A heat treatment method for high carbon chromium bearing steel
By employing a two-stage isothermal salt bath quenching method, the problem of excessively long production cycle for nano-bainitic bearing steel was solved, achieving efficient bainitic transformation and improving the wear resistance of the material.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HENAN UNIV OF SCI & TECH
- Filing Date
- 2023-05-30
- Publication Date
- 2026-05-29
AI Technical Summary
The isothermal quenching process of nanobainitic bearing steel is too long, resulting in an excessively long production cycle and limiting its industrial application.
A two-stage isothermal salt bath quenching method is adopted. First, pre-salt bath quenching is performed to form pre-martensite, and then two-stage isothermal salt bath quenching is performed at different temperatures to shorten the transformation time of nanobainite.
It significantly shortened the bainite transformation time, improved production efficiency, and did not reduce the wear resistance of the material; on the contrary, it improved it.
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Abstract
Description
Technical Field
[0001] This invention relates to a heat treatment method for high-carbon chromium bearing steel, belonging to the field of bearing processing and manufacturing technology. Background Technology
[0002] Martensitic bearing steels suffer from poor toughness and inadequate resistance to hydrogen embrittlement, leading to a significant reduction in service life under harsh environments or impact loads. Nano-bainitic steels, which have emerged in recent years, offer both high hardness and improved toughness, thus significantly enhancing the wear resistance and fatigue resistance of bearing materials in demanding environments. They are considered a revolutionary new material by the bearing industry. Currently, world-renowned bearing manufacturers such as FAG (Germany), SKF (Sweden), and NSK (Japan) have successfully applied nano-bainitic bearing steels to bearings in railways, wind power, and mining applications subjected to immense impact loads and poor lubrication conditions. However, the application of nano-bainitic bearing steels in my country is still in its early stages, with many unresolved issues in their preparation and application. In particular, the formation of nano-bainitic bearing steel requires isothermal quenching at medium to low temperatures. Due to the low temperature and slow atomic diffusion rate during isothermal quenching, the bainitic phase transformation process is extremely slow, resulting in production cycles lasting tens of hours or even days. Therefore, the excessively long isothermal transformation time is the biggest technical bottleneck that severely limits the industrial application of nano-bainitic bearing steel.
[0003] Researchers have proposed various methods to accelerate the transformation of nano-bainite, such as alloying element addition, heat treatment process control, hot deformation, and external field interference. Some of these methods require consideration of raw material costs and steel smelting quality, while others are difficult to implement in bearing steel production. Among these methods, heat treatment process control is the most direct, effective, and easy-to-operate acceleration method for bearing steel production. Currently, nano-bainite transformation is accelerated by modifying the heat treatment process. For example, Chinese invention patent application CN108384928A discloses a method for nano-bainite phase transformation, which includes the following steps: first, austenitizing the target steel material, and then controlling the key nodes of the first-stage isothermal phase transformation process and the key isothermal phase transformation temperature of the second stage. The first-stage time node is the instantaneous maximum rate time node of the bainite phase transformation or the average maximum rate time node; the second-stage phase transformation temperature is the temperature at which the strength of the untransformed supercooled austenite is equal to the strength of the initially supercooled austenite. This method significantly shortens the transformation time by reducing the transformation period of nanobainite, but there is still a desire to further shorten the bainite transformation time to improve production efficiency. Summary of the Invention
[0004] The purpose of this invention is to provide a heat treatment method for high-carbon chromium bearing steel that can significantly shorten the bainite transformation time.
[0005] To achieve the above objectives, the technical solution adopted by this invention is as follows:
[0006] A heat treatment method for high-carbon chromium bearing steel includes the following steps: austenitizing the high-carbon chromium bearing steel after spheroidizing annealing, then performing pre-salt bath quenching, followed by a first-stage isothermal salt bath quenching at a first temperature, and then a second-stage isothermal salt bath quenching at a second temperature; wherein the pre-salt bath quenching temperature is ≤ Ms; the first temperature is > Ms; Ms is the martensitic transformation temperature of the high-carbon chromium bearing steel, in °C; the second temperature is T-5℃~T+5℃, and at T℃, the strength of the high-carbon chromium bearing steel before the transformation of austenite at the beginning of the second-stage isothermal salt bath quenching is equal to the strength of the austenite at the beginning of the first-stage isothermal salt bath quenching.
