A High-Efficiency Gas Nitriding Method

Abstract

This invention discloses a highly efficient gas nitriding method, specifically relating to the field of chemical heat treatment technology for steel surfaces. The highly efficient gas nitriding method provided by this invention first forms a nitrogen diffusion layer on the surface of the metal substrate, then transforms the nitrogen diffusion layer into a metal-nitrogen compound layer, and finally decomposes the metal-nitrogen compound to reform the nitrogen diffusion layer with increased thickness. Within a conventional nitriding time, the nitrided metal surface obtained using the highly efficient nitriding method provided by this invention has a minimum thickness of 189.6 μm, and the thickness and hardness of the nitrided layer can reach a maximum of 326.5 μm and 1205.7 HV, respectively, with a minimum wear rate of only 1.47 × 10⁻⁶. ‑4 mm 3 / Nm.

Description

Technical Field

[0001] This invention relates to the field of chemical heat treatment technology for steel surfaces, and more specifically, to a highly efficient gas nitriding method. Background Technology

[0002] Gas nitriding is one of the most widely used surface modification technologies in industrial production. It has been widely used for surface strengthening of components such as gears, drive shafts, and molds, and can effectively improve the hardness, wear resistance, and corrosion resistance of steel materials.

[0003] Typically, the surface of parts produced by gas nitriding can have a compound region (ε-Fe) on the outermost layer. 2-3 A composite nitriding modified layer consists of N+γ′-Fe4N type nitride and a subsurface nitrogen diffusion zone. However, the compound layer on the part surface suffers from poor toughness and wear resistance due to high internal stress. Current technologies typically remove the compound layer from the part surface after gas nitriding, using the subsurface nitrogen diffusion zone, which offers superior toughness and load-bearing capacity, directly for service. However, the subsurface nitrogen diffusion layer obtained through conventional nitriding processes is often too thin, resulting in poor performance in practical applications. Therefore, there is an urgent need to develop a rapid process that can produce a thick nitriding layer containing only nitrogen diffusion.

[0004] Existing technology provides a surface composite treatment method for high vacuum extrusion die casting molds, which organically combines shot peening technology and gas nitriding technology for surface treatment of extrusion die casting molds. However, the surface composite treatment method provided by the existing technology must combine the nitriding process with the shot peening process, which is cumbersome and cannot achieve efficient nitriding. After 10 hours of nitriding treatment, only a nitrided layer with a thickness of 100μm can be obtained on the metal surface, and the nitrided layer also contains a compound layer with poor wear resistance. Summary of the Invention

[0005] To address the problem that existing nitriding processes cannot quickly obtain a thick nitrided metal surface layer containing only a nitrogen diffusion layer, this invention provides a highly efficient gas nitriding method. By controlling the nitriding temperature, time, and N2 volume concentration ratio at different stages of nitriding, rapid nitriding is achieved, resulting in a thicker nitrided metal surface layer within a conventional nitriding time, and the nitrided layer contains only a nitrogen diffusion layer.

[0006] The above-mentioned objective of this invention is achieved through the following technical solution:

[0007] A highly efficient gas nitriding method includes the following steps:

[0008] S1. Low-temperature diffusion nitriding: The metal substrate is placed in a gas nitriding device, a nitriding gas source is introduced, the nitriding temperature is 450-530℃, the N2 volume concentration accounts for 40-60% of the total concentration of the nitriding gas source, and the nitriding time is more than 1 hour.

[0009] S2. Medium-temperature nitriding: The nitriding temperature is 530-580℃, the N2 volume concentration accounts for less than 40% of the total concentration of the nitriding gas source, and the nitriding time is more than 1 hour;

[0010] S3. High-temperature denitrification and nitriding: The nitriding temperature is 590-650℃, the N2 volume concentration accounts for 60-100% of the total concentration of the nitriding gas source, and the nitriding time is more than 0.5h;

[0011] Low-temperature diffusion nitriding, medium-temperature nitriding, and high-temperature denitriding form a cycle, and the cycle length is ≥2.

