Preparation method of nitriding and carburizing composite nitriding layer of corrosion-resistant nitriding steel part

Abstract

The invention discloses a preparation method of a nitriding and carburizing composite infiltrated layer of a corrosion-resistant nitriding steel part. The preparation method comprises the following steps: firstly, determining the size of a part blank and the infiltrated layer depth of the nitriding steel part; secondly, determining a high-temperature nitriding process according to the depth of a nitriding layer; determining a high-temperature carburizing process according to the depth and hardness of the carburizing layer; and finally, the nitrided steel part is subjected to solution treatment, cold treatment and aging treatment. By adopting the technical scheme provided by the invention, the problem of economic loss caused by possible failure behaviors in practical application due to insufficient comprehensive performance of the gear obtained by the traditional process is solved.

Description

Technical Field

[0001] This invention relates to, but is not limited to, the field of heat treatment technology for steel gear parts, and particularly to a method for preparing a composite nitriding and carburizing layer for corrosion-resistant nitrided steel parts. Background Technology

[0002] With the development of my country's aviation technology, the demand for aviation steel is not only constantly expanding, but it also needs to have the following excellent engineering mechanical properties: high strength, high toughness and excellent corrosion resistance.

[0003] Transmission gears are indispensable components in aerospace equipment. Due to their exposure to humid air or prolonged service, the performance requirements for gears are becoming increasingly stringent. Because gears processed using traditional methods often exhibit insufficient overall performance, they may fail in practical applications, leading to economic losses. Therefore, the performance of gears obtained through traditional processes is gradually failing to meet operational demands. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned technical problems. This invention provides a method for preparing a composite nitriding and carburizing layer for corrosion-resistant nitrided steel parts, in order to solve the problem that gears obtained by traditional processes may fail in practical applications due to insufficient comprehensive performance, resulting in economic losses.

[0005] The technical solution of the present invention: The embodiments of the present invention provide a method for preparing a nitriding and carburizing composite diffusion layer for corrosion-resistant nitriding steel parts, comprising: Step 1: Determine the blank size of the part in order to obtain the bar stock corresponding to the required bar specifications, and determine the diffusion depth of the nitrided steel part. Step 2: The bar stock is machined to form a part blank; Step 3: Place the part blank into a heat treatment furnace and heat it to 980℃~1020℃. Hold it at that temperature for 90min~130min and then cool it in air. Then place the part blank into a heat treatment furnace and heat it to 630℃~690℃. Hold it at that temperature for 360min~420min and then cool it in air. Step 4: Machining the part blank to form a rough-machined part; Step 5: Perform sandblasting on the rough-machined parts, and apply a protective coating to the non-nitrided areas of the rough-machined parts after sandblasting and let them dry. Step 6: Perform nitriding and carburizing treatments on the rough-machined parts after the protective treatment. This includes: performing solution nitriding on the fully protected rough-machined parts, with the nitriding depth reaching the nitriding layer depth determined in Step 1; at this time, the surface hardness of the nitrided layer is usually a conventional hardness, for example, 58HRC~61HRC; and performing vacuum carburizing on the rough-machined parts after solution nitriding, with the carburizing depth reaching at least 25% of the nitrided layer depth; after carburizing treatment, the surface hardness of the nitrided layer is improved, reaching 63~67HRC. Step 7, solution treatment, including: placing the rough-machined parts after low-pressure vacuum carburizing into a solution furnace, holding them at a temperature of 1000℃~1100℃ for 1h~2h, and then cooling them in quenching oil. Step 8, cold treatment, includes: placing the solution-treated rough-machined parts into a chiller, holding them at a temperature of -73℃ to -83℃ for 5 to 6 hours, and then cooling them in air; Step 9, aging treatment, includes: placing the roughly machined parts after the ice treatment into an aging furnace, heating to 472℃~492℃, holding at that temperature for 120min~180min, and then cooling in air.

