A heat treatment process for high-speed bearings

Abstract

This invention belongs to the field of bearing heat treatment technology, specifically relating to a heat treatment process for high-speed bearings. The heat treatment process for high-speed bearings is characterized by the following steps: (1) Heating stage: placing the high-carbon steel workpiece in a heat treatment furnace, heating, controlling the carbon potential in the furnace, and holding at that temperature; (2) Holding stage: continuing to hold at that temperature; (3) Carbon potential increase stage: maintaining the temperature and increasing the carbon potential in the furnace; (4) Carbonitriding stage: performing carbonitriding treatment; (5) Carbon potential reduction stage: reducing the carbon potential; (6) Diffusion stage: holding at that temperature; (7) Quenching stage: after diffusion, transferring the workpiece to a quenching medium for quenching treatment; (8) Tempering stage. This invention significantly improves the surface quality, dimensional stability, mechanical properties, and service reliability of bearing parts through segmented carbonitriding with controlled carbon potential, characteristic quenching media, and precise tempering control, significantly improving surface microstructure quality and enhancing wear resistance and fatigue resistance.

Description

Technical Field

[0001] This invention belongs to the field of bearing heat treatment technology, and specifically relates to a heat treatment process for high-speed bearings. Background Technology

[0002] High-speed bearings, as key components in precision mechanical equipment, are widely used in aerospace, high-speed motors, rail transportation, CNC machine tools, and other fields. Their operating conditions typically involve high speed, heavy load, long lifespan, and high reliability. During high-speed operation, the bearing rings and rolling elements are subjected to alternating contact stress and frictional heat, making them highly susceptible to failure modes such as fatigue spalling, wear, and galling. Therefore, extremely stringent requirements are placed on the surface hardness, wear resistance, contact fatigue strength, and core toughness of bearing components.

[0003] To meet these performance requirements, heat treatment has become an indispensable core step in bearing manufacturing. Through proper heat treatment (especially surface strengthening treatment), while ensuring good toughness and strength in the material core, surface hardness and wear resistance can be significantly improved. Simultaneously, beneficial residual compressive stress is introduced onto the surface, effectively enhancing the bearing's fatigue life and operational stability. Currently, for high-speed bearings made of high-carbon chromium steel or carburized bearing steel, a combined process of chemical heat treatment and quenching and tempering is commonly used. Among these processes, carbonitriding is widely applied because it can simultaneously improve surface hardness, anti-galling, and fatigue strength.

[0004] In the prior art, a typical heat treatment process for high-speed bearings is as follows: Figure 1 As shown, the main processes include: heating, one-step carbon potential increase, homogenization and degassing, carbonitriding, rapid quenching, oil quenching, and low-temperature tempering. This process can achieve a diffusion layer depth of 0.4–0.6 mm on the surface, resulting in a product surface under compressive stress. The retained austenite content is controlled within the range of 20% to 40%, basically meeting the performance requirements of conventional bearings.

[0005] However, this process still has several key technical defects in practical applications, making it difficult to meet the higher requirements of precision high-speed ball bearings for dimensional stability, surface integrity, and high reliability. Specifically:

[0006] (1) Inappropriate carbon potential control leads to a decline in surface quality: The process adopts a "one-step carbon potential increase" method, that is, the carbon potential is increased to the target value in one step and maintained at a high carbon potential for direct carbonitriding, lacking a step-by-step increase / decrease of carbon potential and diffusion stage. This leads to the supersaturation precipitation of carbon and nitrogen atoms on the surface, forming a coarse carbonitride layer (such as Fe3C, Fe4N, etc.) within a 0.05mm range on the surface. This compound layer is brittle and easily becomes the initiation source of fatigue cracks, reducing the contact fatigue life of the bearing.

[0007] (2) High residual austenite content affects dimensional stability: Existing processes control the residual austenite content to 20%~40% through low-temperature tempering, which can alleviate quenching stress, but this content is still too high for precision high-speed bearings. In actual operation, the bearing generates frictional temperature rise (up to 160℃ or more) due to rapid acceleration and deceleration or continuous high-speed operation, which causes the residual austenite to continue to transform into martensite during service, resulting in material volume expansion, which leads to an increase in the internal dimensions of the bearing, a decrease in clearance, and further aggravation of contact stress, ultimately inducing early spalling failure.

[0008] (3) The quenching method leads to severe deformation and low pass rate: The production equipment is a box-type quenching furnace, which uses vertical drop quenching of whole basket products. To prevent soft spots during quenching, fast quenching oil with a fast cooling rate is used. However, the medium has an excessively fast cooling rate and uneven cooling, which can easily cause significant elliptical deformation or warping, especially for thin-walled bearing rings, resulting in a low first pass rate. A large number of subsequent adjustments or scrapping are required, which increases production costs.

