Treatment method for improving dimensional stability of GCr15 gearbox bearing part

Abstract

The invention relates to the field of bearings, and particularly discloses a treatment method for improving the dimensional stability of a GCr15 gearbox bearing part, which comprises the following steps: step 1, heating a workpiece at the temperature of 800-850 DEG C, quenching in quenching nitrate, and cooling to room temperature in a stepped temperature control manner after quenching to obtain a quenched workpiece; 2, the quenched workpiece is subjected to vibration copious cooling composite treatment and then placed in composite oil to be subjected to temperature returning, and a temperature returning workpiece is obtained; the vibration copious cooling composite treatment comprises the following steps: preserving the heat of the quenched workpiece at-150 DEG C to-90 DEG C for 2-4 hours, vibrating the workpiece, and preserving the heat of the workpiece at-80 DEG C to-30 DEG C for 1-2 hours; 3, the temperature-recovered workpiece is subjected to tempering treatment, and a tempered workpiece is obtained; and 4, the tempered workpiece is subjected to vibration and dynamic tempering treatment after being machined, a bearing workpiece is obtained, and the residual oxygen content of the bearing workpiece is smaller than or equal to 1%. And the obtained bearing is high in dimensional stability and excellent in hardness.

Description

Technical Field

[0001] This application relates to the field of bearings, and more specifically, it relates to a treatment method for improving the dimensional stability of bearing parts made of GCr15 in a gearbox. Background Art

[0002] GCr15 bearing steel is a high-carbon chromium bearing steel with less alloy content. Due to its good hardness, wear resistance, and high contact fatigue performance after quenching and tempering, it is widely used in various bearings. At present, the traditional bearing processing technology is to perform a treatment process including a quenching step and a high-temperature tempering step on the GCr15 bearing steel blank bar before rough machining, and then perform steps such as quenching and low-temperature tempering on the machined parts. However, in actual working conditions, bearings need to face the challenges of high-temperature and low-temperature environments. High temperature will cause the hardness of the bearing material to decrease, affecting wear resistance and load-bearing capacity, and thermal expansion will also cause changes in the bearing clearance, which may cause abnormal contact; while low temperature will cause the material to become brittle and shrink, affecting the assembly clearance and rolling performance. The influence of temperature on the bearing performance runs through the entire service life. Therefore, it is crucial for the bearing to maintain dimensional stability in extreme temperature environments. Summary of the Invention

[0003] In order to reduce the dimensional change rate of bearing parts in extreme temperature environments and improve the dimensional stability of bearing parts, this application provides a treatment method for improving the dimensional stability of bearing parts made of GCr15 in a gearbox.

[0004] A treatment method for improving the dimensional stability of bearing parts made of GCr15 in a gearbox provided by this application adopts the following technical solutions: A treatment method for improving the dimensional stability of bearing parts made of GCr15 in a gearbox includes the following steps: Step 1, heat the workpiece at a temperature of 800 - 850 °C, quench it in quenching nitrate, and after quenching, cool it stepwise to room temperature by temperature control to obtain a quenched workpiece; Step 2, perform a vibration cryogenic composite treatment on the quenched workpiece, and then place it in composite oil for temperature recovery to obtain a temperature-recovered workpiece; The vibration cryogenic composite treatment includes: keeping the quenched workpiece at -150 °C to -90 °C for 2 - 4 h, then vibrating the workpiece and keeping it at -80 °C to -30 °C for 1 - 2 h; Step 3, perform a tempering treatment on the temperature-recovered workpiece to obtain a tempered workpiece; Step 4, perform vibration and dynamic tempering treatment on the tempered workpiece after machining to obtain a bearing workpiece, and the retained austenite in the bearing workpiece is ≤ 1%.