[0006] Optionally, in the method for preparing the nitriding and carburizing composite diffusion layer for corrosion-resistant nitrided steel parts as described above, After step 3, the part blank is subjected to a hardness test to ensure that the preliminary hardness of the part blank is within the range of 28HRC~35HRC.

[0007] Optionally, in the method for preparing the nitriding and carburizing composite diffusion layer of corrosion-resistant nitrided steel parts as described above, step 6 includes: Step 61, solution nitriding treatment, including: placing the fully protected rough-machined parts into a solution nitriding furnace, heating to a preheating temperature of 840℃~860℃, holding for 30min~40min, raising the temperature to 950℃~1150℃ at a heating rate of (10±2)℃ / min, holding for 10h~30h, nitrogen pressure ≥2bar, and after holding, cooling to below 60℃ at a pressure ≥3bar before removing from the furnace; Step 62, vacuum carburizing treatment, includes: placing the rough-machined parts after solution nitriding treatment into a low-pressure vacuum carburizing furnace, heating to a temperature of 930℃~1000℃, holding for 10h~30h, and then cooling to below 60℃ under a pressure of ≥3bar after holding.

[0008] Optionally, the method for preparing the nitriding and carburizing composite diffusion layer for corrosion-resistant nitrided steel parts as described above further includes: Step 10: After aging treatment, check the mechanical properties, diffusion depth, core hardness, and surface hardness of the rough-machined parts. If the inspection results meet the preset conditions, the parts are deemed qualified.

[0009] Optionally, in the method for preparing the nitriding and carburizing composite diffusion layer of corrosion-resistant nitrided steel parts as described above, in the preparation method, Before and after solution nitriding, before and after low-pressure vacuum carburizing, and before and after solution treatment, the parts are sandblasted to remove residual coating and surface oxide scale, resulting in a clean surface.

[0010] Optionally, in the method for preparing the nitriding and carburizing composite diffusion layer of corrosion-resistant nitrided steel parts as described above, the nitrided steel parts include: nitrided steel bushings, nitrided steel transmission rods, and nitrided steel gears.

[0011] Optionally, in the method for preparing the nitriding and carburizing composite diffusion layer of corrosion-resistant nitrided steel parts as described above, the nitrided steel parts are nitrided steel gears. In step 1, the penetration depth is determined based on the size, structure, and digital model parameters of the gear parts.

[0012] Optionally, in the method for preparing the nitriding and carburizing composite diffusion layer for corrosion-resistant nitrided steel parts as described above, The machining methods in step 4 include: CNC turning, gear hobbing, and forming rough-machined gears; The gear hobbing process forms a rough-machined gear with a machining allowance of 0.20mm to 0.30mm.

[0013] Optionally, in the method for preparing the nitriding and carburizing composite diffusion layer of corrosion-resistant nitrided steel parts as described above, before step 6, the method further includes: Determine the infiltrated and non-infiltrated regions at the gear tooth and journal positions, and determine the transition region between the infiltrated and non-infiltrated regions based on the gear structure and dimensions.

[0014] The beneficial effects of this invention are as follows: This invention provides a method for preparing a composite nitriding and carburizing layer for corrosion-resistant nitrided steel parts. First, the dimensions of the part blank and the depth of the nitriding layer are determined. Second, a high-temperature nitriding process is determined based on the nitriding layer depth. A high-temperature carburizing process is then determined based on the nitriding layer depth and hardness. Finally, the nitrided steel parts undergo solution treatment, cold treatment, and aging treatment. This invention addresses the need to improve the hardness of exposed parts in aerospace equipment. On one hand, by performing a composite nitriding treatment of solution nitriding and vacuum carburizing on the parts, the surface hardness of the nitrided layer is increased by vacuum carburizing after solution nitriding, resulting in a composite nitrided layer with surface hardness meeting product requirements. On the other hand, by setting reasonable process parameters for the composite nitriding treatment, this invention ultimately obtains a composite nitriding and carburizing layer, ensuring that the mechanical properties, nitriding layer depth, core hardness, and surface hardness of the nitrided steel parts meet design and acceptance requirements. The surface hardness of the nitrided layer is increased to HRC≥63, effectively solving the problem of low hardness in existing corrosion-resistant nitrided steel gear nitrided layers. Attached Figure Description

[0015] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of the present invention and do not constitute a limitation on the technical solutions of the present invention.

