Nitriding gear ring white layer loose repair process

Abstract

The application discloses a kind of nitrogenized gear ring white layer loose repair process, belong to metal material heat treatment technical field;Including to nitrogenized unqualified gear ring is heated to 550 ℃-560 ℃ in stages, diffusion decomposition is carried out, decomposition rate 85%-90%, time 25h-30h;Gear ring is cooled to 500 ℃-510 ℃ with furnace, nitrogen replacement is passed through when cooling;Strong penetration stage, temperature 500 ℃-510 ℃, decomposition rate 30%-40%, time 10h-15h;Gear ring is heated to 520 ℃-530 ℃ with furnace, ammonia replacement is passed through during heating period;Diffusion stage, 520 ℃-530 ℃, decomposition rate 65%-70%, time 15h-20h;Gear ring is cooled to 350 ℃ with furnace;Gear ring is cooled to 100 ℃ with furnace, air cooling to room temperature is discharged;The application can be white layer loose grade from 4-5 grade by pure process means repair to 1-2 grade, without changing surface roughness nor increasing deformation.

Description

Technical Field

[0001] This invention relates to a rework process for a porous white bright layer on a nitrided gear ring, belonging to the field of heat treatment technology for metallic materials. Background Technology

[0002] Currently, gas nitriding treatment is subject to various factors such as poor sealing of production equipment and moisture content of raw gas, resulting in substandard white gloss layers. According to the quality requirements of gear rings, a loose white gloss layer of grade 1-2 is acceptable for important gear rings, and a loose grade 3 is acceptable for some gear rings with less stringent requirements. However, a loose white gloss layer of grade 4-5 caused by moisture content in the atmosphere renders any gear ring unusable. Due to its low efficiency and long processing time, nitriding equipment is mostly large-scale to reduce the cost per kilogram of nitriding. Each batch of nitrided gear rings is valuable, often exceeding 200,000 RMB, making the scrapping of the entire batch unacceptable. The current rework approach is to mechanically remove the loose layer (shot blasting or sandblasting) and then re-nitride. However, for gear rings with high precision requirements that are directly finished after nitriding without further finishing, mechanical removal of the loose layer is not suitable.

[0003] There is an urgent need for a pure process rework method that can reduce rework loading and unloading and shot blasting and sandblasting processes, ensure the surface roughness and dimensional accuracy of the workpiece, and ensure that the loose structure of the white bright layer is improved. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a rework process for the loose white bright layer of nitrided gear rings. This process eliminates the need for unnecessary loading and unloading and mechanical sandblasting or shot blasting, ensuring the dimensional accuracy and surface roughness of the parts while improving the looseness of the white bright layer to level 1-2 through pure process methods.

[0005] This invention is implemented according to the following technical solution:

[0006] A rework process for a porous white coating on a nitrided gear ring includes the following steps:

[0007] S1: For gear rings that fail nitriding, the temperature is gradually increased to 550℃-560℃;

[0008] S2: Diffusion decomposition of the white bright layer on the gear ring, with an ammonia decomposition rate of 85%-90% and a time of 25-30 hours;

[0009] S3: Cool the gear ring to 500℃-510℃ in the furnace;

[0010] S4: The gear ring is subjected to strong permeation treatment, with an ammonia decomposition rate of 30%-40% for 10-15 hours;

[0011] S5: Heat the gear ring to 520℃-530℃ for 0.5 hours;

[0012] S6: The gear ring is subjected to diffusion treatment, with an ammonia decomposition rate of 65%-70% for 15-20 hours.

[0013] S7: The gear ring is rapidly cooled to 350℃ in the furnace;

[0014] S8: The gear ring is rapidly cooled to 100°C in the furnace before being removed from the furnace.

[0015] In some embodiments, the specific method for gradually heating the nitrided gear ring to 550℃-560℃ is as follows:

[0016] Phase 1: Control the temperature of the gear ring to 350℃-400℃, hold for 1 hour, and the heating time is 4 hours.

