Metal valve composite hard sealing surface layer treatment process

Abstract

According to the treatment process for the composite hard sealing surface layer of the metal valve, the QPQ treatment process is adopted, so that the composite hard sealing layer formed on the surface of the sealing ring of the metal valve has excellent hardness, wear resistance and corrosion resistance, the sealing performance of the valve is remarkably improved, and the service life of the valve is remarkably prolonged. Specifically, the diffusion layer enhances the hardness and strength of the valve sealing ring base body, the nitrogen compound layer provides good wear resistance and corrosion resistance, and the metal oxide layer further improves the hardness and corrosion resistance of the surface, so that a multi-layer and multifunctional composite hard sealing structure is formed.

Description

Technical Field

[0001] This invention relates to valve sealing ring processing technology, specifically to a surface layer processing technology for composite hard seals on metal valves. Background Technology

[0002] In existing technologies, metal valves play a crucial role in industrial production, and their sealing performance directly affects the stability and safety of the entire system. However, traditional valve sealing processes often fail to meet the requirements of high hardness, high wear resistance, and high corrosion resistance, leading to problems such as leakage and wear during valve use. Summary of the Invention

[0003] In view of this, the present invention provides a surface layer treatment process for composite hard seals on metal valves.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A surface treatment process for a composite hard seal on a metal valve, wherein the composite hard seal surface layer is located on the valve sealing ring, and the composite hard seal surface layer includes a diffusion layer, a nitrogen compound layer, and a metal oxide layer arranged sequentially from the inside to the outside. The surface treatment process for the composite hard seal surface layer includes a Stellite alloy spraying process and a QPQ treatment process. The QPQ treatment process includes the following steps: Step 1: Pretreatment. The valve sealing ring coated with Stellite alloy is activated by sandblasting or immersed in hydrochloric acid to break the Stellite layer. Passivation film; Step 2: Preheating. Heat the pretreated valve sealing ring to 450-480℃ for 60-90 minutes. Step 3: Medium-temperature nitriding. The preheated valve sealing ring is placed in a nitriding furnace for nitriding treatment. The nitriding temperature is 580℃~600℃, the nitriding time is 120min~240min, and the concentration of the nitriding agent CNO in the nitriding furnace is 30~35%. Step 4: First oxidation: The valve sealing ring that has undergone medium-temperature carburizing is subjected to heating oxidation at a temperature of 400-450℃ for 15-20 minutes. Step 5: Polishing. The valve seal ring that has undergone one oxidation step is mechanically or electrolytically polished. Step Six: Secondary Oxidation Heating. The polished valve sealing ring is subjected to secondary oxidation heating at a temperature of 420-480℃ for 30-60 minutes. Step 7: Aging treatment. The valve sealing ring that has completed secondary oxidation is subjected to aging treatment. The aging treatment temperature is 180-200℃ and the aging treatment time is 120-180min. Step 8: Sealing. Immerse the aging-treated valve sealing ring in a silane coupling agent solution at room temperature for 30 minutes. After immersion, heat to 150°C and cure for 1 hour; or immerse the aging-treated valve sealing ring in hot oil at 80-100°C for 30 minutes.

[0005] Preferably, in the QPQ process, during the heating of the valve sealing ring, the heating rate is ≤5℃ / min, and during the cooling of the valve sealing ring, it is furnace cooled to <300℃ and then air cooled.

[0006] Preferably, salt bath activity adjustment can be performed between steps three and four, by adding a rare earth oxidant during the intermediate-temperature nitriding process. The rare earth oxidant is... The rare earth oxidant The molar percentage in the solution is 0.5%.

[0007] Preferably, the metal oxide layer is made of , and The nitrogen compound layer is composed of CrN, and The diffusion layer is a supersaturated solid solution formed by nitrogen atoms dissolved in a cobalt matrix.

[0008] Preferably, the composite hard seal surface layer is located on the inner surface of the valve sealing ring.

[0009] Preferably, in the first oxidation heating process of step four, a thin oxide film is formed on the valve sealing ring after heating to 400°C.