[0005] In this application, bearing parts are first austenitized under high-temperature conditions and undergo martensite transformation in quenching nitrate salts to form a structure of quenched martensite + carbide + retained austenite. The medium-speed cooling of the quenching nitrate salts combined with stepped temperature control not only avoids the decomposition of supercooled austenite in the high-temperature zone but also inhibits the explosive transformation of martensite in the low-temperature zone, reducing the internal stress gradient and providing a tissue basis for subsequent cryogenic treatment. When performing vibration-assisted cryogenic composite treatment, gradient cryogenic treatment can further increase the conversion rate of retained austenite, promote the transformation of retained austenite to martensite, and avoid excessive cold embrittlement. Through the synergistic effect of mechanical vibration and low-temperature phase transformation, the vibration energy activates dislocation slip and grain boundary migration, induces lattice microplastic deformation, accelerates phase transformation, and releases micro stresses. It can timely release the micro stresses during quenching and cryogenic treatment, simultaneously break the metastable state of RA, further increase the conversion rate of retained austenite. Moreover, combined with composite oil for rewarming, it can also promote the fragmentation of martensite laths, refine the grain size, and make the carbide distribution more uniform. The vibration-assisted cryogenic composite treatment adopted in this application realizes the deep conversion of retained austenite, the efficient release of residual stress, and the ultra-finement of the structure through the coupling effect of mechanical vibration energy and ultra-low temperature phase transformation. The rewarming of the composite oil promotes lubrication and stress relaxation, reduces the risk of microcracks caused by cryogenic treatment, improves surface integrity, and synergistically enhances the comprehensive properties of the material, so that the dimensional change rate of bearing parts in extreme temperature environments is extremely low, significantly improving the dimensional stability of bearing parts.

[0006] After the workpiece undergoes the optimized process steps of this application, quenching generates martensite with a conventional morphology. The vibration-assisted cryogenic composite treatment introduces high-density dislocations and twins, induces the segregation of carbon atoms, and forms nano-scale pre-precipitates (such as ε-carbide). The quenching nitrate salts are selected with specific components and cooled with stepped temperature control to refine the length of martensite needles after quenching and avoid deformation or cracking of the workpiece. After the vibration-assisted cryogenic composite treatment, it is rewarmed in the composite oil with specific components to facilitate the control of tissue morphology and promote a finer and more uniform carbide distribution. Through grain refinement strengthening and dislocation strengthening, a structure with high hardness and high wear resistance can be obtained without the situation of high tissue grade and coarse grains, realizing the excellent dimensional stability and high strength of the bearing under extreme working conditions.

[0007] Tempering the rewarmed workpiece can further decompose the retained austenite, release the quenching stress, stabilize the martensite structure, transform the retained austenite structure to martensite structure, and transform the quenched martensite structure to tempered martensite structure, and the matrix structure becomes tempered martensite structure + carbide + retained austenite structure.

[0008] After processing the tempered workpiece, mechanical vibration is applied to the workpiece. Generally, the processing here is rough machining such as rough grinding. After rough machining, microscopic residual stresses are released through the release of mechanical energy. Coupled with dynamic tempering treatment, the stresses can be gradually released, reducing the stress effect of the processing on the product, thereby reducing product deformation. Finally, the bearing workpiece can be further processed. The dynamic tempering and vibration form a "thermal-mechanical coupling effect" to eliminate residual stresses at multiple scales, ensuring that the final retained austenite is ≤1% and dimensional stability.

[0009] Preferably, in step 1, the stepped controlled cooling to room temperature includes: holding at 170 - 200°C for 20 - 30 min, holding at 100 - 170°C for 1 - 2 h, and cooling to room temperature in a normal temperature environment.

[0010] By adopting the above technical solution, optimizing the process conditions of stepped controlled cooling is beneficial to the smooth transition of phase transformation, helps to refine the grains, and reduces the risk of quenching cracks.

[0011] Preferably, in step 1, the quenching nitrate salt includes raw materials with the following weight percentages: potassium nitrate 30 - 40%, sodium silicate 1 - 5%, sodium nitrite 8 - 15%, and the balance is sodium nitrate.

[0012] Preferably, in step 1, the quenching temperature in the quenching nitrate salt is 170 - 200°C.

[0013] By adopting the above technical solution, optimizing the quenching conditions of the workpiece in the quenching nitrate salt and cooperating with a specific quenching nitrate salt is beneficial to controlling the tissue morphology, optimizing the mechanical properties of the workpiece, and improving the dimensional stability of the workpiece.