[0017] Phase 2: Control the temperature of the gear ring to 550℃-560℃ for 2 hours.

[0018] In some embodiments, in step S2, the ammonia decomposition rate in the diffusion decomposition stage is 85%, and the time is 25h-30h.

[0019] In some embodiments, in step S3, the gear ring is cooled to 500°C-510°C in the furnace, and nitrogen gas is introduced to replace the temperature during the cooling process.

[0020] In some embodiments, the gear ring is cooled to 510°C in the furnace.

[0021] In some embodiments, in step S4, the decomposition rate of the strongly permeable ammonia gas is 35%, and the time is 10h-15h.

[0022] In some embodiments, in step S5, the gear ring is heated to 520°C-530°C for 0.5 hours, and ammonia gas is introduced to replace it during the heating process.

[0023] In some embodiments, the gear ring is heated to 525°C.

[0024] In some embodiments, in step S6, the gear ring is subjected to diffusion treatment, with an ammonia decomposition rate of 70% for 15-20 hours.

[0025] In some embodiments, in step S7, the gear ring is rapidly cooled to 350°C in the furnace, and ammonia gas is introduced to replace it during the cooling process.

[0026] In some embodiments, in step S8, the gear ring is rapidly cooled to 100°C in the furnace and then removed from the furnace, with nitrogen gas introduced during the cooling process for purging.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] This invention provides a rework process for a nitrided gear ring with a loose white bright layer. The process involves heating the gear ring to the white bright layer diffusion temperature using a stepped heating method. Through perfect matching of decomposition rate and temperature, and sufficient heat preservation, the loose white bright layer is decomposed and consumed. Then, the temperature is lowered in the furnace to the strong diffusion temperature of the original nitriding process for strong diffusion treatment, forming a new dense white bright layer on the workpiece surface. Finally, diffusion treatment at the same temperature as the original process is performed to reduce the nitride grade. Since the gear ring is a rework product, the strong diffusion and diffusion times can be appropriately reduced compared to the original process. The purpose of the entire strong diffusion process is to generate a new white bright layer, while diffusion aims to reduce the nitride concentration within the diffusion layer and decrease the appearance of vein-like nitrides. After physical sectioning and testing, the surface hardness of the reworked gear ring is ≥630HV1, the white bright layer porosity is ≤2 (4-5 before rework), the brittleness is ≤2, and the nitride grade is ≤2, all meeting national standards and drawing requirements. Attached Figure Description

[0029] The accompanying drawings, as part of this invention, are provided to further illustrate the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation thereof. Clearly, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0030] In the attached diagram:

[0031] Figure 1 This is a rework process diagram for a porous white layer on a nitrided gear ring according to the present invention.

[0032] Figure 2 This is a rework process diagram for the gear ring provided in Example 1;

[0033] Figure 3 The rework process diagram for the gear ring is provided for Comparative Example 1;

[0034] Figure 4 The rework process diagram for the gear ring provided for Comparative Example 2.

[0035] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0037] First, it should be noted that ℃ is a unit of temperature, representing degrees Celsius, and h is a unit of time, representing hours.

[0038] like Figure 1 As shown, this embodiment of the invention provides a rework process for a porous white bright layer on a nitrided gear ring, comprising the following steps:

[0039] Step 1: After nitriding the furnace, gradually increase the temperature to 550℃-560℃ using a controlled heating rate.

[0040] Phase 1: Control the temperature of the gear ring to 350℃-400℃, hold for 1 hour, and the heating time is 4 hours.

[0041] Phase 1: Preferred temperature increase to 380℃.

[0042] Phase 2: Control the temperature of the gear ring to 550℃-560℃ for 2 hours;

[0043] The optimal temperature for stage two is 560℃.

[0044] It should be noted that the heating rate is controlled by two methods: controlling the heating rate (≤100℃ / h) and step heating, in order to reduce the inconsistency of thermal stress caused by the heating process and reduce deformation.

[0045] Step 2: Perform a whitening layer diffusion decomposition treatment on the gear ring. The ammonia decomposition rate during the diffusion decomposition stage is 85%-90%, and the time is 25-30 hours.