[0012] In the gas nitriding method provided by this invention, the nitriding process is divided into three steps: low-temperature diffusion nitriding, medium-temperature nitriding, and high-temperature denitriding, in order to quickly obtain a thick metal surface nitrided layer containing only a nitrogen diffusion layer. Specifically, in the low-temperature diffusion nitriding process of step S1, a nitrogen-supersaturated nitrogen diffusion layer can be formed. In the medium-temperature nitriding process of step S2, the nitrogen diffusion layer can be quickly transformed into a metal-nitrogen compound (e.g., iron-nitrogen compound) layer. The metal-nitrogen compound then rapidly decomposes in the high-temperature denitriding process of step S3, releasing a large number of active nitrogen atoms that diffuse into deeper layers away from the metal surface. These nitrogen atoms do not recombine to form nitrogen molecules, ultimately forming a dense and thicker metal surface nitrided layer. The resulting metal surface nitrided layer contains only a nitrogen diffusion layer and no metal-nitrogen compound layer. Meanwhile, because the nitrided layer on the metal surface contains only a nitrogen diffusion layer, the metal substrate surface obtained by nitriding using the gas nitriding method provided by this invention has higher surface hardness and wear resistance. This is because, compared to a metal-nitrogen compound layer, nitrogen atoms in the nitrogen diffusion layer can increase the hardness of the nitrided layer through solid solution strengthening, and the nitrogen diffusion layer is dense, capable of withstanding greater friction. Since both the hardness and thickness of the nitrided layer on the metal surface are increased, the wear resistance can be further improved.

[0013] During low-nitrogen-potential nitriding, only a nitrogen diffusion layer forms on the metal surface. However, during high-nitrogen-potential nitriding, the nitrogen diffusion layer partially transforms into a metal-nitrogen compound layer. In this invention, the nitrogen potential for nitriding is primarily controlled by adjusting the N2 volume concentration relative to the total concentration in the nitriding gas source. This N2 volume concentration can be controlled by adjusting the rate at which the nitriding gas source is introduced into the gas nitriding device. The N2 volume concentration directly affects the concentration of active nitrogen atoms in the furnace during gas nitriding; the lower the proportion, the higher the nitrogen potential. Simultaneously, the system temperature also influences the nitrogen potential, specifically, decreasing the nitrogen potential as the temperature decreases.

[0014] Controlling the N2 volume concentration in step S1 to be above 40% of the total nitriding gas concentration and the temperature to below 530°C is to ensure that the nitrogen potential in step S1 is not too high, thus preventing the formation of a compound layer. If a compound layer forms directly in step S1, its dense internal structure will prevent nitrogen atoms from diffusing to deeper positions on the metal substrate surface, making it difficult to form a thick nitriding layer on the metal surface. Conversely, ensuring that the N2 volume concentration in step S1 is below 60% of the total nitriding gas concentration is to ensure a sufficiently high nitrogen potential, allowing nitrogen atoms to form a nitrogen-supersaturated nitrogen diffusion layer on the metal surface. Simultaneously, the presence of certain metal nitrides (solid solutions) within the nitrogen diffusion layer can create grain boundary defects, increasing diffusion channels for active nitrogen atoms and promoting their diffusion. The reaction temperature in step S1 is controlled to be above 450°C to enable nitrogen atoms to diffuse rapidly and form a thicker nitrogen diffusion layer. At the same time, the reaction time is controlled to be above 1 hour to ensure that a sufficiently thick nitrogen diffusion layer is formed. The thickness of the nitrogen diffusion layer is closely related to the thickness of the final nitrided metal surface layer. Therefore, controlling the temperature in step S1 to be above 450°C to enable nitrogen atoms to diffuse rapidly is one of the key factors in obtaining a thick nitrided metal surface layer in this invention.

[0015] The purpose of step S2 is to form a metal-nitrogen compound layer. Therefore, the temperature is higher, reaching above 530°C, while the N2 volume concentration relative to the total concentration of the nitriding gas source is lower, below 40%. This results in a higher nitrogen potential compared to step S1, allowing the metal to react with nitrogen to form a metal-nitrogen compound. Most of the original nitrogen diffusion layer, including its internal metal nitrides, is transformed into a metal-nitrogen compound layer. If the temperature is too high, nitrogen atoms that should form compounds will agglomerate at defects such as grain boundaries, forming active nitrogen molecules, which then evolve into pores. Conversely, if the N2 volume concentration relative to the total concentration of the nitriding gas source is too low, compounds cannot form. Controlling the nitriding time at medium temperature to above 1 hour ensures that the nitrogen diffusion layer is transformed into a metal-nitrogen compound layer as much as possible.

