Heat treatment process for circulating annealing of high-temperature bearing steel

Abstract

The invention discloses a heat treatment process for circulating annealing of high-temperature bearing steel. The heat treatment process comprises the following steps: S1, machining a high-temperature bearing steel raw material into a regular part; s2, oxide skin on the surface of the regular part is removed; s3, the regular part treated in the step S2 is placed in a salt bath furnace and subjected to cyclic annealing machining, cyclic annealing machining comprises first heating treatment and second heating treatment, and the temperature of the first heating treatment is higher than that of the second heating treatment; the regular parts are subjected to heat preservation staying treatment after being subjected to first heating treatment and second heating treatment; and S4, the number of times of circular annealing machining in the step S3 is three, and the regular part is air-cooled to the room temperature after being subjected to three times of circular annealing machining. The problems that when traditional isothermal annealing heat treatment is adopted for traditional high-temperature bearing steel, the process period is too long, the production takt is slow, energy consumption is high, and after subsequent equivalent quenching and tempering final heat treatment, the structure is not small enough, and heat treatment deformation is large are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of bearing processing, in particular to a heat treatment process for cyclic annealing of high-temperature bearing steel. BACKGROUND

[0002] As a typical high-temperature bearing steel, W6Mo5Cr4V2 steel is widely used in the manufacturing field of high-temperature bearings under harsh working conditions such as aerospace engines and high-end equipment transmission systems due to its excellent high-temperature hardness, wear resistance and thermal stability. The quality of its heat treatment directly determines the service life and operational reliability of the bearing.

[0003] In the production and processing of W6Mo5Cr4V2 high-temperature bearing steel, annealing is a key pretreatment process, and its core role is to eliminate internal stress after forging or machining of the material, refine the grain, and reduce the hardness, thereby laying the organizational foundation for subsequent quenching and tempering and other final heat treatment processes. Currently, the traditional isothermal annealing heat treatment process is widely used in the industry. However, the traditional isothermal annealing process has significant technical defects and has been unable to meet the needs of production efficiency, cost control and product precision in current high-end equipment manufacturing: 1. The production cycle is too long and the efficiency is low: the total time of the entire isothermal annealing process usually exceeds 25h, the production rhythm is slow, and it cannot adapt to the high efficiency demand of batch production, resulting in limited production capacity release; 2. High energy consumption: long time high temperature holding and slow furnace cooling process requires continuous consumption of a large amount of energy, which not only increases the production cost, but also contradicts the current development trend of "energy saving and emission reduction" in the industrial field; 3. Poor control of subsequent heat treatment organization and deformation: after traditional isothermal annealing, the parts are prone to form coarse martensite organization and grains during subsequent quenching and tempering processes (such as 1250℃ holding quenching), and the dimensional deformation of the parts such as volume, height and diameter is large, which cannot meet the strict requirements of high-temperature bearings on precise dimensions and uniform organization, thereby affecting the assembly precision and service stability of the bearing. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides a heat treatment process for cyclic annealing of high-temperature bearing steel, which solves the problems of long process cycle, slow production rhythm, high energy consumption and large heat treatment deformation after traditional isothermal annealing of high-temperature bearing steel.

[0005] To achieve the above purpose, the present application provides a heat treatment process for cyclic annealing of high-temperature bearing steel, comprising the following steps: S1, preparing high-temperature bearing steel raw materials, and machining the high-temperature bearing steel raw materials into regular parts; S2, removing the surface oxide scale of the regular parts; S3, placing the regular part treated in step S2 into a salt bath furnace and performing a cyclic annealing process, the cyclic annealing process including a first heating treatment and a second heating treatment, the temperature of the first heating treatment being higher than the temperature of the second heating treatment, the regular part being subjected to the first heating treatment and the second heating treatment and then being subjected to a holding treatment; S4, the cyclic annealing process in step S3 being performed three times, and the regular part being air-cooled to room temperature after the three cyclic annealing processes.

[0006] The application further provides that the temperature of the first heating treatment in step S3 is 850℃±5℃.

[0007] The application further provides that the salt bath medium of the salt bath furnace in step S3 is composed of W(BaCl2)70%+W(NaCl)30%.

[0008] The application further provides that the temperature of the second heating treatment in step S3 is 650℃±5℃.