[0046] The preferred ammonia decomposition rate is 85%, and the time is 30 hours. The purpose of the diffusion decomposition stage is to decompose the loose, white, shiny surface layer through a reversible reaction.

[0047] Step 3: Cool the gear ring to 500℃-510℃ in the furnace;

[0048] The preferred cooling temperature is 510℃. During the cooling process, nitrogen gas is purged to replace the decomposed tissue and prevent it from changing under an unstable atmosphere.

[0049] Step 4: Perform strong permeation treatment on the gear ring, with an ammonia decomposition rate of 30%-40%, for 15-20 hours;

[0050] The preferred ammonia decomposition rate is 35%, and the time is 15 hours; through strong infiltration again, a new dense white and bright layer is formed on the surface of the workpiece.

[0051] Step 5: Heat the gear ring to 520℃-530℃ for 0.5 hours;

[0052] The preferred heating temperature is 525℃. During the heating process, ammonia gas is introduced to replace the layer and prevent the formed white layer from being decomposed and becoming loose again.

[0053] Step 6: Perform diffusion treatment on the gear ring, with an ammonia decomposition rate of 60%-70%, for 15-20 hours;

[0054] The preferred ammonia decomposition rate is 70%, and the time is 20 hours. The purpose of diffusion is to diffuse the vein-like nitrides generated by strong permeation into the depth of the diffusion layer and reduce the size of the nitrides.

[0055] Step 7: Rapidly cool the gear ring to 350℃ in the furnace, purging it with ammonia gas during the cooling process; the ammonia gas is used to prevent the white gloss layer from decomposing again.

[0056] Step 8: Rapidly cool the gear ring to 100°C in the furnace, purging with nitrogen during the cooling process, and then remove it from the furnace and air cool it after reaching the set temperature.

[0057] The following combination Figure 2 , Figure 3 , Figure 4 The specific experimental data further explains and verifies the rework process for the loose white bright layer of the nitrided gear ring.

[0058] Example 1

[0059] 1) Prepare defective gear rings

[0060] Material: 42CrMo;

[0061] The porosity level of the nitrided white gloss layer is grade 5;

[0062] Brittleness grade: 1;

[0063] nitrided surface hardness: 653HV1.

[0064] 2) After the workpiece is loaded into the nitriding furnace, it is heated in stages to 560℃±5℃, and nitrogen is introduced to replace the workpiece throughout the heating process.

[0065] 21) Heat for 4 hours until the temperature reaches 380℃±5℃, then maintain the temperature for 1 hour.

[0066] 22) Heat up for 2 hours until the temperature reaches 560℃±5℃.

[0067] 3) Diffusion decomposition stage: 560℃±5℃, decomposition rate 85%±2%, maintain for 30h.

[0068] 4) Cool the workpiece in the furnace to 510℃±5℃, and purge with nitrogen during the cooling process.

[0069] 5) Strong penetration stage: 510℃±5℃, decomposition rate 35%±2%, maintain for 15h.

[0070] 6) Heat the workpiece to 525℃±5℃, and purge with ammonia gas during the heating process.

[0071] 7) Diffusion stage: 525℃±5℃, decomposition rate 70%±2%, maintain for 20h.

[0072] 8) Cooling stage 1: The furnace is rapidly cooled to 350℃, and ammonia gas is introduced for replacement during the cooling process.

[0073] 9) Cooling stage 2: The furnace is rapidly cooled to 100°C. Nitrogen gas is purged during the cooling stage, and the furnace is air-cooled after reaching the set temperature.

[0074] After completion, the gear ring was subjected to metallographic physical sample testing. The data is shown in Table 1. The gear ring processed using the rework process provided by this invention meets the national standards and drawing requirements.

[0075]

[0076] Table 1 Metallographic test data of gears

[0077] Comparative Example 1 (Rework of the original process)

[0078] 1) Prepare defective gear rings

[0079] Material: 42CrMo;

[0080] The porosity level of the nitrided white gloss layer is grade 5;

[0081] Brittleness grade: 1;

[0082] nitrided surface hardness: 653HV1.

