A processing method of a quick-change connector ring groove

Abstract

This invention discloses a method for processing the annular groove of a quick-connect coupling. This method addresses the structural characteristics of the annular groove in 15-5PH precipitation-hardening stainless steel quick-connect couplings. By reserving a sacrificial machining allowance, a shielding fixture with a homogenizing ring structure is used to cover the non-nitrided area. This homogenizing ring is an annular metal flange located at the end of the shielding window. Ion nitriding is performed, and a uniform closed nitrided layer is formed in the annular groove area through two stages of nitriding. After nitriding, the nitrided layer corresponding to the allowance on the outer surface is ground off, retaining only the nitrided layer in the annular groove and chamfered area. This invention achieves highly uniform wear-resistant strengthening of the annular groove and high corrosion resistance and high precision restoration of the outer surface with minimal removal allowance, while maintaining stable core hardness. It is suitable for precision mass production of quick-connect couplings and can be widely used in the production of high-reliability quick-connect couplings in aerospace, high-pressure hydraulic, and other fields.

Description

Technical Field

[0001] This invention belongs to the field of metal parts assembly and processing technology, and specifically relates to a processing method for a quick-change connector annular groove. Background Technology

[0002] Quick-connect couplings are widely used in high-pressure fluid systems, and their annular groove is a key structural element determining the seal's lifespan. This part is often made of 15-5PH stainless steel and undergoes nitriding treatment to improve the wear resistance of the sealing surface.

[0003] In the current manufacturing of quick-connect couplings, the coordination between machining and surface treatment processes has the following shortcomings: First, the finishing of the annular groove is usually completed before the nitriding process. This means that the stress concentration geometry, such as the small fillet at the root of the annular groove, is already formed before nitriding, and after nitriding, this area is covered by a complete high-hardness brittle layer. Under high-pressure service conditions, the stress concentration at the root of the annular groove caused by its structural shape acts directly on the brittle nitrided layer, leading to increased crack susceptibility and size effects.

[0004] Secondly, finishing after nitriding is limited to the non-annular groove area, while the nitrided layer remains in the annular groove area. This is because traditional machining methods worry that turning after nitriding will damage the dimensional accuracy or edge integrity of the annular groove, and therefore intentionally avoid remachining the nitrided annular groove. This directly results in the inability to remove or reduce the brittle risk of the nitrided layer at the root of the annular groove through mechanical cutting, thus losing the process window for solving the cracking problem using "machining".

[0005] Finally, the process route lacked a "pre-planning, then cutting off" process design. That is, no anti-seepage or excess material removal structure was proactively reserved for the annular groove during the roughing stage, nor was any fine finishing of the critical stress surfaces of the annular groove arranged after nitriding. These are deficiencies in manufacturing process route planning, not merely issues with nitriding process parameters.

[0006] Therefore, the nitrided layer of the quick-connect coupling annular groove manufactured by existing processes is highly susceptible to fatigue cracking under high-pressure alternating loads, with an average mating life of less than 5,000 cycles, severely restricting equipment maintenance cycles and reliability. Therefore, there is an urgent need to develop a manufacturing method that prevents cracking of the annular groove nitrided layer by addressing the machining process, allowance allocation, and cutting steps. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a processing method for quick-connect coupling ring grooves. By controlling the sequence and allowance of machining steps, a nitrided brittle layer is avoided at the root of the ring groove, thereby preventing cracking failure under high pressure conditions and improving the service life of the product.

