A composite carburizing method for preparing a high-load-bearing, anti-friction, self-lubricating functional layer

Abstract

A composite carburizing method for preparing a high-load-bearing, anti-friction, self-lubricating functional layer belongs to the field of alloy processing technology. The purpose of the present invention is to solve the problem that the organization and composition of the diamond-like / graphite-like film and the substrate are too different, resulting in poor bonding between the two. The present invention uses low-temperature plasma carburizing treatment to generate a diamond-like / graphite-like film in situ on the surface of a carburized gear with dispersed carbides, thereby achieving an ultra-low friction coefficient and anti-friction self-lubricating function of the gear and improving the bonding between the carburized layer and the diamond-like / graphite-like film. During the plasma carburizing process of the present invention, the carbon element not only generates a diamond-like / graphite-like film on the surface, but also diffuses inward synchronously to form a gradient functional layer that gradually transitions from a diamond-like structure to a high-concentration carbon. The slowly changing composition difference greatly improves the bonding between the diamond-like / graphite-like film and the carburized layer.

Description

Technical Field

[0001] The invention belongs to the technical field of alloy processing, and in particular relates to a composite carburizing method for preparing a high-load-bearing, friction-reducing, and self-lubricating functional layer. Background Art

[0002] Gears and bearings, as fundamental mechanical components that provide motion and power transmission, can achieve functions such as changing speed and torque, altering the direction and form of motion, and possess advantages such as accurate output transmission ratios, high transmission efficiency, and a wide power range. They play an indispensable role in maintaining the stable operation of machines, instruments, and equipment. Therefore, gears and bearings require strengthening treatment to ensure their stable operation and service life during service. Carburizing is a simple, efficient, and widely used surface strengthening method. After carburizing, gears and bearings retain high toughness in their cores while forming a high-hardness modified layer on the surface. This delays the propagation of cracks that occur when the gears are loaded, thereby increasing the fatigue life of the material.

[0003] However, the current single carburizing treatment still cannot meet the gear's requirements for wear resistance and anti-adhesion, especially under poor lubrication conditions, which requires a composite surface treatment to obtain excellent comprehensive performance. Diamond-like carbon / graphite-like film is a kind of sp 3 and sp 2 A general term for amorphous carbon with hybridized carbon atoms. Studies have shown that carbides have an inductive effect on the growth of diamond-like / graphite-like films, and high-energy plasma bombardment can promote sp 3 bond formation, increasing sp 3 / sp 2 The ratio of 20% to 10% can significantly increase the surface hardness of gears, significantly reduce the friction coefficient, greatly reduce the wear rate of gears and bearings, and inhibit the initiation and propagation of surface fatigue cracks, thereby increasing the fatigue life of gears and bearings. However, the structure and composition of the diamond-like / graphite-like films prepared in most current research differ greatly from those of the substrate, resulting in poor bonding between the two. This makes the gears prone to shedding during actual service, further inducing the formation of microcracks, causing the failure of gears and bearings, and leading to major engineering accidents. All of these factors have greatly limited the application of diamond-like / graphite-like films in gears. Summary of the Invention

[0004] The present invention aims to address the problem of poor bonding between diamond-like / graphite-like films and their substrates due to significant differences in structure and composition. The method provides a composite carburizing method for preparing a high-load-bearing, friction-reducing, self-lubricating functional layer. This method uses low-temperature plasma carburizing to in-situ generate diamond-like / graphite-like films on the surfaces of carburized gears and bearings containing dispersed carbides. This achieves ultra-low friction coefficients and friction-reducing, self-lubricating properties for the gears and bearings, while also enhancing the bonding strength between the carburized layer and the diamond-like / graphite-like film.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A composite carburizing method for preparing a high-load-bearing, anti-friction, self-lubricating functional layer, wherein the heat treatment method is vacuum carburizing + low-temperature plasma carburizing. During the low-temperature plasma carburizing, the core is tempered at the same time. Figure 1 The method is as follows:

[0007] Step 1: Pre-treat the gear steel or bearing steel by grinding the surface of the gear steel or bearing steel with 800# sandpaper, and then clean and dry it to obtain pre-treated gear steel or bearing steel;

