A method of cryogenic ion nitriding of AerMet 100 steel

Abstract

The application discloses a method for low-temperature ion nitriding of AerMet100 steel, and comprises the following steps: a) preheating AerMet100 steel to obtain preheated AerMet100 steel; b) heat treating the preheated AerMet100 steel to obtain an AerMet100 steel sample, wherein the heat treatment comprises solid solution treatment, cryogenic treatment and tempering treatment; and c) performing low-temperature ion nitriding treatment on the AerMet100 steel sample to obtain AerMet100 steel containing a nitriding layer. The method can complete ion nitriding treatment at a lower temperature, avoids deformation of the AerMet100 steel during ion nitriding treatment, ensures that the hardness of the AerMet100 steel is not reduced while forming a nitriding layer on the surface, and improves the wear resistance and fatigue resistance of the AerMet100 steel.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology for metallic materials, and in particular to a method for low-temperature ion nitriding of AerMet100 steel. Background Technology

[0002] AerMet100 is a high-Co-Ni secondary hardening ultra-high-strength steel. After appropriate heat treatment, its tensile strength can reach over 1930 MPa, and its elongation can reach over 14%. In addition to its ultra-high strength, AerMet100 also possesses high elastic modulus, high rigidity modulus, and high toughness, making it a common material for key load-bearing structural components such as aircraft landing gear, brake hook anchors, and fasteners. With the development and application of AerMet100, it has gradually become the preferred material for key transmission components such as aero-engine bearings and gears. However, when used as transmission components or operating in high-temperature environments, higher requirements are placed on its surface properties. Therefore, surface hardening treatment is necessary for AerMet100 steel to improve its fatigue resistance and surface wear resistance.

[0003] Currently, various surface strengthening processes have been applied to high-Co-Ni alloy materials to improve their surface hardness and fatigue resistance, such as laser cladding, plasma rare-earth nitrocarburizing, low-temperature ion nitrocarburizing, and low-temperature ion nitriding. According to relevant research, these processes all harden the surface of AerMet100 materials and significantly improve their wear resistance. However, the improvement in fatigue resistance strongly depends on the formation of residual compressive stress in the surface and subsurface layers. Furthermore, surface strengthening processes typically employ nitriding, shot peening, or ultrasonic peening to meet these requirements.

[0004] However, AerMet100 material is very sensitive to hot working processes. Although ion nitriding is suitable for surface strengthening of high alloy steel, when the temperature of ion nitriding is too high or too low, or the processing time is too long or too short, the matrix of AerMet100 material will continue to precipitate and grow due to the dispersion strengthening phase, resulting in a decrease in the overall performance of the material. It cannot reach the performance before nitriding, especially the hardness and wear resistance.

[0005] Therefore, providing a low-temperature ion nitriding method that can form a nitrided layer on the surface of AerMet100 steel, thereby improving the material's wear resistance without reducing its hardness, is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides a low-temperature ion nitriding method for AerMet100 steel, which can complete the ion nitriding treatment at a lower temperature, avoid deformation of AerMet100 steel during the ion nitriding process, and at the same time ensure that the matrix hardness of AerMet100 steel is not reduced, thus exhibiting good comprehensive performance.

[0007] This invention provides a method for low-temperature ion nitriding of AerMet100 steel, comprising:

[0008] a) Preheating AerMet100 steel to obtain preheated AerMet100 steel;

[0009] b) The preheated AerMet100 steel is subjected to heat treatment to obtain an AerMet100 steel sample. The heat treatment includes solution treatment, cryogenic treatment and tempering treatment.

[0010] c) The AerMet100 steel sample was subjected to low-temperature ion nitriding treatment to obtain AerMet100 steel containing a nitrided layer.

[0011] In some specific implementations, in step a, the preheating temperature is 650°C to 900°C, the preheating holding time is 1h to 2.5h, and the preheating rate is 1°C / min to 20°C / min.

[0012] In some specific implementations, the preheating treatment is followed by a cooling treatment, with a cooling rate of 5°C / min to 20°C / min and a final temperature of 20°C to 25°C.

[0013] In some specific implementations, step a) specifically includes: heating AerMet100 steel from room temperature to 800℃ at a heating rate of 10℃ / min to 20℃ / min, holding at that temperature for 10 min to 30 min, heating from 800℃ to 900℃ at a heating rate of 5℃ / min to 10℃ / min, holding at that temperature for 1 h to 2 h; cooling from 900℃ to 750℃ at a cooling rate of 5℃ / min to 10℃ / min, then cooling from 750℃ to room temperature at a cooling rate of 10℃ / min to 20℃ / min; then heating from room temperature to 650℃ at a heating rate of 5℃ / min to 15℃ / min, holding at that temperature for 10 min to 20 min, then heating from 650℃ to 680℃ at a heating rate of 1℃ / min to 5℃ / min, holding at that temperature for 8-10 h, and after cooling, obtaining preheated AerMet100 steel.