[0016] The purpose of step S3 is to decompose the metal-nitrogen compound. Controlling the N2 volume concentration in step S3 to be above 60% of the total concentration of the nitriding gas source is a prerequisite for reducing the nitrogen potential and decomposing the metal-nitrogen compound. Simultaneously, step S3 also requires temperature control. Below 590℃, the compound layer decomposition rate is low, and some compound layers may even remain, reducing the alloy's wear resistance. Furthermore, the active nitrogen atoms formed during compound layer decomposition may recombine to form nitrogen molecules, causing the nitrided layer on the metal surface to become porous. Above 650℃, the metal matrix undergoes tempering, reducing strength. High temperatures can also lead to excessive decomposition of the compound layer, forming pores in the nitrided layer on the metal surface, reducing the alloy's hardness and wear resistance. Controlling the high-temperature nitriding time to above 0.5 hours ensures complete decomposition of the metal-nitrogen compound.

[0017] Ensuring that low-temperature diffusion nitriding, medium-temperature nitriding, and high-temperature denitriding form a complete cycle, with a cycle length of ≥2, is one of the key factors in this invention for rapidly obtaining a thick nitrided layer on a metal surface. Because each step in the process provided by this invention can be performed quickly, the efficient nitriding process provided by this invention requires only 2.5 hours of nitriding to obtain a nitrided layer on a metal surface containing only a nitrogen diffusion layer. Furthermore, since the nitrogen diffusion layer does not affect the diffusion of active nitrogen atoms, this invention can rapidly increase the thickness of the nitrided layer by increasing the cycle length.

[0018] In a specific embodiment of the present invention, the metal substrate can be steel material, including mold steel and alloy steel, more specifically, any one or two of H13 steel and 8407 mold steel; before placing the substrate into the gas nitriding device, the substrate can be mechanically polished to make the surface roughness of the substrate ≤0.8μm, and after polishing, the metal substrate can be ultrasonically cleaned to remove the grease on the substrate surface; the ammonia gas can be commercially available ammonia gas with a purity of 99.99%.

[0019] Preferably, the nitriding temperature in step S1 is 480–520°C.

[0020] When the nitriding temperature in step S1 is above 480°C, the nitrogen diffusion layer formed is thicker. When the nitriding temperature is below 520°C, the nitrogen diffusion layer is less likely to transform into a metal-nitrogen compound layer.

[0021] More preferably, the nitriding temperature in step S1 is 500–520°C.

[0022] Preferably, the nitriding time in step S1 is 2 to 4 hours.

[0023] When the nitriding time in step S1 is higher than 2 hours, the resulting nitrogen diffusion layer is thicker. When the nitriding time is further increased to higher than 4 hours, the thickness of the nitrogen diffusion layer does not increase significantly and the nitriding process consumes too much energy.

[0024] Preferably, the nitriding temperature in step S2 is 550–570°C.

[0025] When the nitriding temperature in step S2 is higher than 550°C, the nitrogen diffusion layer can be more fully converted into a metal-nitrogen compound layer. When the temperature is increased to 570°C, the nitrogen diffusion layer is basically completely converted. Therefore, when the temperature in step S2 continues to be increased to above 570°C, the nitrogen atoms that should have formed compounds are more likely to agglomerate at defects such as grain boundaries, forming active nitrogen molecules, which then evolve into pores.

[0026] Preferably, in step S2, the N2 volume concentration accounts for 25-35% of the total concentration of the nitriding gas source.

[0027] When the N2 volume concentration in step S2 is less than 35% of the total concentration of the nitriding gas source, the nitrogen potential is lower, and the nitrogen diffusion layer is more likely to transform into a metal-nitrogen compound layer. Controlling the N2 volume concentration to be less than 25% of the total concentration of the nitriding gas source consumes too much energy and requires the introduction of large amounts of ammonia.

[0028] Preferably, the nitriding time in step S2 is 2 to 5 hours.

[0029] Controlling the nitriding time in step S2 to be more than 2 hours allows the nitrogen diffusion layer to be more fully converted into a metal-nitrogen compound layer, while when the nitriding time is higher than 5 hours, the nitrogen diffusion layer has been basically completely converted.

[0030] Preferably, the nitriding temperature in step S3 is 590–620°C.

