Surface composite strengthening method for rapid joint of precipitation hardening stainless steel high-pressure pipe

Abstract

The invention discloses a precipitation hardening stainless steel high-pressure pipe quick joint surface composite strengthening method, and relates to the technical field of stainless steel surface strengthening, which comprises the following steps: S1, rough machining; s2, complete solution treatment is carried out under vacuum or protective atmosphere, and oil quenching is carried out to room temperature; s3, aging treatment is conducted under the vacuum or protective atmosphere, and air cooling is conducted to the room temperature; s4, semi-finish machining is conducted, and the machining allowance is reserved; s5, multi-stage shot blasting treatment is conducted, precise polishing is conducted, and cleaning and drying are conducted; and S6, a gradient / multi-layer Cr / CrN coating or a Cr / CrN / CrCN coating is deposited on the surface of the pipe joint through a low-temperature PVD technology. According to the method, high-quality surface strengthening treatment of the precipitation-hardening stainless steel high-pressure pipe joint surface material is achieved, the requirement for the reliability of the precipitation-hardening stainless steel high-pressure pipe joint surface material under the extreme composite working conditions (high pressure, high abrasion resistance and severe corrosion conditions) is met, and the problems that the service life is short, and reliability is insufficient under the high-load, high-abrasion and severe corrosion environments are effectively solved.

Description

Technical Field

[0001] This invention relates to the field of stainless steel surface strengthening technology, specifically to a method for composite surface strengthening of precipitation-hardening stainless steel high-pressure pipe quick connectors. Background Technology

[0002] High-pressure quick couplings are essential components of aviation hydraulic systems. They achieve rapid connection or disconnection of pipelines through internal sealing structures and external locking mechanisms. Their performance and quality directly affect the operational efficiency and safety of the hydraulic system, and their high reliability is crucial for aircraft lifespan. High-pressure aviation quick couplings must withstand significant loads during operation and possess excellent wear resistance, corrosion resistance, and impact resistance to be suitable for various complex environments. Therefore, high-pressure quick couplings require high levels of pressure resistance, wear resistance, corrosion resistance, fatigue resistance, and surface quality.

[0003] Surface strengthening is an effective means to improve the high pressure resistance, wear resistance, corrosion resistance, and fatigue resistance of high-pressure pipe quick couplings. Currently, surface strengthening technologies mainly include low-temperature gas nitriding / nitriding, electroplating (such as hard chrome plating), laser surface alloying / quenching, shot peening, and PVD coating. Low-temperature gas nitriding / nitriding can improve surface hardness, wear resistance, and fatigue resistance, but it may form chromium nitrides, reducing the surface chromium content, impairing corrosion resistance, and making it unsuitable for acid / damp heat tests. Electroplating has the characteristics of high hardness and wear resistance, but it carries the risk of hydrogen embrittlement, microcracks can easily become corrosion initiation points, it has poor environmental performance, and galvanic corrosion may occur in acidic environments. Laser surface alloying / quenching has excellent properties such as high hardness, pressure resistance, and wear resistance, but the heat-affected zone may change the properties of the substrate, the treatment area is limited, and corrosion resistance is poor. Shot peening can improve fatigue strength and introduce compressive stress, but it does not change the surface chemical composition, the hardness improvement is limited, and its direct contribution to high pressure resistance and corrosion resistance is small; surface roughness is detrimental to wear resistance. PVD coatings are dense ceramic layers with high hardness and bonding strength. PVD coatings (such as CrN, TiN, TiAlN, DLC, etc.) can achieve hardnesses of 2000-3000 HV or higher, significantly improving surface pressure resistance, wear resistance, and resistance to plastic deformation, while meeting high-pressure requirements. They also exhibit excellent corrosion resistance. The dense, smooth coating contributes to wear resistance and mildew resistance. The low-temperature process, typically 200-500°C, significantly lower than the aging temperature of precipitation-hardening stainless steel (approximately 480-620°C), prevents over-aging softening or deformation of the substrate, perfectly preserving its mechanical properties. It is also environmentally friendly, with no risk of hydrogen embrittlement (compared to electroplating), meeting environmental protection requirements. However, pressure-resistant dense ceramic PVD coatings (such as nitride, oxide, and carbide coatings) are characterized by significant brittleness and high internal stress, resulting in a large hardness and stress gradient with the substrate. This leads to weaker bonding strength, reduced fatigue resistance, and decreased high-pressure resistance.