[0008] Step 2: vacuum carburizing the pretreated alloy steel at 850°C to 1000°C and 1000Pa to obtain a carburized layer containing martensite, retained austenite and dispersed carbides on the surface, thereby obtaining the carburized alloy steel; the carburized layer is judged by hardness test, and generally a carburized layer with a hardness higher than 550HV is regarded as an effective carburized layer, and a carburized layer can be obtained within this temperature range;

[0009] Step 3: The carburized alloy steel is subjected to plasma carburizing at a temperature of 100°C to 450°C, a time of 1h to 10h, a voltage of 400V to 900V, and a gas pressure of 40Pa to 500Pa, while achieving core tempering, and in-situ generation of a diamond-like / graphite-like film on the surface of the carburized layer, thereby completing the preparation of a friction-reducing and self-lubricating functional layer on the surface of a high-load-bearing vacuum carburized layer where dispersed carbides are precipitated based on a low-temperature plasma carburizing method.

[0010] Furthermore, in step 2, the pressure of vacuum carburizing is 2000Pa to 3000Pa.

[0011] Furthermore, in step three, plasma carburizing adopts a mixed atmosphere of hydrogen and carbon-containing gas, wherein the carbon-containing atmosphere is any one of carbon monoxide, carbon dioxide, methanol, acetone, methane, ethane, propane, and acetylene, accounting for 1%-30% of the total volume of the mixed carburizing atmosphere.

[0012] Furthermore, in step three, for gear steel and bearing steel without secondary hardening effect, the plasma carburizing process temperature is 180℃~220℃, the time is 4h~10h, the voltage is 500V~800V, and the air pressure is 150Pa~500Pa; for gear steel and bearing steel with secondary hardening effect, the plasma carburizing process temperature is 450℃~500℃, the time is 1h~4h, the voltage is 600V~900V, and the air pressure is 150Pa~400Pa.

[0013] The beneficial effects of the present invention compared to the prior art are:

[0014] 1. The present invention first performs vacuum carburizing treatment on the alloy steel, and a carburized layer composed of martensite (α-Fe), retained austenite (γ-Fe) and fine dispersed carbides is generated on the surface, thereby increasing the carbon content on the alloy surface, obtaining a modified layer with high hardness, and providing a growth site for diamond-like / graphite-like films. Afterwards, a low-temperature plasma carburizing composite process is performed, and under the induction of fine and dense carbides, a diamond-like / graphite-like film is generated in situ on the surface of the carburized layer. The diamond-like / graphite-like film has an ultra-low friction coefficient of 0.04, which reduces the friction coefficient by one order of magnitude compared to vacuum carburizing treatment. At the same time, during the friction process, the diamond-like / graphite-like film has a friction-reducing and self-lubricating function, and the wear marks are narrow, the wear marks are slight, and it has excellent wear resistance.

[0015] 2. During the plasma carburizing process of the present invention, the carbon element not only generates a diamond-like / graphite-like film on the surface, but also simultaneously diffuses inward to form a gradient functional layer that gradually transitions from a diamond-like structure to a high-concentration carbon layer. The slowly changing composition difference greatly enhances the bonding strength between the diamond-like / graphite-like film and the carburized layer.

[0016] 3. During the low-temperature plasma carburizing process, the present invention simultaneously performs tempering treatment on the alloy steel, and the in-situ generation of diamond-like / graphite-like films and the tempering treatment are carried out simultaneously. By adjusting the temperature on the equipment, the carbon content in the atmosphere can be achieved. The operation is simple, the process flow is simplified, energy and time consumption are saved, and the method is applicable to different alloy steels, with a wide range of applications and significant engineering application potential and research value. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the composite carburizing process curve of the wear-resistant, friction-reducing and self-lubricating functional layer;

[0018] Figure 2 The Raman spectra of the surface before and after low-temperature ion carburizing;

[0019] Figure 3 XRD patterns before and after low-temperature ion carburizing;

[0020] Figure 4 This is the cross-sectional metallographic structure diagram of Comparative Example 1 before low-temperature ion carburizing;

