A heat treatment control method for internal and external spline shafts

Abstract

The present invention discloses a heat treatment control method for internal and external spline shafts. The method adopts a technological process of solution + aging treatment, local quenching treatment, cryogenic treatment and aging treatment, which not only solves the different hardness requirements at the internal and external splines of spline shafts with an inner diameter wall thickness of 5 - 15 mm, but also makes the matrix structure of the 17 - 4PH material after heat treatment more uniform, improves the material strength and corrosion resistance, and can maintain a high precision of the product. In addition, after the heat treatment technological process of the present invention, the product quality is stable, the reproducibility and repeatability are good, the hardness of the internal spline part is high and the wear resistance is good, the external spline part is easy to machine, the processing cost is low, the production efficiency is high, it can meet the mass production requirements at a high level, and the product performance is more stable and reliable. It can manufacture spline shafts efficiently, with high quality and in large batches, and can be applied to working environments with high precision requirements and electromagnetic influence such as motors, electric drive axles and electromagnetic rotors.

Description

Technical Field

[0001] The present invention relates to a heat treatment control method for internal and external spline shafts, belonging to the technical field of heat treatment of metal materials. Background Art

[0002] Spline shafts have simple and reliable transmission, high specific power, and irreplaceable status in transmission devices, and are widely used in the aerospace field. With the improvement of the performance of transmission devices, the performance requirements for spline shafts are also higher. One of them is that both the internal and external splines of the spline shaft should be able to support independent structures and meet special technical requirements, such as "tough on the outside and hard on the inside", that is, the external spline has lower hardness but better toughness, while the internal spline requires high hardness, wear resistance, higher material strength and corrosion resistance, and maintains high precision.

[0003] Such as Figure 2 and Figure 3 shown, the hardness requirement for the internal spline of the internal and external spline shaft is above 44HRC, and the hardness of the external spline is 28 - 32HRC. If the existing conventional heat treatment technology processes: solution treatment + cold deformation + aging or solution treatment + quenching and tempering + aging are adopted, either the residual internal stress is not completely eliminated, affecting the service life, or there is too much retained austenite, resulting in unstable and difficult-to-control technical indicators such as hardness, and it is difficult to achieve complete transformation of martensite. The process reproducibility and repeatability are insufficient, mass production is difficult, and the product qualification rate is low. Summary of the Invention

[0004] The present invention provides a heat treatment control method for internal and external spline shafts to control the heat treatment technical indicators of the internal and external spline parts of the spline shaft, meet the technical requirements of the internal and external support independent structures of the spline shaft, and thus improve the overall performance of the spline shaft.

[0005] The technical solution of the present invention: A heat treatment control method for internal and external spline shafts includes the following steps:

[0006] Step 1, solution treatment + aging treatment: First, keep the internal and external spline shafts at a temperature of 1040 - 1060°C for 100 - 120 minutes, quickly cool them in quenching oil at 80 - 90°C for 5 - 8 minutes. After fully draining the oil and cooling to room temperature, then keep them at 630 - 650°C for 140 - 160 minutes. After completion, air-cool to room temperature, and control the surface hardness at 28 - 32HRC;

[0007] Step 2, local quenching treatment: Use an induction heating coil to heat the internal spline part on the internal and external spline shafts. Immediately after the heating ends, spray and cool with a water-based quenching medium, with the cooling water flow rate of 0.2 - 0.5 L / min and the cooling time of 10 - 15 seconds;

[0008] Step 3. Cryogenic treatment: Remove the foreign matters on the surface of the internal and external spline shafts after the local quenching treatment, and then place them in a cryogenic box. Cool them at a cooling rate of -2 to -3 °C / min. When the temperature is cooled to -100 to -120 °C, keep the temperature for 30 to 140 min. After the heat preservation is completed, leave them in the cryogenic box and naturally recover to room temperature;

[0009] Step 4. Aging treatment: Place the internal and external spline shafts in a vacuum heating furnace. The heating process is divided into three stages: In the first stage, heat up to 250 to 260 °C at a rate of 3 to 5 °C / min and keep the temperature for 30 to 40 min; in the second stage, heat up to 350 to 360 °C at a rate of 2 to 4 °C / min and keep the temperature for 20 to 30 min; in the third stage, heat up to 460 to 480 °C at a rate of 1.5 to 3 °C / min and keep the temperature for 100 to 150 min; after the aging is completed, cool it in the furnace to below 80 °C and then take it out of the furnace.