[0016] Figure 1 This is a schematic diagram illustrating the principle of nitriding and carburizing treatment in the preparation method of the nitriding and carburizing composite diffusion layer for corrosion-resistant nitrided steel parts provided in the embodiments of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

[0018] As explained in the background section above, gears obtained through traditional processes may fail in practical applications due to insufficient overall performance, resulting in certain economic losses. Therefore, the performance of gears obtained through traditional processes is gradually failing to meet the application requirements.

[0019] Gears experience complex motion and stress during operation, resulting in diverse forms of damage. Studies show that the main failure modes of gears can be categorized as wear and fatigue. Therefore, to ensure stable long-term operation of gear components, their surfaces should possess high wear resistance and contact fatigue resistance, while the core should have sufficient toughness. This is especially true for parts used in aerospace, satellite, and marine equipment, which not only need to withstand high loads and high speeds but also meet special requirements such as high temperature resistance or corrosion resistance. Therefore, to meet the service performance and lifespan requirements of gears, in addition to taking appropriate measures in material selection, shape design, and application, suitable surface strengthening treatment is essential.

[0020] Based on the above needs, there is an urgent need to advance the research on nitriding and carburizing composite diffusion layer technology for nitrided steel gears, break through the core technology of heat treatment for corrosion-resistant nitrided steel gears, and lay the foundation for extending the application environment of aerospace gears.

[0021] To address the aforementioned problems and the need for composite diffusion layers on nitrided steel gears, this invention provides a method for preparing a composite diffusion layer for corrosion-resistant nitrided steel parts, used to improve the surface hardness of corrosion-resistant nitrided steel gears.

[0022] The present invention provides the following specific embodiments, which can be combined with each other. For the same or similar concepts or processes, they may not be described again in some embodiments.

[0023] The purpose of this invention is to provide a method for preparing a composite nitriding and carburizing layer for corrosion-resistant nitrided steel parts, solving the problem of low hardness of the nitrided steel gear lining. Ultimately, this invention achieves a composite nitriding and carburizing layer, improving the surface hardness of the gear and simultaneously enhancing its reliability.

[0024] The method for preparing a nitriding and carburizing composite diffusion layer on corrosion-resistant nitriding steel parts provided in the present invention includes the following steps: Step 1: Determine the blank size of the part in order to obtain the bar stock corresponding to the required bar specifications, and determine the diffusion depth of the nitrided steel part. Step 2: The bar stock is machined to form a part blank.

[0025] Step 3: Place the rough-machined part blank into a heat treatment furnace and heat it to 980℃~1020℃, hold it for 90min~130min, and then cool it in air; then place the part blank into a heat treatment furnace again and heat it to 630℃~690℃, hold it for 360min~420min, and then cool it in air.

[0026] After this step, the hardness of the part blank is checked to ensure that the preliminary hardness of the part blank is within the range of 28HRC~35HRC.

[0027] Step 4: Machining the part blank to form a rough-machined part.

[0028] Step 5: Perform sandblasting on the rough-machined parts, and apply a protective coating to the non-nitrided areas of the rough-machined parts after sandblasting and let them dry.

[0029] Step 6, solution nitriding treatment: Place the rough-machined parts after protection into a solution nitriding furnace, heat to a preheating temperature of 840℃~860℃, hold for 30min~40min, raise the temperature to 950℃~1150℃ at a heating rate of (10±2)℃ / min, hold for 10h~30h, nitrogen pressure ≥2bar, and after holding, cool to below 60℃ at a pressure ≥3bar before removing from the furnace; After the solution nitriding treatment in the steps, the nitriding depth reaches the nitriding layer depth determined in step 1. At this time, the surface hardness of the nitrided layer of the rough-machined part is usually a conventional hardness, such as 58HRC~61HRC.

