Method for high frequency assisted rotary friction welding of hollow drill string

Abstract

The application provides a method for high-frequency auxiliary rotary friction welding of a hollow drill, and relates to the technical field of rotary friction welding. The hollow drill sample to be welded is passed through a high-frequency induction heating coil, so that the friction zone of the hollow drill sample to be welded is located at the center of the high-frequency induction heating coil, while the heat affected zone is ensured to fall into the high-frequency induction heating coil, and first stage electromagnetic induction heating is carried out. The electromagnetic induction heating coil is of a waist type. Then, rotary friction is carried out under the condition of applying second stage electromagnetic induction heating. After the rotary friction is completed, upsetting deformation is carried out by applying an upsetting force to complete welding, and then oil quenching cooling is carried out to obtain a welded sample. The welded sample is subjected to third stage electromagnetic induction heating to realize stress relief annealing. The method provided by the application not only simplifies the production process, but also greatly improves the service life of the drill.

Description

Technical Field

[0001] This invention relates to the field of rotary friction welding technology, and more particularly to a method for high-frequency assisted rotary friction welding of hollow brazing tools. Background Technology

[0002] 23GrNi3Mo steel is one of the most widely used rock drilling tool steels, extensively used in the manufacture of drill rods. Drill rods, as a common tool for rock drilling, are most widely used for drilling holes in rocks and other structures. Typically, a drill rod consists of three parts: the drill bit, the drill rod, and the drill shank. The drill bit and drill shank each have internal and external threads for connection between the drill rod and the drill shank. For ease of production, the drill rod and the drill bit or drill shank are usually manufactured using a rotary friction welding process, such as... Figure 1 As shown.

[0003] Typically, hollow drill bits produced using rotary friction welding technology require two steps before final processing: a welding process and a heat treatment process. Figure 2 As shown, during friction stir welding, the heat generated by friction at the weld face causes the joint heat to gradually decrease from the weld face to the drill bit matrix, resulting in a rapid temperature change. Recrystallization occurs at the weld end due to friction, while the heat-affected zone (HAZ) near the friction zone experiences coarsening of the microstructure or dissolution of martensite due to high-temperature heat transfer, leading to significant microstructural defects near the weld zone. This coarsening of the HAZ results in a significant weak point, with the strength and ductility of the welded specimen far lower than the matrix. Furthermore, the slow air cooling rate further weakens the HAZ due to heat transfer from the high-temperature zone. Additionally, the welded specimen requires a complex and time-consuming heat treatment process to regulate its microstructure and mechanical properties. Heat-treated drill bits often have a short lifespan, typically less than 72 hours. Summary of the Invention

[0004] The purpose of this invention is to provide a method for high-frequency assisted rotary friction welding of hollow drill bits. The method of this invention not only simplifies the production process, but also significantly improves the life of the drill bits.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for high-frequency assisted rotary friction welding of hollow welding tools, comprising the following steps:

[0007] The hollow brazing sample to be welded is passed through the high-frequency induction heating coil, so that the friction zone of the hollow brazing sample to be welded is located in the center of the high-frequency induction heating coil, while ensuring that the heat-affected zone falls into the high-frequency induction heating coil, to carry out the first stage of electromagnetic induction heating; the electromagnetic induction heating coil is waist-shaped.

[0008] Then, rotational friction is performed under the condition of applying a second stage of electromagnetic induction heating;

[0009] After the rotational friction ends, an upsetting force is applied to perform upsetting deformation to complete the welding. Then, the sample is cooled by oil quenching to obtain the welded specimen.

[0010] The welded specimen was subjected to a third stage of electromagnetic induction heating to achieve stress-relief annealing.

[0011] Preferably, the material of the hollow brazing tool sample to be welded is low-carbon high-alloy steel such as 23GrNi3Mo steel or GDL steel; the outer diameter of the hollow brazing tool to be welded is 50-100mm.

[0012] Preferably, the power of the electromagnetic induction heating in the first stage is 35kW to 50kW, the current is 50A to 100A, and the time is 25s to 120s.

[0013] Preferably, a pressure of 0.5 MPa to 3 MPa is applied between the hollow brazing tool samples to be welded before the first stage of electromagnetic induction heating.

[0014] Preferably, the power of the electromagnetic induction heating in the second stage is 10kW to 30kW, and the current is 50A to 100A.

