid rocket engine adopts for the first time a topological weight reduction contour structure and an integrated structure design with guide ribs in the internal flow channel, integrating multiple parts such as the inlet flange, guide sleeve, and shell. To meet the requirements of low-temperature operation, aerospace-grade Fe-Cr-Ni-Co-Mo series low-temperature martensitic aging stainless steel (code S130) is used.

[0003] The complex structure of the product presents processing interference issues, making it impossible to manufacture the shell using specialized machining methods such as mechanical processing, electrolysis, and electrical discharge machining. Traditional casting forming processes suffer from problems such as hot spots, blind cavities, and dead cavities due to integrated design, resulting in poor product formability and inability to repair defects by welding. Furthermore, Fe-Cr-Ni-Co-Mo low-temperature martensitic aging stainless steel contains a large number of refractory alloying elements, leading to poor fluidity of the alloy liquid and a tendency to produce porosity defects.

[0004] Selective Laser Melting (SLM) is currently the most mature additive manufacturing technology, capable of directly forming complex shapes without molds, achieving a WYSIWYG manufacturing effect. However, due to limitations in forming size and structure, shells cannot be manufactured as a single unit using SLM and must be welded in sections. Furthermore, the high laser energy density and high scanning speed during SLM in additive manufacturing result in extremely rapid cooling (10⁴-10⁷ °C / s), leading to a rapidly solidifying, fine-grained microstructure with a high presence of Laves and σ phases in the matrix, making it prone to cracking defects during welding. Secondly, customized heat treatment processes are required before and after welding to ensure that the strength of the matrix and weld meets usage requirements.

[0005] CN108588582A, "High-strength stainless steel powder for 3D printing under low temperature environment and preparation process", discloses the powder preparation and heat treatment process of Fe-Cr-Ni-Co-Mo high-strength stainless steel under low temperature. It mainly focuses on powder preparation and heat treatment performance control of structural parts, but does not adjust the heat treatment accordingly for welding characteristics.

[0006] CN114101688A, entitled "A Method for Preparing Stainless Steel Components," discloses an additive manufacturing method for Fe-Cr-Ni-Co-Mo series 03Cr11Ni9Co6Mo3 (S-04 steel) and a method for controlling the heat treatment of structural components. This patent is applicable to the integral forming of small-sized structural components, eliminating the need for subsequent welding and corresponding heat treatment.

[0007] In view of the above, there is a need for a welding process and heat treatment control method based on additive manufacturing. Summary of the Invention

[0008] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a connection method for liquid main valve housing based on additive manufacturing. Through the design of welding process and supporting heat treatment process, an additive manufacturing housing for low temperature and high pressure service environment is manufactured, which solves the problems of welding cracks and performance control in additive manufacturing state, and realizes the efficient, high reliability, and integrated structure and function manufacturing of such typical components.

[0009] The technical solution of this invention is:

[0010] A method for connecting and heat-treating valve bodies in additive manufacturing includes:

[0011] S1: Laser melting selective forming process is used to manufacture the upper and lower shells;

[0012] S2: Stress-relieving heat treatment is performed on the upper and lower shells;

[0013] S3: Perform pre-welding homogenization and solution heat treatment on the upper and lower shells obtained in S2;

[0014] S4: Assemble the upper and lower shells using welding fixtures and weld them to obtain the welded shell;

[0015] S5: Remove the welding fixture and inspect the welded parts;

[0016] S6: Perform cold treatment and aging on the welded shell.

[0017] In one embodiment, in step S1, the upper shell and the lower shell are made of aerospace-grade Fe-Cr-Ni-Co-Mo series low-temperature martensitic aging stainless steel (code: S130).

[0018] In one embodiment, the laser melting selective forming process parameters in step S1 are: laser power of 300W to 350W, scanning speed of 900mm / s to 1100mm / s, spot diameter of 0.12mm to 0.14mm, and powder thickness of 0.02mm to 0.03mm.

[0019] In one embodiment, in step S2, the heat treatment is a vacuum stress-relieving treatment. Specifically, the stress-relieving heat treatment can be either air atmosphere heat treatment or vacuum heat treatment. For parts with machining allowances ≥0.5mm on each machined surface, air atmosphere heat treatment is recommended. Specifically, the process involves holding at 470–530℃ for 90–240 minutes, followed by cooling to room temperature in the furnace or in air. For parts containing non-machined surfaces or machining allowances <0.5mm, vacuum heat treatment is used. Specifically, the process involves applying heat at a pressure not exceeding 1.33 × 10⁻⁶ mm. -2 Under conditions of Pa and temperature of 450-550℃, the mixture is kept at a temperature of 1.0-2.0 bar for 110-270 minutes. After the holding period, inert gas is introduced for cooling.