[0030] Step 7, Vacuum carburizing treatment: Place the rough-machined parts after solution nitriding treatment into a low-pressure vacuum carburizing furnace, heat to a temperature of 930℃~1000℃, hold for 10h~30h, and after holding, cool to below 60℃ under a pressure of ≥3bar before removing from the furnace.

[0031] Vacuum carburizing treatment through a series of steps can improve the surface hardness of the carburized layer on the parts, which can reach 63~67 HRC.

[0032] In one embodiment, the solution nitriding thickness in step 6 is, for example, 1.0~2.0 mm, and the vacuum carburizing thickness in step 7 is, for example, 0.5~1.0 mm. Figure 1 The diagram shown is a schematic representation of the nitriding and carburizing processes in the preparation method of the nitriding and carburizing composite diffusion layer for corrosion-resistant nitrided steel parts provided in this embodiment of the invention.

[0033] Step 8, Solution treatment: Place the rough-machined parts after low-pressure vacuum carburizing into a solution furnace, hold at 1000℃~1100℃ for 1h~2h, and then cool in quenching oil. Step 9, cold treatment: Place the solution-treated rough-machined parts into a cryogenic chamber and keep them at a temperature of -73℃ to -83℃ for 5 to 6 hours, and then cool them in the air. Step 10, Aging treatment: Place the roughly machined parts after the cryogenic treatment into an aging furnace, heat to 472℃~492℃, hold for 120min~180min, and then cool in air.

[0034] After the aging process in this step, the mechanical properties, diffusion depth, core hardness, and surface hardness of the rough-machined parts are checked. If the inspection results meet the preset conditions, the parts are deemed qualified.

[0035] It should be noted that in the preparation method provided in the embodiments of the present invention, the parts are sandblasted before and after solution nitriding, before and after low-pressure vacuum carburizing, and before and after solution treatment to remove residual coating and surface oxide scale, thereby obtaining a clean surface. Furthermore, the preparation method provided in the above embodiments is applicable to various types of nitrided steel parts, such as nitrided steel bushings, nitrided steel drive rods, and nitrided steel gears.

[0036] In one implementation of this invention, the nitrided steel part is a nitrided steel gear, and correspondingly, in step 1, the diffusion layer depth is determined based on the size structure and digital model parameters of the gear part.

[0037] For conventional nitrided steel parts, the diffusion depth is, for example, 1.0 mm or more; for nitrided steel gears, the diffusion depth is, for example, 1.2 mm, or possibly 0.8 mm.

[0038] In addition, for nitrided steel gears, the machining methods in step 4 include: CNC turning and gear hobbing, to form a rough-machined gear. In specific implementation, the gear hobbing process forms a rough-machined gear with a machining allowance of 0.20mm~0.30mm.

[0039] Furthermore, for nitrided steel gears, before performing nitriding treatment in step 6, it is also necessary to determine the nitrided and non-nitrided areas at the gear tooth position and journal position, and determine the transition area between the nitrided and non-nitrided areas based on the gear structure and size.

[0040] The method for preparing a nitriding and carburizing composite diffusion layer for corrosion-resistant nitrided steel parts provided in this invention first determines the blank size of the part and the diffusion layer depth of the nitrided steel part; secondly, it determines the high-temperature nitriding process based on the diffusion layer depth; thirdly, it determines the high-temperature carburizing process based on the diffusion layer depth and hardness; and finally, it performs solution treatment, cold treatment, and aging treatment on the nitrided steel part. This invention addresses the hardness improvement requirements of exposed parts in aerospace equipment. On one hand, by performing a composite diffusion treatment of solution nitriding and vacuum carburizing on the part, the surface hardness of the diffusion layer is improved by vacuum carburizing after solution nitriding, resulting in a composite diffusion layer with surface hardness meeting product requirements. On the other hand, by setting reasonable process parameters for the composite diffusion treatment, this invention ultimately obtains a nitriding and carburizing composite diffusion layer, ensuring that the mechanical properties, diffusion layer depth, core hardness, and surface hardness of the nitrided steel part meet design acceptance requirements, and raising the surface hardness of the diffusion layer to HRC≥63, effectively solving the problem of low hardness in existing corrosion-resistant nitrided steel gear diffusion layers.