[0009] (4) Limited selection of quenching medium: Although isothermal quenching oil can reduce deformation, it has high viscosity, poor fluidity and slow heat convection. When quenching in batches, it is easy to cause a sharp increase in local oil temperature and a decrease in cooling capacity. There is a risk of incomplete quenching or soft spots. It is difficult to promote its application under the existing box furnace production conditions.

[0010] In summary, existing heat treatment processes for high-speed bearings have significant shortcomings in terms of surface microstructure control, residual austenite stability, and quenching deformation control, making it difficult to meet the comprehensive performance requirements of precision high-speed ball bearings for high precision, long service life, and high reliability. Therefore, it is urgent to develop a new heat treatment process to solve the above-mentioned technical problems and improve the overall performance and service reliability of high-speed bearings. Summary of the Invention

[0011] The purpose of this invention is to provide a heat treatment process for high-speed bearings.

[0012] To achieve the above objectives, the present invention provides the following technical solution:

[0013] A heat treatment process for high-speed bearings includes the following steps:

[0014] (1) Heating stage: Place the high carbon steel workpiece in the heat treatment furnace, heat it, control the carbon potential in the furnace, and keep it at the temperature;

[0015] (2) Insulation stage: Continue insulation for 15-20 minutes;

[0016] (3) Carbon potential enhancement stage: Maintain the temperature and enhance the carbon potential inside the furnace;

[0017] (4) Carbonitriding stage: Carbonitriding treatment is carried out;

[0018] (5) Carbon potential reduction stage: reducing the carbon potential;

[0019] (6) Diffusion stage: Keep warm for 120-130 min;

[0020] (7) Quenching stage: After diffusion is completed, the workpiece is transferred to the quenching medium for quenching treatment;

[0021] (8) Tempering stage: keep warm at a specific temperature for a certain period of time.

[0022] Preferably, in step (1), the temperature is heated to 800-840℃, while the carbon potential in the furnace is controlled at 0.55-0.65%, and the temperature is maintained for 5-10 minutes.

[0023] Preferably, in step (2), the temperature is maintained at 800-840℃ and the carbon potential is 0.55-0.65% for 15-20 minutes.

[0024] Preferably, step (3) increases the carbon potential in the furnace to 1.00-1.10%.

[0025] Preferably, the carbon potential enhancement time in step (3) lasts for 5-10 minutes.

[0026] Preferably, step (4) involves carbonitriding at 800-840℃ and a carbon potential of 1.00-1.10% for 140-160 minutes.

[0027] Preferably, step (5) reduces the carbon potential to 0.80-0.90%, and the adjustment process lasts for 5-10 minutes.

[0028] Preferably, step (6) is performed at a temperature of 800-840℃ and a carbon potential of 0.80-0.90% for 120-130 minutes.

[0029] Preferably, the quenching starting temperature in step (7) is 70-85℃, and isothermal graded quenching oil is used for cooling, with a viscosity of 50-65 mm. 2 / s, maximum cooling rate 70-85℃ / s, characteristic temperature range 710~735℃.

[0030] The preferred isothermal quenching oil is KERUN®KR488 isothermal quenching oil.

[0031] Preferably, step (8) involves maintaining the temperature at 180-220℃ for 180-240 minutes.

[0032] Preferably, the high-carbon steel workpiece comprises the following components by mass percentage: C 0.95-1.05%, Si 0.15-0.35%, Mn 0.25-0.45%, Cr 1.4-1.6%, Mo ≤ 0.1%, P ≤ 0.02%, S ≤ 0.015%, O ≤ 0.0008%, with the balance being iron.

[0033] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0034] 1. This invention provides an optimized heat treatment process for high-speed bearings. Through segmented carbonitriding with controlled carbon potential, a specific quenching medium, and precise tempering control, it significantly improves the surface quality, dimensional stability, mechanical properties, and service reliability of bearing parts, and significantly improves surface microstructure quality, wear resistance, and fatigue resistance. The multi-stage process, employing gradient carbon potential increase, high carbon potential carbonitriding, carbon potential decrease, and diffusion, avoids the surface carbonitriding oversaturation problem caused by the traditional "one-step carbon potential increase." A slightly lower carbon potential is used in the diffusion stage to promote uniform inward diffusion of carbon and nitrogen atoms, effectively suppressing the formation of coarse carbonitriding particles within 0.05 mm of the surface layer, resulting in a fine, dispersed, and uniform carbonitriding microstructure. This ensures that the carbon content on the working surface of the product is ≥0.9% and the nitrogen content is ≥0.1%, significantly improving surface hardness, wear resistance, tempering stability, and high-temperature performance, meeting the requirements of high-speed, heavy-load operating conditions.