[0083] 2) After the workpiece is loaded into the nitriding furnace, it is heated in stages to 510℃±5℃, and nitrogen is introduced to replace the workpiece throughout the heating process.

[0084] 21) Heat for 4 hours until the temperature reaches 380℃±5℃, then maintain the temperature for 1 hour.

[0085] 22) Heat up for 2 hours until the temperature reaches 510℃±5℃.

[0086] 3) Strong penetration stage: 510℃±5℃, decomposition rate 35%±2%, maintain for 30h.

[0087] 4) Heat the workpiece to 525℃±5℃, and purge with ammonia gas during the heating process.

[0088] 5) Diffusion stage: 525℃±5℃, decomposition rate 70%±2%, maintain for 20h.

[0089] 6) Cooling stage 1: The furnace is rapidly cooled to 350℃, and ammonia gas is introduced for replacement during the cooling process.

[0090] 7) Cooling stage 2: The furnace is rapidly cooled to 100°C. Nitrogen gas is introduced to replace the temperature during the cooling stage. After reaching the set temperature, the furnace is removed and air-cooled.

[0091] After completion, metallographic physical sample testing was performed on the gear ring. The data is shown in Table 2. The porosity depth remained almost unchanged, the total thickness of the white bright layer increased, and the porosity level decreased by one level, but the surface porosity and void situation did not improve significantly.

[0092]

[0093] Table 2 Metallographic test data of gear ring

[0094] Comparative Example 2

[0095] 1) Prepare defective gear rings

[0096] Material: 42CrMo;

[0097] The porosity level of the nitrided white gloss layer is grade 5;

[0098] Brittleness grade: 1;

[0099] nitrided surface hardness: 653HV1.

[0100] 2) After loading the workpiece into the nitriding furnace, the temperature is raised in stages to 530℃±5℃, and nitrogen is introduced to replace the workpiece throughout the entire heating process.

[0101] 21) Heat for 4 hours until the temperature reaches 380℃±5℃, then maintain the temperature for 1 hour.

[0102] 22) Heat up for 2 hours until the temperature reaches 530℃±5℃.

[0103] 3) Diffusion decomposition stage: 530℃±5℃, decomposition rate 85%±2%, maintain for 30h.

[0104] 4) Cool the workpiece in the furnace to 510℃±5℃, and purge with nitrogen during the cooling process.

[0105] 5) Strong penetration stage: 510℃±5℃, decomposition rate 35%±2%, maintain for 15h.

[0106] 6) Heat the workpiece to 525℃±5℃, and purge with ammonia gas during the heating process.

[0107] 7) Diffusion stage: 525℃±5℃, decomposition rate 70%±2%, maintain for 20h.

[0108] 8) Cooling stage 1: The furnace is rapidly cooled to 350℃, and ammonia gas is introduced for replacement during the cooling process.

[0109] 9) Cooling stage 2: The furnace is rapidly cooled to 100°C. Nitrogen gas is purged during the cooling stage, and the furnace is air-cooled after reaching the set temperature.

[0110] After completion, metallographic physical sample testing was performed on the gear ring. The data is shown in Table 3. The porosity of the white bright layer has been improved, but it is still unqualified.

[0111]

[0112] Table 3 Metallographic Inspection Data of Gear Ring

[0113] In summary, based on the test results of Example 1, Comparative Example 1, and Comparative Example 2, this invention provides a rework process for a porous white bright layer on a nitrided gear ring. The process involves heating the gear ring to the white bright layer diffusion temperature using a stepped heating method. Through perfect matching of the decomposition rate and temperature, and after sufficient heat preservation, the porous white bright layer is decomposed and consumed. Then, the temperature is lowered in the furnace to the strong diffusion temperature of the original nitriding process for strong diffusion treatment, forming a new dense white bright layer on the workpiece surface. Finally, the diffusion process is performed at the same temperature as the original process. The diffusion process reduces the nitride grade. Since the gear ring is a rework product, the strong diffusion and diffusion times can be appropriately reduced compared to the original process time. The purpose of the entire strong diffusion process is to generate a new bright white layer, while diffusion is to reduce the concentration of nitrides in the diffusion layer and reduce the occurrence of vein-like nitrides. After actual cutting and testing, the surface hardness of the reworked gear ring is ≥630HV1, the porosity of the bright white layer is ≤2 (4-5 before rework), the brittleness is ≤2, and the nitride grade is ≤2, all of which meet the national standards and drawing requirements.