[0020] In step S2, after heat treatment, the substrate is removed by wire cutting. The inner cavity and outer contour support of the upper and lower shells are machined and removed. The feed rate during wire cutting to remove the substrate and support is controlled at 4-8 mm / min.

[0021] In one embodiment, in step S3, the pre-welding homogenization pretreatment is performed under a pressure not exceeding 1.33 × 10⁻⁶. - 3 Hold the gas at 950–980°C for 90–150 minutes; after holding, cool with argon or high-purity nitrogen at a pressure of not less than 1.0 bar, and then start a circulating cooling process.

[0022] In one embodiment, in step S3, the solution heat treatment is performed at a pressure not exceeding 1.33 × 10⁻⁶. -3 Hold the gas at 650-700℃ for 60-90 minutes; after holding, cool with argon or high-purity nitrogen at a pressure of not less than 2.0 bar and perform circulating cooling.

[0023] In one embodiment, in step S4, the welding method is electron beam welding, which includes tack welding, main welding, and finishing welding. The vacuum degree of the welding chamber is ≤2.7×10⁻⁶. -3 Pa, welding torch vacuum degree ≤2.7×10 -2 Pa. Positioning welding current: 65±10mA, main welding current: 150±20mA, finishing welding current: 65±10mA, welding speed: 600±100mm / min, focusing current: 2000±100mA, working distance: 400±100mm, accelerating voltage: 60kV, scanning waveform: circular, scanning amplitude: 1±0.5mm, scanning frequency: 150±20Hz.

[0024] In one embodiment, in step S6, the cold treatment is to keep the temperature at -(70~80)℃ for 120~180 hours and then allow it to return to room temperature in the air.

[0025] In one embodiment, in step S6, aging is performed by placing the furnace at room temperature and at a pressure not exceeding 1.33 × 10⁻⁶. -3 The temperature is 480℃~520℃ and held for 180~300min; after the holding period, argon or high-purity nitrogen is used for cooling, and the gas pressure is not less than 1.0 bar.

[0026] In one embodiment, the inner wall of the upper housing is provided with a welded locking bottom, which is used to lock onto the inner wall of the lower housing to block the gap between the upper housing and the lower housing from the inside; the thickness δ of the welded locking bottom is related to the butt joint thickness δ1 as δ≥αδ1, where α is 0.1~0.2 and the gap L between the welded locking bottom and the lower housing is 0.1~0.5mm.

[0027] In one embodiment, in step S4, before installing the welding fixture, the ends of the upper and lower housings that mate are precision machined; the welding fixture includes a positioning ring, connecting bolts, and four separate copper pads. The separate copper pads are fan-shaped, and the four separate copper pads form a ring. The separate copper pads are connected to the positioning ring by the connecting bolts. The outer diameter of the positioning ring is smaller than the inner diameter of the lower housing and larger than the outer diameter of the guide sleeve; the outer circumference of the separate copper pads is provided with grooves, and the welding lock bottom is engaged in the grooves.

[0028] In one embodiment, the installation steps of the welding fixture include: a guide sleeve is provided inside the upper housing; a positioning ring is placed on the end face of the guide sleeve as a positioning surface; then, a split copper pad is placed in sequence; a groove is provided on the outer circumference of the split copper pad; a welding lock bottom is engaged in the groove; and the hole on the split copper pad is aligned with the threaded hole of the positioning ring. The positioning ring and the split copper pad are connected by four connecting bolts passing through the open holes and connecting to the threaded holes.

[0029] When disassembling the welding fixture, first remove the four connecting bolts, and then remove the separate copper pads and positioning rings in sequence.

[0030] In summary, this application includes at least the following beneficial technical effects:

[0031] (1) This invention discloses a method for connecting a main valve housing based on additive manufacturing. The resulting matrix has the following properties: room temperature tensile strength greater than 1200 MPa, yield strength greater than 1100 MPa, elongation not less than 10%, reduction of area not less than 40%, room temperature impact energy not less than 80 J, and low temperature impact energy not less than 50 J at -196℃. Furthermore, the internal and surface quality of the weld joint are qualified, conforming to the GJB1718A-2005 Class I weld standard.