[0014] Preferably, the composite oil includes raw materials with the following weight percentages: epoxy polysiloxane 2 - 5%, polyisobutene 1 - 3%, phosphate ester 2 - 5%, and the balance is base oil.

[0015] Furthermore, the base oil can be mineral oil or a mixture of mineral oil and polyalphaolefin (PAO), where the proportion of mineral oil is 80 - 90 wt%.

[0016] Preferably, in step 2, the temperature in the composite oil is 30 - 70°C.

[0017] By adopting the above technical solution, optimizing the component ratio of the composite oil provides a temperature recovery carrier while ensuring cooling uniformity, avoiding workpiece deformation or cracking, reducing surface oxidation of the quenched parts, maintaining the metallic luster, and jointly improving the comprehensive quality of the bearing workpiece with the process route.

[0018] Preferably, in step 3, the tempering treatment includes: tempering at 210 - 225°C for at least 2 h.

[0019] By adopting the above technical solutions, tempering at 210 - 225°C for at least 2 hours, the retained austenite structure continues to transform, controlling the precipitation of carbides and the stabilization of the structure, maintaining the hardness of the workpiece and reducing brittleness, further adjusting the microstructure of the workpiece, promoting the homogenization of the structure, improving the temperature sensitivity of bearing parts, reducing the dimensional change rate of bearing parts in high / low temperature environments, and improving the dimensional stability of bearing parts.

[0020] Preferably, in step 4, the dynamic tempering treatment includes: tempering at 180 - 200°C for 0.5 - 1 hour, and then tempering at 150 - 180°C for 0.5 - 1 hour.

[0021] By adopting the above technical solutions, treating at 180 - 200°C preferentially eliminates large-scale stresses, and treating at 150 - 180°C eliminates grain boundary stresses; combined with high-frequency vibration to promote dislocation rearrangement and inhibit temper brittleness. By dynamic tempering, the content of retained austenite is further reduced, avoiding dimensional changes caused by tissue transformation during long-term use, so that the geometric accuracy of the workpiece can be maintained stable for a long time under temperature fluctuations or long-term loads, and the dimensional change rate is extremely small.

[0022] Preferably, the vibration conditions in steps 1 and 4 are: the frequency is 100 - 200 Hz.

[0023] Furthermore, the vibration time in step 4 is 10 - 20 minutes.

[0024] By adopting the above technical solutions, optimizing the applied vibration frequency and time is beneficial to eliminating residual stresses and preventing dimensional drift caused by the untimely release of subsequent stresses.

[0025] In summary, the present application has the following beneficial effects: The present application uses quenching nitrate + composite oil to protect the surface hardness, cryogenic treatment to refine the core grains, and dynamic tempering to enhance toughness. Through the optimization of the quenching medium, vibration energy-assisted cryogenic treatment (physical promotion of transformation), and vibration-coupled dynamic tempering (thermal-mechanical synergy), deep conversion of retained austenite, efficient release of residual stresses, and ultra-refinement of the structure are achieved, realizing the performance of "low retained austenite - high uniformity - ultra-stability" of GCr15 bearing parts, so that the dimensional change rate of bearing parts in extreme temperature environments is extremely low, significantly improving the dimensional stability of bearing parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is the microstructure diagram of Embodiment 1 of the present application.

[0027] Figure 2 It is the retained austenite strength diagram of Embodiment 1 of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0028] The embodiments of the present invention will be described in detail below in conjunction with examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For specific conditions not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase. Example

