Method for surface nitriding hardening of high-nitrogen martensitic stainless steel and high-nitrogen martensitic stainless steel

Abstract

The application discloses a high-nitrogen martensitic stainless steel surface nitriding superhardening method and high-nitrogen martensitic stainless steel and belongs to the technical field of stainless steel, and solves one of problems that high-nitrogen martensitic stainless steel cannot meet the requirements of high wear resistance and high-temperature resistance in the prior art. The high-nitrogen martensitic stainless steel surface nitriding superhardening method comprises the following steps: step 1, spheroidizing treatment and quenching and tempering treatment; step 2, long-time surface nitriding treatment, and the nitriding time is more than 25 hours; and step 3, organization stabilization tempering. The high-nitrogen martensitic stainless steel prepared by the method has high hardness, good wear resistance and good high-temperature resistance.

Description

Technical Field

[0001] This invention relates to the field of stainless steel technology, and in particular to a method for nitriding and super-hardening of the surface of high-nitrogen martensitic stainless steel and the high-nitrogen martensitic stainless steel itself. Background Technology

[0002] High-nitrogen martensitic stainless steel possesses excellent corrosion resistance, temperature resistance, and fatigue resistance, making it promising for applications in bearings, gears, lead screws, and guide rails. Currently, the surface hardness of high-nitrogen martensitic stainless steel G30Cr15Mo1N, despite its excellent corrosion resistance, is no higher than 60 HRC, and its hardness at 350℃ is only 56 HRC, which still cannot meet the requirements for high wear resistance, fatigue resistance, and high-temperature resistance. Therefore, improving the wear resistance, fatigue resistance, and high-temperature resistance of high-nitrogen martensitic stainless steel has become an urgent problem to be solved. Summary of the Invention

[0003] In view of the above, the present invention aims to provide a method for nitriding and super-hardening of high-nitrogen martensitic stainless steel surface and high-nitrogen martensitic stainless steel, in order to solve the problem that existing high-nitrogen martensitic stainless steel still cannot meet the requirements of high wear resistance and high temperature resistance.

[0004] The objective of this invention is mainly achieved through the following technical solutions:

[0005] On one hand, the present invention provides a method for nitriding and superhardening of high-nitrogen martensitic stainless steel surfaces, comprising:

[0006] Step 1: Spheroidizing treatment and quenching and tempering treatment;

[0007] Step 2: Long-term surface nitriding treatment, with a nitriding time of more than 25 hours;

[0008] Step 3: Stabilization tempering.

[0009] Furthermore, in step 1, the spheroidizing process includes:

[0010] Step 101: Place the high-nitrogen martensitic stainless steel bar into a heating furnace and heat it to 860-880℃, holding it at that temperature for 3.5-4.5 hours.

[0011] Step 102: Cool down to 725-735℃ and maintain the temperature for 3.5-4.5 hours;

[0012] Step 103: Cool down to below 550℃ and then air cool.

[0013] Furthermore, in step 102, the cooling rate is controlled to be 28–32 °C / h.

[0014] Furthermore, in step 103, the cooling rate is controlled to be 28–32 °C / h.

[0015] Furthermore, in step 103, the microstructure of the bar obtained after air cooling is ferrite + uniformly distributed spherical carbides.

[0016] Furthermore, in step 1, the quenching and tempering process includes:

[0017] Step 104: After the bar material treated in step 103 is kept at 1025-1035℃ for 1-2 hours, it is then oil-quenched to room temperature.

[0018] Step 105: Cold treat the bar at -70 to -75°C for 1 to 3 hours;

[0019] Step 106: Keep the bar at 140-160℃ for 3-5 hours.

[0020] Furthermore, the microstructure of the bar obtained after step 106 is a high-nitrogen martensite microstructure with fine primary austenite and uniformly distributed carbides.

[0021] Furthermore, in step 2, the long-term surface nitriding treatment includes: nitriding treatment at 530~560℃ for 20~30h.

[0022] Furthermore, in step 3, the tissue stabilization tempering step includes: holding at 500-650℃ for 2-4 hours.

[0023] The present invention also provides a high-nitrogen martensitic stainless steel, which is prepared by the above method.

[0024] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0025] The high-nitrogen martensitic stainless steel surface nitriding superhardening method of the present invention obtains a refined and homogenized initial microstructure by spheroidizing treatment and quenching and tempering treatment, and then performs long-term surface nitriding treatment combined with final microstructure stabilization tempering. The resulting high-nitrogen martensitic stainless steel has a high surface hardness of ≥62HRC, for example 62~70HRC, with good wear resistance and fatigue resistance.

