Vacuum low-pressure carburizing process for 1Cr11Ni2W2MoV stainless steel

Abstract

The invention relates to the technical field of materials, in particular to a vacuum low-pressure carburizing process of 1Cr11Ni2W2MoV stainless steel, which comprises the following steps: quenching and tempering the stainless steel in a heating furnace; the stainless steel is cleaned, and surface oxide skin and oil dirt are removed; putting the cleaned stainless steel into a vacuum low-pressure carburizing furnace and carrying out pre-oxidation treatment; performing carburizing treatment on the vacuum low-pressure carburizing furnace, and slowly cooling to room temperature in the furnace after carburizing; the stainless steel is heated again in the heating furnace for quenching treatment; the quenched stainless steel is subjected to subzero treatment; after subzero treatment, the stainless steel is subjected to tempering treatment twice, and the vacuum low-pressure carburizing technology ensures the uniformity of a carburized layer, which is very important for improving the wear resistance and prolonging the fatigue life of a part.

Description

Technical Field

[0001] The invention relates to the technical field of materials, and in particular to a vacuum low-pressure carburizing process for 1Cr11Ni2W2MoV stainless steel. Background Art

[0002] 1Cr11Ni2W2MoV is a high-alloy martensitic stainless steel with excellent hot corrosion resistance and mechanical properties. It is commonly used in the aviation, energy, and chemical industries to manufacture components subjected to high temperatures and corrosive environments. However, current heat treatment processes struggle to achieve a uniform carburized layer in this high-alloy steel. For example, patent No. 201310526166.2 discloses a method for preparing a high-temperature vacuum carburized layer on a 1Cr17Ni2 alloy material, as well as a method for low-pressure vacuum carburizing heat treatment of high-temperature carburized stainless steel. The sample processing steps include sample preparation, carburizing, quenching, cryogenic treatment, and high-temperature tempering. These steps are incomplete and have limitations in terms of processing time and environmental considerations. This increases processing time and production costs, inadequately treats deformation and oxidation, and results in poorly uniform carbon layers during the carburization process, resulting in lower material performance.

[0003] Therefore, the vacuum low-pressure carburizing process for 1Cr11Ni2W2MoV proposed in this solution effectively overcomes the uneven carbon layer problem encountered during traditional carburizing by pre-oxidizing the material and then performing the carburizing process in a vacuum low-pressure environment. This technology is particularly suitable for high-alloy steels such as 1Cr11Ni2W2MoV because it allows carburizing to be performed at lower temperatures, thereby reducing the risk of deformation and oxidation during heat treatment. Summary of the Invention

[0004] To solve the above problems, the present invention proposes a vacuum low-pressure carburizing process for 1Cr11Ni2W2MoV stainless steel, which solves the problems in the prior art of incomplete processing steps, insufficient processing time and environment in each step, resulting in increased processing time cost, poor uniformity of the carbon layer during the carburizing process, and lower performance of the processed material.

[0005] This solution provides a vacuum low-pressure carburizing process for 1Cr11Ni2W2MoV stainless steel, comprising the following steps: Step 1: Tempering treatment: The stainless steel is sequentially quenched and then subjected to high-temperature tempering treatment in a heat treatment furnace; Step 2, pre-cleaning: Polish and clean the stainless steel to remove surface oxide scale and oil stains. The polishing and cleaning temperature is room temperature and the polishing and cleaning time is 0.5 to 1 hour. Step 3: Install the furnace: Put the cleaned stainless steel material into the vacuum low-pressure carburizing furnace; Step 4: Pre-oxidation treatment: Pre-oxidation treatment of stainless steel in a vacuum low-pressure carburizing furnace; Step 5: Carburizing-slow cooling treatment: The stainless steel is subjected to vacuum low-pressure carburizing treatment in a vacuum low-pressure carburizing furnace and then slowly cooled to room temperature; Step 6: Quenching treatment: Quenching treatment of stainless steel; Step 7: Cryogenic treatment: Cryogenic treatment of stainless steel to reduce retained austenite; Step 8: Tempering treatment: Temper the stainless steel once to reduce brittleness and internal stress; Step nine, secondary tempering treatment: The stainless steel is subjected to secondary tempering treatment to further reduce internal stress and improve the toughness and wear resistance of the steel.

[0006] Preferred technical solution 1: In step 1, the quenching treatment is to heat to 1000-1050°C (CN103556106B discloses 1020 and 1000°C) in a heating furnace at a heating rate of 12°C / min (CN109735794B only discloses 10°C / min), and keep warm for 1-1.5 h () (CN109735794B discloses 1h), and then quickly put it into oil and cool it to room temperature; the high-temperature tempering treatment is to heat to 660-690°C in a heating furnace at a heating rate of 12°C / min, and keep warm for 2-3 h, and then take it out and air-cool it to room temperature.