[0007] The heat treatment method for high-carbon chromium bearing steel of the present invention involves pre-salting the austenitized high-carbon chromium bearing steel below the temperature at which martensite transformation begins before isothermal salt bath quenching. This pre-salt bath quenching forms a certain amount of pre-martensite, which serves as a preferential nucleation site during the subsequent bainitic transformation, shortening the incubation period of nanobainite. Based on this, isothermal salt bath quenching is performed in two stages to form bainite. The increased temperature in the second stage of isothermal salt bath quenching enhances the phase transformation kinetics, further shortening the transformation period of nanobainite. This method accelerates the nanobainite transformation from both the incubation and transformation stages, significantly reducing the nanobainite transformation time. The heat treatment method for high-carbon chromium bearing steel of the present invention accelerates the nanobainite transformation rate of bearing steel from a heat treatment perspective, with a simple process and low equipment requirements.
[0008] If the pre-salt bath quenching temperature is too low, an excessive amount of pre-martensite will form in a short time, resulting in a decrease in the final bainite transformation temperature. Conversely, if the pre-salt bath quenching temperature is too high, a small amount of pre-martensite will form in a short time, reducing the number of subsequent bainite nucleation sites and diminishing the accelerating effect. Furthermore, the pre-salt bath quenching temperature is Ms-10℃ to Ms-14℃, for example, Ms-12℃, which is 12℃ below the martensite transformation temperature. The pre-salt bath quenching time is 3 to 7 minutes, for example, 5 minutes.
[0009] Furthermore, the first temperature is Ms+40℃ to Ms+70℃. For example, for GCr15SiMo bearing steel or GCr15Si1Mo bearing steel, the first temperature is 210℃.
[0010] Furthermore, the second temperature is T℃. Performing the second stage of isothermal salt bath quenching at T℃ can increase the diffusion rate of elements in the bainite transformation, enhance the phase transformation kinetics, and thus shorten the bainite phase transformation period.
[0011] For high-carbon chromium bearing steel that has not yet undergone spheroidizing annealing, the heat treatment method for high-carbon chromium bearing steel further includes the following steps: spheroidizing annealing the high-carbon chromium bearing steel. The spheroidizing annealing involves first holding at 720℃ for 2 hours, then at 790℃ for 3 hours, then at 720℃ for 4 hours, followed by furnace cooling to 550℃, and finally air cooling. After spheroidizing annealing, a spheroidized pearlite structure is obtained in the high-carbon chromium bearing steel. Further, the high-carbon chromium bearing steel is cleaned to remove surface contaminants before spheroidizing annealing. For example, ultrasonic cleaning can be used.
[0012] The isothermal salt bath quenching uses a mixed salt melt of KNO3 and NaNO2. The mass ratio of KNO3 to NaNO2 in the salt melt is 0.8 to 1.2:1, preferably 1:1.
[0013] Furthermore, to shorten the bainite transformation time, the first stage of isothermal salt bath quenching is terminated when the bainite transformation rate reaches its maximum. The time corresponding to the maximum bainite transformation rate during the first stage of isothermal salt bath quenching is typically less than 2 hours.
[0014] Furthermore, during the second stage of isothermal salt bath quenching, the second stage of isothermal salt bath quenching ends when the required bainite content is reached.
[0015] Furthermore, the mass fraction of carbon in the high-carbon chromium bearing steel is 0.95 to 1.05%, for example, the high-carbon chromium bearing steel is GCr15SiMo bearing steel or GCr15Si1Mo bearing steel.