[0015] Preferably, the pressure applied during the rotary friction welding is 2.5 MPa to 5 MPa, and the time is 8 s to 24 s.

[0016] Preferably, the upsetting force applied during the upsetting deformation is 9MPa to 15MPa, and the holding time is 5s to 10s.

[0017] Preferably, the oil quenching cooling time is 120s to 180s.

[0018] Preferably, the oil quenching cooling is performed by spraying quenching oil.

[0019] Preferably, the power of the third stage electromagnetic induction heating is 2kW to 5kW, the current is 20A to 60A, and the time is 10min to 20min.

[0020] This invention provides a method for high-frequency assisted rotary friction welding of hollow drill bits, comprising the following steps: passing the hollow drill bit sample to be welded through a high-frequency induction heating coil, such that the friction zone of the hollow drill bit sample is located in the center of the high-frequency induction heating coil, while ensuring that the heat-affected zone falls within the high-frequency induction heating coil, and performing a first stage of electromagnetic induction heating; the electromagnetic induction heating coil is waist-shaped; then, under the condition of applying a second stage of electromagnetic induction heating, rotary friction is performed; after the rotary friction is completed, an upsetting force is applied to perform upsetting deformation to complete the welding, followed by oil quenching and cooling to obtain a welded sample; the welded sample is then subjected to a third stage of electromagnetic induction heating to achieve stress-relief annealing.

[0021] This invention first employs a first-stage electromagnetic induction heating process. The purpose of this process is to pre-generate a certain temperature gradient, which has three main effects: 1) reducing the performance degradation caused by sudden temperature changes during welding; 2) shortening the friction heating time; and 3) improving the plasticity of the welded ends through induction heating, resulting in a superior weld joint. Then, under the second-stage electromagnetic induction heating, rotational friction is applied to form a preliminary weld joint. Because the heating coil is waist-shaped (larger diameter at both ends and smaller in the middle), more heat is generated at the welded end face in the middle and less at the ends. High-frequency induction heating avoids the sudden heat transfer from the welded end face to the drill bit substrate that occurs in traditional rotational friction welding, thus preventing significant structural defects in the heat-affected zone. This invention uses oil quenching cooling, which improves the microstructure distribution of the joint, thereby controlling and obtaining a high-strength welding tool. Finally, a third-stage electromagnetic induction heating process is performed to eliminate thermal stress generated during quenching, further improving the microstructure and achieving higher mechanical properties. The results of the embodiments show that the method of this invention increases the service life of the welding tool from less than 72 hours to approximately 200 hours.

[0022] Furthermore, the method of this invention reduces the need for subsequent heat treatment, simplifies the production process, and improves production efficiency. Attached Figure Description

[0023] Figure 1 For workpieces subjected to conventional rotary friction welding;

[0024] Figure 2 This is a process flow diagram for conventional rotary friction welding of hollow brazing tools;

[0025] Figure 3 This is a flowchart of the high-frequency assisted rotary friction welding method for hollow brazing tools according to the present invention;

[0026] Figure 4 This is a schematic diagram of the structure of the equipment used in the high-frequency assisted rotary friction welding of the present invention;

[0027] Figure 5 The microstructure distribution of the specimen obtained by conventional rotary friction welding in Comparative Example 1 is shown in the diagram, where (a) is the friction zone, (b) is the heat-affected zone, and (c) is the matrix.

[0028] Figure 6 For Comparative Example 1, the hardness distribution (a) and local strain during the stress process of a conventional rotary friction welding specimen are shown.

[0029] Figure 7 The microstructure distribution of the welded specimen obtained by high-frequency assisted rotary friction welding in Example 1 is shown in the diagram, where (a) is the friction zone, (b) is the heat-affected zone, and (c) is the matrix.

[0030] Figure 8 The mechanical property distribution diagrams for Example 1 and Comparative Example 1 are shown.

[0031] Figure 9 The strain distribution of the matrix as a function of stress is shown in Example 1, Comparative Example 1, and the matrix.

[0032] Figure 10 The microstructure distribution of the specimen obtained by conventional rotary friction welding in Comparative Example 2 is shown in the diagram, where (a) is the friction zone, (b) is the heat-affected zone, and (c) is the matrix.