[0010] In the above method, the internal and external spline shafts are made of 17-4PH material.

[0011] In the above method, when heating the internal spline part of the internal and external spline shafts with an induction heating coil, it is divided into two-stage heating. The heating time of the first stage is 5 to 7 seconds, the heating time of the second stage is 11 to 13 seconds, the interval time is 0.5 to 1 second, the power is 90 to 100 Kw, and the heating temperature of the second stage is 1020 to 1070 °C. During the processing, the internal and external spline shafts keep rotating, and the rotation speed is 2000 to 2500 revolutions per minute.

[0012] In the above method, the distance between the inner hole of the induction heating coil and the outer circle of the internal and external spline shafts is more than 20 mm. The length of the induction heating coil is 2 to 4 mm longer than the length of the local quenching part of the workpiece. The structure of the induction coil is double-pass water.

[0013] In the above method, during the heating, heat preservation and cooling processes of the aging treatment, the vacuum degree of the vacuum heating furnace is controlled above 1.0×10 -3 Pa.

[0014] Due to the adoption of the above technical solutions, the advantages of the present invention are as follows: The present invention not only solves the different hardness requirements at the internal and external splines of the spline shaft with an inner diameter wall thickness of 5 to 15 mm, but also the matrix structure of the 17-4PH material after heat treatment is more uniform, the material strength and corrosion resistance are both improved, and the high precision of the product can be maintained. In addition, after the heat treatment process flow of the present invention, the product quality is stable, the reproducibility and repeatability are good, the hardness of the internal spline part is high and the wear resistance is good, the external spline part is easy to cut, the processing cost is low, the production efficiency is high, it can meet the mass production requirements at a high level, and the product performance is more stable and reliable. It can manufacture spline shafts efficiently, with high quality and in large batches, and can be applied to working environments with high precision requirements and electromagnetic influence such as motors, electric drive axles and electromagnetic rotors. Brief Description of the Drawings

[0015] Figure 1 is a schematic diagram of the heat treatment process mechanism of the present invention;

[0016] Figure 2 is the front view of the schematic diagram of the internal and external spline shaft structure in the present invention;

[0017] Figure 3 is the side view of the schematic diagram of the internal and external spline shaft structure in the present invention. Detailed Description of the Invention

[0018] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments.

[0019] Embodiment 1

[0020] A heat treatment control method for an internal and external spline shaft of the present invention includes the following steps:

[0021] Step 1: Solution + aging treatment: First, keep the internal and external spline shaft at a temperature of 1040°C for 100 minutes, quickly cool it in quenching oil at 80°C for 5 minutes, fully drain the oil and cool it to room temperature, then keep it at 630°C for 140 minutes, and after completion, air-cool it to room temperature, controlling the surface hardness at 28 HRC;

[0022] Step 2: Local quenching treatment: Use an induction heating coil to heat the internal spline 2 part on the internal and external spline shaft. The inner hole of the induction heating coil is spaced more than 20 mm from the outer circle of the internal and external spline shaft. The length of the induction heating coil is 2 mm longer than the length of the local quenching part of the workpiece. The structure of the induction coil is double-pass water. The processing process is divided into two-stage heating. The first-stage heating time is 5 seconds, the second-stage heating time is 11 seconds, and the interval time is 0.5 seconds. The power is 90 Kw. Among them, the second-stage heating temperature is 1020°C. During the processing, the internal and external spline shaft keeps rotating at a speed of 2000 revolutions per minute. After heating, immediately spray-cool it with a water-based quenching medium. The cooling water flow rate is 0.2 L / min, and the cooling time is 10 seconds;