[0016] Furthermore, the austenitizing temperature is 860–890°C. It is understood that after austenitizing and subsequent cooling, the austenite in the high-carbon chromium bearing steel will gradually transform into other structures such as martensite or bainite.
[0017] Furthermore, the salt melt used in the pre-salt bath quenching is a mixed salt melt of KNO3 and NaNO2. The mass ratio of KNO3 to NaNO2 in the salt melt used in the pre-salt bath quenching is 0.8 to 1.2:1, preferably 1:1.
[0018] Furthermore, the heat treatment method for the high-carbon chromium bearing steel also includes the following steps: after the second stage of isothermal salt bath quenching, the high-carbon chromium bearing steel is air-cooled, then tempered, and then air-cooled again. The tempering temperature after air cooling is 170–210℃, for example, 210℃, and the time is 1–4 hours, for example, 1 hour. Attached Figure Description
[0019] Figure 1 The process flow diagram is for the heat treatment method of high carbon chromium bearing steel in Example 1;
[0020] Figure 2 The microstructure of the heat-treated GCr15SiMo bearing steel in Example 1;
[0021] Figure 3 The microstructure of GCr15SiMo bearing steel under conventional isothermal quenching process in Comparative Example 1.
[0022] Figure 4 The microstructure of GCr15SiMo bearing steel under pre-quenching + isothermal quenching process in Comparative Example 2;
[0023] Figure 5 This is a comparison of the microstructure of GCr15SiMo bearing steel under the two-stage isothermal quenching process in Example 3. Detailed Implementation
[0024] The technical solution of the present invention will be further described below with reference to specific embodiments.
[0025] Orthogonal experiments show that under conventional isothermal quenching processes (i.e., directly isothermal salt bath quenching of austenitized high-carbon chromium bearing steel), with an isothermal quenching temperature of 210℃ and an isothermal quenching time of 8h, the nano-bainite transformation rate in GCr15SiMo bearing steel is 55-58 vol.%. After isothermal salt bath quenching, the steel is air-cooled to room temperature, then reheated to 210℃ for tempering for 1h, followed by air-cooling to room temperature. The GCr15SiMo bearing steel exhibits the best wear resistance after this process. Therefore, in the following examples and comparative examples, the nano-bainite transformation rate of 55-58 vol.% is used as the time marker for the end of isothermal salt bath quenching.
[0026] In the heat treatment methods of the following examples and comparative examples, the salt melt used for pre-salt bath quenching and isothermal salt bath quenching is a mixed salt melt of KNO3 and NaNO2, with a mass ratio of KNO3 to NaNO2 of 1:1.
[0027] Example 1
[0028] The heat treatment method for high-carbon chromium bearing steel in this embodiment, taking GCr15SiMo bearing steel as an example, is as follows: Figure 1 As shown, it includes the following steps:
[0029] 1) Cut GCr15SiMo bearing steel (Ms point 166℃) into small pieces of 40mm×60mm×12mm, and degrease and ultrasonically clean their surfaces.
[0030] 2) GCr15SiMo bearing steel was spheroidized and annealed in a muffle furnace. The spheroidizing and annealing parameters were: 720℃×2h→790℃×3h→720℃×4h, furnace cooled to 550℃, and then air cooled.
[0031] 3) The spheroidized annealed GCr15SiMo bearing steel was austenitized at 870℃ for 20 min in a muffle furnace.
[0032] 4) The austenitized GCr15SiMo bearing steel was pre-salted quenched at 154℃ for 5 minutes in a salt bath furnace.
[0033] 5) The first-stage salt bath temperature was 210℃. To determine the first-stage low-temperature isothermal salt bath time, the pre-salt-bath quenched GCr15SiMo bearing steel was subjected to a series of low-temperature isothermal salt bath quenchings at 210℃ for different times, and its bainite volume content was measured. Then, based on the relationship curve between bainite content and low-temperature isothermal salt bath quenching time, the low-temperature isothermal salt bath quenching time corresponding to the maximum bainite transformation rate was found to be 2 hours. Therefore, the first-stage low-temperature isothermal salt bath quenching treatment of GCr15SiMo bearing steel was carried out in a salt bath furnace at 210℃ for 2 hours.
