A novel carbonitriding process for bearing parts

Abstract

This invention discloses a novel carbonitriding process for bearing parts in the field of metal material surface heat treatment technology. The process includes degreasing and cleaning of the bearing parts, catalytic coating, heating in a methanol atmosphere, carburizing in a methanol and propane atmosphere, carbonitriding in a methanol, propane, and ammonia atmosphere, quenching, and tempering. The catalytic coating solution contains a molybdenum-niobium-boron-nitrogen-oxygen synergistic catalytic agent, which is prepared by complexing, gelling, heat treatment, and activation of ammonium heptamolybdate tetrahydrate, ammonium niobate oxalate hydrate, boric acid, citric acid monohydrate, urea, melamine, and glucose. This invention can form a stable pre-carburized layer before carbonitriding, reducing the risk of carbon depletion on the bearing parts surface and improving the uniformity, surface hardness, wear resistance, and service life of the carbonitrided layer.

Description

Technical Field

[0001] This invention belongs to the field of surface heat treatment technology for metallic materials, and specifically relates to a new carbonitriding process for bearing parts. Background Technology

[0002] Bearing components are widely used in automobiles, construction machinery, precision machine tools, motors, and transmission devices. During their service life, they typically endure alternating contact stress, friction and wear, impact loads, and complex lubrication environments, requiring high levels of surface hardness, wear resistance, fatigue resistance, and dimensional stability. High-carbon chromium bearing steel possesses high hardenability, wear resistance, and contact fatigue strength, making it a commonly used material for bearing rings, rolling elements, and other components. To further improve the surface properties of bearing components, industrial production typically employs gas carbonitriding combined with quenching and tempering heat treatment. This allows carbon and nitrogen to diffuse into the surface of the component, forming a hardened layer that improves the bearing's wear resistance, anti-galling capabilities, and long-term service reliability.

[0003] Existing gas carbonitriding processes typically use methanol as the base atmosphere, with propane used to adjust the carbon potential and ammonia to provide the nitrogen source, completing the carbonitriding treatment in a controlled atmosphere carburizing furnace. While this process boasts mature equipment, low cost, and suitability for mass production, it still has certain shortcomings in actual production. Because the furnace atmosphere is not fully stable during the initial heating phase of the parts, establishing an effective carbon potential requires a certain process. If the carbonitriding stage is entered directly before the carbon potential is stable, the hydrogen produced by ammonia decomposition will further affect the furnace atmosphere balance, causing a tendency for carbon depletion on the surface of the bearing parts. This results in insufficient surface carbon content, decreased uniformity of the hardened layer, localized low hardness, and unstable wear resistance. For bearing parts with high dimensional accuracy requirements, these problems may also cause fluctuations in the quenched microstructure, changes in the proportion of retained austenite, and a decrease in fatigue life during subsequent use.

[0004] Furthermore, traditional processes typically rely on increasing propane supply and extending carburizing or co-diffusion time to compensate for surface carbon deficiency. However, this increases atmosphere consumption and production cycle time, and may lead to risks such as excessively deep carburized layers, coarsening of the microstructure, uneven residual stress, or increased deformation, which are detrimental to the stable control of batch product quality. Therefore, it is necessary to propose a new carbonitriding process suitable for bearing parts without significantly altering existing controlled atmosphere carburizing furnaces and conventional atmosphere systems. Through the synergistic control of pretreatment, catalytic coating, precarburizing, and subsequent carbonitriding, a stable precarburized surface layer is formed on the bearing parts before ammonia gas is introduced. The catalytic material further improves carbon and nitrogen diffusion and the uniformity of the carburized layer, thereby reducing the risk of surface carbon deficiency and improving the surface strengthening effect and service life of the bearing parts. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a novel carbonitriding process for bearing parts.

[0006] A first aspect of the present invention provides a novel carbonitriding process for bearing parts, comprising the following steps:

[0007] S1. By weight, add 100-120 parts of GCr15 bearing parts to a container, add 2-5 parts of anhydrous sodium carbonate and 95-105 parts of deionized water, and treat at 55-65℃; after removal, wipe with anhydrous ethanol and dry to obtain dried GCr15 bearing parts; mix 0.2-0.8 parts of molybdenum-niobium-boron-nitrogen-oxygen synergistic infiltration catalyst, 0.5-1.2 parts of ethyl cellulose, 25-45 parts of anhydrous ethanol and 5-10 parts of acetone to obtain infiltration coating solution; contact the dried GCr15 bearing parts with the infiltration coating solution, dry, and place in a carburizing furnace;

[0008] S2. Nitrogen gas is introduced into the carburizing furnace for replacement, methanol is introduced, and the temperature is raised to 830-850℃ for treatment to obtain the treated GCr15 bearing parts.

[0009] S3. Methanol and propane are introduced into the carburizing furnace to carry out carburizing treatment and obtain pre-carburized GCr15 bearing parts.

[0010] S4. Introduce methanol, propane and ammonia into the carburizing furnace for carbonitriding treatment; after carbonitriding treatment, transfer to quenching oil for quenching, and then temper at 160-190℃.