[0023] Step 3: Cryogenic treatment: Remove the foreign matter on the surface of the internal and external spline shaft after the local quenching treatment, then place it in a cryogenic box, and cool it at a cooling rate of -2°C / min. When the temperature is cooled to -100°C, keep it for 30 minutes. After the heat preservation is completed, leave it in the cryogenic box to naturally return to room temperature;

[0024] Step 4. Aging treatment: Place the internal and external spline shafts in a vacuum heating furnace. The heating process is divided into three stages: In the first stage, heat at a rate of 3°C / min to 250°C and hold for 30 min; in the second stage, heat at a rate of 2°C / min to 350°C and hold for 20 min; in the third stage, heat at a rate of 1.5°C / min to 460°C and hold for 100 min; after the aging is completed, cool in the furnace to below 80°C and then take out of the furnace. During the heating, holding, and cooling processes of the aging treatment, the vacuum degree of the vacuum heating furnace is controlled at 1.0×10 -3 Pa or above.

[0025] Example 2

[0026] A heat treatment control method for an internal and external spline shaft of the present invention includes the following steps:

[0027] Step 1. Solution + aging treatment: First, keep the internal and external spline shafts at a temperature of 1060°C for 120 min, quickly cool in 90°C quenching oil for 8 min. After fully draining the oil and cooling to room temperature, then keep at 650°C for 160 min. After completion, air-cool to room temperature, and control the surface hardness at 32 HRC;

[0028] Step 2. Local quenching treatment: Use an induction heating coil to heat the internal spline part 2 on the internal and external spline shafts. The inner hole of the induction heating coil is spaced more than 20 mm from the outer circle of the internal and external spline shafts. The length of the induction heating coil is 4 mm longer than the length of the local quenching part of the workpiece. The structure of the induction coil is double-pass water. The processing process is divided into two-stage heating. The first-stage heating time is 7 seconds, the second-stage heating time is 13 seconds, with a 1-second interval time in between, and the power is 100 Kw. Among them, the second-stage heating temperature is 1070°C. During the processing, the internal and external spline shafts keep rotating at a rotation speed of 2500 revolutions per minute. After the heating is completed, immediately spray and cool with a water-based quenching medium. The cooling water flow rate is 0.5 L / min, and the cooling time is 15 seconds;

[0029] Step 3. Cryogenic treatment: Remove the foreign matters on the surface of the internal and external spline shafts after the local quenching treatment, and then place them in a cryogenic box. Cool at a cooling rate of -3°C / min. When the temperature is cooled to -120°C, hold for 140 min. After the holding is completed, leave it in the cryogenic box and naturally recover to room temperature;

[0030] Step 4. Aging treatment: Place the internal and external spline shafts in a vacuum heating furnace. The heating process is divided into three stages: In the first stage, heat at a rate of 5°C / min to 260°C and hold for 40 min; in the second stage, heat at a rate of 4°C / min to 360°C and hold for 30 min; in the third stage, heat at a rate of 3°C / min to 480°C and hold for 150 min; after the aging is completed, cool in the furnace to below 80°C and then take out of the furnace. During the heating, holding, and cooling processes of the aging treatment, the vacuum degree of the vacuum heating furnace is controlled at 1.0×10-3 above Pa.