[0033] Figure 11 The microstructure distribution of the welded specimen obtained by high-frequency assisted rotary friction welding in Example 2 is shown in the diagram, where (a) is the friction zone, (b) is the heat-affected zone, and (c) is the matrix.

[0034] Figure 12 The strain distribution of the matrix as a function of stress is shown in Example 2, Comparative Example 2, and the matrix. Detailed Implementation

[0035] like Figure 3 As shown, the present invention provides a method for high-frequency assisted rotary friction welding of hollow welding tools, comprising the following steps:

[0036] The hollow brazing sample to be welded is passed through the high-frequency induction heating coil, so that the friction zone of the hollow brazing sample to be welded is located in the center of the high-frequency induction heating coil, while ensuring that the heat-affected zone falls into the high-frequency induction heating coil, to carry out the first stage of electromagnetic induction heating; the electromagnetic induction heating coil is waist-shaped.

[0037] Then, rotational friction is performed under the condition of applying a second stage of electromagnetic induction heating;

[0038] After the rotational friction ends, an upsetting force is applied to perform upsetting deformation to complete the welding. Then, the sample is cooled by oil quenching to obtain the welded specimen.

[0039] The welded specimen was subjected to a third stage of electromagnetic induction heating to achieve stress-relief annealing.

[0040] like Figure 4 As shown, in this invention, the hollow brazing tool sample to be welded is passed through a high-frequency induction heating coil, so that the friction zone of the hollow brazing tool sample to be welded is located in the center of the high-frequency induction heating coil, while ensuring that the heat-affected zone falls into the high-frequency induction heating coil, and the first stage of electromagnetic induction heating is performed.

[0041] In this invention, the material of the hollow brazing tool sample to be welded is preferably low-carbon high-alloy steel such as 23GrNi3Mo steel or GDL steel; the outer diameter of the hollow brazing tool to be welded is preferably 50-100mm. In the art, the diameter of the hollow brazing tool to be welded is commonly 50mm and 100mm.

[0042] In this invention, the electromagnetic induction heating coil is a tapered type, meaning it has a large diameter at both ends and a small diameter in the middle. This invention uses heating coils with varying diameters to adjust the temperature field during welding by controlling the magnetic flux in different areas of the workpiece. In this invention, the inner diameter of the tapered portion of the high-frequency electromagnetic induction coil is preferably 10mm larger than the outer diameter of the hollow brazing tool to be welded, and the tapered length is preferably 20mm; the angle of the outer extension of the connecting edge is 20°, and the angle between one side and the center line is 10°; the length of one side is preferably 25mm to 35mm, and the number of coil turns is preferably 14 to 20 turns.

[0043] In this invention, the power of the first-stage electromagnetic induction heating is preferably 35kW to 50kW, and is specifically optimized according to the diameter of the hollow welding tool to be welded. The larger the outer diameter of the hollow welding tool, the higher the heating power is preferred. In this invention, when the outer diameter of the hollow welding tool is 50mm, the power of the first-stage electromagnetic induction heating is preferably 36kW; when the outer diameter of the hollow welding tool is 100mm, the power of the first-stage electromagnetic induction heating is preferably 50kW. In this invention, the current of the first-stage electromagnetic induction heating is preferably 50A to 100A, more preferably 60A to 90A; and even more preferably 70A to 80A.

[0044] In this invention, a pressure of 0.5 MPa to 3 MPa, more preferably 1 MPa to 2.5 MPa, is preferably applied between the hollow brazing tool samples to be welded before the first stage of electromagnetic induction heating. Applying a certain clamping force before the first stage of electromagnetic induction heating prevents oxidation of the end faces during the induction heating process.

[0045] In this invention, the preferred duration of the first stage of electromagnetic induction heating is 25s to 120s, more preferably 30s to 100s. The purpose of the first stage of electromagnetic induction heating in this invention is to pre-generate a certain temperature gradient through electromagnetic induction heating, which has three effects: first, it reduces the reduction in product performance caused by temperature abrupt changes during the welding process; second, it shortens the friction heating time; and third, it enables the welded end to have better plasticity through induction heating, resulting in a superior welded joint.

[0046] After the first stage of electromagnetic induction heating is completed, the present invention performs rotational friction under the condition of applying the second stage of electromagnetic induction heating.