[0007] Preferred technical solution 2: In step 4, the pre-oxidation treatment is to heat to 300-400°C in a carburizing furnace at a heating rate of 12°C / min and keep warm for 0-1 hour to form an oxide film on the surface of the martensitic stainless steel, thereby improving the carburizing uniformity and promoting the carburizing process.

[0008] Preferred technical solution three: In step five, the carburizing-slow cooling treatment is to first evacuate the carburizing furnace to a vacuum degree of less than 10 Pa, and then raise the furnace temperature to 1000-1050 ° C at a heating rate of 12 ° C / min for carburizing treatment. The carburizing process consists of several pulse process cycles, and each pulse cycle includes two stages: carburizing and diffusion. Only acetylene is introduced during the carburizing stage, and the acetylene pressure is 10 mbar, and the acetylene flow rate is 5-20 L / min. Only nitrogen is introduced during the diffusion stage, and the nitrogen pressure is 50-80 Pa. The vacuum low-pressure carburizing time is 3-4 h. After carburizing is completed, nitrogen is introduced for slow cooling to room temperature, and the nitrogen pressure is 0.5-2 bar.

[0009] Preferred technical solution four: In step six, the quenching treatment is to place the 1Cr11Ni2W2MoV stainless steel in a heating furnace, raise the furnace temperature to 1025℃~1050℃ at a heating rate of 12℃ / min, and keep it at this temperature for 1~2 hours, and then quickly place it in oil to cool to room temperature.

[0010] Preferred technical solution five: In step seven, the cryogenic treatment is to place the 1Cr11Ni2W2MoV stainless steel in a liquid nitrogen cryogenic box, with a cryogenic temperature of -70 to -80°C and a holding time of 2 to 3 hours.

[0011] Preferred technical solution six: In step eight, the first tempering treatment is to place the 1Cr11Ni2W2MoV stainless steel after deep freezing treatment into a heating furnace, heat it to 160-200°C at a heating rate of 12°C / min, and keep it warm for 2-3 hours, then take it out and air cool it to room temperature.

[0012] Preferred technical solution seven: In step nine, the second tempering treatment is to place the 1Cr11Ni2W2MoV stainless steel after the first tempering treatment into a heating furnace, heat it to 160-200°C at a heating rate of 12°C / min, and keep it warm for 2-3 hours, and then take it out and air cool it to room temperature.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. Uniform carburized layer: Vacuum low-pressure carburizing technology ensures the uniformity of the carburized layer, which is crucial for improving the wear resistance and fatigue life of components. Pre-oxidation treatment also forms an oxide film on the surface of martensitic stainless steel, improving carburizing uniformity and promoting the carburizing process. 2. Reduce deformation and oxidation: Carburizing is performed in a low-pressure environment, reducing the risk of deformation and oxidation during heat treatment; 3. Improve hardness and wear resistance: The surface hardness of 1Cr11Ni2W2MoV stainless steel is significantly improved after carburizing, thereby enhancing its wear resistance; 4. Optimized heat treatment parameters: By precisely controlling the carburizing temperature, time and pressure, the depth and hardness of the carburized layer can be precisely controlled; 5. Environmentally friendly: Vacuum low-pressure carburizing technology reduces the emission of harmful gases and meets the environmental protection requirements of modern industry; 6. Improve production efficiency: Compared with the traditional carburizing process, the vacuum low-pressure carburizing process shortens the processing time and improves production efficiency; 7. Improve fatigue performance: A uniform carburized layer and optimized heat treatment parameters help improve the fatigue strength and durability of components. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the 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 invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0015] Figure 1 This is the process flow chart of this solution; Figure 2 This is the temperature and time variation diagram of this scheme; Figure 3 This is the organizational diagram of the hardened layer of this scheme; Figure 4 The organizational chart at the core of this program; Figure 5 This is the organizational diagram of this scheme with quenching temperature of 1025℃ and holding time of 1.5h; Figure 6 This is the organizational diagram of the tempering treatment temperature of this scheme with 1025℃ and holding time of 1.5h. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0017] The following specific embodiments are used to describe the technical solution of the present invention in detail. The following specific embodiments can be combined or replaced with each other according to actual conditions, and the same or similar concepts or processes may not be described in detail in some embodiments.

