Heat treatment process for shaft parts

Abstract

The invention provides a shaft part heat treatment process which comprises the following steps: S1, normalizing treatment: normalizing a shaft blank in a trolley furnace; s2, rough machining is conducted, specifically, rough machining is conducted on the workpiece subjected to normalizing treatment; s3, aging treatment is conducted, specifically, the workpiece subjected to rough machining is subjected to aging treatment in a tempering furnace; s4, carbonitriding and quenching treatment: performing stage preheating by adopting an atmosphere multi-purpose furnace, introducing methanol, propane and ammonia gas, and then performing strong carburizing, diffusion, secondary carburizing supplementation and quenching; s5, hot straightening treatment is conducted, specifically, the workpiece is bent and corrected after preheating; s6, semi-finish machining is conducted, specifically, semi-finish machining treatment is conducted on the workpiece subjected to hot straightening treatment; s7, qualitative treatment is conducted, specifically, the workpiece obtained after semi-finish machining is heated to 200 DEG C for qualitative treatment; and S8, finish machining is conducted, specifically, the outer circle and the spline of the workpiece subjected to qualitative treatment are machined to the design size. The hardness and hot straightening are improved, the workpiece quality is optimized, the process time is greatly shortened, and the production efficiency is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat treatment, in particular to a normalizing, aging, tempering and carbonitriding heat treatment process of 40Cr shaft workpieces, and particularly relates to a shaft part heat treatment process. BACKGROUND

[0002] 38CrMnAl material is high in cost, and workpieces are difficult to process after nitriding (see Figure 1 ), which affects production efficiency. Therefore, the material is changed to 40Cr, and 40Cr gas nitriding (see Figure 8 ) process test is carried out. There are the following problems in nitriding: (1) the hardness uniformity is poor, and the nitriding layer is shallow, only 0.40mm (see Figure 2 a), and there are local soft spots with hardness <Hv500; (2) when the production cycle is short, the workpiece is not fully stress released, and the deformation is large >0.12mm, and the allowance before nitriding is 0.12mm; (3) the heat straightening needs to control the accuracy within 0.06mm, the pressure control requirement is high, and the operation is difficult. When the pressure is not enough, the workpiece rebounds, and when the pressure is too high, the deformation is >0.12mm. SUMMARY

[0003] The purpose of the present application is to overcome the above-mentioned deficiencies, and to provide a shaft part heat treatment process. By process improvement, the gas nitriding is changed to carbonitriding, the quenching and tempering is changed to normalizing after rough machining, the allowance before heat treatment is increased, and the hardness and heat straightening are improved by using special tooling, thereby optimizing the workpiece quality, greatly reducing the process time, and improving the production efficiency. In order to realize the above technical features, the purpose of the present application is realized as follows: a shaft part heat treatment process, comprising the following steps: S1, normalizing treatment: normalizing treatment of the shaft blank in a trolley furnace to refine the structure; S2, rough machining: rough machining of the workpiece after normalizing treatment, and reserving the finishing allowance; S3, aging treatment: aging treatment of the workpiece after rough machining in a tempering furnace to fully release the cold working stress; S4, carbonitriding and quenching treatment: stage preheating by using an atmosphere multi-purpose furnace, and then introducing methanol, propane and ammonia, and then carrying out strong penetration, diffusion, secondary penetration and quenching; S5, heat straightening treatment: bending correction of the workpiece after preheating, and then aging to release the stress generated by straightening; S6, semi-finishing: semi-finishing of the workpiece after heat straightening treatment, and reserving the finishing allowance; S7, tempering treatment: tempering of the workpiece after semi-finishing at 200℃ to release the cold working stress; S8, finishing: finish the outer circle and spline of the workpiece after qualitative treatment to the designed size.

[0004] Preferably, in S1, during the normalizing process, the shaft blank is heated to 850℃ at a heating rate of 10℃ / min, and then kept for 2h, and then cooled to 600℃ in the furnace, and then air-cooled to room temperature.