[0011] In this invention, the novel carbonitriding process for bearing parts involves first contacting the GCr15 bearing parts with anhydrous sodium carbonate and deionized water. Surface oil, residual processing media, and adsorbed impurities are dispersed, saponified, and removed by the alkaline aqueous phase. The parts are then wiped and dried with anhydrous ethanol, resulting in a clean and easily wettable surface. A synergistic infiltration catalyst of molybdenum, niobium, boron, nitrogen, and oxygen, along with ethyl cellulose, anhydrous ethanol, and acetone, forms an infiltration coating solution. Anhydrous ethanol and acetone cause the ethyl cellulose to swell and disperse, forming a continuous adhesive film during evaporation. This film fixes the synergistic infiltration catalyst to the surface of the GCr15 bearing parts, reducing the shedding of the infiltration components during the initial heating and carburizing stages. After being placed in the carburizing furnace, nitrogen replaces the air inside, reducing the impact of oxidizing gases on the surface of the GCr15 bearing parts. Methanol decomposes in the furnace to form a protective and carburizing atmosphere, establishing a basic carbon potential for the heating stage. Subsequently, methanol and propane are introduced for carburizing. Methanol maintains the base atmosphere, while propane provides supplementary carbon source, allowing activated carbon to adsorb on the surface of the GCr15 bearing parts and diffuse inward, forming a pre-carburized layer. The molybdenum and niobium oxynitride active structures in the molybdenum-niobium-boron-nitrogen-oxygen synergistic infiltration catalyst generate defect sites and active adsorption centers in the reducing carburizing atmosphere, lowering the adsorption and diffusion resistance of activated carbon on the surface. The boron-containing nitrogen-oxygen structure improves interfacial stability, resulting in a more uniform carburized layer distribution. Afterward, methanol, propane, and ammonia are introduced for carbonitriding. Ammonia decomposes to form active nitrogen, which diffuses together with the active carbon provided by methanol and propane onto the surface of the GCr15 bearing parts. Since the carburizing process has already established a high surface carbon potential gradient, the ammonia primarily completes nitrogen replenishment and carbonitriding synergistic diffusion, forming a continuous carbonitriding composite reinforcement layer on the surface. After carbonitriding, the surface is quenched in quenching oil, forming a high-hardness martensite and retained austenite composite structure. Then, tempering is performed to release the quenching stress, further stabilizing the martensite and precipitating molybdenum, niobium-related fine carbonitrides and boron-containing interface structures, thereby improving the surface hardness, wear resistance, diffusion uniformity and service life of GCr15 bearing parts.

[0012] According to a preferred embodiment of the present invention, in step S1, the treatment time at 55-65°C is 10-20 min.

[0013] According to a preferred embodiment of the present invention, in step S2, the time for heating to 830-850°C is 80-100 minutes.

[0014] According to a preferred embodiment of the present invention, in step S3, the carburizing treatment time is 50-70 min.

[0015] According to a preferred embodiment of the present invention, in step S4, the carbonitriding treatment time is 220-260 min, the quenching time is 8-15 min, and the tempering time is 1.5-3 h.

[0016] According to a preferred embodiment of the present invention, the preparation steps of the molybdenum-niobium-boron-nitrogen-oxygen synergistic permeation catalyst include:

[0017] A1. By weight, under nitrogen protection, add 6-10 parts of ammonium heptamolybdate tetrahydrate, 1.2-2.5 parts of ammonium niobate oxalate hydrate, 2-4 parts of boric acid and 8-14 parts of citric acid monohydrate to a reactor, add 60-90 parts of deionized water, and stir at 55-65℃; then add ammonia water to adjust the pH to 3.6-4.0, add 3-5 parts of polyethylene glycol 400 and 10-20 parts of anhydrous ethanol, and heat to 60-70℃ to react and obtain the molybdenum-niobium-boron complex precursor liquid;

[0018] A2. Add 100-140 parts of molybdenum-niobium-boron complex precursor liquid, 10-18 parts of urea, 4-8 parts of melamine, 3-6 parts of glucose and 1-3 parts of polyvinylpyrrolidone to a reaction vessel and stir at 70-80℃; then concentrate under reduced pressure to obtain a concentrate; dry the concentrate to obtain molybdenum-niobium-boron-nitrogen-carbon dry gel.

[0019] A3. Place 15-25 parts of molybdenum-niobium-boron-nitrogen-carbon dry gel in a tube furnace and treat it at 280-320℃ under a nitrogen atmosphere; then treat it at 480-540℃; then switch to a mixed atmosphere composed of nitrogen and ammonia and treat it at 600-650℃, and cool it to room temperature to obtain molybdenum-niobium-boron-nitrogen-oxygen composite powder.

[0020] A4. Add 20-30 parts of molybdenum-niobium-boron-nitrogen-oxygen composite powder, 70-90 parts of anhydrous ethanol, 10-20 parts of deionized water, and 0.1-0.3 parts of sodium oleate to a ball mill jar and ball mill to obtain a suspension slurry; then add ammonia water to adjust the pH to 7.8-8.4 and activate at 50-60℃; filter to obtain a solid product; wash the solid product with anhydrous ethanol and deionized water, vacuum dry, and air jet mill.