[0018] Example 1, please refer to Figures 1-6 , a vacuum low-pressure carburizing process for 1Cr11Ni2W2MoV stainless steel, comprising the following steps: In step 1, the tempering treatment involves heating in a furnace at a rate of 12°C / min to 975–1050°C, preferably 1025°C, and holding for 1–1.5 hours. The steel is then rapidly cooled to room temperature in oil. A 12°C / min rate can inhibit excessive grain growth while ensuring sufficient austenitization, improving the hardness and toughness balance after quenching. However, a faster rate (e.g., 15°C / min) can lead to a large temperature difference between the surface and the core, generating thermal stress and increasing the risk of deformation. While a slower rate can reduce stress, it can also extend the process cycle and reduce efficiency. A holding time of 1.5 hours is recommended to meet carbon diffusion kinetics and balance carburized layer depth with microstructure uniformity. At 975°C, a 1-hour hold can negatively impact carburization by producing a large amount of blocky martensite and retained austenite. At 1025°C, a 1-hour hold effectively improves carburized layer uniformity.

[0019] Furthermore, high-temperature tempering is performed in a furnace at a heating rate of 12°C / min to a temperature of 660-690°C, preferably 675°C, for 2-3 hours, followed by air cooling to room temperature. Using a 12°C / min heating rate can inhibit excessive grain growth while ensuring sufficient austenitization, improving the hardness and toughness match after quenching. A faster heating rate (e.g., 15°C / min) can lead to a large temperature difference between the surface and the core, generating thermal stress and increasing the risk of deformation. While a slower rate can reduce stress, it can also extend the process cycle and reduce efficiency.

[0020] Step 2: Pre-cleaning: Polish and clean the stainless steel to remove surface scale and oil stains. The polishing and cleaning temperature is room temperature and the polishing and cleaning time is 0.5 to 1 hour. Step 3: Install the furnace: Put the cleaned stainless steel material into the vacuum low-pressure carburizing furnace; Step 4: Pre-oxidation treatment: In a carburizing furnace, heat the steel to 300-400°C at a heating rate of 12°C / min and keep the temperature for 0-1 hour to form an oxide film on the surface of the martensitic stainless steel, thereby improving the carburizing uniformity and promoting the carburizing process. Step 5, carburizing-slow cooling treatment. First, evacuate the carburizing furnace to a vacuum with a vacuum degree of less than 10 Pa. Select a low-pressure environment (<10 Pa) where radiation heat transfer is dominant and the temperature uniformity can reach ±3°C to avoid temperature fluctuations caused by convection under high pressure. Then, raise the furnace temperature to 1000-1050°C at a heating rate of 12°C / min for carburizing treatment, preferably 1000-1020°C. The carburizing process consists of several pulse process cycles, each of which includes two stages: carburizing and diffusion. Only acetylene is introduced during the carburizing stage, with an acetylene pressure of 10 mbar and an acetylene flow rate of 5-20 L / min. The acetylene flow rate of 5-20 L / min balances the carbon supply and diffusion rate and optimizes the uniformity of the carburized layer. Adapt to the complex workpiece geometry and equipment capacity to ensure process stability. Only nitrogen is introduced during the diffusion stage, with a nitrogen pressure of 50-80 Pa and a vacuum low-pressure carburizing time of 3-4 h, the depth of the carburized layer is 0.6~1.0mm, and nitrogen is introduced after carburizing to slowly cool to room temperature, with a nitrogen pressure of 0.5~2 bar; Step 6: Quenching treatment: Place the 1Cr11Ni2W2MoV stainless steel in a heating furnace and raise the furnace temperature to 1025-1050°C at a heating rate of 12°C / min, preferably 1025°C, and keep it at this temperature for 1-2 hours. Then quickly place it in oil and cool it to room temperature. Figure 5 The middle one is the metallographic structure diagram of quenching temperature of 1025℃ and holding time of 1.5h.

[0021] Step 7: Cryogenic treatment: Place the 1Cr11Ni2W2MoV stainless steel in a liquid nitrogen cryogenic box at a cryogenic temperature of -70 to -80 °C and keep it at this temperature for 2 to 3 hours. Step 8: Tempering treatment: Place the 1Cr11Ni2W2MoV stainless steel in a heating furnace and heat it to 160-200°C at a heating rate of 12°C / min, and keep it at this temperature for 2-3 hours. Then take it out and air cool it to room temperature to reduce the internal stress after quenching and improve the toughness of the material. Step nine, secondary tempering treatment: Place the 1Cr11Ni2W2MoV stainless steel in a heating furnace, heat it to 160-200°C at a heating rate of 12°C / min, and keep it warm for 2-3 hours. Then take it out and air-cool it to room temperature to further reduce the internal stress after quenching and improve the toughness and wear resistance of the steel.

[0022] After secondary tempering, the hardness of the hardened layer is 58-62HRC, the hardness of the core is 34-47.5HRC, and the retained austenite in the hardened layer does not exceed that of HB5492. Figure 2 Grade 4, carbide in the hardened layer does not exceed that in HB5492 Figure 3 Level 6.

[0023] In addition to the above-mentioned preferred embodiments, the present invention has other implementation modes. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work are within the scope of protection requested by the present invention.