[0004] Therefore, existing single surface strengthening treatment methods cannot meet the surface treatment requirements of precipitation-hardening stainless steel high-pressure pipe quick connectors, which have high requirements for high pressure resistance, wear resistance, corrosion resistance, fatigue resistance, and surface quality. Summary of the Invention

[0005] The purpose of this invention is to provide a surface composite strengthening method for precipitation-hardening stainless steel high-pressure pipe quick connectors, which can achieve high-quality surface strengthening treatment of precipitation-hardening stainless steel quick connectors, meet their reliability performance requirements under extreme composite conditions (high pressure + high wear resistance + severe corrosion conditions), and effectively solve the problems of short service life and insufficient reliability under high load, high wear and severe corrosion environment.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0007] A method for surface composite strengthening of precipitation-hardening stainless steel high-pressure pipe quick couplings includes the following steps:

[0008] S1. Roughly machine the material to the shape of the pipe fitting;

[0009] S2. Place the pipe fitting under a vacuum or protective atmosphere for complete solution treatment, and then oil quench it to room temperature.

[0010] S3. Aging the pipe fittings under vacuum or protective atmosphere, and then air-cooling them to room temperature.

[0011] S4. Perform semi-finishing on the pipe fittings, leaving room for shot peening, polishing and PVD coating;

[0012] S5. Perform multi-stage shot peening on the pipe joint, then perform precision polishing to flatten the surface peaks, retain the valleys and the underlying compressive stress layer, and reduce roughness. After that, clean and dry.

[0013] S6. A gradient / multilayer Cr / CrN coating or Cr / CrN / CrCN coating containing a Cr metal bonding layer is deposited on the surface of the pipe joint using a low-temperature PVD process.

[0014] Furthermore, in step S2 above, during the complete solution treatment, the temperature is maintained at 915-1055 ℃ for 0.5-1 h to allow all alloying elements to completely dissolve into the austenite, forming a uniform single-phase solid solution.

[0015] Furthermore, in step S2 above, the hardness after oil quenching to room temperature is HRC 32-38.

[0016] Furthermore, in step S2 above, during oil quenching, the cooling rate is 20-50 ℃ / s and the oil temperature is 50±10 ℃. After oil quenching, all the supersaturated austenite is transformed into low-carbon lath martensite, forming a uniform supersaturated martensite structure.

[0017] Furthermore, in step S3 above, when aging is performed under vacuum or a protective atmosphere, the temperature is held at 500-600 ℃ for 3-4 h; after removal from the furnace, it is cooled to room temperature by still air. After aging treatment, the hardness is HRC 35-48, the elongation is ≥12%, the reduction of area is ≥45%, and the fracture toughness is [not specified]. .

[0018] Furthermore, in step S5 above, spherical shot is used for multi-stage shot peening. First, large shot is used to introduce deep compressive stress, and then small shot is used to reduce surface roughness. After shot peening, the surface peaks are smoothed and the roughness is reduced by fine polishing, low-speed and low-pressure vibration polishing, magnetorheological polishing or mechanical precision polishing.

[0019] Furthermore, in step S5 above, during shot peening, stainless steel spherical shot or ceramic spherical shot with HRC 50-60 is used. The diameter of the large shot is 0.25-0.45 mm, the diameter of the small shot is 0.05-0.25 mm, the shot peening intensity is 0.15-0.3 mmA(N), the shot peening coverage is ≥200%-400%, the shot peening angle is perpendicular to the incident point, and the shot peening distance is 100-300 mm.

[0020] Furthermore, in step S5 above, the reduced roughness Ra is less than 0.2 μm, in order to form a better adhesion and a uniform residual compressive stress layer with the coating.

[0021] Furthermore, in step S5 above, a graded cleaning process is adopted. First, an alkaline water-based cleaning agent is used for ultrasonic cleaning at 20-30 kHz and 60-70 ℃ for 10-15 min. Then, deionized water, a weakly acidic cleaning agent, or a neutral cleaning agent are used in sequence for ultrasonic rinsing at 40-80 kHz and 50-60 ℃ for 5-10 min. Next, deionized water is used for ultrasonic fine cleaning at room temperature and >80 kHz for 5 min. Finally, the mixture is soaked in deionized water at 70-80 ℃ for 2-3 min and then dried.

[0022] Furthermore, in step S6 above, the PVD process temperature is 250-370 ℃;

[0023] When using a Cr / CrN coating, after online processing in a PVD vacuum chamber, a Cr metal binder layer is deposited first, followed by a CrN transition layer deposition; the thickness of the Cr metal binder layer is 0.1-0.3 μm, the thickness of the CrN transition layer is 3-6 μm, and the total coating thickness is 3.1-6.3 μm.