[0021] In this invention, the formation of the molybdenum-niobium-boron-nitrogen-oxygen synergistic permeation catalyst begins with the complexation and dispersion of ammonium heptamolybdate tetrahydrate, ammonium niobate oxalate hydrate, boric acid, and citric acid monohydrate in deionized water. Upon entering the aqueous phase, ammonium heptamolybdate tetrahydrate forms molybdate oxalate species. Ammonium niobate oxalate hydrate maintains its niobate oxalate coordination structure. The carboxyl and hydroxyl groups in the citric acid monohydrate chelate and bridge with the molybdenum and niobium species, allowing the molybdenum and niobium components to coexist in a mixed complex state in the same liquid phase. Ammonia water adjusts the acidic environment of the system, making it less prone to hydrolysis and polymerization of ammonium niobate oxalate hydrate and the precipitation of hydrated niobium oxides, while also reducing the tendency for excessive condensation of molybdenum species to form insoluble substances. The boron hydroxyl groups of boric acid esterify with the hydroxyl groups in citric acid monohydrate and glucose, forming a boron-oxygen-carbon bridging structure, allowing the boron component to enter the molybdenum-niobium complex network. Polyethylene glycol 400 and anhydrous ethanol were used to adjust the polarity, viscosity, and film-forming state of the molybdenum-niobium-boron complex precursor solution, ensuring relatively uniform dispersion of the components when urea, melamine, glucose, and polyvinylpyrrolidone were subsequently added. Urea and melamine provided nitrogen-rich structural units, glucose provided a polyhydroxy carbon source and enhanced the binding stability of boric acid, and polyvinylpyrrolidone reduced colloidal particle aggregation through adsorption and steric hindrance. During vacuum concentration and drying, the solvent was gradually removed, and the complex, nitrogen-containing components, and polyhydroxy components formed a continuous gel network, yielding a molybdenum-niobium-boron-nitrogen-carbon dry gel. When molybdenum-niobium-boron-nitrogen-carbon dry gel is treated under a nitrogen atmosphere, the coordination structures of citric acid monohydrate, urea, melamine, glucose, and oxalic acid gradually decompose, condense, and carbonize, transforming the molybdenum, niobium, and boron components into dispersed oxides and nitrogen- and carbon-containing frameworks. Subsequently, treatment in a mixed atmosphere of nitrogen and ammonia allows the ammonia to release an active nitrogen source, causing nitriding and oxynitriding transformations on the surface of the molybdenum and niobium oxides. Boric acid-derived structures form boron- and nitrogen-oxygen-containing structures, yielding a molybdenum-niobium-boron-nitrogen-oxygen composite powder. After ball milling the molybdenum-niobium-boron-nitrogen-oxygen composite powder with anhydrous ethanol, deionized water, and sodium oleate, the oleate ions from sodium oleate adsorb onto the powder surface. The weakly alkaline environment regulated by ammonia water hydroxylates the powder surface and forms a stable dispersion interface. Following washing, vacuum drying, and air jet milling, a synergistic infiltration catalyst of molybdenum-niobium-boron-nitrogen-oxygen is obtained.

[0022] According to a preferred embodiment of the present invention, in step A1, the stirring time at 55-65°C is 40-60 min, and the reaction time at 60-70°C is 1-2 h.

[0023] According to a preferred embodiment of the present invention, in step A2, the stirring time at 70-80°C is 60-90 min, the concentration time under reduced pressure is 1-2 h, and the drying time is 8-12 h.

[0024] According to a preferred embodiment of the present invention, in step A3, the treatment time is 1-2 hours when the temperature is raised to 280-320°C, 2-3 hours when the temperature is raised to 480-540°C, and 2-4 hours when the temperature is raised to 600-650°C.

[0025] According to a preferred embodiment of the present invention, in step A4, the ball milling time is 4-8 hours, the activation time at 50-60°C is 2-3 hours, and the vacuum drying time is 6-10 hours.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) This invention uses anhydrous sodium carbonate and deionized water to treat the surface of GCr15 bearing parts, combined with anhydrous ethanol wiping and drying, to remove oil stains, residual processing media and adsorbed impurities from the surface of the GCr15 bearing parts, thereby improving the wettability and adhesion stability of the subsequent catalytic coating solution on the surface of the GCr15 bearing parts. After the catalytic coating solution is formed by mixing molybdenum, niobium, boron, nitrogen and oxygen synergistic catalytic agent, ethyl cellulose, anhydrous ethanol and acetone, it can form a relatively uniform coating layer on the surface of GCr15 bearing parts, so that the molybdenum, niobium, boron, nitrogen and oxygen synergistic catalytic agent maintains stable adhesion during heating, carburizing and carbonitriding processes, and reduces the fluctuation of the diffusion layer caused by insufficient surface cleanliness or uneven coating layer distribution.

[0028] (2) This invention employs a continuous process route of nitrogen replacement, methanol heating treatment, methanol and propane carburizing treatment, and methanol, propane and ammonia carbonitriding treatment, so that the GCr15 bearing parts form a relatively stable pre-carburized surface layer before entering the carbonitriding treatment. The participation of methanol and propane in the carburizing treatment is beneficial to establishing a relatively stable surface carbon concentration gradient; subsequently, methanol, propane and ammonia are introduced for carbonitriding treatment, so that carbon and nitrogen diffuse synergistically on the surface of the GCr15 bearing parts, thereby improving the continuity and uniformity of the carburized layer and reducing the risk of surface carbon depletion, insufficient local hardness and carburized layer depth fluctuation.