[0031] In step S3, when the nitriding temperature is higher than 590℃, the metal-nitrogen compound layer can be decomposed more fully and faster; however, when the temperature is higher than 620℃, the compound layer is prone to excessive decomposition, forming pores in the nitrided layer on the metal surface, reducing the alloy's hardness and wear resistance.

[0032] Preferably, in step S3, the N2 volume concentration accounts for 70-80% of the total concentration of the nitriding gas source.

[0033] In step S3, when the N2 volume concentration accounts for more than 70% of the total concentration of the nitriding gas source, the compound layer can be decomposed more fully. However, when the N2 volume concentration accounts for more than 80% of the total concentration of the nitriding gas source, the nitriding process consumes too much energy.

[0034] Preferably, the nitriding time in step S3 is 1 to 3 hours.

[0035] In step S3, when the nitriding time is higher than 1 hour, the metal-nitrogen compound layer can be fully decomposed. However, when the nitriding time is further increased to 3 hours, the compound layer is basically completely decomposed. Therefore, if the nitriding time is further increased, the nitriding process consumes too much energy.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The efficient gas nitriding method provided by this invention enables the formation of a thick nitrogen diffusion layer on the metal surface, which then transforms into a metal-nitrogen compound layer and finally decomposes back into a nitrogen diffusion layer. Therefore, a nitrided metal surface layer containing only a nitrogen diffusion layer can be obtained. Since the final nitrided metal surface layer contains only a nitrogen diffusion layer and no compound layer, this invention, by increasing the number of nitriding process cycles, achieves a minimum thickness of 189.6 μm within the conventional nitriding time, and the hardness of the nitrided layer can reach a maximum of 1205.7 HV. Therefore, the wear resistance of the obtained nitrided metal surface layer is further improved, with a minimum wear rate of only 1.47 × 10⁻⁶. -4 mm 3 / Nm. Attached Figure Description

[0038] Figure 1 This is a SEM image of the nitrided metal surface layer obtained in Example 1 of the present invention.

[0039] Figure 2 This is a SEM image of the nitrided metal surface layer prepared in Comparative Example 1 of the present invention.

[0040] Figure 3 This is a flowchart of the nitriding method provided by the present invention. Detailed Implementation

[0041] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0042] Example 1

[0043] A highly efficient gas nitriding method includes the following steps:

[0044] S1. Low-temperature diffusion nitriding: H13 steel is placed in a nitriding device, a nitriding gas source is introduced, the nitriding temperature is 520℃, the N2 volume concentration accounts for 40% of the total concentration of the nitriding gas source, and the low-temperature nitriding time is 2h.

[0045] S2. Medium-temperature nitriding: The nitriding temperature is 550℃, the N2 volume concentration accounts for 25% of the total concentration of the nitriding gas source, and the medium-temperature nitriding time is 2h;

[0046] S3. High-temperature denitrification and nitriding: The nitriding temperature is 590℃, the N2 volume concentration accounts for 70% of the total concentration of the nitriding gas source, and the high-temperature nitriding time is 1 hour;

[0047] Low-temperature diffusion nitriding, medium-temperature nitriding, and high-temperature denitriding form a cycle, and the cycle is 2.

[0048] Example 2

[0049] A highly efficient gas nitriding method, which differs from Example 1 in that:

[0050] S2. Medium-temperature nitriding: The N2 volume concentration accounts for 35% of the total concentration of the nitriding gas source.

[0051] Example 3

[0052] A highly efficient gas nitriding method, which differs from Example 1 in that:

[0053] S1. Low-temperature diffusion nitriding: nitriding temperature 450℃, nitriding time 3h;

[0054] S2. Medium-temperature nitriding: nitriding temperature 530℃, nitriding time 4h;

[0055] S3. High-temperature denitrification and nitriding: nitriding time 2 hours.

[0056] Example 4

[0057] A highly efficient gas nitriding method, which differs from Example 1 in that:

[0058] S1. Low-temperature diffusion nitriding: nitriding temperature 530℃, nitriding time 1h;

[0059] S2. Medium-temperature nitriding: nitriding temperature 580℃, nitriding time 1h;

[0060] S3. High-temperature denitrification and nitriding: nitriding temperature 650℃.

[0061] Example 5

[0062] A highly efficient gas nitriding method, which differs from Example 1 in that:

[0063] Place the 8407 mold steel in a nitriding apparatus.