[0008] The technical solution adopted in this invention is as follows: A method for machining a quick-connect coupling annular groove, wherein the quick-connect coupling part is made of 15-5PH precipitation hardening stainless steel and is rough-machined to the process dimensions to have an annular groove structure for sealing. Intermediate heat treatment: The 15-5PH quick-connect connector after rough machining is subjected to solution treatment and aging treatment to obtain a matrix structure with the target core strength and toughness matched; the core hardness of the quick-connect connector is controlled within the range of HRC30~39; Finishing: The outer circular mating surface of the quick-connect connector is pre-machined, and a sacrificial machining allowance greater than the expected nitriding influence layer depth is reserved on the outer circular mating surface; Local nitriding treatment is performed on the annular groove area: all non-nitrided surfaces of the quick-connect coupling are shielded using a tooling, exposing only the annular groove and the chamfered area within an adjacent 0.5mm range. The remaining non-nitrided areas, including the outer circular mating surface, are shielded. Nitriding is performed at a predetermined temperature, and selective nitriding treatment is applied to the exposed annular groove and chamfered area to form a continuous nitrided layer on the bottom surface of the annular groove, the sidewalls of the annular groove, and the chamfered area. The shielding tooling adopts a composite structure of physical shielding and plasma field shielding to reduce the sputtering and penetration effect of nitriding glow in the non-exposed areas. Post-processing: After nitriding, the sacrificial machining allowance of the outer mating surface and the surface layer affected by nitriding are removed to restore the outer mating surface to a state without nitriding layer, while retaining the nitriding layer structure of the annular groove and chamfer area.

[0009] Furthermore, the nitriding treatment is ion nitriding, with a nitriding temperature of 540–580°C, an ammonia flow rate of 900–1000 ml / min, and a nitriding holding time of 36–50 h.

[0010] Furthermore, near the exposed window of the annular groove, the shielding fixture forms a circumferential annular end flange or annular lip. This flange / lip extends towards the opening of the annular groove and maintains a gap of 0.5-2.0 mm with the groove opening. Its function is not to cover the annular groove, but to act as a homogenizing ring to prevent the electric field at the edge of the shielding window from becoming too sharp, reducing glow concentration at the groove opening and chamfer, and avoiding electric field concentration or glow unevenness at the groove, chamfer, and edge positions during local ion nitriding. The inner diameter of the annular flange is smaller than the outer diameter of the annular groove, causing the flange to overlap with the outer wall of the annular groove in the radial direction, with an overlap width ≥1 mm. This ensures that the thickness non-uniformity of the nitrided layer on the bottom surface, side walls, and chamfer of the annular groove after nitriding is ≤15%.

[0011] Furthermore, in step (3), the sacrificial machining allowance is 0.3 to 0.8 mm, preferably 0.5 mm.

[0012] Furthermore, before the nitriding treatment in step (4), the quick-connect parts are subjected to ultrasonic cleaning and surface activation treatment in sequence, and are loaded into the nitriding furnace within 2 hours after the activation treatment is completed.

[0013] Furthermore, in step (4), during the nitriding process, a voltage of 400-800V is used to raise the temperature to the set nitriding temperature in stages, and the heating rate is controlled at 50-80℃ / h to raise the temperature to the preset nitriding temperature. After nitriding, the temperature is cooled to below 150℃ and then removed from the furnace. Through the synergistic effect of the shielding fixture and the cathode bias electric field, the spatial distribution of the glow discharge plasma is reconstructed, so that the plasma active particles are preferentially concentrated in the bottom surface, side wall and chamfer area of ​​the sealing ring groove, and the outer circular mating surface is in a low nitrogen activity or ion deactivation area. The ion nitriding treatment is carried out in two stages. The first stage is the surface activation and initial nitriding stage, which increases the nitrogen potential to form a continuous initial nitrided layer; The second stage is the diffusion homogenization stage, which involves reducing the nitrogen potential or adjusting process parameters to reduce the brittleness of the white layer and promote uniform expansion of the diffusion layer. The solution treatment and aging process ensures that the 15-5PH material maintains its core hardness within the target range after nitriding and avoids strength reduction caused by over-aging.

[0014] Furthermore, after nitriding treatment in step (4), the surface hardness of the nitrided layer in the annular groove is HV620~1050, the thickness of the nitrided layer is ≥0.13mm, and the brittleness level is 1~2.