[0035] 2. This invention effectively controls heat treatment deformation, improves dimensional accuracy and first-pass yield, and introduces a novel quenching medium. Its kinematic viscosity, characteristic temperature, and maximum cooling rate fall between those of rapid quenching oil and isothermal quenching oil. It possesses sufficient cooling capacity to avoid quenching soft spots; good fluidity and rapid heat convection reduce the dramatic temperature rise during whole-basin quenching; and low phase transformation stress significantly reduces elliptical deformation in thin-walled parts (such as rings with a wall thickness coefficient ≤1.14). This achieves post-heat treatment deformation control within ≤0.15%D (where D is the nominal diameter of the part), significantly improving the first-pass yield before grinding, reducing the need for straightening processes, and lowering production costs.

[0036] 3. This invention, through precise control of specific tempering process parameters (such as temperature and time), stably controls the residual austenite content on the product surface within the ideal range of 10%-20%: Lower limit ≥10%: Retaining an appropriate amount of residual austenite absorbs impact energy, improving resistance to rapid acceleration and deceleration, contamination resistance, and fracture toughness; Upper limit ≤20%: Preventing the large-scale decomposition of residual austenite into martensite due to frictional temperature rise during high-speed operation, thus preventing volume expansion, reduced clearance, and premature spalling failure. This significantly improves the dimensional stability and operational reliability of the product under high-speed and high-temperature conditions, making it particularly suitable for precision high-speed ball bearings. Attached Figure Description

[0037] Figure 1This is a flowchart of an existing heat treatment process.

[0038] Figure 2 This is a flowchart of the heat treatment process of the present invention.

[0039] Figure 3 The image shows the metallographic diagram of the heat treatment technology of the workpiece in Comparative Example 1.

[0040] Figure 4 Metallographic image of the workpiece using the heat treatment technology of Example 1.

[0041] Figure 5 This is a schematic diagram of the test report for KERUN® KR218 rapid bright quenching oil.

[0042] Figure 6 This is a schematic diagram of the test report for KERUN® KR488 isothermal graded quenching oil. Detailed Implementation

[0043] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Example 1

[0045] Please see Figure 2 This embodiment provides a heat treatment process for high-speed bearings, including the following steps:

[0046] (1) Heating stage: The high carbon steel workpiece is placed in a heat treatment furnace and heated to 820°C. At the same time, the carbon potential in the furnace is controlled at 0.60% and held for 5 minutes to achieve uniform heating and prevent surface decarburization. The high carbon steel workpiece includes the following components by mass percentage: C 0.98%, Si 0.24%, Mn 0.35%, Cr 1.49%, Mo 0.002%, P 0.012%, S 0.002%, O 0.0008%, with the balance being iron.

[0047] (2) Heat preservation stage: Continue to keep the temperature at 820℃ and carbon potential of 0.60% for 15 minutes to ensure that the overall temperature of the workpiece is uniform and to prepare the microstructure for the subsequent carburizing and nitriding process.

[0048] (3) Carbon potential increase stage: Maintain the temperature at 820℃ and increase the carbon potential in the furnace to 1.05%. The carbon potential increase time lasts for 5 minutes to avoid the carbon potential from rising too quickly and causing the surface carbon concentration to be too high.

[0049] (4) Carbonitriding stage: Carbonitriding treatment is carried out at 820℃ and carbon potential of 1.05% for 140 minutes, so that carbon and nitrogen atoms diffuse into the surface of the workpiece at the same time to form a reinforcement layer of a certain depth.

[0050] (5) Carbon potential reduction stage: Maintain the temperature at 820℃ and reduce the carbon potential to 0.85%. The adjustment process lasts for 5 minutes to prepare for the diffusion stage and avoid the formation of coarse carbides on the surface.

[0051] (6) Diffusion stage: Keep warm for 120 min at 820℃ and carbon potential of 0.85% to allow carbon and nitrogen atoms that have penetrated the surface layer to diffuse inward evenly, reduce the surface concentration gradient, reduce the generation of brittle phase, and improve the uniformity of the infiltrated layer structure.