[0026] The precise control of the sequence of each step and process parameter in the high-nitrogen martensitic stainless steel surface nitriding and superhardening method of the present invention ensures that a refined and homogenized initial microstructure is obtained first, laying a good microstructure preparation for the surface nitriding of high-nitrogen martensitic stainless steel. This ensures that the thickness of the final nitrided layer of high-nitrogen martensitic stainless steel is 0.1-0.2 mm, and that the surface hardness of the high-nitrogen martensitic stainless steel bar is ≥62 HRC, for example, 62-70 HRC. It has high hardness, good wear resistance, and good fatigue resistance. After tempering at 500-650℃, the hardness of the high-nitrogen martensitic stainless steel of the present invention can still be maintained above 62 HRC, demonstrating good high-temperature resistance.

[0027] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of what is particularly pointed out in the written description, claims, and drawings. Attached Figure Description

[0028] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0029] Figure 1 This is a microstructure diagram of the air-cooled bar stock from Example 1;

[0030] Figure 2 This is a microstructure diagram of the bar stock after quenching and tempering in Example 1. Detailed Implementation

[0031] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of the present invention and, together with the embodiments of the present invention, serve to illustrate the principles of the present invention.

[0032] This invention provides a method for nitriding and super-hardening of high-nitrogen martensitic stainless steel surfaces, comprising:

[0033] Step 1: Spheroidizing treatment and quenching and tempering treatment to obtain a refined and homogenized initial microstructure;

[0034] Step 2: Long-term surface nitriding treatment, with a nitriding time of more than 25 hours;

[0035] Step 3: Stabilization tempering.

[0036] Specifically, the composition of the above-mentioned high-nitrogen martensitic stainless steel, by mass percentage, is as follows: C: 0.25%~0.35%, Si≤1.00%, Mn≤1.00%, Cr: 14.0%~16.0%, S: ≤0.01%, P: ≤0.02%, Ni≤0.3%, Mo: 0.85%~1.10%, N: 0.30%~0.50%, with the balance being Fe and unavoidable trace impurities.

[0037] Specifically, in step 1 above, the spheroidizing process includes:

[0038] Step 101: Place the high-nitrogen martensitic stainless steel bar into a heating furnace and heat it to 860-880℃, holding it at that temperature for 3.5-4.5 hours.

[0039] Step 102: Cool to 725-735℃ at a cooling rate of 28-32℃ / h and hold for 3.5-4.5h;

[0040] Step 103: Cool down to below 550℃ at a cooling rate of 28-32℃ / h, then remove from the furnace and air cool.

[0041] Specifically, in step 101 above, the high-nitrogen martensitic stainless steel bar is smelted by pressurized electroslag process, and then subjected to high-temperature diffusion, hot forging or hot rolling, and finally heat softening or spheroidizing treatment to form a bar with a diameter of 15 to 170 mm.

[0042] Specifically, in step 101 above, considering that excessively high temperatures can easily lead to the formation of lamellar carbides and twinned carbides upon cooling, and excessively long holding times can result in excessively low annealing hardness, while excessively low temperatures and short holding times cannot guarantee the spheroidization effect, the heating is controlled at 860–880℃ and held for 3.5–4.5 hours.

[0043] Specifically, in step 102 above, an excessively high cooling rate will result in overly fine carbides and the appearance of flaky carbides; an excessively low cooling rate will result in coarse carbides and low annealing hardness. Therefore, the cooling rate should be controlled at 28–32 °C / h.

[0044] Specifically, step 102 above serves to promote carbide aggregation and growth, ferrite recovery and recrystallization, and stress relief. Considering that excessively high temperatures lead to phase transformation during cooling, preventing the formation of spheroidized structures; excessively long holding times result in overly coarse carbides with insufficient hardness; and excessively low temperatures and short holding times are detrimental to carbide aggregation, growth, and recrystallization, thus hindering spheroidization, the holding temperature is controlled at 725–735℃ for 3.5–4.5 hours.

[0045] Specifically, in step 103 above, an excessively high cooling rate leads to excessive stress, while an insufficient cooling rate prevents complete spheroidization. Therefore, the cooling rate is controlled to be 28–32 °C / h.

[0046] Specifically, in step 103 above, cooling to below 550°C and then air-cooling the product is because recrystallization transformation no longer occurs at this temperature.

