Steel part nitriding method

Abstract

The invention provides a steel part nitriding method, and relates to the technical field of steel surface treatment. According to the method, a specific energizing agent is adopted in the steel part nitriding treatment process, in the energizing agent, yttrium oxide and lanthanum oxide belong to rare earth elements, in the nitriding process, the rare earth elements can adsorb hydrogen and react with hydrogen to generate rare earth hydrides, the rare earth hydrides are subjected to an interface reaction on the steel surface, and rare earth nitrides are generated; the rare earth nitride can permeate into the surface layer of the steel according to defects such as vacancy and short circuit mechanisms, so that the nitriding process is accelerated. And permeation of rare earth elements can refine grains, so that the surface hardness of the steel part is enhanced. Sodium laurate is used as a penetration enhancer and can promote penetration of nitrogen atoms on the surface of the steel part, so that the nitrogen atoms penetrate into the steel part more deeply, and formation of a deeper effective hardened layer is facilitated. In conclusion, by means of the steel part nitriding method, the surface hardness and the effective hardened layer depth of the steel part subjected to nitriding treatment can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of steel surface treatment, in particular to a steel part nitriding method. Background Art

[0002] Nitriding treatment is widely used in the automotive, machinery and aerospace industries. Nitriding treatment, also known as nitriding treatment, is a chemical heat treatment process that allows nitrogen atoms to penetrate into the surface of steel parts at a specific temperature and in a specific medium; steel parts after nitriding treatment generally have better wear resistance, fatigue resistance, corrosion resistance and high temperature resistance. However, at present, the surface hardness of steel parts after nitriding treatment is low, and the effective hardened layer depth is small, resulting in the strength and life of steel parts after nitriding failing to meet the expected requirements. Summary of the invention

[0003] The problem solved by the invention is how to improve the surface hardness and effective hardened layer depth of a steel part after nitriding treatment.

[0004] In order to solve the above problems, the present invention provides a method for nitriding a steel part, comprising:

[0005] Step S1, heating the steel part to obtain a pretreated steel part;

[0006] Step S2, placing the pretreated steel part into a nitriding furnace, introducing ammonia and a catalyst, performing heat-insulating nitriding at a preset temperature, and cooling to room temperature to obtain a nitrided steel part; wherein, during the heat-insulating nitriding process, the pressure of the nitriding furnace is 4 kPa to 7 kPa; and the components of the catalyst include, by weight: 5 to 6 parts of yttrium oxide, 5 to 6 parts of lanthanum oxide, 10 to 20 parts of sodium laurate, 10 to 12 parts of dichloromethane, 20 to 30 parts of ethylene glycol, and 10 to 15 parts of ammonium chloride.

[0007] Optionally, in step S2, the preset temperature is 505°C to 515°C.

[0008] Optionally, in step S2, the flow rate of the penetration catalyst is 5 ml / min to 6 ml / min.

[0009] Optionally, in step S2, the flow rate of the introduced ammonia gas is 20 L / min to 30 L / min.

[0010] Optionally, in step S2, during the heat-insulating nitriding process, the decomposition rate of ammonia is 18% to 40%.

[0011] Optionally, during the heat-insulating nitriding process, the decomposition rate of ammonia is 20% to 30%.

[0012] Optionally, in step S2, the time of the heat preservation nitriding is 15 hours to 20 hours.

[0013] Optionally, in step S1, the temperature of the heating treatment is 360°C to 380°C.

[0014] Optionally, the heating treatment time is 3h to 4h.

[0015] Optionally, in step S1, the material of the steel part is 40Cr steel. The material of the steel part is 40Cr steel, and the components of the 40Cr steel include, by weight percentage: C: 0.37% to 0.44%, Si: 0.17% to 0.37%, Mn: 0.50% to 0.80%, Cr: 0.80% to 1.10%, Ni: 0 to 0.30%, P: 0 to 0.035%, S: 0 to 0.035%, Cu: 0 to 0.25%, Mo: 0 to 0.10%, and the remainder is Fe and unavoidable impurities.