[0014] In some specific implementations, the solution treatment temperature is 877°C to 893°C, the solution treatment holding time is 1h to 3h, and the solution treatment heating rate is 1°C / min to 20°C / min.

[0015] The cryogenic treatment temperature is -81℃ to -65℃, the cryogenic treatment holding time is 1h to 3h, and the cryogenic treatment cooling rate is 1℃ / min to 20℃ / min.

[0016] The tempering temperature is 479°C to 485°C, the holding time of the tempering is 5h to 8h, and the heating rate of the tempering is 1°C / min to 20°C / min.

[0017] In some specific implementations, the cross-sectional hardness of the AerMet100 steel sample is 53.5 HRC to 54.5 HRC.

[0018] In some specific implementations, the low-temperature ion nitriding treatment is further preceded by a sputtering treatment, the sputtering treatment time being 30 min to 60 min, the sputtering treatment voltage being -350V to -300V, the sputtering treatment being carried out under the condition of introducing hydrogen and nitrogen, the sputtering treatment pressure being 50 Pa to 100 Pa, and the flow ratio of hydrogen to nitrogen being 5:1 to 10:1.

[0019] In some specific implementations, the gas pressure of the low-temperature ion nitriding is 250 Pa to 600 Pa, the time of the low-temperature ion nitriding is 5 h to 20 h, and the voltage of the low-temperature ion nitriding treatment is -550 V to -500 V.

[0020] In some specific implementations, in step c, the AerMet100 steel sample is heated to 410℃~440℃, first depressurized to -480V~-450V, pressurized to 250Pa~600Pa, the flow ratio of hydrogen to nitrogen is reduced to 0.3:1~3:1, and then depressurized a second time to -550V~-500V;

[0021] In some specific implementations, the heating rate is 1℃ / min to 5℃ / min, the first depressurization rate is 5V / min to 10V / min, the pressure increase rate is 20Pa / min to 50Pa / min, and the second depressurization rate is 5V / min to 10V / min.

[0022] In some specific implementations, step c is preceded by grinding the AerMet100 steel sample, and the roughness of the ground AerMet100 steel sample is 0.01 μm to 0.8 μm.

[0023] This application first preheats AerMet100 steel to obtain preheated AerMet100 steel; then heat-treats the preheated AerMet100 steel to obtain an AerMet100 steel sample, the heat treatment including solution treatment, cryogenic treatment, and tempering; finally, the AerMet100 steel sample undergoes low-temperature ion nitriding to obtain AerMet100 steel with a nitrided layer. This method can complete the ion nitriding treatment at a relatively low temperature, avoiding deformation of the AerMet100 steel during the process, ensuring that the base hardness of the AerMet100 steel is not reduced while forming a nitrided layer on the surface, and improving the wear resistance and fatigue resistance of the AerMet100 steel. Attached Figure Description

[0024] Figure 1 A flowchart of the low-temperature ion nitriding method for AerMet100 steel provided in this application;

[0025] Figure 2 Metallographic image of AerMet100 ultra-high strength steel with nitrided layer provided in Example 1 of this application;

[0026] Figure 3 Metallographic image of AerMet100 ultra-high strength steel with nitrided layer provided in Example 2 of this application;

[0027] Figure 4 Metallographic image of AerMet100 ultra-high strength steel with nitrided layer provided in Example 3 of this application;

[0028] Figure 5 This is a schematic diagram showing the distribution of hardness test points of the nitrided layer in the longitudinal section of the AerMet100 ultra-high strength steel containing a nitrided layer provided in Examples 1 to 3 of this application.

[0029] Figure 6 This is a hardness trend diagram of the nitrided layer in the longitudinal section of the AerMet100 ultra-high strength steel containing a nitrided layer provided in Examples 1 to 3 of this application;

[0030] Figure 7 This is a schematic diagram showing the distribution of matrix hardness test points on the cross-section of AerMet100 ultra-high strength steel containing a nitrided layer, as provided in Examples 1 to 3 of this application.

[0031] Figure 8The residual stress trend diagrams are for the AerMet100 ultra-high strength steel with nitrided layer provided in Examples 1 to 3 of this application. Detailed Implementation

[0032] It should be understood that the expression “one or more of…” individually includes each of the objects described after the expression, as well as various different combinations of two or more of the described objects, unless otherwise understood from the context and usage. The expression “and / or” combined with three or more described objects should be understood to have the same meaning, unless otherwise understood from the context.

[0033] The terms “including,” “having,” or “containing,” including the use of their grammatical synonyms, should generally be understood as open-ended and non-restrictive, for example, not excluding other unstated elements or steps, unless otherwise specifically stated or understood from the context.

[0034] It should be understood that the order of the steps or the order in which certain actions are performed is not important as long as the invention remains operational. Furthermore, two or more steps or actions can be performed simultaneously.