[0034] 6) Measure the carbon content in the austenite of the GCr15SiMo bearing steel after pre-salt bath quenching, and combine it with the mass fraction of other alloying elements in the GCr15SiMo bearing steel. Substitute these values into the following formula to obtain the residual austenite strength of the GCr15SiMo bearing steel after pre-salt bath quenching, which is the austenite strength at the beginning of the first stage of isothermal salt bath quenching.
[0035] σ r y (MPa)=15.4×(1-0.26×10 -2 T r +0.47×10 -5 T r 2 -0.326×10 -8 T r 3 )×(4.4+23w C +1.3w Si +0.24w Cr
[0036] +0.94w Mo +32w N ), T r =T-25
[0037] In the formula: σ r y— Yield strength of austenite at temperature T (MPa), T— Isothermal quenching temperature (°C), w— Mass fraction of each element in the material (wt.%).
[0038] 7) Measure the carbon content in the residual austenite of the material after the first stage of low-temperature isothermal salt bath quenching, and use this as the carbon content in the residual austenite of the material at the start of the second stage of low-temperature isothermal salt bath quenching. According to the equal strength formula, the austenite strength at the start of the first stage of isothermal salt bath quenching is taken as the strength of the high-carbon chromium bearing steel before the austenite transformation at the start of the second stage of isothermal salt bath quenching. Then, substitute the strength, carbon content, and mass fraction of other elements at the start of the second stage of isothermal salt bath quenching into the formula in step 6), and the isothermal salt bath quenching temperature of the second stage (i.e., the optimal salt bath quenching temperature of the second stage) can be obtained. Calculations show that the optimal salt bath temperature for the second stage of GCr15SiMo bearing steel is 250℃. Performing the second stage of low-temperature isothermal salt bath quenching of GCr15SiMo bearing steel at 250℃ for 1 hour in a salt bath furnace yields bearing steel with a nano-bainite volume content of 56.5 vol.%.
[0039] 8) After the second stage of isothermal salt bath quenching, the GCr15SiMo bearing steel is air-cooled to room temperature, then heated to 210℃ for tempering for 1 hour, and then air-cooled to room temperature again.
[0040] Example 2
[0041] The heat treatment method for high-carbon chromium bearing steel in this embodiment, taking GCr15Si1Mo bearing steel as an example, includes the following steps:
[0042] 1) Cut GCr15Si1Mo bearing steel (Ms point 162℃) into small pieces of 40mm×60mm×12mm, and degrease and ultrasonically clean their surfaces.
[0043] 2) GCr15Si1Mo bearing steel was spheroidized and annealed in a muffle furnace. The spheroidizing and annealing parameters were: 720℃×2h→790℃×3h→720℃×4h, furnace cooled to 550℃, and then air cooled.
[0044] 3) The spheroidized annealed GCr15Si1Mo bearing steel was austenitized at 880℃ for 20 min in a muffle furnace.
[0045] 4) The austenitized GCr15Si1Mo bearing steel was pre-salted quenched at 150℃ for 5 minutes in a salt bath furnace.
[0046] 5) The first-stage salt bath temperature was 210℃. To determine the first-stage low-temperature isothermal salt bath time, the pre-salt-bath quenched GCr15Si1Mo bearing steel was subjected to a series of low-temperature isothermal salt bath quenchings at 210℃ for different times, and its bainite volume content was measured. Then, based on the relationship curve between bainite content and low-temperature isothermal salt bath quenching time, the low-temperature isothermal salt bath quenching time corresponding to the maximum bainite transformation rate was found to be 2 hours. Therefore, the first-stage low-temperature isothermal salt bath quenching treatment of GCr15SiMo bearing steel was carried out in a salt bath furnace at 210℃ for 2 hours.