[0021] Figure 5 This is the cross-sectional metallographic structure diagram after low-temperature ion carburizing in Example 2;

[0022] Figure 6 This is the surface morphology of Comparative Example 1 before low-temperature ion carburizing;

[0023] Figure 7 This is the surface morphology of Example 1 after low-temperature ion carburizing;

[0024] Figure 8 This is the hardness distribution diagram before and after low-temperature ion carburizing;

[0025] Figure 9 The friction coefficient diagram before and after low-temperature ion carburizing;

[0026] Figure 10 This is a comparison of the wear scar width before and after low-temperature ion carburizing in Comparative Example 1;

[0027] Figure 11 This is a comparison of the wear scar width before and after low-temperature ion carburizing in Example 1;

[0028] Figure 12 Surface morphology of the wear scar before and after low-temperature ion carburizing in Comparative Example 1;

[0029] Figure 13 Surface morphology of the wear scar before and after low-temperature ion carburizing in Example 1;

[0030] Figure 14 This is the surface carbon concentration distribution after low-temperature plasma carburizing. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention should be included in the scope of protection of the present invention.

[0032] Example 1:

[0033] 1. Pretreatment: Use 800# sandpaper to polish the surface of 20Cr2Ni4 steel to remove surface oxides and processing marks, and then use acetone to clean and dry to obtain pretreated alloy steel;

[0034] 2. Vacuum carburizing: The pretreated 20Cr2Ni4 steel was vacuum pulse carburized at 900°C, 2000 Pa for 6 hours using a mixture of acetylene and nitrogen at a flow rate of 8 L / min. After carburizing, the steel was oil quenched at 900°C to obtain a carburized layer containing martensite, retained austenite, and fine dispersed carbides, with a carburized layer depth of 0.9-1.1 mm.

[0035] 3. After vacuum carburizing, the 20Cr2Ni4 steel was cleaned again with acetone to remove any residual quenching oil. Low-temperature plasma carburizing was then performed at 200°C, 500V, and 150Pa for 4 hours. Propane and hydrogen were introduced as the reaction gases, with a carbon content of 1% to 10%, to produce diamond-like / graphite-like films.

[0036] 4. Characterize the microstructure and mechanical properties of 20Cr2Ni4 steel after vacuum carburizing + low-temperature plasma carburizing.

[0037] Example 2:

[0038] 1. Pretreatment: Use 800# sandpaper to polish the surface of 17CrNiMo6 steel to remove surface oxides and processing marks, and then use acetone to clean and dry to obtain pretreated alloy steel;

[0039] 2. Vacuum carburizing: The pretreated 17CrNiMo6 steel was subjected to vacuum pulse carburizing at 920°C, 2500 Pa, for 4 hours using a mixture of acetylene and nitrogen at a flow rate of 10 L / min. Following carburizing, the steel was oil quenched at 860°C to obtain a carburized layer containing martensite, retained austenite, and fine dispersed carbides, with a carburized layer depth of 0.9-1.1 mm.

[0040] 3. After vacuum carburizing, the 17CrNiMo6 steel was cleaned again with acetone to remove any residual quenching oil. Low-temperature plasma carburizing was then performed at 180°C, 800V, and 500Pa for 2 hours. Acetone and hydrogen were introduced as the reaction gases, with a carbon content of 60%-80%, to produce diamond-like / graphite-like films.

[0041] 4. Characterize the microstructure and mechanical properties of 17CrNiMo6 steel after vacuum carburizing + low-temperature plasma carburizing.

[0042] Example 3:

[0043] 1. Pretreatment: Use 800# sandpaper to polish the surface of M50NiL steel to remove surface oxides and processing marks, and then use acetone to clean and dry to obtain pretreated alloy steel;

[0044] 2. Vacuum Carburizing: The pretreated M50NiL steel was subjected to vacuum pulse carburizing at 960°C, 3000 Pa, for 4 hours using a mixture of acetylene and nitrogen at a flow rate of 8 L / min. Following carburizing, the steel was oil quenched at 960°C to obtain a carburized layer with a surface thickness of 0.9-1.1 mm, consisting of martensite, retained austenite, and finely dispersed carbides.

