An elongated hole differential nitriding heat treatment method

Abstract

The present application belongs to the technical field of heat treatment, and relates to a differential nitriding heat treatment method for elongated holes. The product to be nitrided includes at least two inner holes with different nitriding requirements. The inner holes are classified according to whether the nitriding requirements are the same, and are respectively subjected to nitriding treatment according to the classification. Before each nitriding, the product area outside the nitriding area of this time is plated with copper for protection, so as to perform differential nitriding. The nitriding heat treatment method in the present application adopts the combination of plating copper + nitriding + plating copper + nitriding, and adjusts the heat treatment process parameters and plating copper to prevent nitriding, so as to achieve different hardness requirements of different elongated inner holes. For the same product, the remaining parts with different nitriding requirements are plated with copper twice during the two nitriding heat treatment periods, so that the different parts finally achieve the requirement of different hardness. The process has good repeatability, improves the wear resistance of the elongated inner hole, and the product quality is stable.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of heat treatment and relates to a differential nitriding heat treatment method for an elongated hole. BACKGROUND

[0002] The commonly used heating methods for the surface heat treatment method for locally increasing the surface hardness of a part include induction heating (high frequency, power frequency, medium frequency), flame heating, laser heating, electron beam heating, electrolyte heating and bath heating. The modified layer meeting the design requirements can be obtained through the surface heat treatment. After the surface hardened layer is obtained by using the surface heating quenching, the core of the part remains the original microstructure and performance unchanged, so that the excellent comprehensive performance of improving the fatigue strength, improving the wear resistance and maintaining the toughness of the core is achieved. If the anti-carburizing or anti-nitriding coating is pre-coated on the surface of the part, the surface chemical heat treatment can also be achieved.

[0003] The induction heating is the most commonly used surface heating quenching method, which has the advantages of simple process, small deformation, high efficiency and easy mechanization and automation of the process, but for the surface heat treatment of the elongated inner hole, especially the blind hole, the surface hardness of the inner hole cannot meet the technical requirements due to the influence of the manufacturing of the inductor and the quenching cooling. SUMMARY

[0004] Therefore, the purpose of the application is to solve the above problems and provide a differential nitriding heat treatment method for an elongated hole.

[0005] To achieve the above purpose, the application provides the following technical scheme.

[0006] The differential nitriding heat treatment method for an elongated hole is characterized in that the nitriding product includes at least two inner holes with different nitriding requirements, the inner holes are classified according to whether the nitriding requirements are the same, and the nitriding treatment is performed according to the classification; before each nitriding, the product area outside the nitriding area is plated with copper for protection, so that the differential nitriding is performed.

[0007] Further, the material of the nitriding product is 35CrMoVA, which includes two specifications of elongated holes of Φ20 and Φ28. Before the nitriding treatment, the preliminary heat treatment is performed: the quenching and tempering treatment is performed at 280-320 HBW; after the quenching and tempering treatment is completed, the inner hole Φ20 is processed to a depth of 123.5 mm and the inner hole Φ28 is processed to a depth of 154 mm; the nitriding requirement of the inner hole Φ20 is that the nitriding depth is 0.3-0.5 mm and the surface hardness is 460-545 HV10; the nitriding requirement of the inner hole Φ28 is that the nitriding depth is 0.3-0.5 mm and the surface hardness is 545-615 HV10.

[0008] Further, the nitriding process of the inner hole Φ20 is that after the product is cleaned, the product is placed on the tooling; the furnace is emptied and the nitrogen flow is 1.0 m 3 / h, after 40 min, close the exhaust valve, and the furnace is heated to 300 DEG C, 400 DEG C, 480 DEG C, each for 1 h, then heated to nitriding temperature 530 DEG C + / - 5 DEG C, the holding time is 25 h, control the ammonia decomposition rate 55-60%, at this time the ammonia flow is 0.25 m 3 / h, the last 5 hours denitrogenation, denitrogenation temperature is 620 DEG C, nitrogen flow is 1.0 m 3 / h, and the furnace is cooled to below 160 DEG C by nitrogen, the furnace cover is opened, and the product is lifted out and air-cooled.

[0009] Further, the nitriding process of the inner hole Φ28 is as follows: after the product is cleaned, it is placed on the tooling; the product is put into the furnace and the air is exhausted, and the nitrogen flow is 1.0 m 3 / h, after 40 min, close the exhaust valve, and the furnace is heated to 300 DEG C, 400 DEG C, 480 DEG C, each for 1 h, then heated to nitriding temperature 530 DEG C + / - 5 DEG C, the holding time is 25 h, control the ammonia decomposition rate 55-60%, at this time the ammonia flow is 0.25 m 3 / h, the last 5 hours denitrogenation, denitrogenation temperature is 595 DEG C, nitrogen flow is 1.0 m 3 / h, and the furnace is cooled to below 160 DEG C by nitrogen, the furnace cover is opened, and the product is lifted out and air-cooled.