[0047] 6) Measure the carbon content in the austenite of the GCr15Si1Mo bearing steel after pre-salt bath quenching, and combine it with the mass fraction of other alloying elements in the GCr15Si1Mo bearing steel. Substitute these values into the following formula to obtain the residual austenite strength of the GCr15Si1Mo bearing steel after pre-salt bath quenching, which is the austenite strength at the beginning of the first stage of isothermal salt bath quenching.
[0048] σ r y (MPa)=15.4×(1-0.26×10 -2 T r +0.47×10 -5 T r 2 -0.326×10 -8 T r 3 )×(4.4+23w C +1.3w Si +0.24w Cr
[0049] +0.94w Mo +32w N ), T r =T-25
[0050] In the formula: σ r y — Yield strength of austenite at temperature T (MPa), T— Isothermal quenching temperature (°C), w— Mass fraction of each element in the material (wt.%).
[0051] 7) Measure the carbon content in the residual austenite of the material after the first stage of low-temperature isothermal salt bath quenching, and use this as the carbon content in the residual austenite of the material at the start of the second stage of low-temperature isothermal salt bath quenching. According to the equal strength formula, the austenite strength at the start of the first stage of isothermal salt bath quenching is taken as the strength of the high-carbon chromium bearing steel before the austenite transformation at the start of the second stage of isothermal salt bath quenching. Then, substitute the strength, carbon content, and mass fraction of other elements at the start of the second stage of isothermal salt bath quenching into the formula in step 6), and the isothermal salt bath quenching temperature of the second stage (i.e., the optimal salt bath quenching temperature of the second stage) can be obtained. Calculations show that the optimal salt bath temperature for the second stage of GCr15Si1Mo bearing steel is 250℃.
[0052] GCr15Si1Mo bearing steel was subjected to a second-stage low-temperature isothermal salt bath quenching at 250℃ for 1 hour in a salt bath furnace to obtain bearing steel with a nano-bainite volume content of 54.6 vol.%.
[0053] 8) After the second stage of isothermal salt bath quenching, the GCr15Si1Mo bearing steel was air-cooled to room temperature, then heated to 210℃ for tempering for 1 hour, and then air-cooled to room temperature again.
[0054] Comparative Example 1
[0055] The heat treatment method for the high-carbon chromium bearing steel in this comparative example includes the following steps:
[0056] Steps 1) to 3) are the same as steps 1) to 3) in Example 1;
[0057] 4) Austenitized GCr15SiMo bearing steel was subjected to low-temperature isothermal salt bath treatment in a salt bath furnace using conventional isothermal quenching process.
[0058] 5) After isothermal salt bath quenching, the GCr15SiMo bearing steel is air-cooled to room temperature, then heated to 210℃ for tempering for 1 hour, and then air-cooled to room temperature again.
[0059] In this comparative example, the low-temperature isothermal salt bath quenching temperatures in step 4) were set to 190℃, 210℃, and 230℃, and the low-temperature salt bath times were changed to 4h, 8h, and 12h. An orthogonal experimental design was conducted, and combined with the results of the friction and wear test machine, the optimal isothermal salt bath quenching temperature for the material with the best wear resistance under conventional isothermal quenching process was found to be 210℃, and the optimal isothermal salt bath quenching time was 8h. At this time, a bearing material with a nano-bainite volume content of 55.6 vol.% was obtained.
[0060] Comparative Example 2
[0061] The heat treatment method for the high-carbon chromium bearing steel in this comparative example includes the following steps:
[0062] Steps 1) to 3) are the same as steps 1) to 3) in Example 1;
[0063] 4) After pre-salting the austenitized GCr15SiMo bearing steel in a salt bath furnace at 154℃ for 5 min, it was then isothermally quenched at 210℃ for 6 h to obtain a bearing material with a nano-bainite volume content of 57.7 vol.%.