[0016] Compared with the related art, the present invention adopts a specific catalyst in the process of nitriding steel parts, and the catalyst is composed of yttrium oxide, lanthanum oxide, sodium laurate, dichloromethane, ethylene glycol, and ammonium chloride in a specific ratio; wherein, yttrium oxide and lanthanum oxide are rare earth elements, and during the nitriding process, rare earth elements can absorb hydrogen and react with hydrogen to form rare earth hydrides, and these rare earth hydrides undergo interfacial reactions on the surface of steel to form rare earth nitrides; rare earth nitrides have high activity and can penetrate into the surface layer of steel according to defects such as vacancies and short-circuit mechanisms, thereby accelerating the nitriding process. The penetration of rare earth elements can refine the grains, change the grain boundary structure, induce grain boundary migration, and restrict the movement of grains, thereby enhancing the surface hardness of the steel parts. Sodium laurate, as a penetration enhancer, can promote the penetration of nitrogen atoms on the surface of steel parts, allowing nitrogen atoms to penetrate deeper into the interior of the steel parts, which is conducive to the formation of a deeper effective hardening layer. Dichloromethane and ethylene glycol are used as solvents to dissolve other components and form a uniform solution, which is conducive to the uniform distribution and penetration of the catalyst during the nitriding process. In addition, the present invention controls the pressure of the nitriding furnace to be relatively high (4kPa to 7kPa) during the nitriding process to ensure the impact rate of the gas in the nitriding furnace on the workpiece surface, which is also conducive to forming a deeper effective hardened layer. In summary, the steel nitriding method of the present invention can improve the surface hardness and effective hardened layer depth of the steel after nitriding treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the process of nitriding a steel part in an embodiment of the present invention. DETAILED DESCRIPTION

[0018] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be interpreted as being limited to the embodiments described herein. On the contrary, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the drawings and embodiments of the present invention are only for exemplary purposes and are not intended to limit the scope of protection of the present invention.

[0019] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0020] The term "including" and its variations used in this article are open inclusions, that is, "including but not limited to"; the term "based on" is "based at least in part on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one other embodiment"; the term "some embodiments" means "at least some embodiments"; the term "optionally" means "optional embodiments". The relevant definitions of other terms will be given in the following description. It should be noted that the concepts of "first" and "second" mentioned in the present invention are used to distinguish different objects, rather than to describe a specific order or a primary and secondary relationship. In addition, the terms "first" and "second" are used only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, the meaning of "multiple" is two or more.

[0021] like Figure 1 As shown, a steel part nitriding method provided by an embodiment of the present invention comprises:

[0022] Step S1, heating the steel part to obtain a pretreated steel part;

[0023] Step S2, placing the pretreated steel part into a nitriding furnace, introducing ammonia and a catalyst, performing heat-insulating nitriding at a preset temperature, and cooling to room temperature to obtain a nitrided steel part; wherein, during the heat-insulating nitriding process, the pressure of the nitriding furnace is 4 kPa to 7 kPa; and the components of the catalyst include, by weight: 5 to 6 parts of yttrium oxide, 5 to 6 parts of lanthanum oxide, 10 to 20 parts of sodium laurate, 10 to 12 parts of dichloromethane, 20 to 30 parts of ethylene glycol, and 10 to 15 parts of ammonium chloride.

[0024] The embodiment of the present invention uses a specific catalyst in the process of nitriding steel parts. The catalyst is composed of yttrium oxide, lanthanum oxide, sodium laurate, dichloromethane, ethylene glycol, and ammonium chloride in a specific ratio; wherein yttrium oxide and lanthanum oxide are rare earth elements. During the nitriding process, rare earth elements can absorb hydrogen and react with hydrogen to form rare earth hydrides. These rare earth hydrides undergo interfacial reactions on the surface of steel to form rare earth nitrides; rare earth nitrides have high activity and can penetrate into the surface layer of steel according to defects such as vacancies and short-circuit mechanisms, thereby accelerating the nitriding process. The penetration of rare earth elements can refine the grains, change the grain boundary structure, induce grain boundary migration, and restrict the movement of grains, thereby enhancing the surface hardness of the steel parts. Sodium laurate, as a penetration enhancer, can promote the penetration of nitrogen atoms on the surface of steel parts, allowing nitrogen atoms to penetrate deeper into the interior of the steel parts, which is conducive to the formation of a deeper effective hardening layer. Dichloromethane and ethylene glycol are used as solvents to dissolve other components and form a uniform solution, which is conducive to the uniform distribution and penetration of the catalyst during the nitriding process. In addition, the present invention controls the pressure of the nitriding furnace to be relatively high (4kPa to 7kPa) during the nitriding process to ensure the impact rate of the gas in the nitriding furnace on the workpiece surface, which is also conducive to forming a deeper effective hardened layer. In summary, the steel nitriding method of the embodiment of the present invention can improve the surface hardness and effective hardened layer depth of the steel after nitriding treatment.

