Heat treatment method for controlling ion nitriding deformation of 38CrMoAlA long-axis worm

Abstract

The invention belongs to the field of hot working treatment, and relates to a heat treatment method for controlling ion nitriding deformation of a 38CrMoAlA long-axis worm, which comprises the following steps: carrying out high-temperature stress relief tempering (530 DEG C, heat preservation for 4.0-4.5 hours) and low-temperature stress relief tempering (220 DEG C, heat preservation for 4.0-4.5 hours) twice, so that the machining stress is effectively eliminated, and the deformation during nitriding is prevented. Meanwhile, the auxiliary tool is used for uniformizing the temperatures of the upper, lower and all parts of the long-shaft worm, and hardness and layer depth uniformization are ensured. The run-out of the worm tooth part and each outer circle after treatment is less than 0.01 mm, the hardness is more than 950 HV, the effective hardened layer depth is about 0.50 mm, and the layer depth difference is less than or equal to 0.04 mm. According to the method, the machining quality and the transmission performance of the worm are remarkably improved, the production cost and the rejection rate are reduced, and the method is suitable for production of high-precision transmission parts.

Description

Technical Field

[0001] The invention belongs to the field of thermal processing and relates to a thermal treatment method for controlling ion nitriding deformation of a 38CrMoAlA long-axis worm. Background Art

[0002] In the field of mechanical manufacturing, especially in the production of high-precision transmission components, 38CrMoAlA long-shaft worms are crucial transmission components. Their performance and quality directly impact the operational stability and lifespan of the entire mechanical system. After quenching and tempering to achieve the desired mechanical properties, worms require further finishing and surface treatment to meet specific hardness, wear resistance, and corrosion resistance requirements. Ion nitriding, as an effective surface strengthening technology, can significantly improve the worm's surface hardness and wear resistance, extending its service life.

[0003] However, during the plasma nitriding process, the worm's long axis structure and complex geometry can easily lead to uneven nitriding, which in turn causes problems such as uneven hardness distribution, large variations in layer depth, and deformation. These problems not only affect the worm's transmission accuracy and performance, but can also increase the difficulty and cost of subsequent processing, and even cause the product to be scrapped.

[0004] Specifically, during the nitriding process, uneven heating of the upper and lower parts of the worm can easily lead to significant differences in hardness distribution. This hardness difference not only affects the worm's wear resistance and fatigue resistance, but can also cause vibration and noise during transmission, reducing the overall efficiency of the mechanical system. Furthermore, deformation during the nitriding process poses a significant challenge. The worm's long axis is prone to bending or twisting at high temperatures, resulting in increased tooth and external runout, making it impossible to meet the requirements of high-precision transmission.

[0005] To address these issues, traditional heat treatment methods often rely on a single tempering process to eliminate mechanical stresses. However, this approach is limited in its effectiveness in controlling nitriding deformation and hardness uniformity. Deformation control is particularly challenging when processing long-axis worms, due to their large length-to-diameter ratio. Furthermore, while some auxiliary tooling can improve nitriding uniformity to a certain extent, these often suffer from complex structures, inconvenient operation, or high costs, limiting their practical application.

[0006] Therefore, developing a heat treatment method that effectively controls the deformation of 38CrMoAlA long-shaft worms during plasma nitriding is of great practical significance and application value for improving the worm's processing quality and transmission performance, while reducing production costs and scrap rates. This method requires comprehensive consideration of factors such as the worm's material properties, geometry, and nitriding process parameters. By optimizing the heat treatment process and auxiliary tooling design, the method achieves uniform hardness and controlled deformation during the nitriding process. Summary of the Invention

[0007] In view of this, the object of the present invention is to provide a heat treatment method for controlling the ion nitriding deformation of a 38CrMoAlA long-axis worm, so as to solve the existing problems.