[0015] Further, the solution treatment in step (2) is carried out in accordance with the standard GJB8268-2014, with a solution temperature of 1038±15℃ and a holding time of not less than 1h. After cooling to room temperature with water, an aging treatment is carried out with an aging temperature of 550~600℃ and a holding time of 4~6h.

[0016] Furthermore, the nitriding and heat preservation process in step (4) is divided into two stages: the heat preservation time in the first stage is 18-28 hours, and the ammonia decomposition rate is controlled at 20%-30%; the heat preservation time in the second stage is 18-22 hours, and the ammonia decomposition rate is controlled at 40%-60%. After nitriding treatment, the hardness of the nitrided layer in the annular groove exhibits a gradient distribution from the surface to the substrate. The hardness in the surface layer is HV800-1050 in the depth range of 0-0.03 mm, the hardness is HV700-800 in the depth range of 0.03-0.08 mm, and the hardness from the depth below 0.08 mm to the interface of the nitrided layer is HV620-700.

[0017] The first stage is the surface activation and initial nitriding stage of the annular groove, which uses a higher glow intensity, a higher ammonia flow rate, and a higher nitrogen potential to form a continuous initial nitrided layer on the bottom surface, sidewalls, and chamfered area of ​​the annular groove. The second stage is the diffusion homogenization stage, which reduces the nitrogen potential or adjusts the pressure, voltage, and temperature to allow the nitrided layer to diffuse inward and reduce the brittleness of the white bright layer. Finally, a continuous wear-resistant nitrided layer is formed in the annular groove and chamfered area, while the core hardness is maintained within the target range.

[0018] Under the condition that the plasma spatial distribution is controlled, selective ion nitriding is performed on the sealing ring groove and the chamfered area to form a continuous closed nitrogen diffusion gradient functional layer structure, wherein a chemical layer is formed on the surface and a diffusion layer is formed at the bottom; after nitriding is completed, the outer circle sacrificial processing layer and the surface layer affected by low-intensity nitrogen activation are removed to restore the outer circle mating surface to the unnitrided metal state, while maintaining the integrity of the closed nitrided functional layer structure of the sealing ring groove.

[0019] This invention optimizes the stress distribution of the shell during the pressure test by adjusting the processing sequence, reserving a sacrificial machining allowance on the outer cylindrical mating surface before nitriding, and removing the allowance and the affected nitrided layer by mechanical grinding after nitriding, so that the outer cylindrical mating surface is restored to a nitrided-free state, leaving only the nitrided layer of the annular groove and the chamfers at both ends, thereby making the joint in the best stress state. Meanwhile, by matching the process parameters of the local shielding ion nitriding process, a gradient nitriding layer with high hardness and low brittleness is obtained in the annular groove, which significantly reduces the stress concentration and cracking tendency at the root of the annular groove. This effect is the result of the combined effects of physical shielding, bias electric field, and homogenization ring. By combining machining allowance, heat treatment process and nitriding removal process, this invention enables the surface hardness of quick-connect couplings to reach HV620~1050, core hardness to reach HRC30~39, the nitrided layer of the annular groove to be intact and crack-free, fatigue life to be greatly extended, the process to be stable, and it is suitable for mass production.

[0020] Beneficial effects:

[0021] (1) By setting an annular metal flange (homogenization ring) at the end of the shielding fixture window and precisely controlling its axial gap with the opening end face of the annular groove to be 0.5-2.0 mm, and using this flange as part of the cathode potential, the electric field distribution at the groove opening, sidewalls and chamfers of the annular groove is effectively homogenized, suppressing glow concentration or discharge shielding caused by abrupt changes in geometry. After testing, the non-uniformity of the nitrided layer thickness at the bottom surface, sidewalls and chamfers of the annular groove after treatment can be controlled within ≤15%, and the surface hardness deviation is ≤HV80, ensuring that the entire surface of the annular groove obtains a continuous and uniform wear-resistant reinforcement layer, avoiding early wear caused by excessively thin local nitrided layers or peeling caused by excessively thick local nitrided layers.