[0047] In this invention, the power of the second-stage electromagnetic induction heating is preferably 10kW to 30kW, more preferably 15kW to 25kW; the current of the second-stage electromagnetic induction heating is preferably 50A to 100A, more preferably 60A to 90A, and even more preferably 70A to 80A. The pressure applied by the rotational friction is preferably 2.5MPa to 5MPa, more preferably 3MPa to 4.5MPa, and even more preferably 3.5MPa to 4MPa; the time is preferably 8s to 24s, more preferably 10s to 20s. By assisting electromagnetic induction heating during the rotational friction process, this invention can avoid the abrupt change in joint heat from the welding end face to the brazing rod matrix caused by traditional rotational friction welding, thereby avoiding the formation of obvious structural defects in the heat-affected zone, and also plays a role in auxiliary heating.

[0048] After the rotary friction welding is completed, the present invention applies an upsetting force to perform upsetting deformation to complete the welding, followed by oil quenching and cooling to obtain a welded sample.

[0049] In this invention, the upsetting force applied during the upsetting deformation is preferably 9 MPa to 15 MPa, more preferably 10 MPa to 13 MPa, and the holding time is preferably 5 s to 10 s, more preferably 6 s to 8 s. This invention optimizes the microstructure around the weld by achieving dynamic recrystallization through upsetting deformation, resulting in a weld microstructure with higher strength, avoiding the appearance of weak zones at the weld, and simultaneously extruding high-temperature material with defects such as oxides and coarse structures from the weld end face.

[0050] In this invention, the oil quenching cooling is preferably achieved by spraying quenching oil; the quenching oil is preferably ordinary flame-retardant quenching oil, and the oil pressure applied during the spraying process is preferably 0.1–0.2 MPa; the oil quenching cooling time is preferably 120–180 s, more preferably 130–150 s. This invention improves the microstructure distribution of the joint through oil quenching cooling, thereby controlling and obtaining high-strength welding tools.

[0051] After the oil quenching cooling is completed, the present invention preferably uses a clean cloth to wipe the quenching oil sprayed on the welding sample dry before proceeding with the subsequent third stage of electromagnetic induction heating.

[0052] After obtaining the welding sample, the present invention performs a third-stage electromagnetic induction heating on the welding sample to achieve stress-relieving annealing.

[0053] In this invention, the power of the third-stage electromagnetic induction heating is preferably 2kW to 5kW, more preferably 3kW to 4kW; the current is preferably 20A to 60A, more preferably 30A to 50A, and even more preferably 35A to 45A; the duration of the third-stage electromagnetic induction heating is preferably 10min to 20min, more preferably 12min to 18min, and even more preferably 14min to 16min. This invention, through third-stage electromagnetic induction heating, eliminates the thermal stress generated during quenching, further improving the microstructure and obtaining higher mechanical properties.

[0054] The following detailed description of the high-frequency assisted rotary friction welding method for hollow brazing tools provided by the present invention, with reference to the embodiments, should not be construed as limiting the scope of protection of the present invention.

[0055] Example 1

[0056] (1) Temperature field establishment stage (electromagnetic induction heating): The material of the hollow brazing tool sample to be welded is 23GrNi3Mo steel with an outer diameter of 50mm. The dimensions of the high-frequency induction heating coil are: inner diameter of the narrow waist part of 60mm, waist length of 20mm, angle of the outer extension part of 20°, single-sided outer extension of 25mm, and 14 turns of the coil. The hollow brazing tool sample to be welded passes through the high-frequency induction heating coil so that the friction zone of the hollow brazing tool sample to be welded is located in the center of the high-frequency induction heating coil, while ensuring that the heat-affected zone falls into the high-frequency induction heating coil. The hollow brazing tools to be welded are placed close together and a pressure of 0.5MPa is applied for electromagnetic induction heating. The electromagnetic induction heating power is 36kW, the current is 60A, and the time is 30s.

[0057] (2) Friction welding stage (electromagnetic induction heating + rotary friction assisted heat generation): In this stage, electromagnetic induction heating and rotary friction are carried out simultaneously. The power of electromagnetic induction is 10kW and the current is 60A. The rotary friction is carried out with the same applied pressure of 2.5MPa for 8s.

[0058] (3) Upsetting deformation stage: The applied upsetting force is 9MPa, and the holding time is 5s;

[0059] (4) Oil quenching: After the upsetting is completed, quenching oil is sprayed at a pressure of 0.2 MPa to complete the quenching of the heat-affected zone of the welded sample. The quenching oil spraying time is 120 s.