[0008] To achieve the above object, the present invention provides the following technical solution: a heat treatment method for controlling the ion nitriding deformation of a 38CrMoAlA long-axis worm, characterized in that it comprises the following steps:

[0009] a) Semi-finishing the worm;

[0010] b) Perform high temperature stress relief tempering on the semi-finished worm;

[0011] c) finishing the worm after high temperature tempering;

[0012] d) Performing low temperature stress relief tempering on the worm after fine processing;

[0013] e) finishing the worm after low temperature tempering;

[0014] f) The worm after fine machining is subjected to ion nitriding, wherein auxiliary tooling is used during ion nitriding to uniformly maintain the temperature of various parts of the worm. The auxiliary tooling is composed of carbon steel pipes and carbon steel discs of the same diameter and different lengths. The position of the discs is adjustable. The combined tooling is installed between every two worms, and an auxiliary cathode plate is installed above the parts and the auxiliary tooling, with a distance of 30 mm from the upper end face of the parts, to uniformly maintain the temperature of the upper and lower parts and various parts of the long-axis worm.

[0015] Optionally, the temperature of the high-temperature stress relief tempering is 530° C., and the holding time is 4.0 to 4.5 hours; the temperature of the low-temperature stress relief tempering is 220° C., and the holding time is 4.0 to 4.5 hours.

[0016] Optionally, during the high-temperature stress relief tempering and the low-temperature stress relief tempering, the worm is placed upright in the sockets evenly distributed in the tempering barrel.

[0017] Optionally, during the high-temperature stress relief tempering, charcoal is added or nitrogen is introduced for protection to prevent an oxidation decarburization layer from forming on the surface of the part.

[0018] Optionally, after the high-temperature stress relief tempering is completed, the temperature is lowered to below 150° C. and then taken out of the furnace for air cooling.

[0019] Optionally, the micro-oxidation generated during the low-temperature stress relief tempering process is removed in a subsequent finishing process.

[0020] Optionally, the carbon steel pipes and carbon steel discs in the auxiliary tooling can be used in a flexible combination, and the length and size of the steel pipes and the size of the discs can be interchangeable.

[0021] Optionally, the auxiliary tool is installed between every two worm gears.

[0022] Optionally, after the ion nitriding, the hardness of each part of the worm meets the requirement of hardness ≥ 900HV, the effective hardened layer depth meets the requirement of 0.45mm to 0.60mm, and the runout of the worm teeth and each outer circle is less than 0.01mm.

[0023] The beneficial effects of the present invention are:

[0024] 1) Improved Hardness Uniformity: This heat treatment method effectively eliminates machine-induced stresses through two stress-relieving annealing steps, one at high temperature and the other at low temperature, preventing excessive deformation caused by stress release during nitriding. Furthermore, the addition of auxiliary tooling during the ion nitriding process evens out the temperature across the entire length of the worm, achieving a more uniform hardness across all parts of the worm, meeting the hardness requirement of ≥900 HV. The hardness of the upper, middle, and lower samples all exceeded 950 HV.

[0025] 2) Controlling the difference in layer depth: By optimizing the heat treatment process and auxiliary tooling design, this method effectively controls the effective hardening layer depth of the worm, so that the maximum difference in layer depth between the upper, middle and lower samples is controlled within 0.04 mm, meeting the requirement of layer depth of 0.45 mm to 0.60 mm, and improving the wear resistance and fatigue resistance of the worm.

[0026] 3) Reduced Deformation: This method significantly reduces worm deformation during nitriding by precisely controlling the temperature and stress state during heat treatment and employing auxiliary tooling to uniformly maintain temperature. Runout deformation of the worm teeth and outer diameters is controlled to within 0.01mm, meeting the requirements of high-precision transmission and improving the worm's transmission accuracy and performance.

[0027] 4) Improved production efficiency and product quality: This heat treatment method simplifies the operation steps and improves production efficiency by optimizing the process flow and auxiliary tooling design. At the same time, by effectively controlling the hardness and deformation of the worm, it improves product quality and the first-time pass rate, while reducing production costs and scrap rates.