[0010] The beneficial effects of this invention are as follows: the combination of Stellite alloy spraying and QPQ treatment processes fully leverages the advantages of both. Stellite alloy spraying provides excellent basic material properties for the valve sealing ring, while the QPQ treatment process further optimizes the microstructure and performance of the surface layer. Specifically, the diffusion layer, nitrogen compound layer, and metal oxide layer in the composite hard seal layer work synergistically. The diffusion layer, as the transition area between the substrate and the surface layer, effectively transfers stress and enhances the overall bonding strength. The nitrogen compound layer, with its high hardness and good wear resistance, resists particle wear and mechanical friction in the medium. The metal oxide layer, with its excellent corrosion resistance, blocks the erosion of the valve sealing ring by corrosive media. Together, these three elements construct a protective barrier, significantly improving the sealing performance of the valve sealing ring and greatly extending its service life. This multi-layered, multi-functional composite hard seal structure enables metal valves to maintain stable sealing performance even under harsh operating conditions, greatly reducing system failures and production losses caused by leakage, while extending the valve's service life and reducing equipment maintenance costs and replacement frequency, resulting in significant economic and social benefits. Attached Figure Description

[0011] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0012] Appendix Figure 1 A 3000x scanning electron microscope image of the composite hard seal surface layer; Appendix Figure 2 A 10,000x scanning electron microscope image of the composite hard seal surface layer; Appendix Figure 3 A 1000x scanning electron microscope image of the composite hard seal surface layer; Appendix Figure 4 A 1000x scanning electron microscope image of the composite hard-sealed interface; Appendix Figure 5 For the appendix Figure 4 The results of energy dispersive spectroscopy analysis; Appendix Figure 6 For the appendix Figure 4 The results of the elemental surface scan analysis. Detailed Implementation

[0013] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] The present invention will now be further described with reference to the accompanying drawings.

[0015] This invention provides the following technical solution: According to the appendix Figure 1-6 As shown, this invention discloses a surface treatment process for a composite hard seal on a metal valve. The composite hard seal surface layer is located on the valve sealing ring and includes a diffusion layer, a nitrogen compound layer, and a metal oxide layer arranged sequentially from the inside out. The surface treatment process for the composite hard seal surface layer includes a Stellite alloy spraying process and a QPQ treatment process. The QPQ treatment process includes the following steps: Step 1: Pretreatment. The valve sealing ring coated with Stellite alloy is activated by sandblasting or immersed in hydrochloric acid to break the Stellite layer. Passivation film; specifically, in this step, sandblasting activation or hydrochloric acid immersion can effectively remove the passivation film on the Stellite alloy layer. The passivation film provides a good surface condition for subsequent processing steps. Sandblasting activation uses high-speed abrasive particles to impact the valve seal surface, removing surface dirt and oxide layers, increasing surface roughness, and improving the adhesion between the coating and the substrate. Hydrochloric acid immersion utilizes the chemical action of hydrochloric acid to... The passivation film reacts, dissolving and removing it. Both methods can achieve the desired removal. The purpose of passivation membranes is to improve penetration efficiency.

[0016] Step Two: Preheating. Heat the pretreated valve sealing ring to 450-480℃ for 60-90 minutes. Specifically, the main purpose of preheating in this step is to bring the valve sealing ring to a suitable temperature range for subsequent nitriding treatment, ensuring the uniformity and efficiency of the nitriding process. During preheating, the microstructure inside the valve sealing ring will undergo certain adjustments, which is beneficial for the diffusion and penetration of nitrogen atoms.

[0017] Step 3: Medium-temperature nitriding. The preheated valve sealing ring is placed in a nitriding furnace for nitriding treatment. The nitriding temperature is 580℃~600℃, and the nitriding time is 120min~240min. The concentration of the nitriding agent CNO in the nitriding furnace is 30~35%. Specifically, in this step, the nitriding treatment involves placing the valve sealing ring in an atmosphere containing active nitrogen atoms, allowing nitrogen atoms to penetrate into the surface layer of the valve sealing ring and form a nitrogen compound layer. Controlling the nitriding temperature within the range of 580℃~600℃ ensures that nitrogen atoms can fully diffuse into the matrix of the valve sealing ring, while avoiding excessively high temperatures that could degrade material properties, and promotes the Co-N reaction, extending the time to compensate for the low diffusion rate. The nitriding time is chosen to maximize efficiency and minimize energy consumption while ensuring the nitriding effect. The concentration of the nitriding agent CNO is controlled at 30~35%. This concentration range provides sufficient active nitrogen atoms to promote the nitriding reaction, while avoiding a decrease in the quality of the nitrided layer due to excessive concentration or a poor nitriding effect due to excessively low concentration.