[0022] (2) This invention fundamentally changes the stress distribution pattern between the nitrided layer and the matrix in the traditional process by designing a processing procedure of "pre-nitriding with a pre-sacrificial machining allowance → local nitriding → mechanical removal of the allowance after nitriding". The nitrided layer on the outer circular mating surface is completely removed, leaving only the nitrided layer at the designed position of the annular groove. This causes the stress concentration area of ​​the joint under high pressure conditions to be spatially misaligned with the brittle nitrided layer, significantly reducing the risk of crack initiation from the machining stage.

[0023] (3) In the processing method, by performing specific solid solution aging pretreatment on 15-5PH material and matching the process parameters of local nitriding, a nitrided layer with high hardness and low brittleness is obtained in the ring groove, breaking through the traditional 15-5PH nitriding temperature limit, the brittleness level of the nitrided layer reaches level 1 to 2, and the surface hardness and core toughness are well coordinated.

[0024] (4) Due to the adoption of the above-mentioned process combination of "pre-reserved allowance + post-nitriding finishing removal", the residual stress introduced during the processing is effectively controlled, and the integrity of the nitrided layer in the annular groove is guaranteed. The pressure resistance and crack spalling resistance of the prepared quick-connect coupling products are significantly improved, and the fatigue life is increased by more than 200% compared with traditional process products, which can meet the long-term use requirements of high reliability conditions.

[0025] (5) Through a specific solution treatment and aging process, the parts achieve a stable target core hardness before nitriding, and the core hardness does not decrease abnormally during the subsequent two-stage ion nitriding process, remaining within the range of 35-45 HRC, thus avoiding the loss of matrix strength due to over-aging. At the same time, the surface hardness of the nitrided layer in the annular groove reaches HV620-1050, the nitriding depth is ≥0.13mm, and the brittleness level is 1-2, realizing the integrated manufacturing of the parts with "high toughness and corrosion resistance in the outer circle and high hardness and wear resistance in the annular groove".

[0026] (6) This invention organically integrates shielding tooling structure design, plasma field control and precision removal processing into a closed-loop process chain. It ensures the outer circle recovery effect by controlling the spatial distribution of the electric field rather than relying on a significant increase in the processing allowance. This not only saves the consumption of valuable materials and processing time, but also ensures that the allowance of the precision recovery processing of the outer circle is highly controllable and the dimensions are stable. It is particularly suitable for the batch pre-production of parts such as quick-change connectors that have strict requirements for the precision of the sealing mating surface. Detailed Implementation

[0027] The exemplary embodiments will now be described in full. However, the exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make the invention more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art. The processing method of the present invention is further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the specific parameters of the embodiments. All schemes that adopt the process design concept of the present invention are within the scope of protection.