[0009] The application further provides that the salt bath medium of the salt bath furnace in step S3 is composed of W(BaCl2)40%+W(KCl)30%+W(NaCl)30%.

[0010] The application further provides that the holding time of the first heating treatment and the second heating treatment in step S3 is 2min / mm.

[0011] The application further provides that the high-temperature bearing steel raw material prepared in step S1 is W6Mo5Cr4V2 high-temperature bearing steel.

[0012] The application further provides that the high-temperature bearing steel raw material prepared in step S1 meets the GB / T 9943 standard.

[0013] The above technical solution has the advantages that: the traditional isothermal annealing process needs to undergo multi-stage long-time high-temperature holding and slow furnace cooling, the overall process is complicated and time-consuming, the production rhythm is slow, and it is difficult to meet the requirements of industrialized batch production on efficiency. The application adopts the innovative design of "high-temperature-low-temperature" two-salt-bath rapid cyclic annealing, matches the accurate holding time and multiple cyclic modes according to the wall thickness of the part, greatly shortens the total time of the whole annealing process, effectively speeds up the production rhythm, significantly improves the production capacity utilization rate of the production line, and can better meet the core needs of modern manufacturing for efficient production.

[0014] The traditional isothermal annealing process needs to maintain a high temperature for a long time, and the subsequent furnace cooling process is time-consuming, which leads to large energy consumption, increases the production cost of enterprises, and is contrary to the development direction of green manufacturing. The salt bath furnace heating method is adopted, the salt bath medium has the characteristics of high heat conduction efficiency and good temperature uniformity, the heating and holding of the part can be quickly realized, and the energy consumption is not needed for a long time to maintain the process state; at the same time, the cycle annealing period is short, unnecessary energy consumption is reduced, the overall energy consumption is significantly reduced, the cost of enterprises is saved, and the development trend of low carbon, environmental protection, energy saving and emission reduction in the industrial field is met.

[0015] Meanwhile, the part treated by the cycle annealing process of the application can form finer martensite structure and more uniform fine grain structure when the subsequent same quenching and tempering process is carried out. Compared with the relatively coarse structure after traditional isothermal annealing, the fine grain and fine martensite structure can significantly improve the high temperature hardness, wear resistance and thermal stability of the material, and at the same time, the toughness and fatigue resistance of the material are enhanced, which is crucial for the application of W6Mo5Cr4V2 high temperature bearing steel, can lay a solid organizational foundation for the long-term stable service of high temperature bearing in aerospace engine, high-end equipment transmission system and other harsh working conditions, and protect the service life and operation reliability of the bearing.

[0016] In the prior art, the size precision of high temperature bearing is extremely high, and the traditional isothermal annealing process is slow in heating and cooling process and has uneven temperature gradient, so that the part is prone to obvious deformation after subsequent quenching and tempering, which not only needs to increase the subsequent machining allowance to correct the size, causing material waste, but also may cause the part to be scrapped due to deformation beyond the allowable range, and even affect the assembly precision and use effect of the bearing. The temperature range, holding time and cooling mode of the cycle annealing process are accurately controlled, the stress distribution in the part is more uniform, the deformation amount in the subsequent quenching and tempering process is effectively reduced, the size of the part is more easy to meet the design requirements, the subsequent machining cost is reduced, the product qualification rate and assembly adaptability are improved, and the precise application of high temperature bearing is protected. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The cycle annealing process route view of the application; Figure 2 The traditional isothermal annealing process route view; Figure 3 The microstructure view of the cycle annealing part quenched in the application; Figure 4 The microstructure view of the traditional isothermal annealing part quenched; Figure 5 The grain size view of the cycle annealing part quenched in the application; Figure 6 The grain size view of the traditional isothermal annealing part quenched; Figure 7 A comparison view of the deformation amount of the part after quenching by the cyclic annealing and the conventional isothermal annealing of the present application. DETAILED DESCRIPTION

[0018] The present application provides a heat treatment process for cyclic annealing of high-temperature bearing steel, comprising the following steps: S1, preparing high-temperature bearing steel raw materials, and machining the high-temperature bearing steel raw materials into regular parts; S2, removing the surface oxide scale of the regular parts; S3, placing the regular parts treated in step S2 into a salt bath furnace and performing cyclic annealing processing, the cyclic annealing processing comprising a first heating treatment and a second heating treatment, the temperature of the first heating treatment being higher than that of the second heating treatment, and the regular parts being subjected to a holding and staying treatment after the first heating treatment and the second heating treatment; S4, the number of cyclic annealing processing in step S3 is three, and the regular parts are air-cooled to room temperature after three cyclic annealing processes.