[0031] Example 3

[0032] A heat treatment control method for an internal and external spline shaft of the present invention includes the following steps:

[0033] Step 1. Solution + aging treatment: First, keep the internal and external spline shaft at a temperature of 1050 °C for 110 min, quickly cool it in quenching oil at 85 °C for 6 min, fully drain the oil and cool it to room temperature, then keep it at 640 °C for 150 min, and after completion, air-cool it to room temperature, controlling the surface hardness at 30 HRC;

[0034] Step 2. Local quenching treatment: Use an induction heating coil to heat the internal spline 2 part on the internal and external spline shaft. The inner hole of the induction heating coil is spaced more than 20 mm from the outer circle of the internal and external spline shaft. The length of the induction heating coil is 3 mm longer than the length of the local quenching part of the workpiece. The structure of the induction coil is double-pass water. The processing process is divided into two-stage heating. The first-stage heating time is 6 seconds, the second-stage heating time is 12 seconds, and the interval time is 0.8 seconds. The power is 95 Kw, and the second-stage heating temperature is 1040 °C. During the processing, the internal and external spline shaft keeps rotating at a speed of 2200 revolutions per minute. After heating, immediately spray-cool it with a water-based quenching medium. The cooling water flow rate is 0.4 L / min, and the cooling time is 12 seconds;

[0035] Step 3. Cryogenic treatment: Remove the foreign matters on the surface of the internal and external spline shaft after the local quenching treatment, then place it in a cryogenic box, and cool it at a cooling rate of -2.5 °C / min. When the temperature is cooled to -110 °C, keep it for 80 min, and after the heat preservation is completed, leave it in the cryogenic box to naturally recover to room temperature;

[0036] Step 4. Aging treatment: Place the internal and external spline shaft in a vacuum heating furnace. The heating process is divided into three stages: The first stage is to heat it to 255 °C at a rate of 4 °C / min and keep it for 35 min; the second stage is to heat it to 355 °C at a rate of 3 °C / min and keep it for 25 min; the third stage is to heat it to 470 °C at a rate of 2 °C / min and keep it for 125 min; after the aging is completed, cool it in the furnace to below 80 °C and then take it out. The vacuum degree of the vacuum heating furnace during the heating, heat preservation, and cooling processes of the aging treatment is controlled at 1.0×10 -3 above Pa.

[0037] In Examples 1 to 3, the temperature control process of the solution + aging treatment process, the aging treatment process, and the cryogenic treatment process uses a thermocouple to measure the temperature. The infrared thermometer is used to measure the surface temperature of the workpiece in the local quenching process. The ionization silicon and resistance silicon are respectively used to measure the vacuum degree in the low-vacuum and high-vacuum states of the pressure in the vacuum heating furnace. The temperature uniformity of the heat treatment equipment furnace is less than ±5°C. The automatic recording instrument is used to record time, temperature, and pressure. The number of monitoring and control thermocouples arranged in the equipment used in each process is not less than 2.

[0038] The working principle of the present invention:

[0039] See Figure 1 , in this embodiment, the internal and external spline shafts are made of 17-4PH material. The 17-4PH material belongs to the typical precipitation-hardening martensitic stainless steel. After the solution + aging treatment process, the hardness can reach 28 - 32 HRC. The aging method is used to make the hardness and strength of the spline shaft meet the design requirements. For the internal spline 2 part of the internal and external spline shafts, the induction heating coil is used for segmented heating to only make the structure of the internal spline 2 austenitized, and then it is rapidly cooled to obtain different hardnesses of the internal spline 2 and the external spline 1. The cryogenic treatment is used to adjust the hardness difference. On the one hand, the retained austenite is further transformed to form lath martensite, showing that the local hardness at the quenched part is higher. On the other hand, by optimizing the aging process, the precipitation and deformation amount are reduced, and the internal and external splines are kept in the state before high-frequency quenching, and fine carbide particles are precipitated and dispersed in the martensite matrix to increase the hardness.

[0040] Among them, the cryogenic treatment is used as a key process, and its functions are as follows: The retained austenite structure after quenching of the 17-4PH material can be completely transformed into lath martensite with the extension of the cryogenic time below the martensite transformation termination temperature (Ms) through cryogenic treatment. More lath martensite not only increases the hardness of the material but also provides the matrix structure for the subsequent precipitation of more intermediate phases, providing a way and method for precisely controlling technical indicators such as the hardness of the internal and external spline parts of the spline shaft. The intermediate phases precipitated by the 17-4PH material are mainly hard and stable phases such as ε-Cu and NbC, which are finely dispersed and attached to the martensite matrix, and can also increase the strength and corrosion resistance of the material within a certain range.