[0029] Example 1 A treatment method for improving the dimensional stability of GCr15 gearbox bearing parts includes the following steps: Step 1: Heat the workpiece at a temperature of 845 ± 5 °C and hold for 1 h, then quench in quenching nitrate salt, the quenching temperature is 195 °C. After quenching, place it at 100 °C for 30 min, then at 150 °C for 2 h, with a cooling rate of 5 °C / min during this period. Finally, cool it to room temperature in a normal temperature environment to obtain a quenched workpiece. The quenching nitrate salt includes the following raw materials by weight percentage: potassium nitrate 37%, sodium silicate 3%, sodium nitrite 11%, and the balance is sodium nitrate; Step 2: Place the quenched workpiece at -120 °C for 2 h, then vibrate the workpiece at a frequency of 130 Hz and place it at -40 °C for 1.5 h, and then place it in a composite oil at 35 °C for warming to obtain a warmed workpiece. The composite oil includes the following raw materials by weight percentage: epoxy polysiloxane 4%, polyisobutene 3%, phosphate ester 4%, and the balance is base oil; among them, the base oil is 88 wt% mineral oil and the balance is poly-α-olefin (PAO); Step 3: Place the warmed workpiece at 215 ± 5 °C for tempering for 3 h, and air-cool it to room temperature to obtain a tempered workpiece; Step 4: After machining the tempered workpiece, vibrate it at a frequency of 160 Hz for 16 min, then use stepwise heating with a heating rate of 5 °C / min, temper at 200 ± 5 °C for 0.8 h, and then place it at 160 °C for tempering for 0.5 h to obtain a bearing workpiece.

[0030] Example 2 The difference from Example 1 is that in Step 1, heat the workpiece at a temperature of 810 ± 5 °C and hold for 1 h, then quench in quenching nitrate salt, the quenching temperature is 200 °C. After quenching, place it at 170 °C for 20 min, then at 100 °C for 1 h, with a cooling rate of 5 °C / min during this period. Finally, cool it to room temperature in a normal temperature environment to obtain a quenched workpiece. The quenching nitrate salt includes the following raw materials by weight percentage: potassium nitrate 30%, sodium silicate 1%, sodium nitrite 15%, and the balance is sodium nitrate; The rest are the same as Example 1.

[0031] Example 3 The difference from Example 1 is that in Step 2, after the quenched workpiece is kept at -90°C for 3 h, the workpiece is vibrated under the condition of a frequency of 100 Hz and then kept at -30°C for 1 h, and then placed in a composite oil at 50°C for rewarming to obtain a rewarmed workpiece; the composite oil comprises raw materials in the following weight percentages: 2% of epoxy polysiloxane, 1% of polyisobutylene, 2% of phosphate ester, and the balance of base oil; wherein the base oil is 80 wt% of mineral oil and the balance of polyalphaolefin (PAO); The rest are the same as those in Example 1.

[0032] Example 4 The difference from Example 1 is that in Step 3, the rewarmed workpiece is tempered at 250°C for 1 h and then air-cooled to room temperature to obtain a tempered workpiece; the rest are the same as those in Example 1.

[0033] Example 5 The difference from Example 1 is that in Step 4, after the tempered workpiece is processed, it is vibrated under the condition of a frequency of 200 Hz for 10 min, then tempered at 180°C for 0.5 h, and then tempered at 150°C for 0.5 h, and then cooled to room temperature to obtain a bearing workpiece; The rest are the same as those in Example 1.

[0034] Example 6 The difference from Example 1 is that in Step 4, after the tempered workpiece is processed, it is vibrated under the condition of a frequency of 50 Hz for 30 min, then tempered at 240°C for 0.5 h, and then cooled to room temperature to obtain a bearing workpiece; the rest are the same as those in Example 1.

[0035] Comparative Example Comparative Example 1 The difference from Example 1 is that in Step 1, the workpiece is heated and kept at a temperature of 790 ± 5°C for 1 h, and then quenched in quenching oil, the quenching temperature is 100°C, and then air-cooled to room temperature to obtain a quenched workpiece; the quenching oil is mineral oil; The rest of the steps are the same as those in Example 1.

[0036] Comparative Example 2 The difference from Example 1 is that in Step 1, the workpiece is heated and kept at a temperature of 790 ± 5°C for 1 h, and then quenched in quenching nitrate, the quenching temperature is 170°C, and then air-cooled to room temperature to obtain a quenched workpiece; the quenching nitrate is composed of 50 wt% of potassium nitrate and 50 wt% of sodium nitrate; In Step 2, the quenched workpiece is kept at -10°C for 2 h, and then placed in mineral oil at room temperature for rewarming to obtain a rewarmed workpiece; The rest of the steps are the same as those in Example 1.