[0032] This invention discloses a method for controlling welding performance and suppressing defects based on additive manufacturing. It proposes a complete heat treatment system suitable for additive manufacturing welding. Compared to the 700-800℃ solution heat treatment for structural parts in additive manufacturing, a pre-weld treatment system suitable for welding is proposed. Pre-treatment is added before solution heat treatment. By increasing the solution temperature (950-980℃) and ensuring sufficient holding time (90-150 min), the atomic motion energy is significantly increased. This effectively eliminates the anisotropy of the matrix structure of parts formed by selective laser melting and also fully dissolves the Laves and σ phases that are harmful to the welding process. Secondly, selecting an appropriate temperature range can prevent rapid grain growth while controlling the atomic diffusion rate. Adding a low-temperature solution heat treatment (650-700℃) after pre-treatment helps transform the ordinary austenite structure obtained after pre-treatment into a non-diffusion austenite structure with high defect density, preparing the microstructure for the formation of high-toughness reverse-transformed austenite during post-weld aging. Post-weld cryogenic treatment allows for rapid cooling of the solution-treated matrix and weld joints to achieve a high-defect-density martensitic microstructure. Post-weld aging treatment can transform the high-defect-density martensite in the matrix and weld joints into reverse-transformed austenite, which can toughen the matrix, and can also eliminate welding stress.

[0033] This invention provides a complete heat treatment process for high-strength stainless steel used at low temperatures, suitable for welding in additive manufacturing conditions. It solves the problems of welding cracks and performance control in additive manufacturing conditions, and realizes efficient, high-reliability, and integrated structural and functional manufacturing of such typical components. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of an embodiment of the present invention;

[0035] Figure 2 for Figure 1 A sectional view;

[0036] Figure 3a This is a front view of the welding fixture. Figure 3b for Figure 3a Sectional view at point AA;

[0037] Figure 4 This is an assembly diagram of the welding fixture.

[0038] Explanation of reference numerals in the attached drawings: 1. Upper housing; 2. Lower housing; 15. Central shaft; 16. Flow guide sleeve; 17. Welded bottom lock;

[0039] 31. Positioning ring; 32. Connecting bolt; 33. Split copper pad; 331. Groove; 311. Positioning ring hole. Detailed Implementation

[0040] The following detailed description of specific embodiments of the present invention aims to provide a better understanding of the invention's solutions and advantages. However, the specific embodiments and examples described below are for illustrative purposes only and are not intended to limit the scope of the invention.

[0041] This embodiment takes a certain model of liquid oxygen main valve as an example, such as Figure 1 and Figure 2 As shown, the housing of a certain type of liquid oxygen main valve includes an upper housing 1 and a lower housing 2. The upper housing 2 contains a central shaft 15 and a flow guide sleeve 16. The flow guide sleeve 16 is fitted on the outside of the central shaft 15. The ends of the central shaft 15 and the flow guide sleeve 16 away from the lower housing 2 are both connected to the upper housing 2. The other end of the central shaft 15 extends into the lower housing 2. The upper housing 2 adopts topology optimization for structural weight reduction design.

[0042] Example 1

[0043] This application discloses a method for connecting and heat-treating valve bodies in additive manufacturing, such as... Figure 1 As shown, it includes the following steps:

[0044] (1) Based on the design 3D model, add machining allowance, forming substrate, and forming process support. Establish a 3D model of the shell suitable for laser melting selective forming process. Use laser melting selective forming process to manufacture upper shell 1 and lower shell 2.

[0045] The process parameters for laser melting selective forming are: laser power of 300W, scanning speed of 1000mm / s, spot diameter of 0.12mm, and powder thickness of 0.02mm.

[0046] (2) Perform stress-relieving heat treatment on the upper shell 1 and lower shell 2 prepared in step (1) and remove the substrate by wire cutting. Process and remove the inner cavity and outer contour support of the upper shell 1 and lower shell 2.

[0047] The heat treatment is a vacuum stress-relieving treatment. Specifically, the stress-relieving heat treatment can be performed using either air atmosphere heat treatment or vacuum heat treatment. For parts with machining allowances ≥0.5mm on all machined surfaces, air atmosphere heat treatment is recommended. The specific procedure is to hold at 470–530℃ for 90–240 minutes, followed by cooling to room temperature in the furnace or in air. For parts with non-machined surfaces or machining allowances <0.5mm, vacuum heat treatment is used. The specific procedure is to apply heat treatment at a pressure not exceeding 1.33 × 10⁻⁶ mm. -2 Under conditions of Pa and temperature of 450-550℃, the mixture is kept at a temperature of 1.0-2.0 bar for 110-270 minutes. After the holding period, inert gas is introduced for cooling.