[0029] (3) The molybdenum-niobium-boron-nitrogen-oxygen synergistic infiltration catalyst is prepared by complexing, concentrating, drying, heat treatment, ball milling, activation, and air jet milling of ammonium heptamolybdate tetrahydrate, ammonium niobate oxalate hydrate, boric acid, citric acid monohydrate, ammonia, polyethylene glycol 400, anhydrous ethanol, urea, melamine, glucose, polyvinylpyrrolidone, and sodium oleate. It can provide a relatively stable infiltration active interface on the surface of GCr15 bearing parts, promoting the adsorption and diffusion of carbon and nitrogen on the surface. After quenching and tempering with quenching oil, a carbon-nitrogen composite reinforced layer with high hardness and stable structure is formed on the surface of GCr15 bearing parts, giving GCr15 bearing parts better wear resistance, fatigue resistance, infiltration uniformity, and service life. Detailed Implementation

[0030] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0031] Example 1

[0032] This embodiment provides a novel carbonitriding process for bearing parts, including the following steps:

[0033] S1. Add 110g of GCr15 bearing parts to a stainless steel container, add 3.5g of anhydrous sodium carbonate and 100g of deionized water, and treat at 60℃ for 15min, turning it over once every 5min during the treatment to ensure that the surface of the GCr15 bearing parts is fully in contact with the anhydrous sodium carbonate aqueous solution; after taking it out, wipe it with 20g of anhydrous ethanol, and then dry it at 80℃ for 30min to obtain the dried GCr15 bearing parts; mix 0.5g of molybdenum-niobium-boron-nitrogen-oxygen synergistic infiltration catalyst, 0.85g of ethyl cellulose, 35g of anhydrous ethanol and 7.5g of acetone, and stir at 400r / min for 30min at 25℃ to obtain the infiltration coating solution; completely immerse the dried GCr15 bearing parts in the infiltration coating solution and keep it for 3min, take it out and let it drain naturally for 2min, and then dry it at 80℃ for 30min to form a continuous coating layer on the surface, and then put it into a carburizing furnace;

[0034] S2. Nitrogen gas is introduced into the carburizing furnace for purging at a flow rate of 5 L / min for 10 min. Then methanol is introduced in a liquid dripping manner into the carburizing furnace at a feed rate of 1.5 mL / min. The temperature is raised to 840℃ and treated for 90 min. During the treatment, the carbon potential in the furnace is controlled at 1.10% to obtain the treated GCr15 bearing parts.

[0035] S3. Continue to introduce methanol and propane into the carburizing furnace. The methanol feed rate is 1.5 mL / min and the propane flow rate is 0.15 L / min. Carburize at 840℃ for 60 min. During the process, control the carbon potential in the furnace to 1.10% to obtain pre-carburized GCr15 bearing parts.

[0036] S4. Methanol, propane, and ammonia are introduced into the carburizing furnace. The methanol feed rate is 1.5 mL / min, the propane flow rate is 0.15 L / min, and the ammonia flow rate is 0.10 L / min. Carbonitriding is performed at 840℃ for 240 min, and the carbon potential in the furnace is controlled at 1.10% during the process. After carbonitriding, the GCr15 bearing parts are transferred to quenching oil at 70℃ for 11.5 min, drained, tempered at 175℃ for 2.25 h, and cooled to room temperature to obtain the carbonitrided bearing parts.

[0037] Preparation steps of molybdenum-niobium-boron-nitrogen-oxygen synergistic permeation catalyst

[0038] A1. Nitrogen gas was introduced into a glass reactor equipped with a stirrer, thermometer, and reflux condenser. 8g of ammonium heptamolybdate tetrahydrate, 1.85g of ammonium niobate oxalate hydrate, 3g of boric acid, and 11g of citric acid monohydrate were added to the reactor, along with 75g of deionized water. The mixture was stirred at 300 rpm for 50 min at 60°C to ensure thorough dispersion and a homogeneous solution. Subsequently, 1.6g of 25% ammonia solution was added dropwise to adjust the pH to 3.8. 4g of polyethylene glycol 400 and 15g of anhydrous ethanol were added, and the mixture was heated to 65°C and reacted at 300 rpm for 1.5 h to obtain the molybdenum-niobium-boron complex precursor solution.

[0039] A2. 120g of molybdenum-niobium-boron complex precursor liquid, 14g of urea, 6g of melamine, 4.5g of glucose and 2g of polyvinylpyrrolidone were added to a reaction vessel and stirred at 300r / min for 75min at 75℃. Then, the mixture was concentrated under reduced pressure at 75℃ and -0.08MPa for 1.5h to obtain a free-flowing concentrate. The concentrate was transferred to a glass tray, and the material thickness was controlled to be 5mm. The concentrate was dried at 105℃ for 10h to obtain molybdenum-niobium-boron-nitrogen-carbon dry gel.

[0040] A3. 20g of molybdenum-niobium-boron-nitrogen-carbon dry gel was crushed to a particle size of less than 2mm and placed in an alumina crucible. The alumina crucible was then placed in the constant temperature zone of a tube furnace and treated under a nitrogen atmosphere with a nitrogen flow rate of 300mL / min. The temperature was raised to 300℃ and treated for 1.5h. The temperature was then raised to 510℃ under a nitrogen atmosphere and treated for 2.5h. Subsequently, the atmosphere was switched to a mixed atmosphere of nitrogen and ammonia, with a nitrogen flow rate of 300mL / min and an ammonia flow rate of 80mL / min. The mixture was treated at 625℃ for 3h. After the treatment, the ammonia flow was stopped and nitrogen protection was maintained. The mixture was then cooled to room temperature to obtain molybdenum-niobium-boron-nitrogen-oxygen composite powder.