[0035] The use of any and all instances or exemplary language such as “e.g.” or “including” in this document is merely intended to better illustrate the invention and is not intended to limit the scope of the invention unless the claims are made. No language in this specification should be construed as indicating that any unclaimed element is essential to the practice of the invention.

[0036] Furthermore, the numerical ranges and parameters used to define the present invention are approximate values, and the relevant values ​​in the specific embodiments have been presented as precisely as possible. However, any value inevitably contains standard deviations due to individual test methods. Therefore, unless explicitly stated otherwise, it should be understood that all ranges, quantities, values, and percentages used in this disclosure are modified with the word "approximately". Here, "approximately" generally means that the actual value is within plus or minus 10%, 5%, 1%, or 0.5% of a specific value or range.

[0037] This application provides a method for low-temperature ion nitriding of AerMet100 steel, comprising:

[0038] a) Preheating AerMet100 steel to obtain preheated AerMet100 steel;

[0039] b) The preheated AerMet100 steel is subjected to heat treatment to obtain an AerMet100 steel sample. The heat treatment includes solution treatment, cryogenic treatment and tempering treatment.

[0040] c) The AerMet100 steel sample was subjected to low-temperature ion nitriding treatment to obtain AerMet100 steel containing a nitrided layer.

[0041] This application uses AerMet100 steel as raw material, and performs preheating treatment, heat treatment, and low-temperature ion nitriding treatment to prepare AerMet100 steel with a nitrided layer. The AerMet100 steel includes, but is not limited to, AerMet100 ultra-high strength steel bars, and this application does not have any special restrictions on the selection of AerMet100 steel.

[0042] See Figure 1 , Figure 1 The flowchart of the low-temperature ion nitriding method for AerMet100 steel provided in this application is as follows: First, the AerMet100 steel is preheated to obtain preheated AerMet100 steel; then, the AerMet100 steel is heat-treated to obtain an AerMet100 steel sample; finally, the AerMet100 steel sample is subjected to low-temperature ion nitriding to obtain AerMet100 steel containing a nitrided layer.

[0043] This application first preheats AerMet100 steel to obtain preheated AerMet100 steel. In some specific implementations, the preheating temperature is 650°C to 900°C, preferably 700°C to 850°C, the preheating holding time is 1 hour to 2.5 hours, preferably 1.5 hours to 2 hours, and the preheating rate is 1°C / min to 20°C / min, preferably 5°C / min to 10°C / min. In some specific implementations, AerMet100 steel is heated from room temperature to 800℃ at a heating rate of 10℃ / min to 20℃ / min, held for 10 min to 30 min, then heated from 800℃ to 900℃ at a heating rate of 5℃ / min to 10℃ / min, and held for 1 h to 2 h. The temperature is then lowered from 900℃ to 750℃ at a cooling rate of 5℃ / min to 10℃ / min, followed by a cooling from 750℃ to room temperature at a cooling rate of 10℃ / min to 20℃ / min. Next, the temperature is raised from room temperature to 650℃ at a heating rate of 5℃ / min to 15℃ / min, held for 10 min to 20 min, then raised from 650℃ to 680℃ at a heating rate of 1℃ / min to 5℃ / min, and held for 8-10 h. After cooling, preheated AerMet100 steel is obtained.

[0044] This application involves cooling preheated AerMet100 steel to obtain cooled AerMet100 steel. In some specific implementations, the cooling rate is 5°C / min to 20°C / min, preferably 10°C / min to 15°C / min, and the final temperature of the cooling process is 20°C to 25°C, preferably 22°C to 24°C.

[0045] This application then applies solution treatment, cryogenic treatment, and tempering to the cooled AerMet100 steel to obtain AerMet100 steel samples. In some specific implementations, the solution treatment temperature is 877°C to 893°C, preferably 880°C to 890°C; the holding time is 1 hour to 3 hours, preferably 1.5 hours to 2.5 hours; and the heating rate is 1°C / min to 20°C / min, preferably 5°C / min to 10°C / min. The cryogenic treatment temperature is -81°C to -65°C, preferably -80°C to -70°C; and the holding time is 1 hour to... The cryogenic treatment is performed at a temperature of 3 hours, preferably -80°C to -70°C, with a cooling rate of 1°C / min to 20°C / min, preferably 5°C / min to 10°C / min. The tempering treatment is performed at a temperature of 479°C to 485°C, preferably 480°C to 483°C, with a holding time of 5 hours to 8 hours, preferably 5.5 hours to 7.5 hours. The tempering treatment is performed at a heating rate of 1°C / min to 20°C / min, preferably 5°C / min to 10°C / min. In some specific implementations, the cross-sectional hardness of the AerMet100 steel sample is 53.5 HRC to 54.5 HRC, which can be 53.5 HRC, 53.6 HRC, 53.7 HRC, 53.8 HRC, 53.9 HRC, 54 HRC, 54.1 HRC, 54.2 HRC, 54.3 HRC, 54.4 HRC, or 54.5 HRC.