[0024] When using a Cr / CrN / CrCN coating, after online processing in a PVD vacuum chamber, a Cr metal binder layer is deposited first, followed by a CrN transition layer, and finally a CrCN functional layer is deposited using a gradient method. The thickness of the Cr metal binder layer is 0.1-0.3 μm, the thickness of the CrN transition layer is 1-3 μm, and the thickness of the CrCN functional layer is 2-3 μm. The total coating thickness is 3-6 μm.

[0025] The present invention has the following beneficial effects:

[0026] 1. Under combined working conditions requiring high pressure, wear resistance, and corrosion resistance, component failure often begins with stress corrosion cracking or brittle fracture, rather than overall yielding. Therefore, "sufficient strength + high toughness and resistance to environmental damage" is safer and has a longer lifespan than "ultimate strength." This invention employs a composite method of heat treatment to strengthen the material matrix, shot peening, and low-temperature multilayer gradient coating to form a gradient distribution transitioning from a tough matrix to a high-hardness surface. This ensures that the surface strengthening system can withstand stringent high pressure, wear resistance, and environmental corrosion resistance, improving matrix support while maintaining corrosion resistance. This effectively supports the high-hardness coating and avoids surface cracking and other problems.

[0027] 2. This invention utilizes vacuum or protective atmosphere solution aging treatment, shot peening pretreatment, and polishing processes to treat precipitation-hardened stainless steel high-pressure quick connectors. Vacuum or protective atmosphere solution aging treatment ensures both the strength and toughness of the matrix and the surface quality. Shot peening pretreatment refines the surface grains and hardens the surface layer, while simultaneously forming a gradient-distributed, deeply influential residual compressive stress layer. Polishing achieves surface smoothness, significantly reducing surface roughness, preserving the residual compressive stress layer, and making the stress distribution of the reinforced layer more uniform. This avoids surface quality issues, deformation, and cracks in the high-pressure quick connectors caused by the processing, improving the precision and product qualification rate of the high-pressure quick connectors.

[0028] 3. The shot peening and polishing steps in this invention are key steps in "pre-fabricating a mechanically compatible substrate for PVD coating". Small-sized hard shot must be used and the intensity must be strictly controlled. In particular, it is emphasized that after shot peening, "selective removal" processes such as vibration polishing, magnetorheological polishing or mechanical precision polishing must be used to remove only the surface peaks and retain the valleys, so as to achieve Ra<0.2μm while retaining more than 70% of the compressive stress.

[0029] 4. The gradient / multilayer coatings (Cr / CrN, Cr / CrN / CrCN) of this invention are "artificial gradient materials" at the micrometer scale, solving the problem of abrupt changes in hardness and modulus. The gradient / multilayer coatings (Cr / CrN, Cr / CrN / CrCN) are not single-layer stacks. They are CrN-based multilayer coatings (Cr / CrN, Cr / CrN / CrCN) with a metal binder layer (Cr) as the base and a gradual change in composition / structure. This is not a simple stacking, but an artificial construction of a "functional gradient material" at the micrometer scale that continuously transitions from metal toughness to ceramic hardness and modulus, solving the contradiction that hardness and toughness cannot be achieved simultaneously, and realizing "hard on the outside and tough on the inside".

[0030] 5. This invention employs a low-temperature multilayer gradient coating, which avoids the influence of temperature on the structure and properties of the substrate, ensuring the comprehensive strength, toughness, and corrosion resistance of the substrate. At the same time, the gradient / multilayer coating has better adhesion and stress distribution in the reinforced layer, replacing the current single-coating surface strengthening technology, avoiding problems such as cracking, and has a lower coefficient of friction and surface precision, effectively improving the surface strengthening quality and lifespan of high-pressure pipe quick connectors, including high pressure resistance, wear resistance, and environmental corrosion resistance. Detailed Implementation

[0031] The present invention will be further illustrated below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0032] Example 1:

[0033] This embodiment provides a method for surface composite strengthening of precipitation-hardening stainless steel high-pressure pipe quick connectors, including the following steps:

[0034] S1. Roughly machine the material to the shape of the pipe fitting;

[0035] S2. Place the pipe fitting under a vacuum or protective atmosphere for complete solution treatment, and then oil quench it to room temperature.

[0036] S3. Aging the pipe fittings under vacuum or protective atmosphere, and then air-cooling them to room temperature.

[0037] S4. Perform semi-finishing on the pipe fittings, leaving room for shot peening, polishing and PVD coating;

[0038] S5. Perform multi-stage shot peening on the pipe joint, then perform precision polishing to flatten the surface peaks, retain the valleys and the underlying compressive stress layer, and reduce roughness. After that, clean and dry.

[0039] S6. A gradient / multilayer Cr / CrN coating or Cr / CrN / CrCN coating containing a Cr metal bonding layer is deposited on the surface of the pipe joint using a low-temperature PVD process.