[0048] The feed rate for wire cutting to remove the substrate and support structure is controlled at 4–8 mm / min.

[0049] Support processing methods include machining and electrical discharge machining.

[0050] (3) Perform quality checks on the upper shell 1 and lower shell 2 processed in step (2) according to the design conditions to obtain components whose internal quality meets the preset conditions.

[0051] Quality inspection includes X-ray inspection, fluorescence inspection, and dimensional inspection.

[0052] (4) Perform pre-welding homogenization and solution heat treatment on the upper shell 1 and lower shell 2 after inspection in step (3).

[0053] The pre-welding heat treatment consists of homogenization pretreatment and solution heat treatment, both conducted under vacuum.

[0054] The homogenization pretreatment process specifically involves applying a pressure not exceeding 1.33 × 10⁻⁶. -3 The gas is kept at 965°C for 90 minutes. After the holding period, it is cooled by argon or high-purity nitrogen with a gas pressure of not less than 1.0 bar, and then circulated for cooling.

[0055] The specific procedure for solution heat treatment is as follows: the pressure is not greater than 1.33 × 10⁻⁶. -3 The gas is kept at 675°C for 60 minutes. After the holding period, it is cooled by argon or high-purity nitrogen at a pressure of not less than 2.0 bar and then circulated for cooling.

[0056] (5) Perform beveling on the upper shell 1 and lower shell 2 after heat treatment in step (4). That is, perform fine machining on the joint ends of the upper shell 1 and lower shell 2 to ensure that the interface has a small roughness.

[0057] The bevel is a plug-in locking structure. The inner wall of the upper shell 1 is provided with a welded locking bottom 17, which is used to engage with the inner wall of the lower shell 2 to block the gap between the upper shell 1 and the lower shell 2 from the inside. The welded locking bottom 17 is inserted into the lower shell 2, forming a plug-in locking structure. The butt joint thickness δ1 is 18mm, the thickness of the welded locking bottom 17 is 2.5mm, the weld width is 0.5mm, the width of the welded locking bottom 17 is 1.5mm, and the gap L between the welded locking bottom 17 and the inner wall of the lower shell 2 is 0.3mm.

[0058] (6) Assemble the upper housing 1 and lower housing 2, and confirm that the gap before welding is not greater than 0.1mm. Check the residual magnetism of the parts and confirm that it is not greater than 1Gs. Assemble the upper housing 1, lower housing 2 and electron beam welding fixture, and perform welding.

[0059] The welding method is electron beam welding, which includes tack welding, main welding, and finishing welding. The vacuum degree of the welding chamber is ≤2.7×10⁻⁶. -3 Pa, welding torch vacuum degree ≤2.7×10 -2 Pa. Positioning welding current: 65mA, main welding current: 150mA, finishing welding current: 65mA, welding speed: 600mm / min, focusing current: 2000mA, working distance: 400mm, accelerating voltage: 60kV, scanning waveform: circular, scanning amplitude: 1mm, scanning frequency: 150Hz.

[0060] The electron beam welding fixture includes a positioning ring 31, multiple split copper pads 33, and connecting bolts 32. The split copper pads 33 are fan-shaped, and the multiple split copper pads 33 form a ring. A mounting groove is provided on one side of each split copper pad 33, and the positioning ring 31 is located within the mounting groove. The split copper pads 33 are connected to the positioning ring 31 via the connecting bolts 32. The outer diameter of the positioning ring 31 is smaller than the inner diameter of the lower housing 2, and the inner diameter of the positioning ring 31 is larger than the inner diameter of the central shaft 15, so that the central shaft 15 can pass through the center of the positioning ring 31. A groove 331 is provided on the outer circumference of each split copper pad 33, and a welding lock bottom 17 is engaged within the groove 331.

[0061] The positioning ring 31 is made of 1Cr18Ni9Ti and has four threaded holes evenly distributed on it. The split copper pad 33 is made of T2 copper and has through holes machined on it. The assembly method is as follows: using the end face of the guide sleeve 16 as the positioning point, first place the positioning ring 31, then place the four split copper pads 33 into the slots. Place the groove 331 of the split copper pad 33 for preventing weld leakage at the welding lock bottom 17, and connect the positioning ring 31 and the split copper pad 33 with the connecting bolts 32.

[0062] (7) After welding, remove the welding fixture, process and remove the welding lock base 17 on the back of the weld, and then perform X-ray fluoroscopic inspection. If the structure of the X-ray fluoroscopic inspection shows that the weld is not fully penetrated, the incomplete welded area needs to be removed and re-welded until the weld is fully penetrated before proceeding to the next step.