[0046] This application then grinds the heat-treated AerMet100 steel to obtain a ground AerMet100 steel sample. In some specific implementations, the roughness of the ground AerMet100 steel sample is 0.01 μm to 0.8 μm, preferably 0.01 μm to 0.4 μm. In some specific implementations, the grinding process includes: grinding the outer surface and upper and lower planes of the AerMet100 steel sample as a whole, and wiping it clean with acetone. The roughness of the ground AerMet100 steel sample is 0.01 μm to 0.8 μm.

[0047] This application describes a sputtering process performed on polished AerMet100 steel to obtain sputtered AerMet100 steel. In some specific implementations, the sputtering time is 30 to 60 minutes, preferably 35 to 55 minutes, and the sputtering voltage is -350V to -300V, preferably -340V to -310V. In some specific implementations, the sputtering is performed under conditions of hydrogen and nitrogen gas, the gas pressure is 50 Pa to 100 Pa, preferably 60 Pa to 90 Pa, and the hydrogen to nitrogen flow ratio is 5:1 to 10:1, preferably 6:1 to 8:1.

[0048] The specific operation of the sputtering treatment is as follows: the heat-treated AerMet100 steel sample is placed on the cathode plate in the ion nitriding furnace, the furnace cover is closed and good sealing is ensured; the furnace cavity of the ion nitriding furnace is evacuated to no more than 10 Pa, and then nitrogen gas is introduced into the furnace cavity until the gas pressure in the furnace cavity rises to 0.6-0.9 bar, and then the heating power supply is turned on to heat the ion nitriding furnace; when the temperature in the ion nitriding furnace rises to 300℃ to 350℃, the vacuum is evacuated again to no more than 10 Pa, and then hydrogen and nitrogen gas are introduced into the furnace cavity simultaneously until the gas pressure in the furnace cavity rises to 50-100 Pa, and then the ion power supply is turned on; while maintaining the introduction of hydrogen and nitrogen gas, the surface of the AerMet100 steel sample is sputtered until the passivation film on the surface of the AerMet100 steel sample is removed.

[0049] This application then subjects the sputtered AerMet100 steel sample to low-temperature ion nitriding to obtain AerMet100 steel containing a nitrided layer. In some specific implementations, the gas pressure for low-temperature ion nitriding is 250 Pa to 600 Pa, preferably 300 Pa to 500 Pa; the time for low-temperature ion nitriding is 5 h to 20 h, preferably 10 h to 18 h; and the voltage for low-temperature ion nitriding is -550 V to -500 V, preferably -540 V to -520 V.

[0050] In some specific implementations, the AerMet100 steel sample is heated to 410℃~440℃, then first depressurized to -480V~-450V, and then pressurized to 250Pa~600Pa, with the hydrogen:nitrogen flow ratio reduced to 0.3:1~3:1. Then, it is depressurized a second time to -550V~-500V. The heating rate is 1℃ / min to 5℃ / min, the first depressurization rate is 5V / min to 10V / min, the pressurization rate is 20Pa / min to 50Pa / min, and the second depressurization rate is 5V / min to 10V / min. In some specific implementations, the hydrogen:nitrogen flow ratio is reduced to 1:1~2:1.

[0051] In some specific implementations, the AerMet100 steel sample is heated to 410℃~440℃, and then the pressure is first reduced to -480V~-450V. After the temperature rise and voltage reduction in the ion nitriding furnace are completed, the hydrogen to nitrogen flow ratio is reduced to 0.3:1~3:1, and the pressure is increased to 250Pa~600Pa. After the pressure increase and hydrogen to nitrogen flow ratio reduction in the ion nitriding furnace are completed, the pressure is reduced to -550V~-500V for the second time. After the temperature, voltage, pressure, and hydrogen to nitrogen flow ratio in the ion nitriding furnace all reach the designed conditions, low-temperature ion nitriding is performed. After the low-temperature ion nitriding treatment is completed, the heating power supply and ion power supply of the ion nitriding furnace are turned off, the hydrogen supply is stopped, and the nitrogen supply is maintained. Then, the blower is turned on to reduce the temperature in the furnace chamber to below 150℃, thus obtaining AerMet100 steel with a nitrided layer.

[0052] The present invention is further illustrated below with reference to the embodiments. The scope of protection of the present invention is not limited to the following embodiments.

[0053] Example 1

[0054] Cylindrical AerMet100 ultra-high strength steel bars with a diameter of 30 mm were placed in a heat treatment furnace. The temperature was increased from room temperature to 800°C at a rate of 15°C / min and held for 20 min. Then, the temperature was increased from 800°C to 900°C at a rate of 8°C / min and held for 1.5 h. The temperature was then decreased from 900°C to 750°C at a rate of 8°C / min, and then decreased from 750°C to room temperature at a rate of 15°C / min. The AerMet100 ultra-high strength steel bars were then removed. Argon gas was introduced during both the heating and cooling processes at a flow rate of 80 L / min.