[0064] Comparative Example 1

[0065] A highly efficient gas nitriding method, which differs from Example 1 in that:

[0066] S1. Low-temperature diffusion nitriding: The nitriding temperature is 540℃, the N2 volume concentration accounts for 25% of the total concentration of the nitriding gas source, and the nitriding time is 50h;

[0067] Steps S2 and S3 are not performed, and the nitriding process is not repeated after step S1 is completed.

[0068] Comparative Example 2

[0069] A highly efficient gas nitriding method, which differs from Example 1 in that:

[0070] S1. Low-temperature diffusion nitriding: nitriding temperature 440℃, N2 volume concentration accounting for 39% of the total concentration of the nitriding gas source, nitriding time 2h;

[0071] S2. Medium-temperature nitriding: nitriding temperature 520℃, N2 volume concentration accounting for 45% of the total concentration of the nitriding gas source, nitriding time 0.5h;

[0072] S3. High-temperature denitrification and nitriding: Nitriding temperature 580℃, N2 volume concentration accounting for 55% of the total concentration of nitriding gas source, nitriding time 1h.

[0073] Comparative Example 3

[0074] A highly efficient gas nitriding method, which differs from Example 1 in that:

[0075] S1. Low-temperature diffusion nitriding: Nitriding temperature 540℃, N2 volume concentration is controlled at 65% of the total concentration of nitriding gas source, and nitriding time is 3h;

[0076] S2. Medium-temperature nitriding: Nitriding temperature 590℃, N2 volume concentration is controlled at 15% of the total concentration of nitriding gas source, nitriding time 4h;

[0077] S3. High-temperature denitrification and nitriding: Nitriding temperature 660℃, N2 volume concentration controlled at 55% of the total concentration of nitriding gas source, nitriding time 2h.

[0078] Comparative Example 4

[0079] A highly efficient gas nitriding method, which differs from Example 4 in that:

[0080] S1. Low-temperature diffusion nitriding: Nitriding time is 4 hours;

[0081] S2. Medium-temperature nitriding: Nitriding time is 2 hours;

[0082] S3. High-temperature denitrification and nitriding: Nitriding time is 4 hours.

[0083] After nitriding is completed according to steps S1 to S3, the cycle is not repeated.

[0084] Performance testing

[0085] Nitriding layer thickness test: The cross-sectional microstructure of the nitriding layer was observed using a scanning electron microscope (SEM), and the thickness of the nitriding layer was measured.

[0086] Nitriding layer hardness test: A microhardness tester was used with a test load of 50g to test the hardness of nitriding layers with different processes.

[0087] Wear resistance test: The wear rate is used to characterize the wear resistance of the nitrided layer on the metal surface. The lower the wear rate, the higher the wear resistance. The wear resistance test is carried out using a room temperature tribometer. WC balls are used as the wear pair. The friction time is 1 hour and the grinding ball speed is 400 rpm.

[0088] Specific test results are shown in Table 1 and... Figures 1-3 .

[0089] Table 1 Performance data for examples and comparative examples

[0090]