[0063] (8) The shell obtained in step (7) is subjected to cold treatment and aging to finally obtain a component whose mechanical properties of both the substrate and the welded joint meet the preset conditions.

[0064] The cold treatment process specifically involves holding the temperature at -75°C for 120 hours and then allowing it to return to room temperature in the air.

[0065] The vacuum aging heat treatment process specifically involves placing the sample in the furnace at room temperature and then aging it at a pressure not exceeding 1.33 × 10⁻⁶. -3 The temperature is 500℃ and held for 180 minutes. After the holding period, the gas is purged with argon or high-purity nitrogen for cooling. The purging pressure is not less than 1.0 bar.

[0066] Mechanical properties of the substrate before heat treatment, the substrate after heat treatment, and the weld of this embodiment were examined. The properties of the substrate before heat treatment are shown in Table 1, and the properties of the substrate and the weld after heat treatment are shown in Tables 2 and 3.

[0067] In the table, Rm (MPa) means tensile strength, Rp0.2 (MPa) means yield strength, A (%) means elongation, Z (%) means reduction of area, and KU2 (J) means impact energy.

[0068] Table 1 Measured properties of the matrix before heat treatment

[0069]

[0070] Table 2 Measured properties of the matrix after heat treatment

[0071]

[0072] Table 3 Measured properties of welds after heat treatment

[0073]

[0074] Example 2

[0075] The difference from Example 1 is as follows:

[0076] After the inspection in step (3), the upper and lower shells were not subjected to homogenization pretreatment, but were directly subjected to pre-welding solution heat treatment in a vacuum medium. The solution heat treatment method was the same as in Example 1.

[0077] The welded shell is subjected to cold treatment and aging to obtain a component in which the mechanical properties of both the substrate and the welded joint meet the preset conditions. The specific method is the same as in Example 1.

[0078] Mechanical properties of the substrate before heat treatment, the substrate after heat treatment, and the weld of this embodiment were examined. The properties of the substrate before heat treatment are shown in Table 1, and the results of the substrate and weld after heat treatment are shown in Tables 4 and 5.

[0079] Table 4. Measured properties of the matrix after heat treatment

[0080]

[0081] Table 5 Measured properties of welds after heat treatment

[0082]

[0083] Example 3

[0084] The difference from Example 1 is as follows:

[0085] After the upper and lower shells are inspected in step (3), they are subjected to pre-welding homogenization pretreatment. After pretreatment, no solution heat treatment is performed. The shells obtained after welding are subjected to cold treatment and aging. Finally, a component whose mechanical properties of both the substrate and the welded joint meet the preset conditions is obtained. The specific method is the same as in Example 1.

[0086] Mechanical properties of the substrate before heat treatment, the substrate after heat treatment, and the weld of this embodiment were examined. The properties of the substrate before heat treatment are shown in Table 1, and the results of the substrate and weld after heat treatment are shown in Tables 6 and 7.

[0087] Table 6 Measured properties of the matrix after heat treatment

[0088]

[0089] Table 7 Measured properties of welds after heat treatment

[0090]

[0091] In Examples 1 and 2, after heat treatment, the weld and matrix properties of Example 1 were significantly improved compared to before heat treatment. Compared to Example 1, Example 2 did not employ homogenization heat treatment, thus failing to fully eliminate the anisotropy of the matrix structure of the laser-melted selectively formed part, and also failing to fully dissolve the Laves and σ phases harmful to the welding process. Therefore, the measured tensile strength and yield strength of the matrix and weld after heat treatment were significantly lower than in Example 1. Example 3 did not undergo solution heat treatment, failing to transform the ordinary austenite structure into a high-defect-density, non-diffusion-type austenite structure, and failing to provide sufficient strengthening phases for post-weld aging. Therefore, the measured tensile strength and yield strength of the matrix and weld after heat treatment were significantly lower than in Example 1. Therefore, the welding process and supporting heat treatment process of this application are equivalent to Example 1, offering better performance and higher reliability.

[0092] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims of the present invention.