[0019] Further, the temperature of the first heating treatment in step S3 is 850℃±5℃.

[0020] Further, the salt bath medium of the salt bath furnace in step S3 is composed of W(BaCl2)70%+W(NaCl)30%.

[0021] Further, the temperature of the second heating treatment in step S3 is 650℃±5℃.

[0022] Further, the salt bath medium of the salt bath furnace in step S3 is composed of W(BaCl2)40%+W(KCl)30%+W(NaCl)30%.

[0023] Further, the holding and staying time of the first heating treatment and the second heating treatment in step S3 is 2min / mm.

[0024] Further, the high-temperature bearing steel raw material prepared in step S1 is W6Mo5Cr4V2 high-temperature bearing steel.

[0025] Further, the high-temperature bearing steel raw material prepared in step S1 meets the GB / T 9943 standard.

[0026] The present application provides a heat treatment process for cyclic annealing of high-temperature bearing steel, comprising the following steps: Example: (1) Prepare W6Mo5Cr4V2 material meeting the GB / T 9943 standard; (2) Machine the material into regular parts with a size of φ10*20mm; (3) remove the surface scale and other defects of the part; (4) the first heating of the cycle annealing uses a salt bath furnace; (5) the temperature is 850℃±5℃, and the composition of the salt bath medium is: W(BaCl2)70%+ W(NaCl)30%; (6) the second heating of the cycle annealing uses a salt bath furnace; (7) the temperature is 650±5℃, and the composition of the salt bath medium is: W(BaCl2)40%+ W(KCl)30%+ W(NaCl)30%; (8) the holding time of each cycle is 2min / mm of single holding time according to the maximum wall thickness of the part; (9) perform 3 cycles, and then air cool to room temperature.

[0027] Comparative Example: (1) prepare W6Mo5Cr4V2 material meeting GB / T 9943 standard; (2) machine the material into regular parts with the size of φ10*20mm; (3) remove the surface scale and other defects of the part; (4) the traditional isothermal annealing process is heated to 860~880℃, and held for 5±3h; (5) slowly furnace cool for 5±3h to 740~750℃, and hold for 5±1h; (6) then slowly furnace cool for more than 10h to below 500℃, and air cool after leaving the furnace.

[0028] The cycle annealed parts of the above examples and the traditional isothermal annealed parts of the comparative example are simultaneously quenched at 1250℃ for 30min, and the grain size, microstructure and deformation of the quenched parts are tested.

[0029] The comparison of the above examples and the comparative example has the following beneficial effects: 1. The above examples and the comparative example are completely consistent in the core prerequisite condition: both use W6Mo5Cr4V2 material meeting GB / T 9943 standard, both are processed into regular parts with the size of φ10*20mm, both remove the surface scale and defects, and the subsequent quenching process (1250℃ for 30min) is completely the same. The only difference is the annealing process, the above examples use the “850±5℃-650±5℃ two-salt bath cycle annealing” proposed by the invention, and the comparative example uses the traditional “isothermal annealing” in the industry. Using the above “single variable” design, the interference of factors such as material specification, part size, surface state and subsequent quenching on the test results is completely eliminated, ensuring that the differences in grain size, microstructure and deformation are only caused by different annealing processes, so that the comparison conclusion has a rigorous scientific basis, avoiding the result deviation caused by multiple variables.

[0030] 2. The above embodiments detail the entire process of the invented cyclic annealing process: from the selection of the salt bath furnace, to the temperature control at 850±5℃ and 650±5℃, the specific proportions of the salt bath medium (BaCl2-NaCl system, BaCl2-KCl-NaCl system), and the key parameters of "holding at 2 min / mm for the maximum wall thickness of the part, followed by air cooling after 3 cycles," all are fully presented. This setup not only clearly demonstrates the specific implementation path of the invented process, facilitating understanding and repeatable operation by industry personnel, but also verifies the feasibility of the process through actual operation. That is, no special customized equipment is required; it can be achieved using a conventional salt bath furnace, and the parameters are controllable and the process is stable, laying a "replicable" foundation for subsequent industrial mass application.