[0041] The following embodiments, using nitrided steel gears as an example, provide a method for preparing a nitriding and carburizing composite diffusion layer on corrosion-resistant nitrided steel parts, including the following steps: (1) Determine the diffusion layer depth based on the size and structure of the gear parts and the numerical model parameters, and determine the blank size to obtain the bar stock corresponding to the required bar specifications; (2) The bar stock is machined to form a gear blank; (3) Preliminary heat treatment: The gear blank is placed in a heat treatment furnace and heated to 980℃~1020℃, held for 90min~130min, and then cooled in air. The gear blank is then placed in a heat treatment furnace and heated to 630℃~690℃, held for 360min~420min, and then cooled in air; hardness is then checked.

[0042] (4) Machining: The gear blank is machined by CNC turning, gear hobbing and other processes to form a rough-machined gear; (5) Protection: The rough-machined gear is sandblasted, and the non-nitrided areas of the rough-machined gear are coated with a protective coating and then dried. (6) Solution nitriding treatment: Place the rough-machined gear after protection into a solution nitriding furnace, heat to a preheating temperature of 840℃~860℃, hold for 30min~40min, raise to 950℃~1150℃ at a heating rate of (10±2)℃ / min, hold for 10h~30h, nitrogen pressure ≥2bar, and after holding, cool to below 60℃ at a pressure ≥3bar before removing from the furnace; (7) Vacuum carburizing treatment: The rough-machined gear after solution nitriding treatment is placed in a low-pressure vacuum carburizing furnace and heated to a temperature of 930℃~1000℃. The holding time is 10h~30h. After the holding time is completed, the gear is cooled to below 60℃ under a pressure of ≥3bar and then removed from the furnace. (8) Solution treatment: The rough-machined gear after low-pressure vacuum carburizing is placed in a solution furnace and kept at a temperature of 1000℃~1100℃ for 1h~2h. Then it is cooled in quenching oil. (9) Cold treatment: The rough-machined gear after solution treatment is placed in a cold machine and kept at a temperature of -73℃ to -83℃ for 5h to 6h, and then cooled in the air; (10) Aging treatment: After the cold treatment, the rough-machined gear is placed in an aging furnace, heated to 472℃~492℃, held for 120min~180min, and then cooled in air.

[0043] (11) Inspection: Send one set of longitudinal and transverse mechanical property test bars for physical and chemical testing. Send the layer depth test material for physical and chemical testing. Metallographic structure and diffusion layer depth ≥1.0mm. 100% test the surface hardness of the parts HRC≥62. 100% test the core hardness of the parts HRC43~47. 100% test the dimensions.

[0044] While the embodiments disclosed in this invention are as described above, they are merely illustrative of the embodiments to facilitate understanding of the invention and are not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and variations in the form and details of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection for this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A method for preparing a nitriding and carburizing composite diffusion layer on corrosion-resistant nitrided steel parts, characterized in that, Includes the following steps: Step 1: Determine the blank size of the part in order to obtain the bar stock corresponding to the required bar specifications, and determine the diffusion depth of the nitrided steel part. Step 2: The bar stock is machined to form a part blank; Step 3: Place the part blank into a heat treatment furnace and heat it to 980℃~1020℃. Hold it at that temperature for 90min~130min and then cool it in air. The blank parts are then placed in a heat treatment furnace and heated to 630℃~690℃, held for 360min~420min, and then cooled in air. Step 4: Machining the part blank to form a rough-machined part; Step 5: Perform sandblasting on the rough-machined parts, and apply a protective coating to the non-nitrided areas of the rough-machined parts after sandblasting and let them dry. Step 6: Perform nitriding and carburizing treatments sequentially on the rough-machined parts after protective treatment, including: performing solution nitriding on the fully protected rough-machined parts, with the nitriding depth reaching the nitriding layer depth determined in Step 1; and performing vacuum carburizing on the rough-machined parts after solution nitriding, with the carburizing depth reaching at least 25% of the nitriding layer depth. Step 7, solution treatment, including: placing the rough-machined parts after low-pressure vacuum carburizing into a solution furnace, holding them at a temperature of 1000℃~1100℃ for 1h~2h, and then cooling them in quenching oil. Step 8, cold treatment, includes: placing the solution-treated rough-machined parts into a chiller, holding them at a temperature of -73℃ to -83℃ for 5 to 6 hours, and then cooling them in air; Step 9, aging treatment, includes: placing the roughly machined parts after the ice treatment into an aging furnace, heating to 472℃~492℃, holding at that temperature for 120min~180min, and then cooling in air.