[0040] In step S2, the complete solution treatment is carried out under vacuum or high-purity argon protection or a protective atmosphere at 915-1055 °C. The purpose is to: 1. Ensure complete dissolution: All alloying elements must be fully dissolved into the austenite to form a homogeneous single-phase solid solution. 2. Prevent overheating: Avoid excessively high temperatures that lead to coarse grains, impairing toughness, and prevent the formation of excessive δ-ferrite. This prevents the formation of soft phases that do not transform during subsequent cooling, which can disrupt the uniformity of the microstructure and become the origin of corrosion and fatigue cracks. Holding at this temperature for 0.5-1 h ensures sufficient heat and component diffusion, allowing the core of the part to also achieve complete solution. Cooling is performed using high-speed quenching oil, rapidly oil quenching to room temperature to suppress the precipitation of any carbides or intermetallic compounds, ensuring that all supersaturated austenite is transformed into low-carbon lath martensite. During oil quenching, the cooling rate is 20-50 ℃ / s, and the oil temperature is 50±10 ℃. After oil quenching, all the supersaturated austenite is transformed into low-carbon lath martensite, forming a uniform supersaturated martensite structure. Insufficient cooling will lead to the precipitation of brittle phases, and the material will not achieve the expected properties. The hardness after oil quenching to room temperature is between HRC 32-38, and the metallographic structure is a uniform supersaturated martensite structure.

[0041] In step S3, the aging treatment is carried out in a vacuum or protective atmosphere, requiring no surface oxidation or decarburization. During aging, the temperature is held at 500-600 ℃ for 3-4 hours, and after removal from the furnace, it is cooled to room temperature by still air. The hardness after aging treatment is between HRC 35-48, elongation ≥12%, reduction of area ≥45%, and fracture toughness... Avoid forced ventilation cooling to prevent the introduction of unnecessary internal stress. Using higher aging temperatures and longer holding times enhances atomic diffusion, allowing the precipitates to fully separate and optimize their size. The precipitates will moderately coarsen to approximately 5-15 nm, with increased interparticle spacing and uniform distribution. This moderate coarsening of the precipitates results in decreased hardness but significantly improved material plasticity, fracture toughness, and stability in corrosive environments.

[0042] In step S5, shot peening aims to improve the surface integrity of the substrate, introduce beneficial residual compressive stress, provide stronger support for the ultra-high hardness PVD coating, reduce plastic deformation of the substrate under load, eliminate the machining-damaged layer, and remove any potential microcracks, residual tensile stress layers, and contaminant layers, thereby improving the adhesion of the coating and the fatigue life of the component. Shot peening uses stainless steel spherical shot (such as 304 or 420 stainless steel) or ceramic spherical shot (such as ZrO2 or Al2O3) with a hardness higher than the substrate's HRC 50-60. Multi-stage shot peening is employed, first using larger shot to introduce deep compressive stress, then using smaller shot to reduce surface roughness. Preferably, the diameter of the large shot is 0.25-0.45 mm, and the diameter of the small shot is 0.05-0.25 mm. The shot shape is spherical; angular shot is prohibited. The shot peening intensity is 0.15-0.3 mmA(N). Excessive intensity may lead to surface over-hardening, microcracks, or deformation. The shot peening coverage should be ≥200%-400% to ensure uniform stress distribution. Excessive coverage may lead to over-processing of the surface, causing peeling or microcracks. The shot peening angle should be perpendicular (90°±15°) to achieve a uniform surface and stress distribution. The shot peening distance should be 100-300 mm. A stable and continuous shot flow should be maintained, considering both the medium velocity and air pressure.

[0043] After shot peening, low-speed, low-pressure precision grinding or polishing is necessary to reduce the peak surface roughness (Ra reduction) while preserving the valleys and the underlying compressive stress layer. This involves smoothing out only the surface "peaks," retaining the "valleys" and the underlying compressive stress layer. Low-speed, low-pressure fine grinding or polishing removes surface protrusions, reducing Ra to below 0.2 μm to facilitate better adhesion to the coating and create a uniform residual compressive stress layer.

[0044] Cleaning is conducted in a separate cleanroom, aiming to remove the vast majority of organic matter, particulate matter, and fingerprints. A tiered cleaning process is employed: first, ultrasonic cleaning with an alkaline water-based cleaner at 20-30 kHz and 60-70 °C for 10-15 minutes; then, ultrasonic rinsing with deionized water, a weakly acidic cleaner, or a neutral cleaner at 40-80 kHz and 50-60 °C for 5-10 minutes; followed by ultrasonic rinsing with deionized water at room temperature and >80 kHz for 5 minutes; and finally, soaking in deionized water at 70-80 °C for 2-3 minutes.