[0041] A4. 25g of molybdenum-niobium-boron-nitrogen-oxygen composite powder, 80g of anhydrous ethanol, 15g of deionized water, and 0.2g of sodium oleate were added to a ball mill jar. Zirconia balls were added as the ball milling medium, with a ball-to-powder mass ratio of 5:1. The mixture was ball milled at 400r / min for 6h to obtain a suspension slurry. Subsequently, 1.4g of ammonia water with a mass concentration of 25% was added to adjust the pH to 8.1. The mixture was then activated by stirring at 300r / min at 55℃ for 2.5h. After filtration, a solid product was obtained. The solid product was washed sequentially with 20g of anhydrous ethanol and 20g of deionized water, and then vacuum dried at 80℃ and -0.08MPa for 8h. The mixture was then pulverized by air jet milling until the powder could pass through a 300-mesh sieve to obtain a molybdenum-niobium-boron-nitrogen-oxygen synergistic infiltration catalyst.

[0042] Example 2

[0043] The difference between this embodiment and Embodiment 1 is that this embodiment provides a new carbonitriding process for bearing parts, including the following steps:

[0044] S1. Add 100g of GCr15 bearing parts to a container, add 2g of anhydrous sodium carbonate and 95g of deionized water, and treat at 55℃ for 10min. After removal, wipe with 15g of anhydrous ethanol and dry until no visible droplets are visible on the surface to obtain dried GCr15 bearing parts. Mix 0.2g of molybdenum-niobium-boron-nitrogen-oxygen synergistic infiltration catalyst, 0.5g of ethyl cellulose, 25g of anhydrous ethanol and 5g of acetone, and stir until the ethyl cellulose is dispersed and the molybdenum-niobium-boron-nitrogen-oxygen synergistic infiltration catalyst is uniformly suspended to obtain infiltration coating solution. Contact the dried GCr15 bearing parts with the infiltration coating solution so that the infiltration coating solution covers the surface of the GCr15 bearing parts. After removal, dry until the surface coating is free of drips and place in a carburizing furnace.

[0045] S2. Nitrogen gas is introduced into the carburizing furnace for replacement, methanol is introduced, and the temperature is raised to 830℃ for 80 minutes to obtain the treated GCr15 bearing parts.

[0046] S3. Methanol and propane are introduced into the carburizing furnace and carburized for 50 minutes to obtain pre-carburized GCr15 bearing parts.

[0047] S4. Methanol, propane and ammonia are introduced into the carburizing furnace for carbonitriding treatment for 220 min. After carbonitriding treatment, the parts are quenched in quenching oil for 8 min, and then tempered at 160℃ for 1.5 h to obtain the carbonitrided bearing parts.

[0048] Preparation steps of molybdenum-niobium-boron-nitrogen-oxygen synergistic permeation catalyst

[0049] A1. Under nitrogen protection, 6g of ammonium heptamolybdate tetrahydrate, 1.2g of ammonium niobate oxalate hydrate, 2g of boric acid and 8g of citric acid monohydrate were added to a reactor, along with 60g of deionized water. The mixture was stirred at 55°C for 40 min. Subsequently, ammonia was added to adjust the pH to 3.6, and 3g of polyethylene glycol 400 and 10g of anhydrous ethanol were added. The mixture was heated to 60°C and reacted for 1 h to obtain the molybdenum-niobium-boron complex precursor solution.

[0050] A2. Add 100g of molybdenum-niobium-boron complex precursor liquid, 10g of urea, 4g of melamine, 3g of glucose and 1g of polyvinylpyrrolidone to a reaction vessel and stir at 70℃ for 60min; then concentrate under reduced pressure for 1h to obtain a concentrate; dry the concentrate for 8h to obtain molybdenum-niobium-boron-nitrogen-carbon dry gel.

[0051] A3. Place 15g of molybdenum-niobium-boron-nitrogen-carbon dry gel in a tube furnace and heat it to 280℃ for 1h under a nitrogen atmosphere; then heat it to 480℃ for 2h; then switch to a mixed atmosphere of nitrogen and ammonia and heat it at 600℃ for 2h, and cool it to room temperature to obtain molybdenum-niobium-boron-nitrogen-oxygen composite powder.

[0052] A4. Add 20g of molybdenum-niobium-boron-nitrogen-oxygen composite powder, 70g of anhydrous ethanol, 10g of deionized water and 0.1g of sodium oleate to a ball mill jar and ball mill for 4 hours to obtain a suspension slurry; then add ammonia water to adjust the pH to 7.8 and activate at 50℃ for 2 hours; filter to obtain a solid product; wash the solid product with 15g of anhydrous ethanol and 15g of deionized water, vacuum dry for 6 hours, and air jet mill to obtain a molybdenum-niobium-boron-nitrogen-oxygen synergistic permeation catalyst.

[0053] Example 3

[0054] The difference between this embodiment and Embodiment 1 is that this embodiment provides a new carbonitriding process for bearing parts, including the following steps:

[0055] S1. Add 120g of GCr15 bearing parts to a container, add 5g of anhydrous sodium carbonate and 105g of deionized water, and treat at 65℃ for 20min. After removal, wipe with 25g of anhydrous ethanol and dry until no visible droplets are visible on the surface to obtain dried GCr15 bearing parts. Mix 0.8g of molybdenum-niobium-boron-nitrogen-oxygen synergistic infiltration catalyst, 1.2g of ethyl cellulose, 45g of anhydrous ethanol and 10g of acetone, and stir until the ethyl cellulose is dispersed and the molybdenum-niobium-boron-nitrogen-oxygen synergistic infiltration catalyst is uniformly suspended to obtain infiltration coating solution. Contact the dried GCr15 bearing parts with the infiltration coating solution so that the infiltration coating solution covers the surface of the GCr15 bearing parts. After removal, dry until the surface coating is free of drips and place in a carburizing furnace.