[0005] Preferably, in S2, during the rough machining process, the outer circle and spline parts of the workpiece are rough machined by turning, cylindrical grinding and vertical milling, and at least 0.60mm finishing allowance is reserved.

[0006] Preferably, in S3, during the aging process, the workpiece is heated to 500℃ at a rate of 10℃ / min, and then kept for 4h, and then cooled to 300℃ in the furnace, and then air-cooled to room temperature.

[0007] Preferably, in S4, it specifically includes: S41: during the preheating process in the atmosphere multi-purpose furnace stage, the temperature is 350℃, 550℃, 750℃ respectively, each kept for 30min, and the heating rate is 10℃ / min; S42: during the carbonitriding process, the methanol and propane pressure is 0.06 MPa and 6.5 MPa respectively, the methanol, propane and ammonia flow rate is 3.7 m 3 / h, 0.25 m 3 / h, 0.20 m 3 / h respectively; after heating to 860℃ at a rate of 10℃ / min, keep uniform for 30min; during the strong permeation stage, the carbon potential is set to 1.10-1.15, and kept for 270-300min; during the diffusion stage, the carbon potential is set to 0.9-1.0, and kept for 240-270min.

[0008] Preferably, in S4, during the carbonitriding process, during the first strong permeation, the temperature is 860℃, and the carbon potential is set to 1.15, and kept for 5h; during the diffusion stage, the temperature is 860℃, the carbon potential is set to 0.9, and kept for 4h; during the second strong permeation, the temperature is 840℃, and the carbon potential is set to 1.0, and kept for 1h; then the temperature is reduced to 830℃, and cooled in the 60℃ super-speed quenching oil, and the quenching oil is continuously stirred to obtain a large amount of martensite structure; the workpiece is timely tempered within 2h after quenching, the temperature is 200℃, and the keeping time is 4h.

[0009] Preferably, in S5, it specifically includes the following steps: S51: in the process of thermal straightening, the preheating temperature is 280 DEG C, the holding time is 4h, after preheating, for the shaft workpiece with quenching deformation below 0.50mm, the bending mode is three-point bending, the total straightening times are 4-5 times, the pressure setting is 7-8MPa, the pressure holding time is 5-6min; for the shaft workpiece with quenching deformation 0.6-0.8mm, the pressure setting is 9-10MPa, the pressure holding time is 6-7min, and the bending is to the deformation within 0.25mm.

[0010] S52: after the above workpiece thermal straightening, the workpiece is heated to 300 DEG C at a rate of 10 DEG C / min, and the temperature is kept for 4h, and then the workpiece is taken out of the furnace and air-cooled to room temperature.

[0011] Preferably, in the S6, the outer circle and spline parts of the workpiece are finished by turning, cylindrical grinding and vertical milling, and at least 0.04mm finishing allowance is reserved.

[0012] Preferably, in the S7, during the qualitative treatment, the workpiece is heated to 200 DEG C at a rate of 10 DEG C / min, and the temperature is kept for 6h, and then the workpiece is taken out of the furnace and air-cooled to room temperature.

[0013] Preferably, in the process of carbonitriding and quenching, a combined tooling is used, which comprises a support rod, a sleeve, a tray and a support frame; the support rod is vertically fixed to the support disc in a threaded manner, and is uniformly distributed at nine positions including the center of the support frame, the four corners and the four edge centers; the sleeve is arranged in the support rod and is sequentially stacked between the tray and the support frame from top to bottom to form a loading rack. During the carbonitriding and quenching process, the workpiece is fixed through the positioning hole of the tray in the form of the protruding part contacting the end face, so as to ensure the stability of the workpiece during cooling; in the carbonitriding process, the porous structure of the tray enables the carbon and nitrogen atoms to fully diffuse on the surface of the workpiece, thereby improving the hardness; when the workpiece is loaded into the furnace, a gap should be left with the positioning hole to prevent local soft spots caused by slow cooling in a small range; the workpiece should be placed symmetrically in front and back to avoid uneven stress on the rack.