[0045] During drying, first use hot air drying followed by vacuum drying. Dry with hot air at 100-120℃ for 15-30 minutes, then at ~10℃. 2 Vacuum drying at mbar and 60 ℃ for 30 min.

[0046] In step S6, the PVD process temperature is 250-370 ℃.

[0047] When using a Cr / CrN coating, after online processing in a PVD vacuum chamber, a Cr metal binder layer is first deposited using a pure Cr target and pure Ar gas, with argon gas used only for metal sputtering. Then, a CrN transition layer is deposited using a pure Cr target and Ar+N2 gas. The thickness of the Cr metal binder layer is 0.1-0.3 μm, the thickness of the CrN transition layer is 3-6 μm, and the total coating thickness is 3.1-6.3 μm.

[0048] When using a Cr / CrN / CrCN coating, after online processing in a PVD vacuum chamber, a Cr metal binder layer is first deposited using a pure Cr target and pure Ar gas, with argon used only for metal sputtering. Next, a CrN transition layer is deposited using a pure Cr target and Ar+N2 gas. Finally, a CrCN functional layer is deposited using a gradient method, with a Cr target and a gradually activated graphite target, introducing carbon sources by gradually changing the carbon (C) content from 0% to the target value (15-25 at.%), achieving a smooth transition in performance. The gas is Ar+N2→Ar+N2+C2H2 (or CH4), gradually introducing hydrocarbon gases. This completes the gradient transition from CrN to CrCN; the Cr metal binder layer thickness is 0.1-0.3 μm, the CrN transition layer thickness is 1-3 μm, and the CrCN functional layer thickness is 2-3 μm; the total coating thickness is 3-6 μm.

[0049] CrN (chromium nitride) coatings have excellent corrosion resistance, moderate hardness, good toughness and adhesion. Compared with other mainstream PVD coatings, they have less brittleness and internal stress, and are chemically / metallurgically and physically compatible with stainless steel. Their corrosion potential is close to that of stainless steel, with low risk of galvanic corrosion. The gradient structure has no penetrating columnar crystal defects, and its corrosion resistance is better than that of TiN. It is particularly suitable for acidic and humid environments.

[0050] This embodiment employs a multi-layered metal bonding layer + CrN-based (Cr / CrN or Cr / CrN / CrCN) gradient / multi-layered PVD coating. This multi-layered structure provides high hardness and excellent adhesion. The strong metallurgical bond between the Cr metal bonding layer and the substrate ensures adhesion, while the gradient transition mitigates hardness and stress, providing a solid load-bearing foundation and high-pressure resistance. It also inhibits crack propagation, further enhancing corrosion resistance, bonding strength, and fatigue life. Simultaneously, the surface CrCN layer offers superior tribological properties compared to pure CrN. This gradient / multi-layered metal bonding layer + CrN-based (Cr / CrN or Cr / CrN / CrCN) gradient / multi-layered PVD coating meets the reliability requirements of precipitation-hardening stainless steel high-pressure quick couplings under extreme combined conditions (high pressure + high wear resistance + harsh corrosion). It provides an excellent chemical barrier to pass harsh environmental tests such as mold, damp heat, salt spray, and acidic atmospheres, effectively solving problems such as short life and insufficient reliability under high load, high wear, and harsh corrosion environments.

[0051] Online processing within the PVD vacuum chamber:

[0052] 1) High-temperature baking: The workpiece is heated to 250-350℃ (within a safe temperature range) under vacuum and maintained for a period of time to deeply remove adsorbed water vapor and gas from the surface. Purpose: To heat the workpiece, causing the adsorbed water vapor and gas on its surface and inside to desorb. Vacuum degree: Better than 5×10 -3 Pa. Time: 30-60 minutes (depending on workpiece quality and load).

[0053] 2) Argon Ion Bombardment Cleaning: High-purity argon gas is introduced, and a high negative bias voltage (-800V to -1200V) is applied. Purpose: To use high-energy argon ions to physically sputter away the last few atomic layers of contaminants and the natural chromium oxide film, exposing a fresh, highly reactive metal surface. Parameters (requires fine-tuning based on equipment): Gas: High-purity argon gas (purity ≥99.999%). Pressure: 0.5-2.0 Pa (to generate stable glow plasma). Bias Voltage: Apply a DC pulse or radio frequency bias voltage to the workpiece. The bias voltage is critical: For stainless steel, it is typically between -800V and -1200V. Too high a voltage may cause overheating or damage to the substrate; too low a voltage will result in insufficient cleaning. Time: 10-30 minutes. The endpoint is determined by observing the plasma color and current stability.