2. The method for preparing a nitriding and carburizing composite diffusion layer for corrosion-resistant nitrided steel parts according to claim 1, characterized in that, After step 3, the part blank is subjected to a hardness test to ensure that the preliminary hardness of the part blank is within the range of 28HRC~35HRC.

3. The method for preparing the nitriding and carburizing composite diffusion layer for corrosion-resistant nitrided steel parts according to claim 1, characterized in that, Step 6 includes: Step 61, solution nitriding treatment, including: placing the fully protected rough-machined parts into a solution nitriding furnace, heating to a preheating temperature of 840℃~860℃, holding for 30min~40min, raising the temperature to 950℃~1150℃ at a heating rate of (10±2)℃ / min, holding for 10h~30h, nitrogen pressure ≥2bar, and after holding, cooling to below 60℃ at a pressure ≥3bar before removing from the furnace; Step 62, vacuum carburizing treatment, includes: placing the rough-machined parts after solution nitriding treatment into a low-pressure vacuum carburizing furnace, heating to a temperature of 930℃~1000℃, holding for 10h~30h, and then cooling to below 60℃ under a pressure of ≥3bar after holding.

4. The method for preparing the nitriding and carburizing composite diffusion layer for corrosion-resistant nitrided steel parts according to claim 1, characterized in that, Also includes: Step 10: After aging treatment, check the mechanical properties, diffusion depth, core hardness, and surface hardness of the rough-machined parts. If the inspection results meet the preset conditions, the parts are deemed qualified.

5. The method for preparing the nitriding and carburizing composite diffusion layer for corrosion-resistant nitrided steel parts according to claim 1, characterized in that, In the preparation method described above Before and after solution nitriding, before and after low-pressure vacuum carburizing, and before and after solution treatment, the parts are sandblasted to remove residual coating and surface oxide scale, resulting in a clean surface.

6. The method for preparing a nitriding and carburizing composite diffusion layer on corrosion-resistant nitrided steel parts according to any one of claims 1 to 5, characterized in that, The nitrided steel parts include: nitrided steel bushings, nitrided steel transmission rods, and nitrided steel gears.

7. The method for preparing a nitriding and carburizing composite diffusion layer for corrosion-resistant nitrided steel parts according to claim 6, characterized in that, The nitrided steel part is a nitrided steel gear. In step 1, the penetration depth is determined based on the size, structure, and digital model parameters of the gear parts.

8. The method for preparing a nitriding and carburizing composite diffusion layer for corrosion-resistant nitrided steel parts according to claim 7, characterized in that, The machining methods in step 4 include: CNC turning, gear hobbing, and forming rough-machined gears; The gear hobbing process forms a rough-machined gear with a machining allowance of 0.20mm to 0.30mm.

9. The method for preparing a nitriding and carburizing composite diffusion layer for corrosion-resistant nitrided steel parts according to claim 7, characterized in that, Before step 6, the following are also included: Determine the infiltrated and non-infiltrated regions at the gear tooth and journal positions, and determine the transition region between the infiltrated and non-infiltrated regions based on the gear structure and dimensions.

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