[0114] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0115] Furthermore, those skilled in the art will understand that although some embodiments described herein include certain features found in other embodiments but not others, combinations of features from different embodiments are also within the scope of protection of this invention and form different embodiments. For example, in the embodiments described above, those skilled in the art can use them in combination based on known technical solutions and the technical problems to be solved by this application.

[0116] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A rework process for a loose white bright layer on a nitrided gear ring, characterized in that, Includes the following steps: S1: For gear rings that fail nitriding, the temperature is gradually increased to 550℃-560℃; S2: Diffusion decomposition of the white bright layer on the gear ring, with an ammonia decomposition rate of 85%-90% and a time of 25-30 hours; S3: Cool the gear ring to 500℃-510℃ in the furnace; S4: The gear ring is subjected to strong permeation treatment, with an ammonia decomposition rate of 30%-40% for 10-15 hours; S5: Heat the gear ring to 520℃-530℃ for 0.5 hours; S6: The gear ring is subjected to diffusion treatment, with an ammonia decomposition rate of 65%-70% for 15-20 hours. S7: The gear ring is rapidly cooled to 350℃ in the furnace; S8: The gear ring is rapidly cooled to 100°C in the furnace before being removed from the furnace.

2. The rework process for a loose white bright layer on a nitrided gear ring according to claim 1, characterized in that, The specific method for gradually increasing the temperature to 550℃-560℃ for gear rings that fail nitriding is as follows: Phase 1: Control the temperature of the gear ring to 350℃-400℃, hold for 1 hour, and the heating time is 4 hours. Phase 2: Control the temperature of the gear ring to 550℃-560℃ for 2 hours.

3. The rework process for a loose white bright layer on a nitrided gear ring according to claim 1, characterized in that: In step S2, the ammonia decomposition rate in the diffusion decomposition stage is 85%, and the time is 25-30 hours.

4. The rework process for a loose white bright layer on a nitrided gear ring according to claim 1, characterized in that: In step S3, the gear ring is cooled to 500℃-510℃ in the furnace, and nitrogen gas is introduced to replace it during the cooling process.

5. The rework process for a loose white bright layer on a nitrided gear ring according to claim 4, characterized in that: The gear ring was cooled to 510℃ during furnace operation.

6. The rework process for a loose white bright layer on a nitrided gear ring according to claim 1, characterized in that: In step S4, the decomposition rate of the strong-permeation ammonia gas is 35%, and the time is 10-15 hours.

7. The rework process for a loose white bright layer on a nitrided gear ring according to claim 1, characterized in that: In step S5, the gear ring is heated to 520℃-530℃ for 0.5 hours, and ammonia gas is introduced to replace it during the heating process.

8. The rework process for a loose white bright layer on a nitrided gear ring according to claim 7, characterized in that: The gear ring is heated to 525℃.

9. The rework process for a loose white bright layer on a nitrided gear ring according to claim 1, characterized in that: In step S6, the gear ring is subjected to diffusion treatment, with an ammonia decomposition rate of 70% for 15-20 hours.

10. The rework process for a loose white bright layer on a nitrided gear ring according to claim 1, characterized in that: In step S7, the gear ring is rapidly cooled to 350°C in the furnace, and ammonia gas is introduced for replacement during the cooling process. In step S8, the gear ring is rapidly cooled to 100°C in the furnace and then removed from the furnace. Nitrogen gas is introduced to replace the temperature during the cooling process.

Images