[0045] 3. After vacuum carburizing, the M50NiL steel was cleaned again with acetone to remove any residual quenching oil. Plasma carburizing was then performed at 450°C, 650V, and 300Pa for 4 hours. Carbon dioxide and hydrogen were introduced as the reaction gases, with a carbon content of 20%-30%, to produce diamond-like / graphite-like films.

[0046] 4. Characterize the microstructure and mechanical properties of M50NiL steel after vacuum carburizing + low-temperature plasma carburizing.

[0047] Comparative Example 1:

[0048] 1. Pretreatment: Use 800# sandpaper to polish the surface of 20Cr2Ni4 steel to remove surface oxides and processing marks, and then use acetone to clean and dry to obtain pretreated alloy steel;

[0049] 2. Vacuum carburizing: The pretreated 20Cr2Ni4 steel was vacuum pulse carburized at 900°C, 2000 Pa, for 4 hours using an acetylene + ethylene mixture at a flow rate of 8 L / min. Following carburization, the steel was oil quenched at 900°C, resulting in a 20Cr2Ni4 steel surface composed of carbon-containing martensite, retained austenite, and fine dispersed carbides, with a carburized layer depth of 0.9-1.1 mm.

[0050] 3. Clean the vacuum carburized 20Cr2Ni4 steel again with acetone to remove the residual quenching oil on the surface, then place it in a drying oven at 200°C for 4 hours, and then air cool it after the insulation is completed.

[0051] 4. Characterize the microstructure and mechanical properties of 20Cr2Ni4 steel after vacuum carburizing.

[0052] Tissue Characterization:

[0053] Depend on Figure 2 As can be seen, the Raman curve of Comparative Example 1 is smooth and without fluctuation, indicating that vacuum carburization alone cannot produce a diamond-like / graphite-like film on the alloy surface. However, the products obtained from Examples 1, 2, and 3 after vacuum carburization and plasma carburization all exhibit the characteristic peaks D and G of a typical amorphous carbon structure, indicating that after low-temperature ion carburization, all three successfully form diamond-like / graphite-like films on the carburized layer surface.

[0054] Depend on Figure 3 As can be seen, the carburized layer of Comparative Example 1 contains carbon martensite, retained austenite, and fine carbides. According to the national standard GB / T 25744-2010, the generated martensite and retained austenite are both classified as Grade 1. After plasma carburization, the carburized layer of Example 1 precipitates more carbides with smaller diameters, providing more optimal formation sites for diamond-like / graphite-like films and promoting the formation of diamond-like / graphite-like films.

[0055] Figure 4 and 5In Comparative Example 1, a large number of dispersed carbides precipitated within approximately 500 μm from the carburized layer surface. The closer to the surface, the greater the number of carbides, providing numerous growth sites for diamond-like / graphite-like films and significantly inducing and promoting their formation. After plasma carburization, the carbides in Example 2 were reduced in diameter, more evenly distributed, and their number further increased.

[0056] Depend on Figure 6 and 7 As can be seen, after vacuum carburizing, the surface of Comparative Example 1 exhibits a tortoise-shell morphology and is relatively rough, with a large number of carbide particles with a diameter of 1-2 μm precipitated on the surface. After plasma carburizing, a fine and dense diamond-like / graphite-like film structure is formed on the surface, significantly reducing the surface roughness of the vacuum carburized layer.

[0057] Comparison of mechanical properties:

[0058] Figure 8 The hardness distribution diagram before and after low-temperature ion carburizing. In Example 1, while low-temperature plasma carburizing was used to generate diamond-like / graphite-like films, tempering treatment was also performed simultaneously. The hardness of the final carburized layer was similar to that of Comparative Example 1, still maintaining 800HV. 0.1 The surface hardness of the infiltrated layer is 900HV. 0.1 , then at 800HV 0.1 There is a hardness platform of about 650 μm in length. The surface hardness of Example 3 is as high as 950 HV. 0.1 .