[0037] Comparative Example 3 The difference from Example 1 is that Steps 3 and 4 are omitted, and the workpiece after temperature recovery is directly placed in tempering at 180°C for 0.5 h, and then cooled to room temperature to obtain the bearing workpiece; the remaining steps are the same as those in Example 1.

[0038] Performance detection test The hardness of the workpieces obtained in Examples 1-6 and Comparative Examples 1-3 was measured according to GB / T 230.1-2008 "Rockwell hardness test for metallic materials", and the results were recorded in Table 1. The workpieces obtained in Examples 1-7 and Comparative Examples 1-4 were placed at a temperature of 160°C and continuously worked for 72 h. The bearing dimensions before and after work were measured, and the bearing dimension change rate was calculated. The results were recorded in Table 1.

[0039] Table 1 Hardness / HRC Dimensional change rate / ‰ Example 1 60.5 0.03 Example 2 58.5 0.06 Example 3 60 0.05 Example 4 58 0.03 Example 5 59.5 0.05 Example 6 58 0.04 Comparative Example 1 56 0.32 Comparative Example 2 55 0.35 Comparative Example 3 59 0.32 Through Example 1 and in combination with Figure 1-2 and Table 1, it can be seen that this application uses quenching nitrate + composite oil to protect the surface hardness, cryogenic treatment to refine the core grains, and dynamic tempering to improve toughness. Through the optimization of the quenching medium, vibration energy-assisted cryogenic treatment (physical promotion of transformation), and vibration-coupled dynamic tempering (thermal-mechanical synergism), the deep transformation of retained austenite, the efficient release of residual stress, and the ultra-refinement of the structure are realized, achieving the performance of "low retained austenite - high uniformity - ultra-stability" of GCr15 bearing parts, so that the dimension change rate of bearing parts in extreme temperature environments is extremely low, significantly improving the dimensional stability of bearing parts.

[0040] From Examples 1 and Comparative Examples 1-2 and in conjunction with Table 1, it can be seen that for the processing of Steps 1 and 2, changing the processing steps or omitting some processes both result in a decrease in the hardness of the workpiece and a significant increase in dimensional instability. This is because the bearing parts are first austenitized under high-temperature conditions and martensite transformation occurs in the quenching nitrate salt to form a structure of quenched martensite + carbide + retained austenite. The medium-speed cooling of the quenching nitrate salt combined with stepped temperature control not only avoids the decomposition of supercooled austenite in the high-temperature zone but also inhibits the explosive transformation of martensite in the low-temperature zone, reducing the internal stress gradient and providing a tissue basis for subsequent cryogenic treatment. When performing vibration cryogenic composite treatment, gradient cryogenic treatment can further increase the conversion rate of retained austenite, promote the transformation of retained austenite to martensite, and avoid excessive cold brittleness at the same time. Through the synergistic effect of mechanical vibration and low-temperature phase transformation, the vibration energy activates dislocation slip and grain boundary migration, induces lattice micro-plastic deformation, accelerates phase transformation and releases micro-stresses, timely releases the micro-stresses during quenching and cryogenic treatment, and at the same time breaks the metastable state of RA, further increasing the conversion rate of retained austenite. Moreover, combined with composite oil temperature recovery, it can also promote the fragmentation of martensite laths, refine the grain size, and make the carbide distribution more uniform. The vibration cryogenic composite treatment adopted in this application realizes the deep conversion of retained austenite, the efficient release of residual stress, and the ultra-refinement of the structure through the coupling effect of mechanical vibration energy and ultra-low temperature phase transformation. The composite oil temperature recovery promotes lubrication and stress relaxation, reduces the risk of micro-cracks caused by cryogenic treatment, improves surface integrity, and synergistically improves the comprehensive performance of the material, so that the dimensional change rate of bearing parts in an extreme temperature environment is extremely low, significantly improving the dimensional stability of bearing parts.