[0014] The present application has the following beneficial effects: 1. The heat treatment process and the combined tooling disclosed by the present application solve the instability problems of 40Cr shaft nitriding hardness and thermal straightening, and through process optimization and special combined tooling, the hardness of the shaft workpiece is improved from HRC 49-50 to HRC 58-60; for deformation, the reserved amount is increased from 0.12mm to 0.60mm and the penetration layer depth is increased from 0.40mm to 1.00mm, which reduces the difficulty of subsequent thermal straightening and grinding process and reduces the process time.

[0015] 2、The present application improves the process, changes the gas nitriding to carbonitriding, after rough machining, changes the quenching and tempering to normalizing, increases the allowance before heat treatment, and uses special tooling to improve the hardness and hot straightening, optimizes the workpiece quality, greatly reduces the process time, and improves the production efficiency.

[0016] 3、The present application changes the traditional quenching and tempering to normalizing in the preliminary heat treatment of 40Cr shaft workpieces, the normalizing is cooled in air, and the deformation is smaller than that of quenching and tempering. The nitriding is changed to carbonitriding, and the allowance before quenching is changed from 0.12mm to 0.60mm, reducing the difficulty of hot straightening, and shortening the overall process time.

[0017] 4、The present application uses the above-mentioned combined tooling, in the process of heating and quenching, the workpiece is fixed by the protruding part in contact with the end face through the tray positioning hole, ensuring the stability of the workpiece during cooling. In carbonitriding, the porous structure of the tray allows carbon and nitrogen atoms to fully diffuse on the surface of the workpiece, thereby improving the hardness. When the workpiece is loaded into the furnace, a gap should be left with the positioning hole to prevent local soft spots caused by slow cooling in a small area. The workpiece should be placed symmetrically in front and back to avoid uneven stress on the rack.

[0018] 5、The combined tooling disclosed by the present application has a simple structure and is easy to operate. The loading capacity and efficiency are obviously better than those of gas nitriding. The process disclosed by the present application has a workpiece surface hardness better than that of the gas nitriding process, a deeper penetration layer, improved subsequent hot straightening efficiency, and reduced overall composite process time. BRIEF DESCRIPTION OF DRAWINGS

[0019] The present application will be further described below in conjunction with the drawings and examples.

[0020] Figure 1 The present application is a 40Cr shaft part structure diagram.

[0021] Figure 2 The present application is a 40Cr shaft part structure diagram.

[0022] Figure 3 The present application is a 40Cr shaft part structure diagram.

[0023] Figure 4 The present application is a 40Cr shaft part structure diagram.

[0024] Figure 5 The present application is a 40Cr shaft part structure diagram.

[0025] Figure 6 The present application is a 40Cr shaft part structure diagram.

[0026] Figure 7 The present application is a 40Cr shaft part structure diagram.

[0027] Figure 8It is a 40Cr gas nitriding process.

[0028] In the diagram: support rod 1, sleeve 2, tray 3, support frame 4. Detailed Implementation The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0029] The traditional process is as follows: rough machining - aging - conditioning - straightening - semi-finishing - qualitative analysis - gas nitriding - straightening - semi-finishing - qualitative analysis - finishing; To address the shortcomings of existing processes, this invention improves the process and develops a new process: Normalizing - rough machining - aging - carbonitriding - straightening - aging - semi-finishing - qualitative analysis - finishing.

[0030] Example 1: This embodiment provides a heat treatment process for 40Cr shaft-type workpieces, including the following steps: S1: Normalizing treatment, the blank is heated to 850℃ in the furnace at a heating rate of 10℃ / min and held for 2 hours. Then the furnace is cooled to 600℃ and the blank is air-cooled to room temperature.

[0031] S2: Rough machining, rough machining of the outer circle and spline of the workpiece is performed by turning, external cylindrical grinding and vertical milling, leaving a 0.60mm finishing allowance.