[0028] Example 1: This embodiment describes the machining of a quick-connect coupling for an aviation hydraulic system. The material is 15-5PH precipitation-hardening stainless steel. The part includes a sealing ring groove. Part name: outer shell, mating outer diameter Φ26f8, ring groove R2.25, chamfer R1.5±0.1, material: 15-5PH. The specific machining steps are as follows: Rough machining: Roughly machine the shape according to the dimensions of the part drawing, leaving a 1mm allowance for finishing; Intermediate heat treatment: Solution treatment was carried out according to GJB8268-2014 standard, with a solution temperature of 1040℃, a holding time of 1.5h, and water cooling to room temperature; then aging treatment was carried out, with an aging temperature of 580℃, a holding time of 4h, and air cooling. The core hardness of the part was tested to be HRC35. Finishing: Chamfer the annular groove and both ends to the final dimensions R2.25 and R1.5±0.1, and leave a machining allowance of 0.5mm on the outer surface to Φ26.5±0.1; Nitriding pretreatment: The oil stains on the surface of the parts are removed by ultrasonic cleaning in sequence, the surface to be nitrided is activated, the passivation film is removed, and the parts are placed in the nitriding furnace within 1.5 hours after activation. Localized nitriding: High-temperature resistant anti-seepage fixtures are used to shield all non-nitrided surfaces, exposing only the annular groove and the chamfered ends. The gap between the flange end face of the fixture and the opening end face of the annular groove is 1.2mm. Ion nitriding is performed at 560℃ under conditions of 600V voltage and a heating rate of 60℃ / h, with two-stage heat preservation: the first stage is 24h (ammonia flow rate 950ml / min, decomposition rate 25%), and the second stage is 20h (ammonia flow rate 950ml / min, decomposition rate 50%). The furnace pressure is maintained at 650Pa. After nitriding, the furnace is cooled to 120℃ before being removed from the furnace. Post-processing: Fine grinding of the outer cylindrical surface completely removes the nitriding layer corresponding to the reserved 0.5mm allowance, leaving only the nitriding layer in the annular groove and chamfer area; Since a 0.5mm sacrificial machining allowance was reserved on the outer cylindrical surface before nitriding and completely removed by grinding after nitriding, the mating surface of the outer cylindrical surface is restored to a state without nitriding layer, effectively eliminating the additional stress that the nitriding layer in this area may introduce. Complete the remaining machining processes and performance testing.

[0029] The test results of the quick-connect coupling prepared in this embodiment are as follows: no cracks or damage were found on the surface of the parts after flaw detection. The surface hardness of the nitrided layer in the annular groove is HV820, the thickness of the nitrided layer is 0.15mm, and the brittleness level is 1. Pressure resistance test procedure: Connect the shell to the process component, the connection pressure is 32.5 MPa, connect ≥3 times, and hold the pressure for 10 minutes each time. There should be no problems such as cracking of the nitrided layer after the connection is completed. Life test procedure: docking life pressure: 21.7MPa, docking ≥15000 times without nitriding layer cracking or other problems; Other test procedures: Pressure pulse, vibration durability, acceleration and other tests were conducted as required, and all requirements were met.

[0030] The quick-connect couplings produced by the above processing method have an intact and non-peeling nitrided layer in the annular groove, and no cracks are generated after the pressure test. The fatigue life is more than twice that of the traditional local nitriding process.

[0031] Example 2:

[0032] This embodiment verifies the technical effect of the lower limit of the parameter range of this patent. The experimental subject is a 15-5PH precipitation-hardening stainless steel quick-connect coupling, and the processing steps are as follows: Rough machining: Roughly machine the shape according to the dimensions of the part drawing, leaving a 1mm allowance for finishing; Intermediate heat treatment: Solution treatment was performed according to GJB 8268-2014 standard, with a solution temperature of 1038℃ and a holding time of 1.5h, followed by water cooling to room temperature; then aging treatment was performed, with an aging temperature of 580℃ and a holding time of 5h, followed by air cooling. The core hardness of the part was tested and found to be HRC33, which meets the requirements. Finishing: Chamfer the annular groove and both ends with 0.5mm to the final design size, and leave a machining allowance of 0.5mm on the outer circle surface; Nitriding pretreatment: Ultrasonic cleaning is used to remove oil stains from the surface of the parts, the surface to be nitrided is activated, the passivation film is removed, and the parts are placed in the nitriding furnace within 1.2 hours after activation. Localized nitriding: All non-nitriding surfaces are shielded using anti-seepage fixtures, exposing only the annular groove and the chamfered areas at both ends. The gap between the flange end face of the fixture and the opening end face of the annular groove is 2mm. After being loaded into the nitriding furnace, the temperature is increased to 540℃ at a rate of 50℃ / h. The heat preservation process is divided into two stages: the first stage is heat preservation for 18h, with an ammonia flow rate of 850ml / min, controlling the ammonia decomposition rate at 20%, and maintaining the furnace pressure at 500Pa; the second stage is heat preservation for 18h, with an ammonia flow rate of 850ml / min, controlling the ammonia decomposition rate at 40%, and maintaining the furnace pressure at 500Pa; after nitriding is completed, the furnace is cooled to 140℃ before being removed from the furnace. Post-processing: Fine grinding of the outer cylindrical surface completely removes the reserved 0.5mm machining allowance, leaving only the nitrided layer on the annular groove and chamfered area.