[0041] In summary, the present invention not only solves the different hardness requirements of the spline shaft with an inner diameter wall thickness δ of 5 to 15 mm at the internal spline 2 and the external spline 1, but also makes the matrix structure of the 17-4PH material more uniform after heat treatment. The material strength and corrosion resistance are both improved, and the product can maintain a high precision. In addition, after the heat treatment process flow of the present invention, the product quality is stable, with good reproducibility and repeatability. The internal spline 2 has a high hardness and good wear resistance, while the external spline 1 is easy to machine, with low processing costs and high production efficiency, which can meet the mass production requirements at a relatively high level. Moreover, the product performance is more stable and reliable, and the spline shaft can be manufactured efficiently, with high quality and in large batches, and can be applied to working environments with high precision requirements and electromagnetic influence, such as motors, electric drive axles, and electromagnetic rotors.

Claims

1. A heat treatment control method for an internal and external spline shaft, characterized in that It includes the following steps: Step 1, solution treatment + aging treatment: First, keep the internal and external spline shafts at a temperature of 1040 - 1060 °C for 100 - 120 min, quickly cool them in quenching oil at 80 - 90 °C for 5 - 8 min. After fully draining the oil and cooling to room temperature, then keep them at 630 - 650 °C for 140 - 160 min. After completion, air-cool them to room temperature, and control the surface hardness at 28 - 32 HRC; Step 2, local quenching treatment: Use an induction heating coil to heat the internal spline part on the internal and external spline shafts. Immediately after the heating ends, spray and cool it with a water-based quenching medium. The cooling water flow rate is 0.2 - 0.5 L / min, and the cooling time is 10 - 15 seconds; Step 3, cryogenic treatment: Remove the foreign matters on the surface of the internal and external spline shafts after the local quenching treatment, and then place them in a cryogenic box. Cool them at a cooling rate of -2 - -3 °C / min. When the temperature is cooled to -100 - -120 °C, keep the temperature for 30 - 140 min. After the heat preservation ends, leave them in the cryogenic box to naturally recover to room temperature; Step 4, aging treatment: Place the internal and external spline shafts in a vacuum heating furnace. The heating process is divided into three stages: In the first stage, heat up to 250 - 260 °C at a rate of 3 - 5 °C / min and keep it for 30 - 40 min; In the second stage, heat up to 350 - 360 °C at a rate of 2 - 4 °C / min and keep it for 20 - 30 min; In the third stage, heat up to 460 - 480 °C at a rate of 1.5 - 3 °C / min and keep it for 100 - 150 min; After the aging ends, cool it in the furnace to below 80 °C and then take it out of the furnace; When using an induction heating coil to heat the internal spline part of the internal and external spline shafts, it is heated in two sections. The heating time of the first section is 5 - 7 seconds, the heating time of the second section is 11 - 13 seconds, and the interval time between them is 0.5 - 1 second. The power is 90 - 100 Kw. Among them, the heating temperature of the second section is 1020 - 1070 °C. During the processing, the internal and external spline shafts keep rotating, and the rotation speed is 2000 - 2500 revolutions per minute; The distance between the inner hole of the induction heating coil and the outer circle of the internal and external spline shafts is more than 20 mm. The length of the induction heating coil is 2 - 4 mm longer than the length of the local quenching part of the workpiece. The structure of the induction coil is double-pass water.

2. The heat treatment control method for an internal and external spline shaft according to claim 1, characterized in that: The internal and external spline shafts are made of 17-4PH material.

3. The heat treatment control method for an internal and external spline shaft according to claim 1, characterized in that: During the heating, heat preservation and cooling processes of the aging treatment, the vacuum degree of the vacuum heating furnace is controlled above 1.0×10 -3 Pa.

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