[0032] S3: Aging treatment. The workpiece is heated to 500℃ in the furnace at a rate of 10℃ / min and held for 4 hours. The furnace is then cooled to 300℃, and the workpiece is air-cooled to room temperature after removal from the furnace.

[0033] S4: Carbonitriding and quenching treatment, using a multi-purpose atmosphere furnace for stage preheating, introducing methanol, propane and ammonia, and performing carbonitriding and quenching at 860℃; S41: The preheating stages described above are at temperatures of 350℃, 550℃, and 750℃, respectively, with each temperature held for 30 minutes. The heating rate is 10℃ / min.

[0034] S42: In the above carbonitriding process, the pressures of methanol and propane introduced are 0.06 MPa and 6.5 MPa, respectively, and the flow rates of methanol, propane, and ammonia are 3.7, 0.25, and 0.20 m³, respectively. 3 / h. Heat to 860℃ at a rate of 10℃ / min, then allow to settle for 30 min. During the strong infiltration stage, set the carbon potential to 1.10-1.15 and hold for 270-300 min. During the diffusion stage, set the carbon potential to 0.9-1.0 and hold for 240-270 min.

[0035] Further, in the carbonitriding process, in the first strong nitriding in S42, the temperature is 860℃, the holding time is 5h, and the carbon potential is set to 1.15. In the diffusion stage, the temperature is 860℃, the carbon potential is set to 0.9, and the holding time is 4h. In the second replenishing nitriding, the temperature is 840℃, the holding time is 1h, and the carbon potential is set to 1.0. The second replenishing nitriding is at a lower temperature, which is beneficial to reduce deformation and grain coarsening. Then, the temperature is lowered to 830℃, and the workpiece is cooled in the 60℃ super-speed quenching oil, and the quenching oil is continuously stirred to obtain a large amount of martensite structure. The workpiece is timely tempered within 2h after quenching, the temperature is 200℃, and the holding time is 4h.

[0036] S5: heat straightening treatment, preheating the workpiece, and then using a hydraulic machine to implement the press bending correction. After straightening, the workpiece is aged in a tempering furnace to release the stress generated by straightening.

[0037] S51: in the heat straightening process, in S4, the preheating temperature is 280℃, and the holding time is 4h. After preheating, for the shaft workpiece with quenching deformation of 0.50mm or less, the press bending mode is three-point bending, and the total straightening times are 4-5 times. The pressure is set to 7-8MPa, and the holding time is 5-6min. For the shaft workpiece with quenching deformation of 0.6-0.8mm, the pressure is set to 9-10MPa, the holding time is 6-7min, and the press bending is to the deformation within 0.25mm.

[0038] S52: after the heat straightening of the workpiece, the workpiece is heated to 300℃ at a rate of 10℃ / min, and the holding time is 4h. Then, the workpiece is taken out of the furnace and air-cooled to room temperature.

[0039] S6: semi-finishing, the outer circle and spline parts of the workpiece are finished by turning, cylindrical grinding and vertical milling, and a finishing allowance of 0.04mm is reserved.

[0040] S7: qualitative treatment, the workpiece is heated to 200℃ at a rate of 10℃ / min, and the holding time is 6h. The furnace is cooled to air cooling to room temperature.

[0041] S8: finishing, the outer circle, spline and other parts of the workpiece are machined to size.

[0042] Comparative Example 1: The same material workpiece as in Example 1 is selected, and the gas nitriding process is carried out according to the attached Figure 8 The workpiece is processed by the gas nitriding process.