[0064] 5) After isothermal salt bath quenching, the GCr15SiMo bearing steel is air-cooled to room temperature, then heated to 210℃ for tempering for 1 hour, and then air-cooled to room temperature again.
[0065] Comparative Example 3
[0066] The heat treatment method for the high-carbon chromium bearing steel in this comparative example includes the following steps:
[0067] Steps 1) to 3) are the same as steps 1) to 3) in Example 1;
[0068] 4) After isothermal salt bath quenching of austenitized GCr15SiMo bearing steel at 210℃ for 2 hours in a salt bath furnace, it was then isothermal salt bath quenched at 250℃ for 2 hours to obtain bearing material with a nano-bainite volume content of 55.5 vol.%.
[0069] 5) After isothermal salt bath quenching, the GCr15SiMo bearing steel is air-cooled to room temperature, then heated to 210℃ for tempering for 1 hour, and then air-cooled to room temperature again.
[0070] Comparative Example 4
[0071] The heat treatment method for the high-carbon chromium bearing steel in this comparative example includes the following steps:
[0072] Steps 1) to 3) are the same as steps 1) to 3) in Example 2;
[0073] 4) Austenitized GCr15Si1Mo bearing steel was subjected to isothermal salt bath treatment in a salt bath furnace using conventional isothermal quenching process to obtain bearing material with a nano-bainite volume content of 53.5 vol.%; the isothermal salt bath treatment temperature was 210℃ and the time was 8h.
[0074] 5) After isothermal salt bath quenching, the GCr15Si1Mo bearing steel is air-cooled to room temperature, then heated to 210℃ for tempering for 1 hour, and then air-cooled to room temperature again.
[0075] Comparative Example 5
[0076] The heat treatment method for the high-carbon chromium bearing steel in this comparative example includes the following steps:
[0077] Steps 1) to 3) are the same as steps 1) to 3) in Example 2;
[0078] 4) After pre-salting the austenitized GCr15Si1Mo bearing steel in a salt bath furnace at 150℃ for 5 min, it was then isothermally quenched at 210℃ for 6 h to obtain a bearing material with a nano-bainite volume content of 54.1 vol.%.
[0079] 5) After isothermal salt bath quenching, the GCr15Si1Mo bearing steel is air-cooled to room temperature, then heated to 210℃ for tempering for 1 hour, and then air-cooled to room temperature again.
[0080] Comparative Example 6
[0081] The heat treatment method for the high-carbon chromium bearing steel in this comparative example includes the following steps:
[0082] Steps 1) to 3) are the same as steps 1) to 3) in Example 2;
[0083] 4) Austenitized GCr15Si1Mo bearing steel was isothermally quenched in a salt bath furnace at 210℃ for 2 hours, and then isothermally quenched in a salt bath at 250℃ for 2.5 hours to obtain bearing material with a nano-bainite volume content of 55.8 vol.%.
[0084] 5) After isothermal salt bath quenching, the GCr15Si1Mo bearing steel is air-cooled to room temperature, then heated to 210℃ for tempering for 1 hour, and then air-cooled to room temperature again.
[0085] The microstructures of the heat-treated high-carbon chromium bearing steels in Example 1 and Comparative Examples 1-3 are as follows: Figures 2-5 As shown. By Figures 2-5 It can be seen that the microstructure of GCr15SiMo bearing steel under different heat treatment processes mainly consists of nano-bainite, retained austenite, carbides and a small amount of martensite, and the bainite content in its microstructure is quite similar.
[0086] Friction and wear tests were conducted on the high-carbon chromium bearing steels after heat treatment in Examples 1 and 2, the high-carbon chromium bearing steel after isothermal salt bath quenching at 210℃ for 8 hours in Comparative Example 1, and the high-carbon chromium bearing steel after heat treatment in Comparative Example 4 using a friction and wear testing machine. During the test, the load was 200 N, the frequency was 3 Hz, the friction stroke was 6 mm, and the time was 30 min. After the friction and wear test, the wear volume of the samples was measured using a three-dimensional profilometer. The wear rates of different materials were obtained by substituting the values into the formula: Volumetric Wear Rate = Wear Volume / (Friction Distance × Load). The results are shown in Table 1.