[0033] Performance test results: The thickness of the nitrided layer in the annular groove is 0.13 mm. The surface layer has a hardness of HV802 at a depth of 0 to 0.03 mm, HV715 at a depth of 0.03 to 0.08 mm, and HV625 at a depth of 0.08 mm to the interface of the nitrided layer. The brittleness level of the nitrided layer is 2. Pressure resistance test procedure: Connect the shell to the process component, the connection pressure is 32.5 MPa, connect ≥3 times, and hold the pressure for 10 minutes each time. There should be no problems such as cracking of the nitrided layer after the connection is completed. Life test procedure: docking life pressure: 21.7MPa, docking ≥15000 times without nitriding layer cracking or other problems; Other test procedures: Pressure pulse, vibration durability, acceleration and other tests were conducted as required, and all requirements were met.

[0034] The results show that by reserving a machining allowance for the outer diameter and thoroughly grinding it away after nitriding, the additional stress caused by the nitrided layer on the outer diameter is effectively eliminated, enabling the machining method of the present invention to still achieve excellent crack resistance under the lower limit of parameters.

[0035] Example 3:

[0036] The experimental subject was the same model 15-5PH quick-connect connector, and the processing steps were as follows: Rough machining: Roughly machine the shape according to the dimensions of the part drawing, leaving a 1mm allowance for finishing; Intermediate heat treatment: Solution treatment was performed according to GJB 8268-2014 standard, with a solution temperature of 1053℃. After holding at this temperature for 1 hour, the solution was water-cooled to room temperature. Subsequently, aging treatment was performed at an aging temperature of 600℃. After holding at this temperature for 4 hours, the solution was air-cooled. The core hardness of the part was tested and found to be HRC31, which meets the requirements. Finishing: Chamfer the annular groove and both ends with 0.5mm to the final design size, and leave a machining allowance of 0.7mm on the outer circle surface; Nitriding pretreatment: Ultrasonic cleaning is used to remove oil stains from the surface of the parts, the surface to be nitrided is activated, the passivation film is removed, and the parts are placed in the nitriding furnace within 2 hours after activation. Localized nitriding: All non-nitriding surfaces are shielded using anti-seepage tooling, exposing only the annular groove and the chamfered areas at both ends. After being loaded into the nitriding furnace, the temperature is increased to 580℃ at a rate of 80℃ / h. The heat preservation process is divided into two stages: the first stage is heat preservation for 28 hours, with an ammonia flow rate of 1050ml / min, controlling the ammonia decomposition rate at 30%, and maintaining the furnace pressure at 800Pa; the second stage is heat preservation for 22 hours, with an ammonia flow rate of 1050ml / min, controlling the ammonia decomposition rate at 60%, and maintaining the furnace pressure at 800Pa. After nitriding is completed, the furnace is cooled to 120℃ before being removed from the furnace. Post-processing: Fine grinding of the outer cylindrical surface completely removes the reserved 0.7mm machining allowance, leaving only the nitrided layer on the annular groove and chamfered area.

[0037] Performance test results: The thickness of the nitrided layer in the ring groove is 0.14 mm. The hardness of the surface layer at a depth of 0-0.03 mm is HV1042, the hardness at a depth of 0.03-0.08 mm is HV796, and the hardness from a depth of 0.08 mm to the interface of the nitrided layer is HV698. The brittleness level of the nitrided layer is 2. Pressure resistance test procedure: Connect the shell to the process component, the connection pressure is 32.5 MPa, connect ≥3 times, and hold the pressure for 10 minutes each time. There should be no problems such as cracking of the nitrided layer after the connection is completed. Life test procedure: docking life pressure: 21.7MPa, docking ≥15000 times without nitriding layer cracking or other problems; Other test procedures: Pressure pulse, vibration durability, acceleration and other tests were conducted as required, and all requirements were met.