[0060] (5) Induction heating annealing stage: After quenching and cooling, wipe the sprayed quenching oil dry with a clean cloth, and then use induction heating for stress relief annealing. The specific induction heating power is 2kW, the current is 60A, and the time is 10min.

[0061] Example 2

[0062] (1) Temperature field establishment stage (electromagnetic induction heating): The hollow brazing tool sample to be welded is made of 23GrNi3Mo steel with an outer diameter of 100mm. The high-frequency induction heating coil has an inner diameter of 110mm for the narrow waist, a waist length of 20mm, an outer extension angle of 20°, a single-sided outer extension of 35mm, and 20 coil turns. The hollow brazing tool sample to be welded passes through the high-frequency induction heating coil, so that the friction zone of the hollow brazing tool sample to be welded is located in the center of the high-frequency induction heating coil, while ensuring that the heat-affected zone falls into the high-frequency induction heating coil. The hollow brazing tools to be welded are placed close together and a pressure of 0.5MPa is applied for electromagnetic induction heating. The electromagnetic induction heating power is 50kW, the current is 100A, and the time is 30s.

[0063] (2) Friction welding stage (electromagnetic induction heating + rotary friction assisted heat generation): In this stage, electromagnetic induction heating and rotary friction are carried out simultaneously. The power of electromagnetic induction is 10kW and the current is 60A. The rotary friction is carried out with the same applied pressure of 2.5MPa for 8s.

[0064] (3) Upsetting deformation stage: The applied upsetting force is 9MPa, and the holding time is 5s;

[0065] (4) Oil quenching: After the upsetting is completed, quenching oil is sprayed at a pressure of 0.2 MPa to complete the quenching of the heat-affected zone of the welded sample. The quenching oil spraying time is 120 s.

[0066] (5) Induction heating annealing stage: After quenching and cooling, wipe the sprayed quenching oil dry with a clean cloth, and then use induction heating for stress relief annealing. The specific induction heating power is 2kW, the current is 60A, and the time is 10min.

[0067] Comparative Example 1

[0068] The same sample to be welded as in Example 1 was used, except that the conventional rotary friction welding method was used for welding. The specific welding parameters are shown in Table 1.

[0069] Table 1 Comparative Example 1 Traditional Rotary Friction Welding Conditions

[0070] parameter 2.5MPa 4s 3.7MPa 10s 9MPa 7s air cooling

[0071] The heat treatment process adopted is as follows: the sample is annealed at 880℃ for 2 hours, then oil-cooled, and the cooled sample is stress-relief annealed at 200℃ for 4 hours, and then air-cooled.

[0072] Comparative Example 2

[0073] The same sample to be welded as in Example 2 was used, except that the conventional rotary friction welding method was used for welding. The specific welding parameters are shown in Table 2.

[0074] Table 2 Comparative Example 2 Traditional Rotation Friction Welding Conditions

[0075] parameter 2.5MPa 6s 3.7MPa 14s 13MPa 7s air cooling

[0076] The heat treatment process adopted is as follows: the sample is annealed at 880℃ for 2 hours, then oil-cooled, and the cooled sample is stress-relief annealed at 200℃ for 4 hours, and then air-cooled.

[0077] Structural and performance characterization:

[0078] The microstructure of the welded specimen (after heat treatment) of Comparative Example 1 was observed, and the results are as follows: Figure 5 As shown, Figure 5 In the diagram, (a) is the friction zone, (b) is the heat-affected zone, and (c) is the substrate. Figure 5 It is known that during friction stir welding, the heat generated by friction at the end faces causes the heat of the joint to gradually decrease from the welding end face to the brazing rod matrix. Recrystallization occurs at the welding end due to friction, such as... Figure 5 As shown in (a); the heat-affected zone near the friction zone experiences coarsening of the microstructure or dissolution of martensite due to high-temperature heat transfer, resulting in obvious microstructural defects near the weld zone, such as... Figure 5 As shown in (b), the coarsening of the microstructure in the heat-affected zone (HAZ) leads to the formation of significant weak areas. These weak areas have low hardness. Figure 6 (a) Fracture during deformation is more likely to occur in areas of weak strength. Figure 6 (b) The strength and ductility of welded specimens are much lower than those of the base material, such as... Figure 9 As shown.