[0018] Step 4: Primary oxidation. The valve sealing ring, after medium-temperature carburizing, undergoes heating oxidation at 400-450℃ for 15-20 minutes. Specifically, in this step, the primary oxidation temperature and time are controlled within the ranges of 400-450℃ and 15-20 minutes, respectively, because... It has strong self-protection properties, so micropores can be replenished through short-term oxidation, and a dense layer can also be formed. This thin film not only has excellent antioxidant properties, but also effectively prevents further oxidation reactions, protecting the valve seal from corrosion by the high-temperature oxidizing environment.

[0019] Step 5: Polishing. The valve sealing ring, after the first oxidation, is then mechanically or electrolytically polished. Specifically, in this step, when using mechanical polishing, Ra ≤ 0.2 μm is required to obtain a smoother surface, reducing surface roughness and facilitating subsequent secondary oxidation. Electrolytic polishing, on the other hand, further refines the surface microstructure through electrochemical action, improving surface quality. Polishing not only enhances the appearance of the valve sealing ring but, more importantly, removes minute defects and impurities formed during the first oxidation process, providing a good surface foundation for subsequent secondary oxidation heating.

[0020] Step Six: Perform secondary oxidation heating on the polished valve sealing ring at a temperature of 420-480℃ for 30-60 minutes. Specifically, the main purpose of this secondary oxidation heating in this step is to strengthen the sealing ring. The membrane improves corrosion resistance and makes The film is more uniform and dense, enhancing the hardness and wear resistance of the valve seal. During the secondary oxidation process, the selection of heating temperature and time is equally crucial, ensuring... The membrane needs to be sufficiently strengthened, but excessively high temperatures and prolonged oxidation times must be avoided to prevent a decline in the performance of the valve sealing ring matrix. Therefore, the secondary oxidation temperature is controlled within the range of 420-480℃, a temperature range that ensures... The membrane's strengthening effect is achieved while avoiding adverse effects on the valve sealing ring substrate. The heating oxidation time is selected between 30-60 minutes to ensure... The uniformity and density of the membrane improves processing efficiency; during the secondary oxidation process, the surface of the valve sealing ring... The film is further strengthened, forming a harder, more wear-resistant, and corrosion-resistant surface layer.

[0021] Step Seven: Aging Treatment. The valve sealing ring, after secondary oxidation, undergoes aging treatment at a temperature of 180-200℃ for 120-180 minutes. Specifically, in this step, aging treatment is crucial for eliminating internal stress and stabilizing the bonding force between the nitride phase, oxide layer, and matrix. During aging, the microstructure inside the valve sealing ring is adjusted, and the bonding force between the nitride phase, oxide layer, and matrix is ​​enhanced, thereby improving overall hardness and wear resistance. Simultaneously, aging treatment effectively eliminates internal stress generated in previous treatment steps, preventing deformation or cracking of the valve sealing ring due to stress concentration during use. Controlling the aging temperature within the range of 180-200℃ and the time within 120-180 minutes ensures optimal aging results, preventing material performance degradation due to excessively high temperatures or long times, and avoiding negative effects from excessively low temperatures or short times.

[0022] Step 8: Sealing. Immerse the aged valve sealing ring in a silane coupling agent solution at room temperature for 30 minutes, followed by heating to 150℃ and curing for 1 hour; or immerse the aged valve sealing ring in hot oil at 80-100℃ for 30 minutes. Specifically, in this step, when using silane coupling agent sealing, the silane coupling agent can penetrate into the tiny pores on the surface of the valve sealing ring, reacting chemically with the surface metal oxide layer to form chemical bonds, thereby improving the surface sealing and corrosion resistance. Heating and curing further promote the bonding between the silane coupling agent and the metal oxide layer, enhancing the stability and durability of the sealing layer. When using hot oil sealing, the hot oil can penetrate into the tiny pores on the surface of the valve sealing ring, filling the pores and forming a dense sealing layer, effectively preventing the erosion of external media. At the same time, hot oil also has a certain lubricating effect, which can reduce friction and wear of the valve sealing ring during use and extend its service life.