Claims

1. A method for connecting and heat-treating valve bodies in additive manufacturing, characterized in that: include S1: Laser melting selective forming process is used to manufacture the upper shell (1) and lower shell (2); S2: Perform stress-relief heat treatment on the upper shell (1) and the lower shell (2); S3: The upper shell (1) and lower shell (2) obtained in S2 are subjected to pre-welding homogenization pretreatment and solution heat treatment; In step S3, the pre-welding homogenization pretreatment is performed under a pressure not exceeding 1.33 × 10⁻⁶. -3 Hold at 950-980°C for 90-150 minutes; after holding, cool with argon or high-purity nitrogen at a pressure of not less than 1.0 bar and perform circulating cooling. In step S3, the solution heat treatment is performed at a pressure not exceeding 1.33 × 10⁻⁶. -3 Hold at 650-675℃ for 60-90 minutes; after holding, cool with argon or high-purity nitrogen at a pressure of not less than 2.0 bar and perform circulating cooling. S4: The upper shell (1) and lower shell (2) after processing in step S3 are assembled using welding fixtures and welded to obtain the welded shell; the inner wall of the upper shell (1) is provided with a welding lock bottom (17), and the welding lock bottom (17) is provided on the inner wall of the lower shell (2) to block the gap between the upper shell (1) and the lower shell (2) from the inside; the thickness δ of the welding lock bottom (17) and the thickness δ1 at the joint are related as δ≥αδ1, where α is 0.1~0.2; the gap L between the welding lock bottom (17) and the lower shell (2) is 0.1~0.5mm; the thickness at the joint is the length of the contact surface between the upper shell (1) and the lower shell (2); S5: Remove the welding fixture and inspect the welded shell; S6: Perform cold treatment and aging on the welded shell.

2. The method for connecting and heat-treating valve bodies suitable for additive manufacturing according to claim 1, characterized in that: In step S1, the upper shell (1) and the lower shell (2) are made of aerospace-grade Fe-Cr-Ni-Co-Mo series low-temperature martensitic aging stainless steel.

3. The method for connecting and heat-treating valve bodies suitable for additive manufacturing according to claim 1, characterized in that: In step S6, the cold treatment involves keeping the temperature at -70~80℃ for 120~180 hours and then allowing it to return to room temperature in the air.

4. The method for connecting and heat-treating valve bodies suitable for additive manufacturing according to claim 3, characterized in that: In step S6, aging is performed by placing the furnace at room temperature and at a pressure not exceeding 1.33 × 10⁻⁶. -3 Hold at 480℃~520℃ for 180~300min; after holding, cool with argon or high-purity nitrogen at a pressure of not less than 1.0 bar.

5. A method for connecting and heat-treating valve bodies suitable for additive manufacturing according to claim 1, characterized in that: In step S4, before installing the welding fixture, the ends of the upper shell (1) and the lower shell (2) that mate are precision machined. The welding fixture includes a positioning ring (31), connecting bolts (32), and multiple split copper pads (33). The positioning ring (31) has evenly distributed threaded holes. The split copper pads (33) are fan-shaped with smooth holes. The four split copper pads (33) form a ring and are connected to the positioning ring (31) by connecting bolts (32). The outer diameter of the positioning ring (31) is smaller than the inner diameter of the lower housing (2) to ensure that the positioning ring (31) can be installed smoothly. The outer circumference of the split copper pads (33) has a groove (331), and the welding lock bottom (17) is locked in the groove (331). When assembling the welding fixture, the end face of the upper shell (1) guide sleeve (16) is used as the positioning surface. The positioning ring (31) is placed, and then the split copper pad (33) is placed in sequence. The outer circumference of the split copper pad (33) is provided with a groove (331). The welding lock bottom (17) is stuck in the groove (331). The light hole on the split copper pad (33) is aligned with the threaded hole of the positioning ring (31). The positioning ring (31) is connected to the split copper pad (33) by passing the light hole through the connecting bolt (32) and connecting it with the threaded hole. When disassembling the welding fixture, first remove the four connecting bolts (32), and then remove the split copper pad (33) and the positioning ring (31) in sequence.

6. A method for connecting and heat-treating valve housings suitable for additive manufacturing according to claim 5, characterized in that: The split copper pad (33) has an installation groove on one side, and the positioning ring (31) is located in the installation groove.

7. A method for connecting and heat-treating valve housings suitable for additive manufacturing according to claim 5, characterized in that: The installation steps of the welding fixture include: a guide sleeve (16) is provided inside the upper shell (1), a positioning ring (31) is placed with the end face of the guide sleeve (16) as the positioning surface, and then a split copper pad (33) is placed in each of them. The groove (331) of the split copper pad (33) for preventing weld leakage is placed at the welding lock bottom (17), and the positioning ring (31) is connected to the split copper pad (33) by the connecting bolt (32).

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