[0043] After the treatment, the relevant data are checked, and the results are shown in Table 1. Table 1 Comparison of the results of two heat treatment processes

[0044] Taking 30 pieces as an example, the effects of the process of the present application and the original process are compared, and the results are shown in Table 2. Table 2 Comparison of heat treatment process results of 30 workpieces

[0045] Example 2 Referring to Figures 3-6 In the carbonitriding and quenching process, a combined tooling is used, which comprises a support rod 1, a sleeve 2, a tray 3 and a support frame 4; the support rod 1 is vertically fixed to the support frame 4 in a threaded manner, and is uniformly distributed at nine positions including the center and the four corners and the four edge centers of the support frame 4; the sleeve 2 is arranged in the support rod 1 and is sequentially stacked between the tray 3 and the support frame 4 from top to bottom, and is combined into a loading frame. In the quenching process, the workpiece is fixed by the tray positioning hole in a manner that the protruding part is in contact with the end face, so as to ensure the stability of the workpiece during cooling. In the carbonitriding process, the porous structure of the tray enables the carbon and nitrogen atoms to fully diffuse on the surface of the workpiece, thereby improving the hardness. When the workpiece is loaded into the furnace, a gap should be left with the positioning hole to prevent local soft spots caused by slow cooling in a small range. The workpiece should be placed symmetrically in front and back to avoid uneven stress on the loading frame.

[0046] Example 3 The present application provides a kind of heat treatment process of 40Cr shaft workpiece, comprising the following steps: S1: normalizing treatment, normalizing blank, refine grain, improve processing performance.S2: workpiece is carried out cold working, with allowance 0.60mm complete rough machining.S3: aging treatment, workpiece is heated to 500 DEG C aging, release processing stress.S4: carbonitriding and quenching, workpiece is preheated to 350 DEG C, 550 DEG C, 750 DEG C in stage, then heated to 860 DEG C, and methanol, propane and ammonia gas are introduced to carry out strong penetration, diffusion and replenishment, then in 60 DEG C ultra-speed oil cooling, obtain martensite structure.S5: heat straightening treatment, with certain pressure and time multiple three point type bending, then 300 DEG C aging is carried out.S6: workpiece is carried out cold working, with allowance 0.04mm complete rough machining.S7: heated to 200 DEG C, and qualitative is carried out.S8: cold working to size.The tooling disclosed in the present application has simple structure and convenient operation.The loading capacity and efficiency are obviously better than gas nitriding.The workpiece surface hardness of the process disclosed in the present application is better than that of gas nitriding process, the penetration layer is deeper, the subsequent heat straightening efficiency is improved, and the overall composite process time is reduced.

Claims

1. A process for heat treating a shaft part, characterized in that, The method comprises the following steps: S1, normalizing treatment: the shaft blank is normalized in a trolley furnace to refine the structure; S2, rough machining: the workpiece after normalizing treatment is rough machined and a finishing allowance is reserved; S3, aging treatment: the workpiece after rough machining is aged in a tempering furnace to fully release the cold working stress; S4, carbonitriding and quenching treatment: a multi-purpose furnace is used for preheating, methanol, propane and ammonia are introduced, and then strong penetration, diffusion, secondary penetration and quenching are carried out; S5, hot straightening treatment: the workpiece is pressed and bent to correct after preheating, and then the stress generated by straightening is released by aging; S6, semi-finishing machining: the workpiece after hot straightening treatment is semi-finished and a finishing allowance is reserved; S7, qualitative treatment: the semi-finished workpiece is heated to 200 DEG C for qualitative treatment to release the cold working stress; S8, finishing machining: the workpiece after qualitative treatment is finished to the designed size.

2. The process for heat treatment of shaft parts according to claim 1, characterized in that: In the S1, the shaft blank is heated to 850 DEG C at a heating rate of 10 DEG C / min in the furnace, and then the furnace is cooled to 600 DEG C, and the workpiece is air cooled to room temperature after being taken out of the furnace.

3. The process for heat treatment of shaft parts according to claim 1, characterized in that: In the S2, the workpiece is rough machined by turning, cylindrical grinding and vertical milling, and a finishing allowance of at least 0.60 mm is reserved.

4. The process of claim 1, wherein: In the S3, the workpiece is heated to 500 DEG C at a rate of 10 DEG C / min in the furnace, and then the furnace is cooled to 300 DEG C, and the workpiece is air cooled to room temperature after being taken out of the furnace.