[0056] S2. Nitrogen gas is introduced into the carburizing furnace for replacement, methanol is introduced, and the temperature is raised to 850℃ for 100 minutes to obtain the treated GCr15 bearing parts.

[0057] S3. Methanol and propane are introduced into the carburizing furnace and carburized for 70 minutes to obtain pre-carburized GCr15 bearing parts.

[0058] S4. Methanol, propane and ammonia are introduced into the carburizing furnace for carbonitriding treatment for 260 min. After carbonitriding treatment, the parts are quenched in quenching oil for 15 min, and then tempered at 190℃ for 3 h to obtain the carbonitrided bearing parts.

[0059] Preparation steps of molybdenum-niobium-boron-nitrogen-oxygen synergistic permeation catalyst

[0060] A1. Under nitrogen protection, 10g of ammonium heptamolybdate tetrahydrate, 2.5g of ammonium niobate oxalate hydrate, 4g of boric acid and 14g of citric acid monohydrate were added to a reactor, along with 90g of deionized water. The mixture was stirred at 65°C for 60 min. Subsequently, ammonia was added to adjust the pH to 4.0, and 5g of polyethylene glycol 400 and 20g of anhydrous ethanol were added. The mixture was heated to 70°C and reacted for 2 h to obtain the molybdenum-niobium-boron complex precursor solution.

[0061] A2. Add 140g of molybdenum-niobium-boron complex precursor liquid, 18g of urea, 8g of melamine, 6g of glucose and 3g of polyvinylpyrrolidone to a reaction vessel and stir at 80℃ for 90min; then concentrate under reduced pressure for 2h to obtain a concentrate; dry the concentrate for 12h to obtain molybdenum-niobium-boron-nitrogen-carbon dry gel.

[0062] A3. Place 25g of molybdenum-niobium-boron-nitrogen-carbon dry gel in a tube furnace and heat it to 320℃ for 2h under a nitrogen atmosphere; then heat it to 540℃ for 3h; then switch to a mixed atmosphere of nitrogen and ammonia and heat it at 650℃ for 4h. Cool it to room temperature to obtain molybdenum-niobium-boron-nitrogen-oxygen composite powder.

[0063] A4. Add 30g of molybdenum-niobium-boron-nitrogen-oxygen composite powder, 90g of anhydrous ethanol, 20g of deionized water and 0.3g of sodium oleate to a ball mill jar and ball mill for 8 hours to obtain a suspension slurry; then add ammonia water to adjust the pH to 8.4 and activate at 60℃ for 3 hours; filter to obtain a solid product; wash the solid product with 25g of anhydrous ethanol and 25g of deionized water, vacuum dry for 10 hours, and air jet mill to obtain a molybdenum-niobium-boron-nitrogen-oxygen synergistic permeation catalyst.

[0064] Comparative Example 1

[0065] The difference between this comparative example and Example 1 is that 0.5g of the molybdenum-niobium-boron-nitrogen-oxygen synergistic permeation catalyst is not added in step S1; otherwise, it is the same as Example 1.

[0066] Comparative Example 2

[0067] The difference between this comparative example and Example 1 is that 3g of boric acid is not added in step A1, while the rest is the same as in Example 1.

[0068] Comparative Example 3

[0069] The difference between this comparative example and Example 1 is that 1.85g of ammonium niobate oxalate hydrate is not added in step A1, while the rest is the same as in Example 1.

[0070] A series of standardized tests were conducted on the new carbonitriding process for bearing parts described in Examples 1-3 and Comparative Examples 1-3.

[0071] Five samples were taken from the carbonitrided GCr15 bearing parts prepared in Examples 1-3 and Comparative Examples 1-3, respectively. All samples were cleaned with anhydrous ethanol to remove surface oil before testing and dried at 60°C for 30 min.

[0072] For surface hardness testing, the test surface of the GCr15 bearing part was sanded and polished step by step with sandpaper until the surface was free of oxide scale, oil stains and obvious scratches. The Rockwell hardness tester was used for testing with a diamond conical indenter. The initial test force was 98.07N and the total test force was 1471N. Five positions were evenly selected along the circumference of each GCr15 bearing part for indentation testing. The distance between the centers of adjacent indentations was not less than 3mm and the distance between the center of the indentation and the edge was not less than 2mm. A total of 25 test values ​​were obtained for each group. After removing outliers caused by indentation overlap, edge collapse or surface defects, the average value was taken. The result is expressed as HRC.

[0073] During the effective hardened layer depth test, the GCr15 bearing part was radially cut, and the cross-section was inlaid, ground, polished and etched before being placed on the stage of the microhardness tester. The starting test point was 0.03 mm from the surface, and the test was carried out point by point along the direction perpendicular to the surface toward the core. The test load was 1.961 N, the holding time was 15 s, and the distance between adjacent test points was 0.05 mm. Three test lines were tested for each sample. When the microhardness decreased to the position corresponding to 550 HV, the vertical distance from that position to the sample surface was recorded. The average value of all test lines of 5 samples in each group was taken as the effective hardened layer depth, and the result was expressed in mm.

[0074] For surface carbon content testing, the surface of GCr15 bearing parts was polished, cleaned and dried. The carbon content in the range of 0-50μm from the surface was continuously etched and detected using glow discharge spectroscopy. Three test areas were selected for each sample, and the area of ​​each area was kept consistent. Before the test, a blank sample of the same material was used to correct the background signal. The integral average value of carbon content in the range of 0-50μm was taken as the surface carbon content of the sample. The average value of 5 samples in each group was taken, and the result was expressed as a percentage.