[0028] 5) Expanded Applications: This heat treatment method is not only suitable for ion nitriding of 38CrMoAlA long-shaft worms, but can also be applied to the surface treatment of other long-shaft parts with similar structures. By adjusting process parameters and auxiliary tooling design, the nitriding requirements of parts of different materials and sizes can be met, broadening the application range of this heat treatment method.

[0029] 6) Improved overall mechanical system performance: Because the hardness and deformation of the worm are effectively controlled, this heat treatment method can reduce vibration and noise during the transmission process, improving the overall efficiency and stability of the mechanical system. At the same time, the worm's wear resistance and fatigue resistance are also improved, extending the service life of the mechanical system.

[0030] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:

[0032] Figure 1 is a schematic diagram of a worm of the present invention;

[0033] Figure 2 It is a schematic diagram of the auxiliary tooling of the present invention.

[0034] Reference numerals: worm 1, carbon steel pipe 2, carbon steel disc 3. DETAILED DESCRIPTION

[0035] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0036] Among them, the accompanying drawings are only for illustrative purposes and represent only schematic diagrams rather than actual pictures, and should not be understood as limiting the present invention. In order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the accompanying drawings.

[0037] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0038] See also Figures 1 and 2 This heat treatment method controls deformation during ion nitriding of a 38CrMoAlA long-shaft worm. After quenching and tempering, the 38CrMoAlA long-shaft worm undergoes semi-finishing and stress relief through high-temperature tempering at 530°C. After finishing, it undergoes stress relief through low-temperature tempering at 220°C. During ion nitriding, auxiliary tooling is added to even out the temperature across the upper and lower sections of the worm. This method achieves uniform hardness and layer depth requirements across the worm while controlling runout deformation of the outer diameter and teeth to within 0.01mm. This addresses the significant hardness difference and, in particular, deformation issues associated with the upper and lower sections of the worm.

[0039] Example 1,

[0040] The process flow of the present invention is: semi-finishing → high temperature stress relief tempering → finishing → low temperature stress relief tempering → finishing → ion nitriding; specifically:

[0041] 1. High temperature stress relief tempering: parts diagram as follows Figure 1 38CrMoAlA long shaft worm 1 is tempered and semi-finished, and the parts are as follows Figure 1 Place the sockets evenly spaced upright in the tempering barrel in the orientation shown. Heat to 530°C and hold for 4.0-4.5 hours to eliminate mechanical stress and prevent excessive deformation during nitriding. Add charcoal before loading the furnace or use nitrogen protection during the heating and holding process to prevent oxidation of the parts during high-temperature tempering, which can lead to an oxidized decarburized layer on the surface and insufficient surface hardness during nitriding. After holding, cool the parts to below 150°C and air cool them before removing them from the furnace.

[0042] 2. Low temperature stress relief tempering: After finishing, the parts are Figure 1 Place the sockets evenly spaced in the tempering barrel in the orientation shown. Heat to 220°C and hold for 4.0-4.5 hours to temper and eliminate finishing stresses and prevent significant deformation during nitriding. Micro-oxidation on the part surface during low-temperature tempering will be removed during subsequent finishing.

[0043] 3. After finishing, enter the ion nitriding process.

[0044] Example 2,

[0045] Auxiliary tooling such as Figure 2 , which is composed of carbon steel pipe 2 and carbon steel disc 3 of the same diameter and different lengths. Figure 2 The position of the tooling disc is adjustable, and the assembly device is placed between every two worm gears 1. Finally, an auxiliary cathode plate is installed on the parts and the auxiliary tooling, with a distance of about 30 mm from the upper end surface of the parts to evenly distribute the temperature of the upper and lower parts of the long-axis worm gear 1 and all parts.

[0046] Test results of the upper, middle and lower position samples and the worm 1 body: ① The hardness of the sample, the body teeth and the outer circle of each part is greater than 950HV, meeting the required hardness ≥900HV; ② The effective hardened layer depth is about 0.50mm, and the maximum difference in layer depth between the upper, middle and lower samples is 0.04mm, meeting the required layer depth of 0.45mm~0.60mm; ③ The runout of the worm 1 teeth and each outer circle is less than 0.01mm.