[0038] The results show that even under the upper limit of parameters, by reserving a machining allowance for the outer circle and completely grinding it away after nitriding, the additional stress introduced by the nitrided layer on the outer circle can still be effectively eliminated, so that the product can obtain high surface hardness while maintaining excellent crack resistance, further verifying the core role of the machining process design.

[0039] Comparative Example 1: The same type of quick-connect coupling was processed using traditional methods. No sacrificial machining allowance was left on the outer circular surface before nitriding. Both the annular groove and the outer circle were machined to their final dimensions before localized nitriding. After nitriding, a waterproofing fixture was used to shield the outer circular surface. Other process parameters were the same as in Example 1. Test results: The surface hardness of the nitrided layer in the annular groove was HV790, the nitrided layer thickness was 0.14 mm, and the brittleness level was 2. Cracking of the nitrided layer in the annular groove occurred after holding the pressure for 8 minutes in a 32.5 MPa pressure test, and the coupling life was only 4300 cycles.

[0040] This comparative example shows that even with the same nitriding parameters, if the processing procedure of "leaving a margin + removing after nitriding" is not adopted, the nitrided layer on the outer circle mating surface will introduce additional stress, resulting in a significant decrease in the crack resistance of the ring groove.

[0041] Comparative Example 2: This comparative example only adjusts the nitriding parameters without changing the processing steps. In the processing steps, no sacrificial processing allowance is left on the outer cylindrical surface (same as Comparative Example 1). Only the ammonia decomposition rate in the nitriding and heat preservation stage is adjusted to: 15% in the first stage and 65% in the second stage. The remaining processing steps are the same as in Example 1.

[0042] Performance test results: The surface hardness of the nitrided layer in the annular groove is HV1120, and the brittleness level is 3; the nitrided layer in the annular groove cracked after holding the pressure for 8 minutes in a 32.5MPa pressure test, and the butt joint life was only 5200 cycles.

[0043] This comparative example shows that even if the surface hardness is significantly increased by adjusting the nitriding parameters, the brittleness of the nitrided layer actually increases and the cracking problem cannot be solved if the process design of "leaving a margin + post-nitriding removal" is not adopted. This proves that the core contribution of this invention lies in the improvement of the processing procedure, rather than simply the optimization of nitriding parameters.

[0044] As can be seen from the above embodiments and comparative examples, the quick-connect couplings manufactured using the processing method of the present invention, which involves "reserving a margin – local nitriding – shielding tooling – post-nitriding finishing," achieve a nitrided layer thickness of 0.14 mm in the annular groove, a surface hardness of HV1042 with a progressively decreasing trend, and a stable brittleness level of 2. In pressure tests, they achieve ≥3 cycles / 10 minutes without cracking, and a fatigue life exceeding 15,000 cycles without failure. These results demonstrate that the processing method of the present invention fundamentally improves the stress state of the annular groove through process combinations, significantly enhancing the product's crack resistance and service reliability.

[0045] It should be noted that this invention employs a staged process to control the ammonia decomposition rate in the local nitriding step. The first stage forms a continuous initial nitrided layer under low decomposition rate (high nitrogen potential). The second stage increases the decomposition rate (decreases nitrogen potential), shifting the nitriding process from rapid growth of the surface compound layer to deepening of the diffusion layer, thereby controlling the effective hardened layer depth to be no less than 0.13 mm. The selection of these process parameters is coordinated with the aforementioned processing steps to ensure that after subsequent finishing to remove the outer diameter allowance, the annular groove area retains a complete, low-brittle nitrided functional layer.

[0046] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, are all covered within the scope of the claims of the present invention.