[0055] The AerMet100 ultra-high strength steel bar was placed back into the heat treatment furnace and heated from room temperature to 650°C at a rate of 10°C / min, held for 15 min, then heated from 650°C to 680°C at a rate of 3°C / min, held for 9 h, and then cooled with the furnace to obtain the preheated AerMet100 ultra-high strength steel bar. Argon gas was introduced during both the heating and furnace cooling processes at a flow rate of 80 L / min.

[0056] The preheated AerMet100 ultra-high strength steel bars were placed in a vacuum furnace at 885℃ for solution treatment for 1 hour, and then oil-quenched. Next, the AerMet100 ultra-high strength steel bars were placed in a cryogenic treatment furnace at -73℃ for 1 hour, and then allowed to naturally warm to room temperature. Finally, the AerMet100 ultra-high strength steel bars were placed in an air furnace at 482℃ for tempering for 5 hours, and then air-cooled to obtain heat-treated AerMet100 ultra-high strength steel with a hardness of 54HRC, or 578HV.

[0057] AerMet100 ultra-high strength steel samples with a diameter of 30 mm and a height of 20 mm were cut from heat-treated AerMet100 ultra-high strength steel using wire cutting. The surface of the AerMet100 ultra-high strength steel sample was polished as a whole and wiped clean with an organic solvent. The roughness of the AerMet100 ultra-high strength steel sample after polishing was 0.45 μm.

[0058] An AerMet100 ultra-high strength steel sample was placed on the cathode plate inside an ion nitriding furnace. The furnace lid was closed, ensuring a good seal. The furnace chamber was evacuated to 10 Pa, and nitrogen gas was then introduced into the furnace chamber until the pressure inside the furnace chamber reached 0.8 bar. The heating power supply was then turned on to heat the ion nitriding furnace. After the temperature inside the ion nitriding furnace reached 320°C, the furnace was evacuated again to 10 Pa. Hydrogen and nitrogen gas were then introduced into the furnace chamber simultaneously (hydrogen to nitrogen flow ratio of 8:1) until the pressure inside the furnace chamber reached 80 Pa. The ion power supply was then turned on. While maintaining the introduction of hydrogen and nitrogen gas, the surface of the AerMet100 ultra-high strength steel sample was sputtered for 45 min at a sputtering voltage of -320 V to obtain an AerMet100 ultra-high strength steel sample with the passivation film removed.

[0059] The temperature inside the ion nitriding furnace was increased from 320℃ to 425℃ at a heating rate of 3℃ / min. Then, the voltage inside the ion nitriding furnace was decreased from -320V to -465V at a voltage reduction rate of 8V / min. The gas pressure inside the ion nitriding furnace was increased from 80Pa to 425Pa at a voltage increase rate of 35Pa / min. The hydrogen to nitrogen flow ratio was decreased from 8:1 to 1.5:1. The voltage inside the ion nitriding furnace was decreased from -465V to -525V at a voltage reduction rate of 8V / min. Then, the AerMet100 ultra-high strength steel sample was subjected to low-temperature ion nitriding treatment for 12 hours. The heating power and ion power supply of the ion nitriding furnace were turned off, and the hydrogen supply was stopped, while the nitrogen supply was maintained until the gas pressure inside the ion nitriding furnace dropped to 0.8 bar. Then, the blower was turned on to reduce the temperature inside the furnace to 150℃, thus obtaining AerMet100 ultra-high strength steel with a nitrided layer.

[0060] Example 2

[0061] Cylindrical AerMet100 ultra-high strength steel bars with a diameter of 30 mm were placed in a heat treatment furnace. The temperature was increased from room temperature to 800°C at a heating rate of 10°C / min and held for 30 min. The temperature was then increased from 800°C to 900°C at a heating rate of 5°C / min and held for 2 h. The temperature was then decreased from 900°C to 750°C at a cooling rate of 5°C / min, and then decreased from 750°C to room temperature at a cooling rate of 10°C / min. The AerMet100 ultra-high strength steel bars were then removed. Argon gas was introduced during both the heating and cooling processes at a flow rate of 50 L / min.

[0062] The AerMet100 ultra-high strength steel bars were placed back into the heat treatment furnace and heated from room temperature to 650°C at a rate of 5°C / min, and held for 20 min. Then, the temperature was increased from 650°C to 680°C at a rate of 1°C / min and held for 10 h. The bars were then cooled in the furnace to obtain the treated AerMet100 ultra-high strength steel bars. Argon gas was introduced during both the heating and furnace cooling processes at a flow rate of 50 L / min.