[0010] Further, before each nitriding, the copper plating thickness of the non-nitriding area is greater than or equal to 0.03 mm, and after the nitriding is completed, the inner hole oxide skin is removed by polishing, and the copper plating layer is removed.

[0011] The beneficial effects of the present application are as follows:

[0012] The nitriding heat treatment method in the present application adopts the combination of copper plating + nitriding + copper plating + nitriding, and the heat treatment process parameters are adjusted to prevent the penetration of copper plating, so that different hardness requirements are obtained for different slender inner holes. For the same product, the remaining parts which have different nitriding requirements are plated with copper twice during the two nitriding heat treatment periods, so that the requirement of obtaining different hardness for different parts is finally realized. The process has good repeatability, improves the wear resistance of the slender inner hole, and the product quality is stable.

[0013] Other advantages, objects, and features of the present application will be set forth in part in the following specification, and in part will become apparent to those skilled in the art from the following specification, or can be learned from the practice of the present application. The objects and other advantages of the present application can be realized and attained by the below description. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to make the purpose, technical scheme and advantages of the present application clearer, the preferred detailed description of the present application will be given below in combination with the drawings, in which:

[0015] Figure 1The structure schematic diagram of the nitriding product in the application.

[0016] Figure 2 The structure schematic diagram of the nitriding product in the application. Figure 1 The nitriding process curve diagram of the Φ20 inner hole.

[0017] Figure 3 The structure schematic diagram of the nitriding product in the application. Figure 1 The nitriding process curve diagram of the Φ28 inner hole. DETAILED DESCRIPTION

[0018] The advantages and effects of the application can be easily understood by those skilled in the art from the description. The application can also be implemented or applied in other different embodiments, and the details in the description can be modified or changed based on different views and applications without departing from the spirit of the application. It should be noted that the diagrams provided in the following examples only illustrate the basic concept of the application in a schematic manner, and the following examples and features in the examples can be combined with each other without conflict.

[0019] The drawings are only used for illustrative description, and the representation is only a schematic diagram, not a physical diagram, and cannot be understood as a limitation of the application. In order to better illustrate the embodiments of the application, some components in the drawings may be omitted, enlarged or reduced, and do not represent the actual size of the product. It is understandable for those skilled in the art that some well-known structures and their descriptions in the drawings may be omitted.

[0020] The same or similar reference numerals in the drawings of the embodiments of the application correspond to the same or similar components; in the description of the application, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", "front", "back" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the terms describing the positional relationship in the drawings are only used for illustrative description, and cannot be understood as a limitation of the application, and for those skilled in the art, the specific meaning of the above terms can be understood according to the specific situation.

[0021] Please refer to Figure 1 The application discloses a differential nitriding heat treatment method for an elongated hole, the product to be nitrided includes at least two inner holes with different nitriding requirements, the inner holes are classified according to whether the nitriding requirements are the same, and the nitriding treatment is performed according to the classification; during each nitriding, the product area outside the nitriding area of this time is plated with copper for protection, so that the differential nitriding is realized.

[0022] The material of the nitriding product in this embodiment is 35CrMoVA, including two specifications of elongated holes Φ20 and Φ28, which are arranged in parallel. Before nitriding treatment, preliminary heat treatment is performed: quenching and tempering treatment 280-320HBW; after quenching and tempering, the inner hole Φ20 with a depth of 123.5 mm and the inner hole Φ28 with a depth of 154 mm are processed by fine turning and milling; the nitriding requirements of the inner hole Φ20 are: nitriding depth 0.3-0.5 mm, surface hardness 460-545HV10; the nitriding requirements of the inner hole Φ28 are: nitriding depth 0.3-0.5 mm, surface hardness 545-615HV10.

[0023] Specifically, the nitriding process of the inner hole Φ20 is: after the product is cleaned, it is placed flat on the tooling; air is exhausted into the furnace, and the nitrogen flow rate is 1.0 m 3 / h, the exhaust valve is closed after 40 min, the furnace is heated to 300℃, 400℃, 480℃ respectively for 1 h, then the nitriding temperature is increased to 530±5℃, the holding time is 25 h, the ammonia decomposition rate is controlled to be 55-60%, at this time the ammonia flow rate is 0.25 m 3 / h, the last 5 hours are denitriding, the denitriding temperature is 620℃, and the nitrogen flow rate is 1.0 m 3 / h; after cooling to below 160℃ by nitrogen, the furnace cover is opened, the product is lifted out and air cooled.