[0047] Specifically, in step 103 above, the microstructure of the rod obtained after air cooling is ferrite + uniformly distributed spherical carbides. The spherical carbides are evenly distributed, and most (mostly meaning more than 95%) are around 1 μm in size (e.g., 0.3–1.5 μm). Under a metallographic microscope, the carbides appear as small particles with black edges and gray cores. Based on observations across the entire field of view, the largest diameter carbide does not exceed 5 μm.

[0048] Specifically, in step 1 above, the quenching and tempering process includes:

[0049] Step 104: After the bar material treated in step 103 is kept at 1025-1035℃ for 1-2 hours, it is then oil-quenched to room temperature.

[0050] Step 105: Cold treat the bar at -70 to -75°C for 1 to 3 hours;

[0051] Step 106: Keep the bar at 140-160℃ for 3-5 hours.

[0052] Specifically, in step 104 above, considering that excessively high temperature leads to excessively large grain size and excessive retained austenite; excessively long holding time leads to excessively large grain size and excessive retained austenite; excessively low temperature leads to excessively low hardness after cold treatment and tempering; and excessively short holding time easily leads to excessively low hardness after cold treatment and tempering, the holding time is controlled at 1025-1035℃ for 1-2 hours.

[0053] Specifically, the microstructure of the bar obtained after step 106 is a high-nitrogen martensite microstructure with fine primary austenite and uniformly distributed carbides. For example, the average grain size of the primary austenite is about 10 μm (e.g., the average grain size of the primary austenite is 8–12 μm), and the size of most (mostly referring to more than 95%) carbides is between 1 and 2 μm, with the largest diameter carbide not exceeding 5 μm. This fine primary austenite and uniformly distributed high-nitrogen martensite microstructure provides a good microstructure preparation for surface nitriding of high-nitrogen martensitic stainless steel.

[0054] Specifically, in step 2 above, considering that the surface hardness generally decreases with increasing nitriding temperature, while the nitriding layer depth continuously increases with rising nitriding temperature; excessively high nitriding temperatures easily promote the formation of vein-like structures, causing tissue growth, and simultaneously resulting in a loose nitrided layer and increased brittleness; excessively long holding times easily lead to over-nitriding, making the material brittle; excessively low temperatures and excessively short holding times easily lead to insufficient nitriding layer depth. Therefore, the steps for controlling long-term surface nitriding treatment include: nitriding treatment at 530–560℃ for 20–30 hours.

[0055] Specifically, in step 2 above, the depth of the nitrided layer is 0.1 to 0.2 mm.

[0056] Specifically, in step 3 above, considering that excessively high tempering temperatures can lead to changes in the infiltrated layer and core structure, resulting in a significant decrease in the hardness of both, the steps for controlling the stabilization of the structure during tempering include: holding at 500–650℃ for 2–4 hours to improve the stability of the hardened layer.

[0057] Specifically, in step 3 above, the depth of the nitrided layer in the high-nitrogen martensitic stainless steel bar after microstructure stabilization and tempering is 0.1–0.2 mm. The surface microstructure is nitride microstructure, and the core microstructure is tempered troostite.

[0058] This invention also provides a high-nitrogen martensitic stainless steel, prepared by the above method. The surface microstructure of the high-nitrogen martensitic stainless steel bar is a nitride structure, and the core microstructure is tempered troostite. The surface hardness is ≥62HRC, for example, 62-70HRC. It has high hardness and good wear resistance. After tempering at 500-650℃, the hardness of the high-nitrogen martensitic stainless steel of this invention can still be maintained above 62HRC, and it has good high-temperature resistance.

[0059] This invention also provides an application of a nitriding superhardening method for the surface of high-nitrogen martensitic stainless steel, which can be used in bearings, gears, lead screws and guide rails.

[0060] Compared with the prior art, the high-nitrogen martensitic stainless steel surface nitriding superhardening method of the present invention obtains a refined and homogenized initial microstructure by spheroidizing treatment and quenching and tempering treatment, and then performs long-term surface nitriding treatment combined with final microstructure stabilization tempering. The resulting high-nitrogen martensitic stainless steel has a high surface hardness of ≥62HRC, for example 62~70HRC, with high hardness, good wear resistance, and good fatigue resistance.