[0023] Furthermore, in the QPQ processing, during the heating of the valve sealing ring, the heating rate is ≤5℃ / min, and during the cooling of the valve sealing ring, it is furnace cooled to <300℃ and then air cooled. Specifically, in this embodiment, because Stellite alloy has low thermal conductivity and high thermal stress sensitivity, excessively rapid heating or cooling can easily cause microcracks. Therefore, the heating rate is set to ≤5℃ / min; the cooling method is furnace cooling to <300℃ followed by air cooling, avoiding water cooling or air cooling, to ensure that the valve sealing ring is heated evenly during the heating and cooling process, reducing the generation of thermal stress, preventing defects such as microcracks caused by excessive thermal stress, thereby ensuring the overall performance and service life of the valve sealing ring.

[0024] Furthermore, salt bath activity adjustment can be performed between steps three and four, by adding a rare earth oxidant during the intermediate-temperature nitriding process. The rare earth oxidant is... The rare earth oxidant The molar percentage in the solution is 0.5%. Specifically, in this embodiment, by adding a rare earth catalyst to the nitriding salt bath, the passivation film on the surface of the Stellite alloy can be destroyed, thereby increasing the decomposition activity of cyanate (CNO⁻). Experiments show that adding 0.5% CeCl₃ increases the nitriding rate of Stellite 21 by 40% and significantly improves the uniformity of the compound layer.

[0025] Furthermore, the metal oxide layer is composed of , and The nitrogen compound layer is composed of CrN, and The diffusion layer is composed of a supersaturated solid solution formed by nitrogen atoms dissolved in a cobalt matrix. Specifically, in this embodiment, the metal oxide layer is composed of... , and The composition gives the valve sealing ring surface excellent oxidation and corrosion resistance, enabling it to withstand the erosion of high temperatures and corrosive media. Nitrogen compound layer CrN, and The formation of this layer further improves the hardness and wear resistance of the valve sealing ring, enhancing its surface mechanical properties. Meanwhile, the diffusion layer, as a supersaturated solid solution formed by nitrogen atoms dissolved in the cobalt matrix, not only strengthens the matrix's properties but also provides solid support for the metal oxide and nitrogen compound layers.

[0026] Furthermore, the composite hard seal surface layer is located on the inner surface of the valve sealing ring. Specifically, in this embodiment, placing the composite hard seal surface layer on the inner surface of the valve sealing ring maximizes its sealing performance and wear resistance. During valve operation, the inner surface of the sealing ring is in close contact with the valve seat, bearing the effects of medium pressure and friction. Therefore, the composite hard seal surface layer treatment process provided by this invention can significantly improve the service life and sealing effect of the valve sealing ring, ensuring stable valve operation.

[0027] Furthermore, in the primary oxidation heating process of step four, a thin oxide film is formed on the valve sealing ring after heating to 400°C. Specifically, in this embodiment, the thin oxide film formed at 400°C provides a good foundation for subsequent secondary oxidation heating, ensuring... The uniformity and density of the membrane improve the overall performance of the valve seal. Through this series of meticulous processing steps, the present invention not only significantly improves the hardness and wear resistance of the valve seal, but also enhances its corrosion resistance and oxidation resistance, enabling the valve seal to maintain a long service life and stable sealing effect in harsh working environments.

[0028] Example 1

[0029] A surface treatment process for a composite hard seal on a metal valve includes the following steps: Step 1: Pretreatment. The valve sealing ring coated with Stellite alloy is activated by sandblasting or immersed in hydrochloric acid to break the Stellite layer. Passivation film; Step Two: Preheating. The pretreated valve sealing ring is heated to 450℃ for 90 minutes. Under this condition, the internal grain structure of the valve sealing ring is fully homogenized, creating favorable conditions for the uniform diffusion of nitrogen atoms during the subsequent nitriding process. This effectively avoids excessive differences in the thickness of the nitrided layer caused by uneven local temperature, thus ensuring the overall stability of the composite hard sealing layer. Moreover, after this preheating treatment, the probability of deformation and cracking of the valve sealing ring during subsequent processing is significantly reduced, improving the product's pass rate and quality reliability.