[0025] In some embodiments of the present invention, in step S2, the preset temperature is 505°C to 515°C.

[0026] In some embodiments of the present invention, in step S2, the flow rate of the penetration catalyst is 5 ml / min to 6 ml / min; the flow rate of the ammonia gas is 20 L / min to 30 L / min.

[0027] In some embodiments of the present invention, in step S2, during the heat preservation nitriding process, the decomposition rate of ammonia is 18% to 40%; preferably, during the heat preservation nitriding process, the decomposition rate of ammonia is 20% to 30%.

[0028] In some embodiments of the present invention, in step S2, the time of the heat preservation nitriding is 15 hours to 20 hours.

[0029] In some embodiments of the present invention, in step S1, the temperature of the heating treatment is 360° C. to 380° C.; and the time of the heating treatment is 3 h to 4 h.

[0030] In some embodiments of the present invention, exemplarily, in step S1, the material of the steel part is 40Cr steel, and the components of the 40Cr steel include, by weight percentage: C: 0.37% to 0.44%, Si: 0.17% to 0.37%, Mn: 0.50% to 0.80%, Cr: 0.80% to 1.10%, Ni: 0 to 0.30%, P: 0 to 0.035%, S: 0 to 0.035%, Cu: 0 to 0.25%, Mo: 0 to 0.10%, and the remainder is Fe and unavoidable impurities.

[0031] The present invention is further described below in conjunction with specific embodiments. It should be noted that, in terms of weight percentage, the components of the 40Cr steel used in the following embodiments and comparative examples include: C: 0.40%, Si: 0.20% to 0.37%, Mn: 0.60%, Cr: 1.00%, Ni: 0.15%, P: 0.015%, S: 0.010%, Cu: 00.10%, Mo: 0.05%, and the balance is Fe and unavoidable impurities.

[0032] Example 1

[0033] A1. The steel part is subjected to heat treatment to obtain a pretreated steel part; wherein the material of the steel part is 40Cr steel, the heating treatment temperature is 370°C, and the heating time is 3.5h.

[0034] A2. Put the pretreated steel part into a nitriding furnace, introduce ammonia and a catalyst, perform heat preservation nitriding at a preset temperature, and cool to room temperature to obtain a nitrided steel part; wherein the preset temperature is 510°C, the flow rate of the catalyst is 5.5 ml / min, the flow rate of the ammonia is 25 L / min, the heat preservation nitriding time is 17.5 h, and during the heat preservation nitriding process, the pressure of the nitriding furnace is 5.5 kPa, and the decomposition rate of ammonia is 30%; the components of the catalyst are, by weight: 5.5 parts of yttrium oxide, 5.5 parts of lanthanum oxide, 15 parts of sodium laurate, 11 parts of dichloromethane, 25 parts of ethylene glycol, and 12.5 parts of ammonium chloride.

[0035] Example 2

[0036] A1. The steel part is subjected to heat treatment to obtain a pretreated steel part; wherein the material of the steel part is 40Cr steel, the heating treatment temperature is 360°C, and the time is 4 hours.

[0037] A2. Put the pretreated steel part into a nitriding furnace, introduce ammonia and a catalyst, perform heat preservation nitriding at a preset temperature, and cool to room temperature to obtain a nitrided steel part; wherein the preset temperature is 505°C, the flow rate of the catalyst is 5 ml / min, the flow rate of the ammonia is 20 L / min, the heat preservation nitriding time is 20 h, and during the heat preservation nitriding process, the pressure of the nitriding furnace is 4 kPa, and the decomposition rate of ammonia is 30%; the components of the catalyst are: 5 parts of yttrium oxide, 5 parts of lanthanum oxide, 10 parts of sodium laurate, 10 parts of dichloromethane, 20 parts of ethylene glycol, and 10 parts of ammonium chloride in parts by weight.

[0038] Example 3

[0039] A1. The steel part is subjected to heat treatment to obtain a pretreated steel part; wherein the material of the steel part is 40Cr steel, the heating treatment temperature is 380°C, and the heating time is 3h.