[0052] (7) Quenching stage: After diffusion is complete, the workpiece is quickly transferred to the quenching medium for quenching treatment. The initial quenching temperature is approximately 80℃, and isothermal graded quenching oil is used for cooling. The isothermal graded quenching oil is KERUN®KR488 isothermal graded quenching oil (see...). Figure 6 This process yields a martensitic structure, improving surface hardness and wear resistance.

[0053] (8) Tempering stage: Hold at 200℃ for 210 min to eliminate quenching stress and stabilize martensitic structure.

[0054] Comparative Example 1

[0055] This comparative example represents a heat treatment process using existing technology, specifically:

[0056] A heat treatment process for high-speed bearings includes the following steps:

[0057] (1) Heating stage: The high-carbon steel workpiece is placed in the heat treatment furnace and heated to 790°C. At the same time, the carbon potential in the furnace is controlled at 0.6%, and the temperature is held for 5 minutes. The high-carbon steel workpiece comprises the following components by mass percentage: C 0.98%, Si 0.24%, Mn 0.35%, Cr 1.49%, Mo 0.002%, P 0.012%, S 0.002%, O 0.0008%, with the balance being iron.

[0058] (2) Temperature and carbon potential equalization stage: After the temperature is raised, the furnace temperature is raised to 820℃, and the carbon potential is stabilized at 1.055% at this temperature for 10 minutes.

[0059] (3) Carbonitriding stage: Carbonitriding treatment was carried out at a temperature of 820℃ and a carbon potential of 1.05% for 270 minutes.

[0060] (4) Quenching stage: After carbonitriding is completed, the workpiece is removed from the furnace and quickly transferred to the quenching medium. The quenching medium is KERUN® KR218 fast bright quenching oil; see Figure 5 The initial quenching temperature is approximately 60℃, followed by quenching and cooling.

[0061] (5) Tempering stage: Hold at 160℃ for 210 min.

[0062] Performance testing

[0063] According to the requirements of standard JB / T7363, the carbon and nitrogen contents of the high-carbon steel workpiece in Comparative Example 1 were determined, and the results are shown in Table 1 (carbon and nitrogen content data before improvement). The high-carbon steel workpiece was heat-treated according to the method of Example 1, and the results are shown in Table 2 (carbon and nitrogen content data after improvement). The residual austenite content of the high-carbon steel bearing in Comparative Example 1 after heat treatment was determined, and the results are shown in Table 3. The high-carbon steel workpiece was heat-treated according to the method of Example 1, and the residual austenite content was determined, and the results are shown in Table 4. Metallographic images of the workpieces in Comparative Example 1 and Example 1 are shown below. Figure 3-4 .

[0064] Table 1 Carbon and nitrogen content of high-carbon steel workpieces

[0065]

[0066] Table 2 Carbon and nitrogen content of high-carbon steel workpieces after heat treatment

[0067]

[0068] Table 3 Comparative Example 1 Residual Austenite Content

[0069]

[0070] Table 4 Residual austenite content in Example 1

[0071]

[0072] As shown in Tables 3-4, compared with Comparative Example 1, the heat treatment process of Example 1 significantly reduced the residual austenite content on the surface and in the core of the bearing steel. This indicates that the process of Example 1 is more advantageous in controlling microstructure stability, thereby resulting in superior dimensional stability, wear resistance, and fatigue life, which are crucial for high-speed bearings.

[0073] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A heat treatment process for high speed bearings, characterized in that, It comprises the following steps: (1) warming-up stage: put high-carbon steel workpiece in heat treatment furnace, heat to temperature 800-840℃, control carbon potential in furnace at 0.55-0.65%, keep for 5-10min; (2) keeping temperature stage: keep temperature 800-840℃, carbon potential 0.55-0.65%, keep for 15-20min; (3) carbon potential increasing stage: keep temperature, increase carbon potential in furnace to 1.00-1.10%, carbon potential increasing time lasts for 5-10min; (4) carbonitriding stage: carbonitriding at temperature 800-840℃, carbon potential 1.00-1.10%, lasts for 140-160min; (5) carbon potential decreasing stage: decrease carbon potential to 0.80-0.90%, adjusting process lasts for 5-10min; (6) diffusion stage: keep temperature 800-840℃, carbon potential 0.80-0.90%, keep for 120-130min; (7) Quenching stage: after diffusion, the workpiece is transferred to the quenching medium for quenching treatment, the quenching starting temperature is 70-85℃, isothermal step quenching oil is used for cooling, the quenching oil viscosity is 50~65mm 2 / s, the maximum cooling speed is 70-85℃ / s, and the characteristic temperature is in the range of 710~735℃; (8) tempering stage: keep temperature 180-220℃, keep for 180-240min.

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