[0047] This process employs two stress-relief tempering steps, high and low temperature, to eliminate mechanical stresses and prevent significant deformation during nitriding. In particular, it utilizes flexible auxiliary tooling (interchangeable steel pipe lengths and sizes, as well as disc sizes) to evenly distribute the temperature across the worm shaft during nitriding, ensuring uniform hardness and layer depth, and controllable deformation. This process has been applied to ion nitriding of various machine tool spindles, achieving excellent results in terms of first-pass yield, quality uniformity, and deformation control.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A heat treatment method for controlling the ion nitriding deformation of a 38CrMoAlA long-axis worm, characterized in that: The following steps are involved: a) Semi-finishing the worm; b) Perform high temperature stress relief tempering on the semi-finished worm; c) finishing the worm after high temperature tempering; d) Performing low temperature stress relief tempering on the worm after fine processing; e) finishing the worm after low temperature tempering; f) The worm after fine machining is subjected to ion nitriding, wherein auxiliary tooling is used during ion nitriding to uniformly maintain the temperature of various parts of the worm. The auxiliary tooling is composed of carbon steel pipes and carbon steel discs of the same diameter and different lengths. The position of the discs is adjustable. The combined tooling is installed between every two worms, and an auxiliary cathode plate is installed above the parts and the auxiliary tooling, with a distance of 30 mm from the upper end face of the parts, to uniformly maintain the temperature of the upper and lower parts and various parts of the long-axis worm.

2. A heat treatment method for controlling ion nitriding deformation of a 38CrMoAlA long-axis worm according to claim 1, characterized in that: The temperature of the high-temperature stress relief tempering is 530° C., and the holding time is 4.0 to 4.5 hours; the temperature of the low-temperature stress relief tempering is 220° C., and the holding time is 4.0 to 4.5 hours.

3. A heat treatment method for controlling ion nitriding deformation of a 38CrMoAlA long-axis worm according to claim 2, characterized in that: During the high-temperature stress relief tempering and the low-temperature stress relief tempering, the worm is placed upright in the sockets evenly distributed in the tempering barrel.

4. The heat treatment method for controlling ion nitriding deformation of a 38CrMoAlA long-axis worm according to claim 2, characterized in that: During the high-temperature stress relief tempering, charcoal is added or nitrogen is introduced for protection to prevent an oxidation decarburization layer from forming on the surface of the part.

5. The heat treatment method for controlling ion nitriding deformation of a 38CrMoAlA long-axis worm according to claim 2, characterized in that: After the high temperature stress relief tempering is completed, the temperature is lowered to below 150° C. and then taken out of the furnace for air cooling.

6. The heat treatment method for controlling ion nitriding deformation of a 38CrMoAlA long-axis worm according to claim 1, characterized in that: The micro-oxidation produced during the low-temperature stress relief tempering process is removed in the subsequent finishing process.

7. The heat treatment method for controlling ion nitriding deformation of a 38CrMoAlA long-axis worm according to claim 1, characterized in that: The carbon steel pipes and carbon steel discs in the auxiliary tooling can be used in a flexible combination, and the length and size of the steel pipes and the size of the discs can be interchangeable.

8. The heat treatment method for controlling ion nitriding deformation of a 38CrMoAlA long-axis worm according to claim 7, characterized in that: The auxiliary tool is arranged between every two worm gears.

9. The heat treatment method for controlling ion nitriding deformation of a 38CrMoAlA long-axis worm according to claim 1, characterized in that: After the ion nitriding, the hardness of each part of the worm meets the requirement of hardness ≥ 900HV, the effective hardened layer depth meets the requirement of 0.45mm to 0.60mm, and the runout of the worm teeth and each outer circle is less than 0.01mm.

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