[0061] The precise control of the sequence of each step and process parameter in the high-nitrogen martensitic stainless steel surface nitriding and superhardening method of the present invention ensures that a refined and homogenized initial microstructure is obtained first, laying a good microstructure preparation for the surface nitriding of high-nitrogen martensitic stainless steel. This ensures that the thickness of the final nitrided layer of high-nitrogen martensitic stainless steel is 0.1-0.2 mm, and that the surface hardness of the high-nitrogen martensitic stainless steel bar is ≥62 HRC, for example, 62-70 HRC. It has high hardness, good wear resistance, and good fatigue resistance. After tempering at 500-650℃, the hardness of the high-nitrogen martensitic stainless steel in the embodiments of the present invention can still be maintained above 62 HRC, demonstrating good high-temperature resistance.

[0062] The advantages of precise control of process parameters in the nitriding and superhardening method for high-nitrogen martensitic stainless steel surfaces of the present invention are demonstrated below with specific embodiments and comparative examples.

[0063] Examples 1-3

[0064] The present invention provides a method for nitriding and super-hardening of high-nitrogen martensitic stainless steel surface and the high-nitrogen martensitic stainless steel. The composition of the high-nitrogen martensitic stainless steel in the embodiment is as follows by mass percentage: C: 0.25%~0.35%, Si≤1.00%, Mn≤1.00%, Cr: 14.0%~16.0%, S: ≤0.01%, P: ≤0.02%, Ni≤0.3%, Mo: 0.85%~1.10%, N: 0.30%~0.50%, with the balance being Fe and unavoidable trace impurities.

[0065] Example 1 describes a nitriding super-hardening method for high-nitrogen martensitic stainless steel surfaces, which includes:

[0066] Step 101: Place the high-nitrogen martensitic stainless steel bar with a diameter of Φ30mm into the heating furnace and heat it to 870℃ and hold it for 4 hours;

[0067] Step 102: Cool down to 730℃ at a cooling rate of 30℃ / h and hold for 4 hours;

[0068] Step 103: Cool the material to below 550℃ at a cooling rate of 30℃ / h, then remove it from the furnace and air-cool it; the microstructure of the resulting bar after air cooling is as follows. Figure 1 As shown, the microstructure consists of ferrite and uniformly distributed spherical carbides. The spherical carbides are evenly distributed, and most (more than 95%) are approximately 1 μm in size (e.g., 0.3–1.5 μm). Under a metallographic microscope, the carbides appear as small particles with black borders and gray cores. Based on observations across the entire field of view, the largest diameter carbide does not exceed 5 μm.

[0069] Step 104: After the bar material treated in step 103 is kept at 1030℃ for 1 hour, it is then oil-quenched to room temperature.

[0070] Step 105: Cold treat the bar at -73℃ for 2 hours;

[0071] Step 106: Hold the bar at 150℃ for 4 hours. The resulting bar has the following microstructure. Figure 2 As shown, the microstructure consists of fine primary austenite and uniformly distributed high-nitrogen martensite. For example, the average grain size of the primary austenite is about 10 μm (e.g., the average grain size of the primary austenite is 8 to 12 μm), and the size of most (mostly referring to more than 95%) carbides is about 1 to 2 μm, with the largest diameter carbide not exceeding 5 μm.

[0072] Step 2: Nitriding treatment at 550℃ for 30 hours; the thickness of the nitrided layer is 0.2 mm;

[0073] Step 3, Microstructure Stabilization Tempering: After holding at 500℃ for 2.5h, the thickness of the nitrided layer of the high-nitrogen martensitic stainless steel bar after microstructure stabilization tempering is 0.2mm. The surface microstructure is nitride microstructure, and the core microstructure is tempered troostite.

[0074] The high-nitrogen martensitic stainless steel bar prepared by the method in this embodiment has a surface microstructure of nitrides and a core microstructure of tempered troostite. The surface hardness is 70 HRC.

[0075] Example 2

[0076] The composition of the high-nitrogen martensitic stainless steel in this embodiment is the same as that in Example 1, and will not be repeated here.

[0077] The nitriding and super-hardening method for high-nitrogen martensitic stainless steel surface in this embodiment includes:

[0078] Step 101: Place the high-nitrogen martensitic stainless steel bar with a diameter of Φ20mm into the heating furnace and heat it to 870℃ and hold it for 4 hours;

[0079] Step 102: Cool down to 725℃ at a cooling rate of 29℃ / h and hold for 4.5h;

[0080] Step 103: Cool the material to below 550℃ at a cooling rate of 29℃ / h, then remove it from the furnace and air cool it. The microstructure of the bar obtained after air cooling is ferrite + uniformly distributed spherical carbides. The spherical carbides are evenly distributed, and most (mostly referring to more than 95%) are about 1μm in size (e.g., 0.4~1.4μm). According to observations across the entire field of view, the size of the largest diameter carbide does not exceed 5μm.