[0054] 3) Argon ion bombardment of the workpiece surface physically sputters away microscopic oxides, impurities, and adsorbed layers. This is the most crucial step, exposing a fresh, highly active metal surface that greatly enhances coating adhesion. The bombardment time is 20-80 minutes, ensuring thorough cleaning without damaging the substrate, further activating the surface, removing microscopic oxides, and guaranteeing good adhesion between the coating and the substrate.

[0055] The PH13-8Mo, 15-5PH and 17-4PH materials were composite-strengthened according to the method shown in Example 1, and their properties were tested. The results are shown in Table 1.

[0056] Table 1. Performance test results of different materials after composite reinforcement

[0057]

[0058] Example 2:

[0059] This embodiment provides a method for surface composite strengthening of precipitation-hardening stainless steel high-pressure pipe quick connectors, including the following steps:

[0060] S1. Roughly machine the material to the shape of the pipe fitting;

[0061] S2. Place the pipe fitting under vacuum or a protective atmosphere for complete solution treatment, and then oil quench it to room temperature; during complete solution treatment, hold it at 1000 ℃ for 0.8 h; during oil quenching, the cooling rate is 30 ℃ / s, and the oil temperature is 50±10 ℃.

[0062] S3. Aging the pipe fittings under vacuum or protective atmosphere, and then air-cool them to room temperature; during aging, keep them at 550℃ for 3 hours.

[0063] S4. Perform semi-finishing on the pipe fittings, leaving room for shot peening, polishing and PVD coating;

[0064] S5. Perform multi-stage shot peening on the pipe joint, followed by precision polishing to flatten the surface peaks, retain the troughs and the underlying compressive stress layer, and reduce roughness. Then clean and dry. For shot peening, use HRC 50-60 stainless steel or ceramic spherical shot. The diameter of the large shot is 0.3 mm, and the diameter of the small shot is 0.1 mm. The shot peening intensity is 0.1 mmA(N), the shot peening coverage is ≥200%-400%, the shot peening angle is perpendicular, and the shot peening distance is 100-300 mm. For cleaning, first use an alkaline water-based cleaning agent for ultrasonic cleaning at 20 kHz and 60 ℃ for 10 min, then use a weak acidic cleaning agent (2 vt% nitric acid solution) for ultrasonic rinsing at 40 kHz and 50 ℃ for 5 min, then use deionized water for ultrasonic fine cleaning at room temperature and >80 kHz for 5 min, and finally soak in 75 ℃ deionized water for 2... Drying: During drying, first use hot air drying followed by vacuum drying; dry with hot air at 120 ℃ for 30 min, then at ~10 ℃ for ~10 min. 2 Vacuum drying at mbar and 60 ℃ for 30 min;

[0065] S6. A gradient / multilayer Cr / CrN / CrCN coating containing a metal binder layer is deposited on the surface of the pipe joint using a low-temperature PVD process. The PVD process temperature is 300 ℃. After online processing in a PVD vacuum chamber, the Cr metal binder layer is deposited first, followed by the CrN transition layer, and then the gradient CrCN functional layer is deposited. The thickness of the Cr metal binder layer is 0.1-0.3 μm, the thickness of the CrN transition layer is 1-3 μm, and the thickness of the CrCN functional layer is 2-3 μm. The total coating thickness is 3-6 μm.

[0066] Example 3:

[0067] This embodiment provides a method for surface composite strengthening of precipitation-hardening stainless steel high-pressure pipe quick connectors, including the following steps:

[0068] S1. Roughly machine the material to the shape of the pipe fitting;

[0069] S2. Place the pipe fitting under vacuum or a protective atmosphere for complete solution treatment, and then oil quench it to room temperature. During complete solution treatment, hold it at 915 ℃ for 0.5 h. During oil quenching, the cooling rate is 20 ℃ / s and the oil temperature is 50±10 ℃.

[0070] S3. Aging the pipe joint under vacuum or protective atmosphere, and then air-cool it to room temperature; during aging treatment, keep it at 500℃ for 3 hours.