[0041] From Examples 1 and Comparative Example 3 and in conjunction with Table 1, it can be seen that only performing a conventional tempering on the temperature-recovered workpiece at 180°C results in a high hardness of the workpiece but poor dimensional stability. This is because tempering the temperature-recovered workpiece can further decompose retained austenite, release quenching stress, and stabilize the martensite structure, causing the retained austenite structure to transform into martensite structure and the quenched martensite structure to transform into tempered martensite structure, and the matrix structure becomes tempered martensite structure + carbide + retained austenite structure. After machining the tempered workpiece, mechanical vibration is applied to the workpiece to release micro-residual stress through mechanical energy. Combined with dynamic tempering treatment, stress can be gradually released, reducing the stress effect of the processing on the product, thereby reducing product deformation. The "thermal-mechanical coupling effect" is formed by dynamic tempering and vibration to eliminate residual stress at multiple scales, ensuring that the final retained austenite ≤ 1% and dimensional stability.

[0042] This specific embodiment is only an explanation of this application and does not limit this application. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, but as long as it is within the scope of the claims of this application, it is protected by the patent law.

Claims

1. A treatment method for improving the dimensional stability of bearing parts in a gearbox made of GCr15, characterized in that, It includes the following steps: Step 1: Heat the workpiece at a temperature of 800 - 850 °C, quench it in quenching nitrate salt, and after quenching is completed, perform stepwise controlled temperature cooling to room temperature to obtain a quenched workpiece; Step 2: Perform vibration cryogenic composite treatment on the quenched workpiece, and then place it in composite oil for temperature recovery to obtain a temperature-recovered workpiece; The vibration cryogenic composite treatment includes: keeping the quenched workpiece at -150 °C to -90 °C for 2 - 4 h, then vibrating the workpiece and keeping it at -80 °C to -30 °C for 1 - 2 h; Step 3: Perform tempering treatment on the temperature-recovered workpiece to obtain a tempered workpiece; Step 4: After machining the tempered workpiece, perform vibration and dynamic tempering treatment to obtain a bearing workpiece, and the retained austenite in the bearing workpiece is ≤1%; 2. The processing method for improving the dimensional stability of GCr15-made gearbox bearing parts according to claim 1, characterized in that: In the said Step 1, the stepwise controlled temperature cooling to room temperature includes: keeping at 170 - 200 °C for 20 - 30 min, keeping at 100 - 170 °C for 1 - 2 h, and cooling to room temperature in a normal temperature environment; 3. The treatment method for improving the dimensional stability of GCr15-made gearbox bearing parts according to claim 2, wherein: In the said Step 1, the quenching nitrate salt includes raw materials with the following weight percentages: potassium nitrate 30 - 40%, sodium silicate 1 - 5%, sodium nitrite 8 - 15%, and the balance is sodium nitrate; 4. The treatment method for improving the dimensional stability of the bearing parts of the gearbox made of GCr15 according to claim 3, characterized in that: In the said Step 1, the quenching temperature in the quenching nitrate salt is 170 - 200 °C; 5. The processing method for improving the dimensional stability of the bearing parts of the gearbox made of GCr15 according to claim 1, characterized in that: The composite oil includes raw materials with the following weight percentages: epoxy polysiloxane 2 - 5%, polyisobutylene 1 - 3%, phosphate ester 2 - 5%, and the balance is base oil; 6. The processing method for improving the dimensional stability of GCr15-made gearbox bearing parts according to claim 5, characterized in that: In the said Step 2, the temperature in the composite oil is 30 - 70 °C; 7. The treatment method for improving the dimensional stability of the bearing parts of the gearbox made of GCr15 according to claim 1, characterized in that: In the said Step 3, the tempering treatment includes: tempering at 210 - 225 °C for at least 2 h; 8. The treatment method for improving the dimensional stability of GCr15-made gearbox bearing parts according to claim 1, characterized in that: In the said Step 4, the dynamic tempering treatment includes: tempering at 180 - 200 °C for 0.5 - 1 h, and then tempering at 150 - 180 °C for 0.5 - 1 h; 9. The treatment method for improving the dimensional stability of the bearing parts of the gearbox made of GCr15 according to claim 1, characterized in that: The vibration conditions in the said Step 2 and Step 4 are: the frequency is 100 - 200 Hz.

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