[0081] Step 104: After the bar material treated in step 103 is kept at 1025℃ for 1.5h, it is then oil-quenched to room temperature.

[0082] Step 105: Cold treat the bar at -73℃ for 2 hours;

[0083] Step 106: Hold the bar at 140℃ for 5 hours. The resulting bar has a microstructure of fine primary austenite and high-nitrogen martensite with uniformly distributed carbides. For example, the average grain size of the primary austenite is about 10 μm (e.g., the average grain size of the primary austenite is 8 to 11 μm), and the size of most (mostly refers to more than 95%) carbides is about 1 to 2 μm, with the largest diameter carbide not exceeding 5 μm.

[0084] Step 2: Nitriding treatment at 550℃ for 30 hours; nitrided layer thickness 0.2 mm;

[0085] Step 3, Microstructure Stabilization Tempering: After holding at 600℃ for 2 hours, the thickness of the nitrided layer of the high-nitrogen martensitic stainless steel bar after microstructure stabilization tempering is 0.2 mm. The surface microstructure is nitride, and the core microstructure is tempered troostite.

[0086] The high-nitrogen martensitic stainless steel bar prepared by the method in this embodiment has a surface microstructure of nitrides and a core microstructure of tempered troostite, with a surface hardness of 68 HRC.

[0087] Example 3 describes a nitriding super-hardening method for high-nitrogen martensitic stainless steel surfaces, which includes:

[0088] Step 101: Place the high-nitrogen martensitic stainless steel bar with a diameter of Φ30mm into the heating furnace and heat it to 870℃ and hold it for 4 hours;

[0089] Step 102: Cool down to 730℃ at a cooling rate of 30℃ / h and hold for 4 hours;

[0090] Step 103: Cool the material to below 550℃ at a cooling rate of 30℃ / h, then remove it from the furnace and air-cool it; the microstructure of the resulting bar after air cooling is as follows. Figure 1 As shown, the microstructure consists of ferrite and uniformly distributed spherical carbides. The spherical carbides are evenly distributed, and most (more than 95%) are approximately 1 μm in size (e.g., 0.3–1.5 μm). Under a metallographic microscope, the carbides appear as small particles with black borders and gray cores. Based on observations across the entire field of view, the largest diameter carbide does not exceed 5 μm.

[0091] Step 104: After the bar material treated in step 103 is kept at 1030℃ for 1 hour, it is then oil-quenched to room temperature.

[0092] Step 105: Cold treat the bar at -73℃ for 2 hours;

[0093] Step 106: Hold the bar at 150℃ for 4 hours. The resulting bar has a microstructure of fine primary austenite and high-nitrogen martensite with uniformly distributed carbides. For example, the average grain size of the primary austenite is about 10 μm (e.g., the average grain size of the primary austenite is 8 to 12 μm), and the size of most (mostly refers to more than 95%) carbides is about 1 to 2 μm, with the largest diameter carbide not exceeding 5 μm.

[0094] Step 2: Nitriding treatment at 550℃ for 30 hours; the thickness of the nitrided layer is 0.2 mm;

[0095] Step 3, Microstructure Stabilization Tempering: After holding at 650℃ for 2.5h, the thickness of the nitrided layer of the high-nitrogen martensitic stainless steel bar after microstructure stabilization tempering is 0.2mm. The surface microstructure is nitride microstructure, and the core microstructure is tempered troostite.

[0096] The high-nitrogen martensitic stainless steel bar prepared by the method in this embodiment has a surface microstructure of nitrides and a core microstructure of tempered troostite. The surface hardness is 62 HRC.

[0097] In summary, the surface hardness of the high-nitrogen martensitic stainless steel in the embodiments of the present invention all reaches above 62HRC, exhibiting high hardness and good wear resistance; after tempering at 500-650℃, the hardness of the high-nitrogen martensitic stainless steel in the embodiments of the present invention can still be maintained above 62HRC, demonstrating good high-temperature resistance.

[0098] The inventors conducted extensive experimental research during the research process, and some poorly performing solutions are now presented as comparative examples.

[0099] Comparative Example 1

[0100] This comparative example provides a nitriding hardening method for the surface of high-nitrogen martensitic stainless steel. Its composition is the same as in Example 1 and will not be repeated here. The method includes:

[0101] Step 1 is the same as in Example 1;

[0102] Step 2: Nitriding at 520℃ for 20 hours.

[0103] The high-nitrogen martensitic stainless steel bars prepared by the method in this comparative example have almost no nitrided layer on their surface.