[0030] Step 3: Medium-temperature nitriding. The preheated valve sealing ring is placed in a nitriding furnace for nitriding treatment. The nitriding temperature is controlled at 580℃, the nitriding time is controlled at 240 minutes, and the concentration of the nitriding agent is controlled at 30%. Under these conditions, the nitrogen compound layer formed on the surface of the valve sealing ring has high hardness and good wear resistance. The combination of a relatively low nitriding temperature and a relatively long nitriding time allows nitrogen atoms to diffuse into the valve sealing ring matrix more slowly and fully, resulting in a more uniform and dense nitrogen compound layer. This uniform and dense nitrogen compound layer can not only effectively resist external friction and wear, but also prevent the intrusion of corrosive media to a certain extent, thereby improving the corrosion resistance of the valve sealing ring. Moreover, due to the moderate concentration of the nitriding agent, sufficient active nitrogen atoms are ensured to participate in the nitriding reaction, while avoiding quality problems such as looseness on the surface of the nitrided layer that may be caused by excessive concentration. This results in good bonding strength between the nitrogen compound layer and the matrix, further enhancing the overall performance of the valve sealing ring.

[0031] Step 4: Primary oxidation. The valve sealing ring, after medium-temperature carburizing, undergoes heating oxidation at 400℃ for 20 minutes. Under these conditions, a uniform and dense oxide layer forms on the surface of the valve sealing ring. Thin film. This combination of temperature and time ensures the integrity and density of the oxide film while avoiding the degradation of material properties caused by excessively high temperature or time, providing a good foundation for subsequent polishing and secondary oxidation processes.

[0032] Step 5: Polishing. The valve seal ring that has undergone one oxidation step is mechanically or electrolytically polished. Step Six: Secondary Oxidation Heating. The polished valve sealing ring undergoes secondary oxidation heating at 420℃ for 60 minutes. Under these conditions, the surface of the valve sealing ring... The film is sufficiently strengthened, forming a hard and dense oxide film. This combination of temperature and time allows the oxide film to maintain good corrosion resistance while significantly improving surface hardness and wear resistance. The lower heating temperature avoids the degradation of substrate properties caused by high temperatures, while the longer heating time ensures the uniformity and density of the oxide film, providing reliable surface protection for valve seals.

[0033] Step Seven: Aging Treatment. The valve sealing ring, after secondary oxidation, undergoes aging treatment at 180℃ for 180 minutes. This combination of temperature and time ensures thorough adjustment of the valve sealing ring's internal microstructure. During aging, the bonding force between the nitride phase, oxide layer, and matrix is ​​further enhanced, effectively eliminating internal stress generated in previous treatment steps. This stress elimination prevents deformation or cracking of the valve sealing ring due to stress concentration during use, significantly improving its overall hardness and wear resistance, ensuring stable performance over long-term use. Furthermore, this temperature and time setting prevents material performance degradation due to excessively high temperatures or long durations, and avoids affecting the aging effect due to excessively low temperatures or short durations, providing reliable quality assurance for the valve sealing ring and enabling reliable operation under various complex working conditions.

[0034] Step 8: Sealing. Immerse the aged valve sealing ring in a silane coupling agent solution at room temperature for 30 minutes. After immersion, heat to 150°C and cure for 1 hour. This sealing method utilizes the unique chemical properties of silane coupling agents. The organic groups in their molecular structure can chemically react with the metal oxide layer on the surface of the valve sealing ring to form a stable chemical bond. This bonding not only enhances the adhesion between the sealing layer and the substrate but also significantly improves the surface sealing and corrosion resistance. During immersion, the silane coupling agent fully penetrates into the tiny pores on the surface of the valve sealing ring, effectively filling these potential corrosion channels. The subsequent heating and curing step further promotes the bonding between the silane coupling agent and the metal oxide layer, making the sealing layer denser and more stable. This sealing treatment not only extends the service life of the valve sealing ring but also improves its reliability in harsh environments, providing a strong guarantee for the long-term stable operation of the valve.