[0063] The preheated AerMet100 ultra-high strength steel bars were placed in a vacuum furnace at 885℃ for solution treatment for 1 hour, and then oil-quenched. Next, the AerMet100 ultra-high strength steel bars were placed in a cryogenic treatment furnace at -73℃ for cryogenic treatment for 1 hour, and then allowed to naturally warm to room temperature. Finally, the AerMet100 ultra-high strength steel bars were placed in an air furnace at 482℃ for tempering for 5 hours, and then air-cooled to obtain heat-treated AerMet100 ultra-high strength steel with a hardness of 54HRC, or 578HV.

[0064] AerMet100 ultra-high strength steel samples with a diameter of 30 mm and a height of 20 mm were cut from heat-treated AerMet100 ultra-high strength steel using wire cutting. The surface of the AerMet100 ultra-high strength steel sample was polished as a whole and wiped clean with an organic solvent. The roughness of the AerMet100 ultra-high strength steel sample after polishing was 0.45 μm.

[0065] An AerMet100 ultra-high strength steel sample was placed on the cathode plate inside an ion nitriding furnace. The furnace lid was closed, ensuring a good seal. The furnace chamber was evacuated to 10 Pa, and nitrogen gas was then introduced into the furnace chamber until the pressure inside the furnace chamber reached 0.6 bar. The heating power supply was then turned on to heat the ion nitriding furnace. After the temperature inside the ion nitriding furnace reached 300℃, the furnace was evacuated again to 10 Pa. Hydrogen and nitrogen gas were then introduced into the furnace chamber simultaneously (hydrogen to nitrogen flow ratio of 5:1) until the pressure inside the furnace chamber reached 50 Pa. The ion power supply was then turned on. While maintaining the introduction of hydrogen and nitrogen gas, the surface of the AerMet100 ultra-high strength steel sample was sputtered for 60 min at a sputtering voltage of -350V to obtain an AerMet100 ultra-high strength steel sample with the passivation film removed.

[0066] The temperature inside the ion nitriding furnace was increased from 300℃ to 410℃ at a heating rate of 1℃ / min; the voltage inside the ion nitriding furnace was decreased from -350V to -480V at a depressurization rate of 5V / min; then the gas pressure inside the ion nitriding furnace was increased from 50Pa to 250Pa at a pressure increase rate of 20Pa / min, and the hydrogen to nitrogen flow ratio was decreased from 5:1 to 0.3:1; then the voltage inside the ion nitriding furnace was decreased from -480V to -550V at a depressurization rate of 5V / min; the AerMet100 ultra-high strength steel sample was subjected to low-temperature ion nitriding treatment for 5 hours; the heating power and ion power supply of the ion nitriding furnace were turned off, and the hydrogen supply was stopped, while the nitrogen supply was maintained until the gas pressure inside the ion nitriding furnace dropped to 0.6 bar. Then the blower was turned on to reduce the temperature inside the furnace chamber to 150℃, thus obtaining AerMet100 ultra-high strength steel with a nitrided layer.

[0067] Example 3

[0068] Cylindrical AerMet100 ultra-high strength steel bars with a diameter of 30 mm were placed in a heat treatment furnace and heated from room temperature to 800°C at a heating rate of 20°C / min, and held for 10 min; then heated from 800°C to 900°C at a heating rate of 10°C / min, and held for 1 h; then cooled from 900°C to 750°C at a cooling rate of 10°C / min, and then cooled from 750°C to room temperature at a cooling rate of 20°C / min, and then the AerMet100 ultra-high strength steel bars were removed; argon gas was introduced during both heating and cooling processes, and the argon gas flow rate was 100 L / min.

[0069] The AerMet100 ultra-high strength steel bars were placed back into the heat treatment furnace and heated from room temperature to 650°C at a rate of 15°C / min, and held for 10 min. Then, the temperature was increased from 650°C to 680°C at a rate of 5°C / min and held for 8 h. The bars were then cooled in the furnace to obtain preheated AerMet100 ultra-high strength steel bars. Argon gas was introduced during both the heating and furnace cooling processes at a flow rate of 100 L / min.

[0070] The preheated AerMet100 ultra-high strength steel bars were placed in a vacuum furnace at 885℃ for solution treatment for 1 hour, and then oil-quenched. Next, the AerMet100 ultra-high strength steel bars were placed in a cryogenic treatment furnace at -73℃ for cryogenic treatment for 1 hour, and then allowed to naturally warm to room temperature. Finally, the AerMet100 ultra-high strength steel bars were placed in an air furnace at 482℃ for tempering for 5 hours, and then air-cooled to obtain heat-treated AerMet100 ultra-high strength steel with a hardness of 54HRC, or 578HV.

[0071] AerMet100 ultra-high strength steel samples with a diameter of 30 mm and a height of 20 mm were cut from heat-treated AerMet100 ultra-high strength steel using wire cutting. The surface of the AerMet100 ultra-high strength steel sample was polished as a whole and wiped clean with an organic solvent. The roughness of the AerMet100 ultra-high strength steel sample after polishing was 0.45 μm.