Claims

1. A vacuum low-pressure carburizing process for 1Cr11Ni2W2MoV stainless steel, characterized in that: The steps include: Step 1: quenching and tempering treatment, wherein the quenching and tempering treatment is carried out on the stainless steel in a heat treatment furnace in sequence, wherein: The quenching treatment is to heat to 1000-1050°C in a heating furnace at a heating rate of 12°C / min and keep the temperature for 1-1.5 hours, and then quickly put it into oil to cool to room temperature; The high temperature tempering treatment is to heat to 660-690°C in a heating furnace at a heating rate of 12°C / min, and keep the temperature for 2-3 hours, and then take out and air cool to room temperature; Step 2: Pre-cleaning: polish and clean the stainless steel to remove surface oxide scale and oil stains. The polishing and cleaning temperature is room temperature and the polishing and cleaning time is 0.5 to 1 hour. Step 3: Loading the furnace: Load the stainless steel material cleaned in step 2 into a vacuum low-pressure carburizing furnace; Step 4: pre-oxidation treatment; Step 5: Carburizing-slow cooling treatment: Carburizing the stainless steel under vacuum and low pressure in a vacuum and low pressure carburizing furnace, and then slowly cooling to room temperature; Step six, quenching treatment, quenching the stainless steel; Step 7: Cryogenic treatment: Cryogenic treatment of stainless steel to reduce retained austenite Step 8: Tempering treatment: Temper the stainless steel once to reduce brittleness and internal stress.

2. A vacuum low-pressure carburizing process for 1Cr11Ni2W2MoV stainless steel according to claim 1, characterized in that: Also includes: Step nine: secondary tempering treatment. Perform secondary tempering treatment on the stainless steel to further reduce internal stress and improve the toughness and wear resistance of the steel.

3. A vacuum low-pressure carburizing process for 1Cr11Ni2W2MoV stainless steel according to claim 2, characterized in that: In the step nine, the second tempering treatment is to place the 1Cr11Ni2W2MoV stainless steel after the first tempering treatment into a heating furnace, heat it to 160-200°C at a heating rate of 12°C / min, and keep it warm for 2-3 hours, and then take it out and air-cool it to room temperature.

4. A vacuum low-pressure carburizing process for 1Cr11Ni2W2MoV stainless steel according to claim 1 or 2, characterized in that: In step 4, the pre-oxidation treatment is to heat the carburizing furnace to 300-400°C at a heating rate of 12°C / min and keep it warm for 0-1 hour to form an oxide film on the surface of the martensitic stainless steel, improve the carburizing uniformity, and promote the carburizing process.

5. A vacuum low-pressure carburizing process for 1Cr11Ni2W2MoV stainless steel according to claim 4, characterized in that: In the step 5, the carburizing-slow cooling treatment is first performed by evacuating the carburizing furnace to a vacuum degree of less than 10 Pa, and then raising the furnace temperature to 1000-1050 ° C at a heating rate of 12 ° C / min for carburizing treatment. The carburizing process consists of several pulse process cycles, each pulse cycle including two stages of carburizing and diffusion, wherein, During the carburizing stage, only acetylene is introduced, with an acetylene pressure of 10 mbar and an acetylene flow rate of 5 to 20 L / min; During the diffusion stage, only nitrogen gas is introduced with a nitrogen pressure of 50-80 Pa. The vacuum low-pressure carburizing time is 3-4 h. After carburizing is completed, nitrogen gas is introduced for slow cooling to room temperature with a nitrogen pressure of 0.5-2 bar.

6. A vacuum low-pressure carburizing process for 1Cr11Ni2W2MoV stainless steel according to claim 5, characterized in that: In step six, the quenching treatment is to place the 1Cr11Ni2W2MoV stainless steel in a heating furnace, raise the furnace temperature to 1025-1050°C at a heating rate of 12°C / min, and keep the temperature for 1-2 hours, and then quickly put it in oil to cool to room temperature.

7. A vacuum low-pressure carburizing process for 1Cr11Ni2W2MoV stainless steel according to claim 6, characterized in that: In step seven, the cryogenic treatment is to place the 1Cr11Ni2W2MoV stainless steel into a liquid nitrogen cryogenic box, with a cryogenic temperature of -70 to -80°C and a holding time of 2 to 3 hours.

8. The vacuum low-pressure carburizing process for 1Cr11Ni2W2MoV stainless steel according to claim 7, characterized in that: In step eight, the first tempering treatment is to place the cryogenically treated 1Cr11Ni2W2MoV stainless steel in a heating furnace, heat it to 160-200°C at a heating rate of 12°C / min, and keep it warm for 2-3 hours, then take it out and air-cool it to room temperature.

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