[0091] As can be seen from Table 1, the nitriding layer on the metal surface obtained by using the high-efficiency gas nitriding method provided by the present invention contains only a nitrogen diffusion layer and does not contain a metal-nitrogen compound layer. Data from Examples 1-4 show that when the nitriding temperatures in steps S1-S3 of the nitriding method provided by the present invention are preferably 480-520℃, 550-570℃, and 590-620℃, respectively, and the nitriding time and N2 volume concentration relative to the total concentration of the nitriding gas source are also within the preferred ranges, the resulting nitrided metal surface layer exhibits superior comprehensive performance in terms of hardness, thickness, and wear resistance. When the nitriding temperature in each step S1 to S3 is lower than the preferred range (Example 3), the thickness of the nitrogen diffusion layer obtained in step S1 is smaller, and therefore the final thickness of the nitrided layer on the metal surface is also smaller. When the nitriding temperature in each step S1 to S3 is higher (Example 4), the excessively high temperature in step S2 easily causes nitrogen atoms that should form compounds to agglomerate at defects such as grain boundaries, evolving into pores. Furthermore, the excessively high temperature in step S3 easily leads to excessive decomposition of the compound layer, also forming pores in the nitrided layer on the metal surface, reducing the alloy's hardness and wear resistance. Therefore, although the nitrided layer on the metal surface obtained in Example 4 is thicker, its hardness is lower, and its wear resistance is also reduced. The results from Example 5 show that the nitriding method provided by this invention is not only applicable to H13 steel but also to 8407 mold steel. The results from Example 4 and Comparative Example 4 show that, under the same total nitriding time, nitriding temperature, and N2 volume concentration relative to the total concentration of the nitriding gas source, forming a cycle of low-temperature diffusion nitriding, medium-temperature nitriding, and high-temperature denitriding is more conducive to increasing the thickness of the nitrided layer on the metal surface. Therefore, the nitriding method provided in Example 4 can obtain a thicker nitrided layer on the metal surface in a shorter time. The data from Comparative Example 1 show that conventional nitriding methods in the art cannot obtain a nitrided layer on the metal surface with excellent comprehensive performance in terms of thickness, hardness, and wear resistance. Although the thickness is relatively high, the nitrided layer on the metal surface contains a compound layer, resulting in poor wear resistance. The data from Comparative Examples 2 and 3 show that when the nitriding temperature, N2 volume concentration as a percentage of the total nitriding gas source, and nitriding time in each step S1 to S3 are higher or lower, it cannot be guaranteed that the nitrided layer on the metal surface contains only a nitrogen diffusion layer. Therefore, the wear resistance of the nitrided layer decreases. At the same time, in Comparative Example 2, because the nitriding temperature in each step is too low, the process of nitrogen diffusion layer formation, compound layer formation, and compound layer decomposition cannot be fully carried out. Therefore, the thickness of the nitrided layer on the metal surface decreases, and the hardness also decreases.

[0092] Figure 1 This is a SEM image of the nitrided metal surface layer obtained in Example 1 of the present invention. Figure 2 This is a SEM image of the nitrided metal surface layer prepared in Comparative Example 1 of this invention. From... Figures 1-2It can be seen that the thickness of the nitrided layer on the metal surface obtained in Example 1 of the present invention is greater.

[0093] Figure 3 This is a flowchart of the efficient nitriding method provided by the present invention.

[0094] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A highly efficient gas nitriding method, characterized in that, Includes the following steps: S1. Low-temperature diffusion nitriding: The metal substrate is placed in a gas nitriding device, a nitriding gas source is introduced, the nitriding temperature is controlled at 450-530℃, the N2 volume concentration accounts for 40-60% of the total concentration of the nitriding gas source, and the nitriding time is more than 1 hour. S2. Medium-temperature nitriding: The nitriding temperature is controlled at 530-580℃, the N2 volume concentration is less than 40% of the total concentration of the nitriding gas source, and the nitriding time is more than 1 hour; S3. High-temperature denitrification and nitriding: The nitriding temperature is controlled at 590-650℃, the N2 volume concentration accounts for 60-100% of the total concentration of the nitriding gas source, and the nitriding time is more than 0.5h; The low-temperature diffusion nitriding, medium-temperature nitriding, and high-temperature denitriding nitriding form a cycle, and the cycle is ≥2.

2. The high-efficiency gas nitriding method as described in claim 1, characterized in that, The nitriding temperature in step S1 is 480–520°C.

3. The high-efficiency gas nitriding method as described in claim 2, characterized in that, The nitriding temperature in step S1 is 500–520°C.

4. The high-efficiency gas nitriding method as described in claim 1, characterized in that, The nitriding time in step S1 is 2 to 4 hours.

5. The high-efficiency gas nitriding method as described in claim 1, characterized in that, The nitriding temperature in step S2 is 550–570°C.

6. The high-efficiency gas nitriding method as described in claim 1, characterized in that, In step S2, the N2 volume concentration accounts for 25-35% of the total concentration of the nitriding gas source.

7. The high-efficiency gas nitriding method as described in claim 1, characterized in that, The nitriding time in step S2 is 2 to 5 hours.

8. The high-efficiency gas nitriding method as described in claim 1, characterized in that, The nitriding temperature in step S3 is 590–620°C.

9. The high-efficiency gas nitriding method as described in claim 1, characterized in that, In step S3, the N2 volume concentration accounts for 70-80% of the total concentration of the nitriding gas source.

10. The high-efficiency gas nitriding method as described in claim 1, characterized in that, The nitriding time in step S3 is 1 to 3 hours.

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