[0072] An AerMet100 ultra-high strength steel sample was placed on the cathode plate inside an ion nitriding furnace. The furnace lid was closed, ensuring a good seal. The furnace chamber was evacuated to 10 Pa, and nitrogen gas was then introduced into the furnace chamber until the pressure inside the furnace chamber reached 0.9 bar. The heating power supply was then turned on to heat the ion nitriding furnace. Once the temperature inside the ion nitriding furnace reached 350°C, the furnace was evacuated again to 10 Pa. Hydrogen and nitrogen gas were then introduced into the furnace chamber simultaneously (hydrogen to nitrogen flow ratio of 10:1) until the pressure inside the furnace chamber reached 100 Pa. The ion power supply was then turned on. While maintaining the introduction of hydrogen and nitrogen gas, the surface of the AerMet100 ultra-high strength steel sample was sputtered for 30 min at a sputtering voltage of -300 V to obtain an AerMet100 ultra-high strength steel sample with the passivation film removed.

[0073] The temperature inside the ion nitriding furnace was increased from 350℃ to 440℃ at a heating rate of 5℃ / min, and the voltage inside the ion nitriding furnace was decreased from -300V to -450V at a depressurization rate of 10V / min. The gas pressure inside the ion nitriding furnace was increased from 100Pa to 600Pa at a pressure increase rate of 50Pa / min, and the hydrogen to nitrogen flow ratio was decreased from 10:1 to 3:1. The voltage inside the ion nitriding furnace was decreased from -450V to -500V at a depressurization rate of 10V / min. The AerMet100 ultra-high strength steel sample was subjected to low-temperature ion nitriding treatment for 20 hours. The heating power and ion power supply of the ion nitriding furnace were turned off, and the hydrogen supply was stopped while nitrogen supply was maintained until the gas pressure inside the ion nitriding furnace dropped to 0.9 bar. Then, the blower was turned on to reduce the temperature inside the furnace chamber to 150℃, thus obtaining AerMet100 ultra-high strength steel with a nitrided layer.

[0074] The microstructure of the nitrided layer and matrix of the AerMet100 steel with nitrided layer provided in Examples 1 to 3 was observed using an optical metallographic microscope. The metallographic images of the longitudinal section of the AerMet100 steel with nitrided layer are shown below. Figures 2 to 4 As shown in the figure, the nitrided microstructure of the AerMet100 ultra-high strength steel samples in the three examples only shows typical supersaturated martensite, and no bright white layer or vein-like structure is observed.

[0075] For the AerMet100 steel with a nitrided layer provided in Examples 1 to 3, the hardness gradient of the nitrided layer was measured using a Vickers hardness tester with a load of 200g and a loading time of 30s. Nitrogen atoms gradually diffused from the surface of the AerMet100 ultra-high strength steel sample into the interior, thus forming a nitrided layer. The distribution of hardness test points of the nitrided layer on the longitudinal section of the AerMet100 steel containing the nitrided layer is shown in the figure. Figure 5As shown, the longitudinal section of the sample is rectangular, with a long side of 30 mm and a short side of 20 mm. Using the centerline of the long side as a reference, intersecting lines were drawn on both sides of the centerline. Hardness was measured at the centerline of the long side and at the endpoints of the intersecting lines, for a total of ten points. The perpendicular distances from each point to the long side of the sample (i.e., the sample surface) were 0 μm, 30 μm, 45 μm, 60 μm, 75 μm, 90 μm, 110 μm, 130 μm, 150 μm, and 170 μm, respectively. The hardness trend of the nitrided layer on the longitudinal section of the AerMet100 steel containing the nitrided layer is as follows: Figure 6 As shown in the figure, the nitrided layers of AerMet100 steel in the three embodiments all formed a typical nitriding hardness gradient distribution, with the surface hardness of the samples reaching between 1100-1200 HV.

[0076] For the AerMet100 steel with a nitrided layer provided in Examples 1 to 3, the hardness gradient of the matrix was measured using a Rockwell hardness tester with a load of 120 kg and a loading time of 10 s. The distribution of matrix hardness test points on the cross-section of the AerMet100 steel with the nitrided layer is shown in the figure. Figure 7 As shown, the cross-section of the sample is circular with a diameter of 30 mm. Two circles are drawn outward from the center with radii of 7.5 mm and 10 mm respectively. Finally, a hardness value is measured at the center, four hardness values ​​are measured evenly on the circumference with a radius of 7.5 mm, and four hardness values ​​are measured evenly on the circumference with a radius of 10 mm. The hardness measurement points on the two circumferences are staggered. The hardness values ​​of each measurement point are shown in Table 1.

[0077] Table 1

[0078]

[0079] The data in Table 1 shows that the matrix hardness of AerMet100 steel with nitriding layer remains within the range of 54±0.5HRC. This indicates that while forming a nitriding layer on the surface of AerMet100 ultra-high strength steel, it is also possible to ensure that the matrix hardness of AerMet100 ultra-high strength steel does not decrease.