[0071] S4. Perform semi-finishing on the pipe fittings, leaving room for shot peening, polishing and PVD coating;

[0072] S5. Perform multi-stage shot peening on the pipe joint, followed by precision polishing to flatten the surface peaks, retain the troughs and the underlying compressive stress layer, and reduce roughness. Then clean and dry. For shot peening, use HRC 50-60 stainless steel spherical shot or ceramic spherical shot. The diameter of the large shot is 0.3 mm, and the diameter of the small shot is 0.1 mm. The shot peening intensity is 0.1 mmA(N), the shot peening coverage is ≥200%-400%, the shot peening angle is perpendicular to the incident point, and the shot peening distance is 100-300 mm. For cleaning, first use an alkaline water-based cleaning agent for ultrasonic cleaning at 20 kHz and 60 ℃ for 10 min, then use a weak acidic cleaning agent (2 vt% nitric acid solution) for ultrasonic rinsing at 40 kHz and 50 ℃ for 5 min, then use deionized water for ultrasonic fine cleaning at room temperature and >80 kHz for 5 min, and finally soak in 70 ℃ deionized water for 2... Drying: During drying, first use hot air drying followed by vacuum drying; dry with hot air at 100 ℃ for 15 min, then at ~10 ℃ for ~10 min. 2 Vacuum drying at mbar and 60 ℃ for 30 min;

[0073] S6. A gradient / multilayer Cr / CrN / CrCN coating containing a metal binder layer is deposited on the surface of the pipe joint using a low-temperature PVD process. The PVD process temperature is 250 ℃. After online processing in a PVD vacuum chamber, the Cr metal binder layer is deposited first, followed by the CrN transition layer, and then the gradient CrCN functional layer is deposited. The thickness of the Cr metal binder layer is 0.1-0.3 μm, the thickness of the CrN transition layer is 1-3 μm, and the thickness of the CrCN functional layer is 2-3 μm; the total coating thickness is 3-6 μm.

[0074] Example 4:

[0075] This embodiment provides a method for surface composite strengthening of precipitation-hardening stainless steel high-pressure pipe quick connectors, including the following steps:

[0076] S1. Roughly machine the material to the shape of the pipe fitting;

[0077] S2. Place the pipe fitting under vacuum or a protective atmosphere for complete solution treatment, and then oil quench it to room temperature. During complete solution treatment, hold it at 1055 ℃ for 0.5 h. During oil quenching, the cooling rate is 50 ℃ / s and the oil temperature is 50±10 ℃.

[0078] S3. Aging the pipe fittings under vacuum or a protective atmosphere, and then air-cooling them to room temperature; during aging, keep them at 600℃ for 4 hours.

[0079] S4. Perform semi-finishing on the pipe fittings, leaving room for shot peening, polishing and PVD coating;

[0080] S5. Perform multi-stage shot peening on the pipe joint, followed by precision polishing to flatten the surface peaks, retain the troughs and the underlying compressive stress layer, and reduce roughness. Then clean and dry. For shot peening, use HRC 50-60 stainless steel spherical shot or ceramic spherical shot. The diameter of the large shot is 0.3 mm, and the diameter of the small shot is 0.1 mm. The shot peening intensity is 0.1 mmA(N), the shot peening coverage is ≥200%-400%, the shot peening angle is perpendicular, and the shot peening distance is 100-300 mm. For cleaning, first use an alkaline water-based cleaning agent for ultrasonic cleaning at 20 kHz and 60 ℃ for 10 min, then use a weak acidic cleaning agent (2 vt% nitric acid solution) for ultrasonic rinsing at 40 kHz and 50 ℃ for 5 min, then use deionized water for ultrasonic fine cleaning at room temperature and >80 kHz for 5 min, and finally soak in 80 ℃ deionized water for 3 minutes. Drying: During drying, first use hot air drying followed by vacuum drying; dry with hot air at 120 ℃ for 30 min, then at ~10 ℃ for ~10 min. 2 Vacuum drying at mbar and 60 ℃ for 30 min;

[0081] S6. A gradient / multilayer Cr / CrN coating containing a metal binder layer is deposited on the surface of the pipe joint using a low-temperature PVD process. The PVD process temperature is 370 ℃. After online processing in a PVD vacuum chamber, the Cr metal binder layer is deposited first, followed by the CrN transition layer. The thickness of the Cr metal binder layer is 0.1-0.3 μm, and the thickness of the CrN transition layer is 3-6 μm. The total coating thickness is 3.1-6.3 μm.

[0082] The above description is only a preferred embodiment of the present invention and is 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 surface composite strengthening of precipitation-hardening stainless steel high-pressure pipe quick couplings, characterized in that, Includes the following steps: S1. Roughly machine the material to the shape of the pipe fitting; S2. Place the pipe fitting under a vacuum or protective atmosphere for complete solution treatment, and then oil quench it to room temperature. S3. Aging the pipe fittings under vacuum or protective atmosphere, and then air-cool them to room temperature. S4. Perform semi-finishing on the pipe fittings, leaving room for shot peening, polishing and PVD coating; S5. Perform multi-stage shot peening on the pipe joint, then perform precision polishing to flatten the surface peaks, retain the valleys and the underlying compressive stress layer, and reduce roughness. After that, clean and dry. S6. A gradient / multilayer Cr / CrN coating or Cr / CrN / CrCN coating containing a Cr metal bonding layer is deposited on the surface of the pipe joint using a low-temperature PVD process.