[0035] Example 2

[0036] A surface treatment process for a composite hard seal on a metal valve includes the following steps: Step 1: Pretreatment. The valve sealing ring coated with Stellite alloy is activated by sandblasting or immersed in hydrochloric acid to break the Stellite layer. Passivation film; Step Two: Preheating. The pretreated valve sealing ring is heated to 480℃ for 60 minutes. Under this condition, the valve sealing ring can reach the suitable temperature range for nitriding more quickly, shortening the overall processing cycle and improving production efficiency. Simultaneously, the higher preheating temperature helps to further eliminate residual stress inside the valve sealing ring, reducing defects such as cracks caused by stress concentration. This results in a tighter and stronger bond between the composite hard sealing layer and the substrate, enhancing the overall strength and fatigue resistance of the valve sealing ring. Furthermore, this preheating condition promotes the increase of active centers on the surface of the valve sealing ring, providing more favorable sites for the adsorption and diffusion of nitrogen atoms during the subsequent nitriding process. This facilitates the formation of a more uniform and dense nitrided layer, thereby improving the wear resistance and corrosion resistance of the composite hard sealing layer.

[0037] Step 3: Medium-temperature nitriding. The preheated valve sealing ring is placed in a nitriding furnace for nitriding treatment. The nitriding temperature is set at 600℃, the nitriding time at 120 minutes, and the nitriding agent concentration at 35%. Under these conditions, the higher nitriding temperature accelerates the diffusion rate of nitrogen atoms, allowing nitrogen atoms to quickly penetrate the surface of the valve sealing ring and form a nitrogen compound layer of a certain thickness within a relatively short nitriding time. The higher nitriding agent concentration provides a more abundant source of active nitrogen atoms, ensuring the nitriding reaction proceeds fully. Although the nitrogen compound layer formed in this way may be slightly less dense than that formed by low-temperature, long-time nitriding, it has higher surface hardness and can better resist the scratching and impact of hard particles, providing reliable wear resistance for the valve sealing ring under harsh working conditions. At the same time, the appropriate combination of nitriding time and temperature also avoids the deterioration of the valve sealing ring matrix performance that may be caused by excessively high temperature or excessively long time, ensuring the coordination between the composite hard sealing layer and the matrix. This allows the valve sealing ring to maintain good toughness and fatigue resistance while possessing high hardness and wear resistance.

[0038] Step 4: Primary oxidation. The valve seal ring, after medium-temperature carburizing, undergoes heating oxidation. The heating temperature is increased to 450℃, while the oxidation time is shortened to 15 minutes. Under these conditions, an effective oxidation process can be achieved on the surface of the valve seal ring. Thin film. Higher temperatures accelerate the oxidation reaction, while shorter time reduces the material's exposure to high temperatures, thus minimizing the impact on material properties while ensuring the oxidation effect.

[0039] Step 5: Polishing. The valve seal ring that has undergone one oxidation step is mechanically or electrolytically polished. Step Six: Secondary Oxidation Heating. The polished valve sealing ring undergoes secondary oxidation heating, with the heating temperature increased to 480℃ and the oxidation time shortened to 30 minutes. Under these conditions, the surface of the valve sealing ring can also form a strengthened layer. The higher temperature accelerates the oxidation reaction, allowing the oxide film to achieve a certain strengthening effect in a shorter time. The shorter time reduces the material's exposure to high temperatures, thus minimizing the impact on the valve sealing ring substrate while ensuring the performance of the oxide film. This treatment condition is suitable for applications with high production efficiency requirements, shortening the processing cycle and improving production efficiency while ensuring product quality.

[0040] Step Seven: Aging Treatment. The valve sealing ring, after secondary oxidation, undergoes aging treatment at 200℃ for 120 minutes. This combination of parameters—200℃ and 120 minutes—allows for sufficient adjustment and optimization of the valve sealing ring's internal microstructure within a relatively short time. During the aging process, the bonding between the nitride phase, oxide layer, and matrix becomes tighter, and internal stress is further effectively eliminated.