[0031] 3. The process of "holding at 860~880℃ - slow furnace cooling to 740~750℃ and holding - continued slow furnace cooling to below 500℃" used in the above comparative example is the industry-standard solution for annealing W6Mo5Cr4V2 high-temperature bearing steel, and it is also the benchmark against which the invention aims to address the pain points (long cycle, high energy consumption, coarse microstructure, and large deformation). Using it as a comparative example allows for a direct comparison of the advantages of the invention's process: compared to the traditional isothermal annealing process of "long holding time + slow furnace cooling," the cyclic annealing process of the embodiment shows optimization in process efficiency and energy consumption, as well as improvements in subsequent quenching and tempering microstructure and part deformation, all of which can be directly demonstrated by comparing the test results with those of the comparative example.

[0032] 4. The three key indicators of "grain size, microstructure, and deformation" tested in the above embodiments and comparative examples precisely correspond to the core pain points of traditional annealing processes and the core advantages of the invention: grain size and microstructure are directly related to the mechanical properties of materials (high-temperature hardness, wear resistance, and toughness), and are key metrics for addressing the "coarse microstructure" problem of traditional processes; deformation directly relates to the dimensional accuracy of parts, and is the core evaluation dimension for addressing the "large deformation" problem of traditional processes. By comparing these three indicators, the value of the invented process can be fully verified. It solves the production pain points of "long cycle time and high energy consumption" in traditional processes, improves material properties by optimizing grain size and microstructure, and ensures part accuracy by controlling deformation. This achieves dual verification of "production efficiency" and "product quality," allowing the invention's advantages to cover the entire chain of needs from production to application.

[0033] The above shows and describes the basic principles and main features of the present application and the advantages of the present application, and those skilled in the art should understand that the present application is not limited to the above embodiments, and the above embodiments and descriptions in the specification are only to illustrate the principles of the present application, and various changes and improvements can be made without departing from the spirit and scope of the present application, and these changes and improvements all fall within the scope of the claimed present application, and the scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A heat treatment process for cyclic annealing of high temperature bearing steel, characterized in that: The method comprises the following steps: S1, preparing high-temperature bearing steel raw materials, and processing the high-temperature bearing steel raw materials into regular parts through machining; S2, removing the surface oxide scale of the regular parts; S3, placing the regular parts processed through step S2 into a salt bath furnace and performing cyclic annealing processing, the cyclic annealing processing comprising a first heating treatment and a second heating treatment, the temperature of the first heating treatment being higher than that of the second heating treatment, and the regular parts being subjected to the first heating treatment and the second heating treatment and then being subjected to holding and staying treatment; S4, the number of cyclic annealing processing in step S3 is three, and the regular parts are air-cooled to room temperature after being subjected to the three cyclic annealing processing.

2. A heat treatment process for cyclic annealing of high temperature bearing steel as claimed in claim 1, wherein: The temperature of the first heating treatment in step S3 is 850℃±5℃.

3. A heat treatment process for cyclic annealing of high temperature bearing steel as claimed in claim 1, wherein: The salt bath medium of the salt bath furnace in step S3 comprises W(BaCl2)70%+W(NaCl)30%.

4. A heat treatment process for cyclic annealing of high temperature bearing steel as claimed in claim 1, wherein: The temperature of the second heating treatment in step S3 is 650℃±5℃.

5. A heat treatment process for cyclic annealing of high temperature bearing steel as claimed in claim 1, wherein: The salt bath medium of the salt bath furnace in step S3 comprises W(BaCl2)40%+W(KCl)30%+W(NaCl)30%.

6. A heat treatment process for cyclic annealing of high temperature bearing steel as claimed in claim 1 wherein: The holding and staying time of the first heating treatment and the second heating treatment in step S3 is both 2min / mm.

7. A heat treatment process for cyclic annealing of high temperature bearing steel as claimed in claim 1 wherein: The high-temperature bearing steel raw materials prepared in step S1 are W6Mo5Cr4V2 high-temperature bearing steel.

8. A heat treatment process for cyclic annealing of high temperature bearing steel as claimed in claim 1, wherein: The high-temperature bearing steel raw materials prepared in step S1 meet the GB / T 9943 standard.

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