[0075] For the surface nitrogen content test, the same sample preparation and glow discharge spectroscopy analysis method as the surface carbon content were used. The nitrogen content in the range of 0-50 μm from the surface was continuously etched and detected. Three test areas were selected for each sample, avoiding indentation, crack and edge positions. The integral average value of nitrogen content in the range of 0-50 μm was taken as the surface nitrogen content of the sample. The average value of 5 samples in each group was taken and the result was expressed as %.

[0076] During the wear loss test, GCr15 bearing parts were cut into planar specimens of uniform size. The test surfaces were ground and polished until the roughness was uniform. Before the test, the specimens were ultrasonically cleaned with anhydrous ethanol for 10 minutes and dried at 60℃ for 30 minutes. The initial mass was weighed using a balance with an accuracy of 0.1 mg. Then, a dry friction and wear test was performed using a reciprocating friction and wear tester. The wear part was a cemented carbide ball, the load was 20 N, the reciprocating frequency was 10 Hz, the stroke was 5 mm, and the test time was 60 minutes. After the test, the wear debris was cleaned with anhydrous ethanol and dried. The mass after wear was weighed again. The difference in mass before and after the test was taken as the wear loss. Five specimens were tested in each group and the average value was taken. The result is expressed in mg.

[0077] For rolling contact fatigue life testing, GCr15 bearing parts were machined into rolling contact fatigue specimens of uniform dimensions. Before testing, the specimens were cleaned and dried with anhydrous ethanol. The rolling contact fatigue testing machine was used, with a contact stress of 4.0 GPa, a rotation speed of 3000 r / min, and a lubricating oil temperature of 40℃. The lubrication method remained consistent. During the test, the vibration signal and surface condition of the specimens were continuously monitored. Failure was defined as the appearance of visible spalling, crack propagation, or a sudden increase in vibration signal on the specimen surface. The number of cycles before failure was recorded. Five specimens were tested in each group, and the average value was taken. The results were expressed as a multiplier of 10. 6 This is a secondary representation.

[0078] The performance test data above are shown in Table 1.

[0079] Table 1: Performance Test Results

[0080]

[0081] As can be seen from the above, the surface hardness of Examples 1-3 is 61.8-63.2 HRC, which is significantly higher than that of Comparative Examples 1-3 (59.4-61.0 HRC). This indicates that after using a molybdenum-niobium-boron-nitrogen-oxygen synergistic infiltration catalyst and combining it with pre-carburizing and carbonitriding treatment, the surface strengthening degree of GCr15 bearing parts is higher, solving the problem of insufficient surface hardness after conventional carbonitriding.

[0082] The effective hardened layer depth of Examples 1-3 is 0.32-0.43 mm, which is higher than that of Comparative Examples 1-3 (0.24-0.31 mm). This indicates that the present invention can promote the diffusion of carbon and nitrogen into the inner side of the surface layer, making the hardened layer deeper and improving the problems of insufficient infiltration layer and shallow reinforcement layer.

[0083] The surface carbon content of Examples 1-3 was 0.98-1.12%, which was higher than that of Comparative Examples 1-3 (0.86-0.97%). Among them, Comparative Example 1 had the lowest surface carbon content, only 0.86%, when no molybdenum-niobium-boron-niobium-oxygen synergistic catalyst was added. This shows that the present invention effectively reduces the surface carbon deficiency problem that may be caused by ammonia participating in carbonitriding by first carburizing and then carbonitriding and introducing a molybdenum-niobium-boron-niobium-oxygen synergistic catalyst.

[0084] The surface nitrogen content of Examples 1-3 was 0.19-0.29%, which was higher than that of Comparative Examples 1-3 (0.10-0.18%). This indicates that the molybdenum-niobium-boron-nitrogen-oxygen synergistic infiltration catalyst can improve the adsorption and diffusion effect of active nitrogen after ammonia decomposition on the surface of GCr15 bearing parts, making the carbon-nitrogen composite reinforcement layer more complete.

[0085] The wear loss of Examples 1-3 was 3.6-5.0 mg, which was significantly lower than that of Comparative Examples 1-3 (6.9-9.8 mg). This indicates that the improvement of surface hardness, effective hardened layer depth, and surface carbon and nitrogen content jointly enhanced the wear resistance of GCr15 bearing parts, solving the problem of insufficient wear resistance after existing processing.

[0086] The rolling contact fatigue life of Examples 1-3 is 13.7 × 10⁻⁶. 6 -18.5×10 6 This is higher than the 7.2 × 10⁻⁶ in Comparative Examples 1-3. 6 -10.1×10 6 This demonstrates that the carbon-nitrogen composite reinforcing layer formed by the present invention can improve the ability of GCr15 bearing parts to withstand alternating contact stress and extend their service life.

[0087] Meanwhile, in Comparative Example 2, after removing boric acid, the wear weight loss increased to 6.9 mg, and the rolling contact fatigue life decreased to 10.1 × 10⁻⁶. 6 In Comparative Example 3, after removing ammonium oxalate hydrate from niobate, the wear weight loss increased to 7.4 mg and the rolling contact fatigue life decreased to 9.4 × 10⁻⁶. 6 This demonstrates that both boron and niobium components contribute to the stability of the carbonitriding interface, uniform carbon and nitrogen diffusion, and surface strengthening. Furthermore, after using a complete molybdenum-niobium-boron-nitrogen-oxygen synergistic carbonitriding body in Examples 1-3, all performance characteristics are superior to those of the comparative examples. This proves that the present invention can solve the technical problems of surface carbon depletion, insufficient diffusion depth, low hardness, poor wear resistance, and short rolling contact fatigue life in the carbonitriding of existing bearing parts.