[0040] A2. Put the pretreated steel part into a nitriding furnace, introduce ammonia and a catalyst, perform heat preservation nitriding at a preset temperature, and cool to room temperature to obtain a nitrided steel part; wherein the preset temperature is 515°C, the flow rate of the catalyst is 6 ml / min, the flow rate of the ammonia is 30 L / min, the heat preservation nitriding time is 15 h, and during the heat preservation nitriding process, the pressure of the nitriding furnace is 7 kPa, and the decomposition rate of ammonia is 30%; by weight, the components of the catalyst include: 6 parts of yttrium oxide, 6 parts of lanthanum oxide, 20 parts of sodium laurate, 12 parts of dichloromethane, 30 parts of ethylene glycol, and 15 parts of ammonium chloride.

[0041] Comparative Example 1

[0042] The difference from Example 1 is that in step A2, the components of the penetration catalyst are: 5 parts of lanthanum oxide, 10 parts of sodium laurate, 10 parts of dichloromethane, 20 parts of ethylene glycol, and 10 parts of ammonium chloride.

[0043] Comparative Example 2

[0044] The difference from Example 1 is that in step A2, the components of the penetration catalyst are: 5 parts of yttrium oxide, 5 parts of lanthanum oxide, 10 parts of dichloromethane, 20 parts of ethylene glycol, and 10 parts of ammonium chloride.

[0045] Experimental example

[0046] The surface hardness and effective hardened layer depth of the nitrided steel parts prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were tested, and the results are shown in Table 1. It can be seen from Table 1 that compared with Comparative Examples 1 to 2, the surface hardness of the nitrided steel parts prepared in Examples 1 to 3 is higher and the effective hardened layer depth is deeper.

[0047] Table 1

[0048] serial number Surface hardness (HV) Effective hardened layer depth (mm) Example 1 837 0.46 Example 2 845 0.42 Example 3 851 0.50 Comparative Example 1 810 0.40 Comparative Example 2 830 0.30

[0049] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A method for nitriding a steel part, characterized in that: include: Step S1, heating the steel part to obtain a pretreated steel part; Step S2, placing the pretreated steel part into a nitriding furnace, introducing ammonia and a catalyst, performing heat-insulating nitriding at a preset temperature, and cooling to room temperature to obtain a nitrided steel part; wherein, during the heat-insulating nitriding process, the pressure of the nitriding furnace is 4 kPa to 7 kPa; and the components of the catalyst include, by weight: 5 to 6 parts of yttrium oxide, 5 to 6 parts of lanthanum oxide, 10 to 20 parts of sodium laurate, 10 to 12 parts of dichloromethane, 20 to 30 parts of ethylene glycol, and 10 to 15 parts of ammonium chloride.

2. The method for nitriding a steel part according to claim 1, characterized in that: In the step S2, the preset temperature is 505°C to 515°C.

3. The method for nitriding a steel part according to claim 1, characterized in that: In step S2, the flow rate of the penetration catalyst is 5 ml / min to 6 ml / min.

4. The method for nitriding a steel part according to claim 1, characterized in that: In step S2, the flow rate of the introduced ammonia gas is 20 L / min to 30 L / min.

5. The method for nitriding a steel part according to claim 1, characterized in that: In the step S2, during the heat preservation nitriding process, the decomposition rate of ammonia is 18% to 40%.

6. The method for nitriding a steel part according to claim 5, characterized in that: During the heat preservation nitriding process, the decomposition rate of ammonia is 20% to 30%.

7. The method for nitriding a steel part according to claim 1, characterized in that: In the step S2, the time of the heat preservation nitriding is 15 hours to 20 hours.

8. The method for nitriding a steel part according to claim 1, characterized in that: In the step S1, the temperature of the heating treatment is 360°C to 380°C.

9. The method for nitriding a steel part according to claim 8, characterized in that: The heating treatment time is 3h to 4h.

10. The method for nitriding a steel part according to claim 1, characterized in that: In the step S1, the material of the steel part is 40Cr steel. The components of the 40Cr steel include, by weight percentage: C: 0.37% to 0.44%, Si: 0.17% to 0.37%, Mn: 0.50% to 0.80%, Cr: 0.80% to 1.10%, Ni: 0 to 0.30%, P: 0 to 0.035%, S: 0 to 0.035%, Cu: 0 to 0.25%, Mo: 0 to 0.10%, and the remainder is Fe and unavoidable impurities.

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