[0079] The microstructure of the sample after welding in Example 1 was observed, and the results are as follows: Figure 7 As shown, Figure 7 In the diagram, (a) is the friction zone, (b) is the heat-affected zone, and (c) is the substrate. Figure 7 It can be seen that the present invention effectively refines the microstructure of the joint and effectively homogenizes the microstructure of the welded sample. This effectively improves the distribution of mechanical properties of the joint and eliminates weak areas in mechanical properties, such as... Figure 8 As shown. This invention greatly enhances the mechanical properties of the joint, including its strength and elongation. Figure 9The strength and elongation of the traditional rotary friction welded specimens are as follows: σ 0.2 =812MPa; σ b =1093MPa; A=4.95%, the strength and elongation of the welded specimen in Example 1 of this invention are respectively: σ 0.2 =1140MPa; σ b =1511MPa; A=7.57%. The welded specimen obtained by this invention avoids breakage at the weld joint during use.

[0080] Microstructural observation of the welded sample of Comparative Example 2 showed that, similar to Comparative Example 1, a significantly coarsened microstructure and martensite dissolution were also observed near the friction zone. Figure 10 In Example 2, the microstructure of the sample obtained by high-frequency assisted rotary friction welding was significantly homogenized, with an effect similar to that of Example 1. Figure 11 As shown. Compared with Comparative Example 2, the welded specimen of Example 2 also showed a significant improvement in mechanical properties in terms of strength and elongation. The strength and elongation of the specimen of Comparative Example 2, which was welded using conventional rotary friction welding, were as follows: σ 0.2 =818MPa; σ b =1097MPa; A=4.05%, the strength and ductility of the welded specimen in Embodiment 2 of the present invention are respectively: σ 0.2 =1077MPa; σ b =1457MPa; A=7.73%, such as Figure 12 As shown.

[0081] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle 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 method for high-frequency assisted rotary friction welding of hollow welding tools, comprising the following steps: The hollow welding tool sample to be welded is passed through the high-frequency induction heating coil, ensuring that the friction zone of the sample is located in the center of the coil while the heat-affected zone falls within it. This initiates the first stage of electromagnetic induction heating. The high-frequency induction heating coil is waist-shaped, with a larger diameter at both ends and a smaller diameter in the middle. This results in more heat being generated at the welding end face in the middle and less at the ends, thus avoiding the abrupt change in heat transfer from the welding end face to the welding tool substrate that occurs in traditional rotary friction welding. The outer angle of the coil on both sides is 20°, and the angle between each side and the centerline is 10°. Then, rotational friction is performed under the condition of applying a second stage of electromagnetic induction heating; After the rotational friction ends, an upsetting force is applied to perform upsetting deformation to complete the welding. Then, the sample is cooled by oil quenching to obtain the welded specimen. The welded specimen was subjected to a third stage of electromagnetic induction heating to achieve stress-relief annealing.

2. The method of claim 1, wherein, The hollow brazing tool sample to be welded is made of low-carbon high-alloy steel; the outer diameter of the hollow brazing tool to be welded is 50~100mm.

3. The method according to claim 1, characterized in that, The power of the first stage electromagnetic induction heating is 35kW~50kW, the current is 50A~100A, and the time is 25s~120s.

4. The method according to any one of claims 1 or 3, characterized in that, Before the first stage of electromagnetic induction heating, a pressure of 0.5MPa to 3MPa is applied between the hollow brazing tool samples to be welded.

5. The method according to claim 1, characterized in that, The power of the second stage electromagnetic induction heating is 10kW~30kW, and the current is 50A~100A.

6. The method according to claim 1 or 5, characterized in that, The pressure applied by the rotational friction is 2.5MPa~5MPa, and the time is 8s~24s.

7. The method according to claim 1, characterized in that, The upsetting force applied during the upsetting deformation is 9MPa~15MPa, and the holding time is 5s~10s.

8. The method according to claim 1, characterized in that, The oil quenching cooling time is 120s~180s.

9. The method according to claim 1 or 8, characterized in that, The oil quenching cooling is achieved by spraying quenching oil for cooling.

10. The method according to claim 1, characterized in that, The third stage of electromagnetic induction heating has a power of 2kW~5kW, a current of 20A~60A, and a time of 10min~20min.

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