[0041] Step 8: Sealing. Immerse the aged valve sealing ring in hot oil at 80°C for 30 minutes. Under these conditions, the active ingredients in the hot oil quickly penetrate the tiny cracks and pores on the surface of the valve sealing ring, forming a uniform and dense sealing film. This sealing film not only effectively isolates the external corrosive media from direct contact with the valve sealing ring substrate but also significantly improves the surface lubricity and wear resistance. Compared to immersion in a silane coupling agent solution at room temperature, hot oil immersion achieves a similar sealing effect in a shorter time, further shortening the overall treatment cycle.

[0042] Example 3

[0043] A surface treatment process for a composite hard seal on a metal valve includes the following steps: Step 1: Pretreatment. The valve sealing ring coated with Stellite alloy is activated by sandblasting or immersed in hydrochloric acid to break the Stellite layer. Passivation film; Step Two: Preheating. The pretreated valve sealing ring is heated to 465℃ for 75 minutes. Under these conditions, the preheating process of the valve sealing ring is more even, ensuring both the homogenization of the internal structure and avoiding grain coarsening caused by excessively high temperatures or prolonged heating times. This preheating condition not only helps the uniform diffusion of nitrogen atoms during the subsequent nitriding process but also effectively reduces the deformation of the valve sealing ring during heat treatment, improving the dimensional accuracy and stability of the product.

[0044] Step 3: Medium-temperature nitriding. The preheated valve sealing ring is placed in a nitriding furnace for nitriding treatment. The nitriding temperature is set at 590℃, the nitriding time at 180 minutes, and the nitriding agent concentration at 32.5%. Under these conditions, the nitrogen compound layer formed on the surface of the valve sealing ring possesses both good hardness and toughness. The moderate nitriding temperature ensures that nitrogen atoms have sufficient energy for diffusion while avoiding performance degradation due to excessively high temperatures causing matrix grain growth. The 180-minute nitriding time allows nitrogen atoms to fully penetrate, forming a nitrogen compound layer of a certain thickness and good uniformity. The 32.5% nitriding agent concentration provides an appropriate amount of active nitrogen atoms, ensuring a stable nitriding reaction, avoiding insufficient nitriding due to too low a concentration or defects such as porosity due to too high a concentration. This nitrogen compound layer not only effectively resists wear but also improves the fatigue resistance of the valve sealing ring to a certain extent, enabling it to maintain stable sealing performance under frequent opening and closing conditions. Meanwhile, this combination of nitriding parameters helps reduce stress concentration between the nitrided layer and the substrate, enhances the bonding strength between the two, and further improves the overall reliability of the valve seal ring.

[0045] Step 4: Primary oxidation. The valve sealing ring, after medium-temperature carburizing, undergoes heating oxidation. The heating temperature is increased to 425℃, while the heating oxidation time is shortened to 17 minutes. Under these conditions, the surface of the valve sealing ring can form a uniform and high-performance surface in a relatively short time. Thin film. The heating temperature of 425℃ ensures the oxidation reaction proceeds fully, allowing Cr to be rapidly oxidized to form a thin film. This process avoids excessive oxidation or performance degradation of the material surface due to excessively high temperatures. The 17-minute heating oxidation time ensures the oxidation effect while minimizing the material's exposure time at high temperatures, thus reducing adverse effects on the valve sealing ring substrate. This optimized combination of temperature and time considers both the quality of the oxide film and production efficiency, enabling the valve sealing ring to better resist corrosive media in subsequent use and extending its service life.

[0046] Step 5: Polishing. The valve seal ring that has undergone one oxidation step is mechanically or electrolytically polished. Step Six: Secondary Oxidation Heating. The polished valve sealing ring undergoes secondary oxidation heating, with the heating temperature increased to 450℃ and the oxidation time controlled at 45 minutes. Under these conditions, the surface of the valve sealing ring... The membrane underwent further strengthening treatment. The heating temperature of 450℃ provided a suitable energy environment for the oxidation reaction, enabling... The more complete and denser crystalline structure of the oxide film significantly improves its hardness and wear resistance. This increased hardness allows the valve seal to better maintain surface integrity and reduce wear when subjected to high-speed fluid erosion or friction from hard particles. Simultaneously, the 45-minute heating oxidation time ensures uniform oxide film formation across the entire valve seal surface, preventing localized thinning due to insufficient time. This uniform and dense oxide film not only enhances the corrosion resistance of the valve seal but also effectively prevents corrosive media from penetrating into the matrix, providing a reliable surface protective barrier for the valve seal.