Claims

1. A method for machining the annular groove of a quick-connect coupling, characterized in that: (1) Quick-connect coupling parts are made of 15-5PH precipitation hardening stainless steel and are rough machined to the process dimensions to have annular groove structure for sealing; (2) Intermediate heat treatment: The 15-5PH quick-connect connector after rough machining is subjected to solution treatment and aging treatment to obtain a matrix structure with matching core strength and toughness. (3) Finishing: The outer circular mating surface of the quick-connect connector is pre-machined, and a sacrificial machining allowance greater than the expected nitriding influence layer depth is reserved on the outer circular mating surface; the sacrificial machining allowance is 0.3 to 0.8 mm; (4) Local nitriding treatment of the annular groove area: The tooling is used to shield all non-nitrided surfaces of the quick-connect connector, exposing only the annular groove and the chamfered area within an adjacent 0.5mm range. The remaining non-nitrided areas, including the outer circular mating surface, are shielded. Nitriding is performed at a predetermined temperature, and selective nitriding treatment is performed on the exposed annular groove and chamfered area to form a continuous nitrided layer on the bottom surface of the annular groove, the side wall of the annular groove, and the chamfered area. The tooling adopts a composite structure of physical shielding and plasma field shielding to reduce the sputtering and penetration effect of nitriding glow in the non-exposed area. (5) Post-treatment: After nitriding, the sacrificial machining allowance of the outer circle mating surface and the surface layer affected by nitriding are removed to restore the outer circle mating surface to a state without nitriding layer, while retaining the nitriding layer structure of the annular groove and chamfer area.

2. The method for processing the quick-connect coupling annular groove according to claim 1, characterized in that, The nitriding treatment described in step (4) is ion nitriding, with a nitriding temperature of 540-580℃, an ammonia flow rate of 900-1000 ml / min, a nitriding holding time of 36-50 h, a voltage of 400-800 V, and a staged heating method to reach the set nitriding temperature. The heating rate is controlled at 50-80℃ / h to reach the preset nitriding temperature. After nitriding is completed, the furnace is cooled to below 150℃ before being removed from the furnace.

3. The method for processing the quick-connect coupling annular groove according to claim 1, characterized in that, The shielding fixture described in step (4) has an annular end flange extending circumferentially at one end near the exposed window of the annular groove. The annular end flange extends toward the opening of the annular groove and maintains an axial gap of 0.5 to 2.0 mm with the opening end face of the annular groove, thus forming a homogenization ring structure.

4. The method for processing the quick-connect coupling annular groove according to claim 1, characterized in that, In step (3), the preferred allowance for sacrificial machining is 0.5 mm.

5. The method for processing the quick-connect coupling annular groove according to claim 1, characterized in that, Before nitriding in step (4), the quick-connect parts are subjected to ultrasonic cleaning and surface activation treatment in sequence. After activation treatment, they are placed in the nitriding furnace within 2 hours.

6. The method for processing the quick-connect coupling annular groove according to claim 1, characterized in that, After nitriding treatment in step (4), the surface hardness of the nitrided layer in the annular groove is HV620~1050, the thickness of the nitrided layer is ≥0.13mm, and the brittleness level is 1~2.

7. The method for processing the quick-connect coupling annular groove according to claim 1, characterized in that, The solution treatment in step (2) shall be carried out in accordance with the standard GJB8268-2014. The solution temperature is 1038±15℃ and the holding time is not less than 1h. After cooling to room temperature, the aging treatment shall be carried out. The aging temperature is 550~600℃ and the holding time is 4~6h.

8. The method for processing the quick-connect coupling annular groove according to claim 2, characterized in that, The nitriding and heat preservation process in step (4) is divided into two stages: the first stage heat preservation time is 18-28h, and the ammonia decomposition rate is controlled at 20%-30%; the second stage heat preservation time is 18-22h, and the ammonia decomposition rate is controlled at 40%-60%.