5. The process of claim 1, wherein: The S4 specifically comprises: S41: in the multi-purpose furnace preheating process, the temperature is 350 DEG C, 550 DEG C and 750 DEG C respectively, each for 30 min, and the heating rate is 10 DEG C / min; S42: In the carbonitriding process, the methanol and propane pressures are 0.06 MPa and 6.5 MPa respectively, and the flow rates of methanol, propane and ammonia are 3.7 m 3 / h, 0.25 m 3 / h, 0.20 m 3 / h respectively; after being heated to 860°C at a rate of 10°C / min, the temperature is kept for 30 min; in the strong permeation stage, the carbon potential is set to 1.10-1.15, and the temperature is kept for 270-300 min; in the diffusion stage, the carbon potential is set to 0.9-1.0, and the temperature is kept for 240-270 min.

6. The process for heat treatment of shaft parts according to claim 5, characterized in that: In the S4, in the carbonitriding process, the first strong penetration is at a temperature of 860 DEG C for 5 h, and the carbon potential is set to 1.15; the diffusion stage is at a temperature of 860 DEG C, the carbon potential is set to 0.9, and the holding time is 4 h; The second penetration is at a temperature of 840 DEG C for 1 h, the carbon potential is set to 1.0, and then the temperature is lowered to 830 DEG C, and the workpiece is cooled in a 60 DEG C super-speed quenching oil, and the quenching oil is continuously stirred to obtain a large amount of martensite structure; the workpiece is timely tempered within 2 h after quenching, the temperature is 200 DEG C, and the holding time is 4 h.

7. The process of claim 1, wherein: The S5 specifically comprises the following steps: S51: in the hot straightening process, the preheating temperature is 280 DEG C, and the holding time is 4 h; after preheating, the shaft workpiece with a quenching deformation of less than 0.50 mm is pressed and bent in a three-point bending mode, the total straightening times is 4-5, the pressure is set to 7-8 MPa, and the holding time is 5-6 min; for the shaft workpiece with a quenching deformation of 0.6-0.8 mm, the pressure is set to 9-10 MPa, the holding time is 6-7 min, and the workpiece is pressed and bent to a deformation of less than 0.25 mm. S52: after the workpiece is hot straightened, the workpiece is heated to 300 DEG C at a rate of 10 DEG C / min in the furnace, and then the workpiece is air cooled to room temperature after being taken out of the furnace.

8. The process of claim 1, wherein: In the S6, the workpiece is finished by turning, cylindrical grinding and vertical milling, and a finishing allowance of at least 0.04 mm is reserved.

9. The process of claim 1, wherein: In the S7, in the qualitative treatment process, the workpiece is heated to 200 DEG C at a rate of 10 DEG C / min with the furnace, and the furnace is cooled to room temperature after holding for 6h.

10. The process of claim 1, wherein: In the carbonitriding and quenching process, a combined tooling is used, which comprises a support rod (1), a sleeve (2), a tray (3) and a support frame (4); the support rod (1) is fixed vertically to the support frame (4) in a threaded manner, and is uniformly distributed at nine positions including the center and the four corners and the four edge center positions of the support frame (4); the sleeve (2) is arranged in the support rod (1), and is sequentially stacked between the tray (3) and the support frame (4) from top to bottom, and is combined into a loading rack; In the carbonitriding and quenching process, the workpiece is fixed in the positioning hole of the tray (3) in a manner that the protruding part is in contact with the end face, so as to ensure the stability of the workpiece during cooling; in the carbonitriding process, the porous structure of the tray enables the carbon and nitrogen atoms to fully diffuse on the surface of the workpiece, thereby improving the hardness; when the workpiece is loaded into the furnace, a gap is left with the positioning hole to prevent local soft spots caused by slow cooling in a small range; The workpieces are placed symmetrically in front and back to avoid uneven stress on the rack.

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