[0059] Figure 9 The friction coefficient of alloy steel before and after ion carburizing is 0.45 for Comparative Example 1. After low-temperature plasma carburizing, Examples 1-3 generate in-situ diamond-like / graphite-like films on the carburized layer, significantly reducing the friction coefficient. The friction coefficient of Example 2 is 0.1, and that of Example 3 is 0.125. Example 1 achieves the largest reduction, reaching 0.04, a reduction of an order of magnitude. At 2000 seconds into the friction and wear test, the friction coefficient is further reduced, demonstrating the friction-reducing and self-lubricating properties of the diamond-like / graphite-like films.

[0060] Figure 10 and 11 The wear scar morphology of Comparative Example 1 is compared with that of Example 1. The wear scar width of Comparative Example 1 reaches 980 μm, while the wear scar width of Example 1 is 293 μm, which is only 1 / 3 of that of Comparative Example 1 and is much smaller than that of Comparative Example 1.

[0061] Figure 12 and Figure 13The surface morphology after the friction and wear test of Comparative Example 1 and Example 1 is shown. Large pieces of carburized layer peeled off in the scratches of Comparative Example 1, and the peeled carburized layer was severely oxidized, indicating that the carburized layer of Comparative Example 1 was severely damaged under the synergistic effect of severe adhesive wear and oxidative wear, resulting in deep and wide wear marks. However, no furrows were found on the surface of Example 1, and the diamond-like / graphite-like film was not damaged by the grinding balls, leaving only very slight wear marks on the surface. Due to the presence of the diamond-like / graphite-like film, the plastic deformation resistance of the surface of Example 1 was significantly improved, thereby fundamentally changing the wear mechanism in the friction and wear process and greatly enhancing the wear resistance of Example 1. In addition, the diamond-like / graphite-like film did not fall off after the friction and wear test, indicating that it has a strong bonding force with the carburized layer matrix.

[0062] Figure 14 This is the surface carbon concentration profile of Example 1. Within 1 μm of the surface, the carbon concentration rapidly decreases from 45wt% to 10wt%. As the distance from the surface increases, the carbon concentration first smoothly transitions to 5wt%, then slowly decreases along the depth of the carburized layer. The high carbon concentration on the surface provides the elements that form the diamond-like / graphite-like film, and the slowly decreasing carbon concentration gradient ensures a stable transition from the diamond-like structure to the high-carbon gradient functional layer. This slowly changing composition significantly enhances the bonding between the diamond-like / graphite-like film and the carburized layer.

Claims

1. A composite carburizing method for preparing a high-load-bearing, anti-friction, self-lubricating functional layer, characterized by: The method is: Step 1: Pre-treat the gear steel or bearing steel without secondary hardening effect by polishing the surface of the gear steel or bearing steel with 800# sandpaper, and then clean and dry it to obtain pre-treated gear steel or bearing steel; the gear steel or bearing steel without secondary hardening effect is 20Cr2Ni4 steel or 17CrNiMo6 steel; Step 2: vacuum carburizing the pretreated gear steel or bearing steel at 850°C to 920°C and 2000Pa to 3000Pa, followed by oil quenching to obtain a carburized layer containing martensite, retained austenite, and dispersed carbides on the surface, thereby obtaining a carburized alloy steel; the depth of the carburized layer is 0.9 to 1.1 mm; Step 3: Plasma carburizing the carburized alloy steel at a temperature of 180°C to 200°C for 4 hours to 10 hours, a voltage of 500V to 800V, and a pressure of 150Pa to 500Pa, while simultaneously achieving core tempering, in situ generating a diamond-like / graphite-like film on the surface of the carburized layer, thereby completing the preparation of a friction-reducing and self-lubricating functional layer on the surface of the high-load-bearing vacuum carburized layer where dispersed carbides are precipitated based on the low-temperature plasma carburizing method; In step three, plasma carburizing uses a mixed atmosphere of hydrogen and carbon-containing gas, wherein the carbon-containing atmosphere is any one of carbon monoxide, carbon dioxide, methanol, acetone, methane, ethane, propane, and acetylene, accounting for 1% to 10% of the total volume of the mixed carburizing atmosphere.

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