[0104] Comparative Example 2

[0105] This comparative example provides a nitriding hardening method for the surface of high-nitrogen martensitic stainless steel. Its composition is the same as in Example 1 and will not be repeated here. The method includes:

[0106] Step 1 is the same as in Example 1;

[0107] Step 2: Nitriding at 570℃ for 20 hours, resulting in a nitrided layer depth of 0.1m.

[0108] The high-nitrogen martensitic stainless steel bars prepared by the method in this comparative example show surface cracks during surface hardness testing, indicating that their nitrided layer is brittle.

[0109] Comparative Example 3

[0110] This comparative example provides high-nitrogen martensitic stainless steel bars, which are made of the same material as in Example 1. This comparative example does not subject the high-nitrogen martensitic stainless steel bars to nitriding treatment; instead, it directly studies their hardness after tempering at 500–650°C. The results are as follows:

[0111] Original hardness: 61 HRC, hardness after tempering at 500℃: 55 HRC, hardness after tempering at 600℃: 43 HRC, hardness after tempering at 650℃: 35 HRC.

[0112] In summary, the surface hardness of the high-nitrogen martensitic stainless steel in the embodiments of the present invention all reaches above 62HRC, exhibiting high hardness and good wear resistance; after tempering at 500-650℃, the hardness of the high-nitrogen martensitic stainless steel in the embodiments of the present invention can still be maintained above 62HRC, demonstrating good high-temperature resistance.

[0113] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for nitriding and super-hardening the surface of high-nitrogen martensitic stainless steel, characterized in that, include: Step 1: Spheroidizing treatment and quenching and tempering treatment; Step 2: Long-term surface nitriding treatment, with parameters of 550℃×30h; Step 3: Stabilization tempering; The composition of the high-nitrogen martensitic stainless steel, by mass percentage, is as follows: C: 0.25%~0.35%, Si≤1.00%, Mn≤1.00%, Cr: 14.0%~16.0%, S: ≤0.01%, P: ≤0.02%, Ni≤0.3%, Mo: 0.85%~1.10%, N: 0.30%~0.50%, with the balance being Fe and unavoidable trace impurities; In step 1, the spheroidizing process includes: Step 101: Place the high-nitrogen martensitic stainless steel bar into a heating furnace and heat it to 860~880℃, then hold it for 3.5~4.5 hours. Step 102: Cool down to 725~735℃ and maintain the temperature for 3.5~4.5 hours; Step 103: Cool down to below 550℃ and remove from the furnace for air cooling; In step 102, the cooling rate is controlled to be 28~32℃ / h; In step 103, the cooling rate is controlled to be 28~32℃ / h; In step 103, the microstructure of the bar obtained after air cooling is ferrite + uniformly distributed spherical carbides; more than 95% of the spherical carbides have a size of 0.3~1.5μm. In step 1, the quenching and tempering process includes: Step 104: After the bar material treated in step 103 is kept at 1025~1035℃ for 1~2 hours, it is then oil-quenched to room temperature. Step 105: Cold treat the bar at -70~-75℃ for 1~3 hours; Step 106: Keep the bar at 140~160℃ for 3~5 hours; The microstructure of the bar obtained after step 106 is a high-nitrogen martensite microstructure with fine primary austenite and uniformly distributed carbides; the average grain size of the primary austenite is 8~12μm, and the size of the largest diameter carbide does not exceed 5μm; In step 3, the depth of the nitrided layer of the high-nitrogen martensitic stainless steel bar after microstructure stabilization and tempering is 0.1~0.2mm, the surface microstructure is nitride microstructure, and the core microstructure is tempered troostite. The high-nitrogen martensitic stainless steel has good high-temperature resistance.

2. The method for nitriding and super-hardening the surface of high-nitrogen martensitic stainless steel according to claim 1, characterized in that, In step 102, the cooling rate is controlled to be 28~30℃ / h.

3. The method for nitriding and super-hardening the surface of high-nitrogen martensitic stainless steel according to claim 1, characterized in that, In step 103, the cooling rate is controlled to be 28~30℃ / h.

4. The method for nitriding and super-hardening the surface of high-nitrogen martensitic stainless steel according to any one of claims 1 to 3, characterized in that, In step 3, the tissue stabilization tempering step includes: holding at 500~650℃ for 2~4 hours.

5. A high-nitrogen martensitic stainless steel, characterized in that, The high-nitrogen martensitic stainless steel is prepared by the method described in any one of claims 1 to 4.

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