[0087] Table 1. Results of friction and wear experiments
[0088] Example 1 Example 2 Comparative Example 1 Comparative Example 4 <![CDATA[Wear rate (×10 -6 mm 3 ·m -1 ·N -1 )]]> 1.38 1.79 1.46 1.95
[0089] As shown in Table 1, Examples 1-2, after undergoing pre-salt bath quenching followed by two-stage isothermal salt bath quenching on the basis of Comparative Examples 1 and 4, did not experience a decrease in wear resistance; on the contrary, their wear resistance was improved.
Claims
1. A heat treatment method for shortening the nano-bainite transformation time of high-carbon chromium bearing steel, characterized in that: Includes the following steps: The high-carbon chromium bearing steel after spheroidizing annealing is austenitized, then pre-quenched in a salt bath, followed by a first stage of isothermal salt bath quenching at a first temperature, and then a second stage of isothermal salt bath quenching at a second temperature. The first stage of isothermal salt bath quenching ends when the bainite transformation rate reaches its maximum; the second stage of isothermal salt bath quenching ends when the desired nano-bainite content is reached. The mass fraction of carbon in the high-carbon chromium bearing steel is 0.95~1.05%. Ms-14℃≤The temperature of the pre-salt bath quenching≤Ms, and the pre-salt bath quenching time is 3~7min; the first temperature is Ms+40℃~Ms+48℃; Ms is the martensitic transformation temperature of high carbon chromium bearing steel, ℃; The second temperature is T-5℃~T+5℃. At T℃, when the second stage of isothermal salt bath quenching begins, the high carbon chromium bearing steel has not yet transformed into austenite and its strength is equal to the austenite strength at the beginning of the first stage of isothermal salt bath quenching.
2. The heat treatment method for shortening the nano-bainite transformation time of high-carbon chromium bearing steel according to claim 1, characterized in that: The pre-salt bath quenching temperature is Ms-10℃~Ms-14℃.
3. The heat treatment method for shortening the nano-bainite transformation time of high-carbon chromium bearing steel according to claim 1 or 2, characterized in that: The pre-salt bath quenching time is 3-5 minutes.
4. The heat treatment method for shortening the nano-bainite transformation time of high-carbon chromium bearing steel according to claim 1 or 2, characterized in that: The first temperature is 210℃.
5. The heat treatment method for shortening the nano-bainite transformation time of high-carbon chromium bearing steel according to claim 1 or 2, characterized in that: The second temperature is T℃.
6. The heat treatment method for shortening the nano-bainite transformation time of high-carbon chromium bearing steel according to claim 1 or 2, characterized in that: The time corresponding to the maximum bainite transformation rate is less than 2 hours.
7. The heat treatment method for shortening the nano-bainite transformation time of high-carbon chromium bearing steel according to claim 1 or 2, characterized in that: The required nanobainite content is 55–58 vol.%.
8. The heat treatment method for shortening the nano-bainite transformation time of high-carbon chromium bearing steel according to claim 1 or 2, characterized in that: The first temperature is Ms+42℃~Ms+48℃.
9. The heat treatment method for shortening the nano-bainite transformation time of high-carbon chromium bearing steel according to claim 1 or 2, characterized in that: The high-carbon chromium bearing steel is GCr15SiMo bearing steel or GCr15Si1Mo bearing steel.
10. The heat treatment method for shortening the nano-bainite transformation time of high-carbon chromium bearing steel according to claim 1 or 2, characterized in that: It also includes the following steps: After the second stage of isothermal salt bath quenching, the high-carbon chromium bearing steel is air-cooled, then tempered, and then air-cooled again.