[0024] The nitriding process of the inner hole Φ28 is: after the product is cleaned, it is placed flat on the tooling; air is exhausted into the furnace, and the nitrogen flow rate is 1.0 m 3 / h, the exhaust valve is closed after 40 min, the furnace is heated to 300℃, 400℃, 480℃ respectively for 1 h, then the nitriding temperature is increased to 530±5℃, the holding time is 25 h, the ammonia decomposition rate is controlled to be 55-60%, at this time the ammonia flow rate is 0.25 m 3 / h, the last 5 hours are denitriding, the denitriding temperature is 595℃, and the nitrogen flow rate is 1.0 m 3 / h; after cooling to below 160℃ by nitrogen, the furnace cover is opened, the product is lifted out and air cooled.

[0025] Before each nitriding, the thickness of the plated copper in the non-nitriding area is ≥0.03 mm, after nitriding is completed, the inner hole oxide skin is polished and removed, the plated copper layer is removed, and the copper layer is used for anti-permeation.

[0026] The combination of copper plating + nitriding + copper plating + nitriding makes the hardness of the elongated inner holes Φ20 and Φ28 be 460-545HV10 and 545-615HV10 respectively; and ensures that the hardness of the remaining parts except the inner hole meets the quenching and tempering hardness 280-320HBW. By using the methods of nitriding and copper plating anti-permeation, different hardnesses are obtained in different parts of the same product, the wear resistance of the elongated hole is improved, the process repeatability is good, and the product quality stability can be ensured.

[0027] Finally, it is to be explained that the above embodiments are only used to illustrate the technical solutions of the present application but not to limit the present application. Although the present application 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 application can be modified or equivalently replaced without departing from the purpose and scope of the present application, and all of them should be covered in the scope of the claims of the present application.

Claims

1. A method of differential nitriding heat treatment of elongated holes, characterized in that: The product to be nitrided includes at least two inner holes with different nitriding requirements, the inner holes are classified according to whether the nitriding requirements are the same, and are respectively subjected to nitriding treatment according to the classification; before each nitriding, the area of the product except the nitriding area of this time is subjected to copper plating protection to perform differential nitriding; The material of the nitrided product is 35CrMoVA, including two specifications of Φ20 and Φ28 elongated holes, before nitriding treatment, preliminary heat treatment is performed: quenching and tempering treatment 280~320HBW; after quenching and tempering, the inner hole Φ20 is precisely machined to a depth of 123.5mm and the inner hole Φ28 is precisely machined to a depth of 154mm; the nitriding requirement of the inner hole Φ20 is: nitriding depth 0.3~0.5mm, surface hardness 460~545HV10; the nitriding requirement of the inner hole Φ28 is: nitriding depth 0.3~0.5mm, surface hardness 545~615HV10; The nitriding process of the inner hole Φ20 is: after the product is cleaned, it is placed on the tool; the air is exhausted into the furnace, the nitrogen gas flow is 1.0 m 3 / h, the exhaust valve is closed after 40 min, the furnace is heated to 300℃, 400℃ and 480℃ respectively for 1h, then it is heated to the nitriding temperature of 530±5℃, the holding time is 25h, the ammonia decomposition rate is controlled to be 55~60%, at this time the ammonia gas flow is 0.25 m 3 / h, the nitrogen is withdrawn for the last 5 hours, the nitrogen withdrawal temperature is 620℃, the nitrogen gas flow is 1.0 m 3 / h; the furnace is cooled to below 160℃ by nitrogen, the furnace cover is opened, the product is lifted out and air cooled; The nitriding process of the inner hole Φ28 is as follows: after the product is cleaned, it is placed on the tool; the air is exhausted into the furnace, the nitrogen gas flow is 1.0 m 3 / h, the exhaust valve is closed after 40 min, the furnace is heated to 300℃, 400℃ and 480℃ respectively for 1h, then it is heated to the nitriding temperature of 530±5℃, the holding time is 25h, the ammonia decomposition rate is controlled to be 55~60%, at this time the ammonia gas flow is 0.25 m 3 / h; the nitrogen is withdrawn for the last 5 hours, the nitrogen withdrawal temperature is 595℃ and the nitrogen gas flow is 1.0 m 3 / h; the temperature is reduced to below 160℃ by nitrogen gas, the furnace cover is opened, the product is lifted out and air cooled.

2. The method of differential nitriding heat treatment of elongated holes according to claim 1, characterized in that: Before each nitriding, the copper plating thickness of the non-nitriding area is greater than or equal to 0.03mm, after the nitriding is completed, the inner hole oxide skin is polished and removed, and the copper plating layer is removed.

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