Claims

1. A novel carbonitriding process for bearing parts, characterized in that, Includes the following steps: S1. By weight, add 100-120 parts of GCr15 bearing parts to a container, add 2-5 parts of anhydrous sodium carbonate and 95-105 parts of deionized water, and treat at 55-65℃; after removal, wipe with anhydrous ethanol and dry to obtain dried GCr15 bearing parts; mix 0.2-0.8 parts of molybdenum-niobium-boron-nitrogen-oxygen synergistic infiltration catalyst, 0.5-1.2 parts of ethyl cellulose, 25-45 parts of anhydrous ethanol and 5-10 parts of acetone to obtain infiltration coating solution; contact the dried GCr15 bearing parts with the infiltration coating solution, dry, and place in a carburizing furnace; S2. Nitrogen gas is introduced into the carburizing furnace for replacement, methanol is introduced, and the temperature is raised to 830-850℃ for treatment to obtain the treated GCr15 bearing parts. S3. Methanol and propane are introduced into the carburizing furnace to carry out carburizing treatment and obtain pre-carburized GCr15 bearing parts. S4. Introduce methanol, propane and ammonia into the carburizing furnace for carbonitriding treatment; after carbonitriding treatment, transfer to quenching oil for quenching, and then temper at 160-190℃.

2. The novel carbonitriding process for bearing parts according to claim 1, characterized in that, In step S1, the treatment time at 55-65℃ is 10-20 minutes.

3. The novel carbonitriding process for bearing parts according to claim 1, characterized in that, In step S2, the heating time to 830-850℃ is 80-100 minutes.

4. The novel carbonitriding process for bearing parts according to claim 1, characterized in that, In step S3, the carburizing treatment time is 50-70 minutes.

5. The novel carbonitriding process for bearing parts according to claim 1, characterized in that, In step S4, the carbonitriding treatment time is 220-260 min, the quenching time is 8-15 min, and the tempering time is 1.5-3 h.

6. The novel carbonitriding process for bearing parts according to any one of claims 1-5, characterized in that, The preparation steps of the molybdenum-niobium-boron-nitrogen-oxygen synergistic infiltration catalyst include: A1. By weight, under nitrogen protection, add 6-10 parts of ammonium heptamolybdate tetrahydrate, 1.2-2.5 parts of ammonium niobate oxalate hydrate, 2-4 parts of boric acid and 8-14 parts of citric acid monohydrate to a reactor, add 60-90 parts of deionized water, and stir at 55-65℃; then add ammonia water to adjust the pH to 3.6-4.0, add 3-5 parts of polyethylene glycol 400 and 10-20 parts of anhydrous ethanol, and heat to 60-70℃ to react and obtain the molybdenum-niobium-boron complex precursor liquid; A2. Add 100-140 parts of molybdenum-niobium-boron complex precursor liquid, 10-18 parts of urea, 4-8 parts of melamine, 3-6 parts of glucose and 1-3 parts of polyvinylpyrrolidone to a reaction vessel and stir at 70-80℃; then concentrate under reduced pressure to obtain a concentrate; dry the concentrate to obtain molybdenum-niobium-boron-nitrogen-carbon dry gel. A3. Place 15-25 parts of molybdenum-niobium-boron-nitrogen-carbon dry gel in a tube furnace and treat it at 280-320℃ under a nitrogen atmosphere; then treat it at 480-540℃; then switch to a mixed atmosphere composed of nitrogen and ammonia and treat it at 600-650℃, and cool it to room temperature to obtain molybdenum-niobium-boron-nitrogen-oxygen composite powder. A4. Add 20-30 parts of molybdenum-niobium-boron-nitrogen-oxygen composite powder, 70-90 parts of anhydrous ethanol, 10-20 parts of deionized water, and 0.1-0.3 parts of sodium oleate to a ball mill jar and ball mill to obtain a suspension slurry; then add ammonia water to adjust the pH to 7.8-8.4 and activate at 50-60℃; filter to obtain a solid product; wash the solid product with anhydrous ethanol and deionized water, vacuum dry, and air jet mill.

7. The novel carbonitriding process for bearing parts according to claim 6, characterized in that, In step A1, the stirring time at 55-65℃ is 40-60 minutes, and the reaction time at 60-70℃ is 1-2 hours.

8. The novel carbonitriding process for bearing parts according to claim 6, characterized in that, In step A2, the stirring time at 70-80℃ is 60-90 min, the concentration time under reduced pressure is 1-2 h, and the drying time is 8-12 h.

9. The novel carbonitriding process for bearing parts according to claim 6, characterized in that, In step A3, the treatment time is 1-2 hours when the temperature is raised to 280-320℃, 2-3 hours when the temperature is raised to 480-540℃, and 2-4 hours when the temperature is raised to 600-650℃.

10. The novel carbonitriding process for bearing parts according to claim 6, characterized in that, In step A4, the ball milling time is 4-8 hours, the activation time at 50-60℃ is 2-3 hours, and the vacuum drying time is 6-10 hours.

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