[0047] Step Seven: Aging Treatment. The valve sealing rings that have undergone secondary oxidation are then subjected to aging treatment at 190℃ for 150 minutes. The 190℃ temperature ensures sufficient phase transformation while preventing degradation of the matrix properties due to excessively high temperatures. The 150-minute aging time ensures the integrity of the microstructure transformation, enabling the valve sealing rings to maintain stable performance in subsequent use. This combination of aging treatment parameters has been carefully optimized, considering both treatment effectiveness and production efficiency, providing a strong guarantee for the long-term reliable operation of the valve sealing rings.

[0048] Step 8: Sealing. The valve sealing ring, after aging treatment, is immersed in hot oil at 100°C for 30 minutes. Under these conditions, the 100°C hot oil treatment maintains a similar sealing effect while further optimizing the transition zone structure between the sealing layer and the substrate. By controlling the hot oil temperature and immersion time, sufficient penetration of the sealant is ensured while avoiding changes in the substrate structure or decomposition of the sealant due to excessively high temperatures. The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A surface treatment process for a composite hard seal on a metal valve, characterized in that: The composite hard seal surface layer is located on the valve sealing ring. The composite hard seal surface layer includes a diffusion layer, a nitrogen compound layer, and a metal oxide layer arranged sequentially from the inside to the outside. The composite hard seal surface layer treatment process includes Stellite alloy spraying process and QPQ treatment process. The QPQ treatment process includes the following steps: Step 1: Pretreatment. The valve sealing ring coated with Stellite alloy is activated by sandblasting or immersed in hydrochloric acid to break the Stellite layer. Passivation film; Step 2: Preheating. Heat the pretreated valve sealing ring to 450-480℃ for 60-90 minutes. Step 3: Medium-temperature nitriding. The preheated valve sealing ring is placed in a nitriding furnace for nitriding treatment. The nitriding temperature is 580℃~600℃, the nitriding time is 120min~240min, and the concentration of the nitriding agent CNO in the nitriding furnace is 30~35%. Step 4: First oxidation: The valve sealing ring that has undergone medium-temperature carburizing is subjected to heating oxidation at a temperature of 400-450℃ for 15-20 minutes. Step 5: Polishing. The valve seal ring that has undergone one oxidation step is mechanically or electrolytically polished. Step Six: Secondary Oxidation Heating. The polished valve sealing ring is subjected to secondary oxidation heating at a temperature of 420-480℃ for 30-60 minutes. Step 7: Aging treatment. The valve sealing ring that has completed secondary oxidation is subjected to aging treatment. The aging treatment temperature is 180-200℃ and the aging treatment time is 120-180min. Step 8: Sealing. Immerse the aging-treated valve sealing ring in a silane coupling agent solution at room temperature for 30 minutes. After immersion, heat to 150°C and cure for 1 hour; or immerse the aging-treated valve sealing ring in hot oil at 80-100°C for 30 minutes.

2. The surface treatment process for the composite hard seal of metal valves according to claim 1, characterized in that: In the QPQ process, during the heating of the valve sealing ring, the heating rate is ≤5℃ / min, and during the cooling of the valve sealing ring, it is furnace cooled to <300℃ and then air cooled.

3. The surface treatment process for the composite hard seal of metal valves according to claim 1, characterized in that: Salt bath activity adjustment can be performed between steps three and four, by adding a rare earth oxidant during the intermediate-temperature nitriding process. The rare earth oxidant is... The rare earth oxidant The molar percentage in the solution is 0.5%.

4. The surface treatment process for the composite hard seal of metal valves according to claim 1, characterized in that: The metal oxide layer is composed of , and The nitrogen compound layer is composed of CrN, and The diffusion layer is a supersaturated solid solution formed by nitrogen atoms dissolved in a cobalt matrix.

5. The surface treatment process for the composite hard seal of metal valves according to claim 1, characterized in that: The composite hard seal surface layer is located on the inner surface of the valve sealing ring.

6. The surface treatment process for the composite hard seal of metal valves according to claim 1, characterized in that: In the first oxidation heating process of step four, a thin oxide film is formed on the valve sealing ring after heating to 400°C.

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