2. The surface composite strengthening method for precipitation-hardening stainless steel high-pressure pipe quick couplings according to claim 1, characterized in that, In step S2, during the complete solution treatment, the temperature is maintained at 915-1055 ℃ for 0.5-1 h to allow all alloying elements to completely dissolve into the austenite and form a uniform single-phase solid solution.

3. The surface composite strengthening method for precipitation-hardening stainless steel high-pressure pipe quick couplings according to claim 2, characterized in that, In step S2, the hardness after oil quenching at room temperature is HRC 32-38.

4. The surface composite strengthening method for precipitation-hardening stainless steel high-pressure pipe quick couplings according to claim 3, characterized in that, In step S2, during oil quenching, the cooling rate is 20-50 ℃ / s and the oil temperature is 50±10 ℃. After oil quenching, all the supersaturated austenite is transformed into low-carbon lath martensite, forming a uniform supersaturated martensite structure.

5. The surface composite strengthening method for precipitation-hardening stainless steel high-pressure pipe quick couplings according to claim 1, characterized in that, In step S3, during aging treatment under vacuum or a protective atmosphere, the temperature is held at 500-600 ℃ for 3-4 h; after removal from the furnace, it is cooled to room temperature by still air. After aging treatment, the hardness is HRC 35-48, elongation ≥12%, reduction of area ≥45%, and fracture toughness... .

6. The surface composite strengthening method for precipitation-hardening stainless steel high-pressure pipe quick couplings according to claim 1, characterized in that, In step S5, multi-stage shot peening is performed using spherical shot. First, large shot is used to introduce deep compressive stress, and then small shot is used to reduce surface roughness. After shot peening, the surface peaks are smoothed and the roughness is reduced by fine polishing, low-speed and low-pressure vibration polishing, magnetorheological polishing, or mechanical precision polishing.

7. The surface composite strengthening method for precipitation-hardening stainless steel high-pressure pipe quick couplings according to claim 6, characterized in that, In step S5, during shot peening, stainless steel spherical shot or ceramic spherical shot with HRC 50-60 is used. The diameter of the large shot is 0.25-0.45 mm, the diameter of the small shot is 0.05-0.25 mm, the shot peening intensity is 0.15-0.3 mmA(N), the shot peening coverage is ≥200%-400%, the shot peening angle is perpendicular to the incident point, and the shot peening distance is 100-300 mm.

8. The surface composite strengthening method for precipitation-hardening stainless steel high-pressure pipe quick couplings according to claim 6, characterized in that, In step S5, the reduced roughness Ra is less than 0.2 μm to facilitate the formation of a better adhesion and uniform residual compressive stress layer with the coating.

9. The surface composite strengthening method for precipitation-hardening stainless steel high-pressure pipe quick couplings according to claim 1, characterized in that, In step S5, a tiered cleaning process is employed. First, an alkaline water-based cleaning agent is used for ultrasonic cleaning at 20-30 kHz and 60-70 ℃ for 10-15 min. Then, deionized water, a weakly acidic cleaning agent, or a neutral cleaning agent are used sequentially for ultrasonic rinsing at 40-80 kHz and 50-60 ℃ for 5-10 min. Next, deionized water is used for ultrasonic fine cleaning at room temperature and >80 kHz for 5 min. Finally, the mixture is soaked in deionized water at 70-80 ℃ for 2-3 min and then dried.

10. The surface composite strengthening method for precipitation-hardening stainless steel high-pressure pipe quick couplings according to claim 1, characterized in that, In step S6, the PVD process temperature is 250-370 ℃; When using a Cr / CrN coating, after online processing in a PVD vacuum chamber, a Cr metal binder layer is deposited first, followed by a CrN transition layer. The thickness of the Cr metal binder layer is 0.1-0.3 μm, the thickness of the CrN transition layer is 3-6 μm, and the total coating thickness is 3.1-6.3 μm. When using a Cr / CrN / CrCN coating, after online processing in a PVD vacuum chamber, a Cr metal binder layer is deposited first, followed by a CrN transition layer, and finally a CrCN functional layer is deposited using a gradient method. The thickness of the Cr metal binder layer is 0.1-0.3 μm, the thickness of the CrN transition layer is 1-3 μm, and the thickness of the CrCN functional layer is 2-3 μm. The total coating thickness is 3-6 μm.

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