[0080] For the AerMet100 steel with nitrided layer provided in Examples 1 to 3, the surface roughness of the AerMet100 steel with nitrided layer before and after nitriding was measured using a roughness measuring instrument. Each sample was measured three times, and the average value was taken. The measurement results are shown in Table 2. The data in Table 2 show that the surface roughness of the AerMet100 ultra-high strength steel remained basically unchanged before and after nitriding, and the average roughness was controlled at around 0.45 μm.

[0081] Table 2

[0082]

[0083] For the three embodiments described above, the residual stress of the nitrided layer was tested using an XRD residual stress analyzer. The residual stress trend of the AerMet100 steel containing the nitrided layer is as follows: Figure 8 As shown in the figure, the residual compressive stress of AerMet100 steel containing a nitrided layer decreases with increasing nitriding depth, forming a gradient structure similar to the hardness curve. In all three embodiments, the residual stress of the nitrided layer reaches approximately -1000 MPa, and this high-pressure stress state can be maintained for a certain distance near the sample surface. Furthermore, normal stress appears at depths of 75 μm, 89 μm, and 112 μm in the nitrided layers of the three embodiments, respectively. According to the residual stress test results, with the extension of nitriding time, the residual compressive stress appears at deeper depths in the sample. This corresponds to the relationship between nitriding time and the hardness distribution of the nitrided layer; that is, the deeper the nitrided layer, the greater the residual compressive stress and the better the fatigue resistance.

[0084] For the AerMet100 steel with nitrided layer provided in Examples 1 to 3, a rotational bending fatigue test was conducted on the AerMet100 steel with nitrided layer using a rotational bending fatigue testing machine. The test temperature was room temperature, Kt=1, and the rotational speed was 3000 rpm. Each sample was tested three times, and the test results are shown in Table 3.

[0085] Table 3

[0086]

[0087] The data in Table 3 show that when the maximum stress is 980 MPa, the number of cycles for the AerMet100 ultra-high strength steel sample before nitriding is 1.1 × 10⁻⁶. 6 The number of cycles for the AerMet100 ultra-high strength steel samples after nitriding was approximately 8.1-9.3 × 10⁻⁶. 6 It can be seen that the fatigue resistance of AerMet100 steel containing the nitrided layer is significantly improved.

[0088] 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 equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for low-temperature ion nitriding of AerMet100 steel, characterized in that, include: a) Preheating AerMet100 steel to obtain preheated AerMet100 steel; step a) specifically includes: heating AerMet100 steel from room temperature to 800℃ at a heating rate of 10℃ / min to 20℃ / min, holding at that temperature for 10 min to 30 min, heating from 800℃ to 900℃ at a heating rate of 5℃ / min to 10℃ / min, holding at that temperature for 1 h to 2 h; heating at a heating rate of 5℃ / min to 10℃ / min The temperature was lowered from 900℃ to 750℃ at a cooling rate of 10℃ / min to 20℃ / min, then lowered to room temperature at a cooling rate of 5℃ / min to 15℃ / min. The temperature was then raised from room temperature to 650℃ at a heating rate of 5℃ / min to 15℃ / min, held for 10min to 20min, and then raised from 650℃ to 680℃ at a heating rate of 1℃ / min to 5℃ / min, held for 8-10h. After cooling, the preheated AerMet100 steel was obtained. b) The preheated AerMet100 steel is subjected to heat treatment to obtain an AerMet100 steel sample. The heat treatment includes solution treatment, cryogenic treatment and tempering treatment. c) The AerMet100 steel sample was subjected to low-temperature ion nitriding treatment to obtain AerMet100 steel containing a nitrided layer.

2. The method according to claim 1, characterized in that, The solution treatment temperature is 877°C to 893°C, the solution treatment holding time is 1h to 3h, and the solution treatment heating rate is 1°C / min to 20°C / min. The cryogenic treatment temperature is -81℃ to -65℃, the cryogenic treatment holding time is 1h to 3h, and the cryogenic treatment cooling rate is 1℃ / min to 20℃ / min. The tempering temperature is 479°C to 485°C, the holding time of the tempering is 5h to 8h, and the heating rate of the tempering is 1°C / min to 20°C / min.

3. The method according to claim 1, characterized in that, The cross-sectional hardness of the AerMet100 steel sample was 53.5 HRC to 54.5 HRC.

4. The method according to claim 1, characterized in that, The low-temperature ion nitriding treatment is preceded by a sputtering treatment, the sputtering treatment time is 30 min to 60 min, the sputtering treatment voltage is -350V to -300V, the sputtering treatment is carried out under the condition of hydrogen and nitrogen gas, the sputtering treatment gas pressure is 50 Pa to 100 Pa, and the flow ratio of hydrogen to nitrogen gas is 5:1 to 10:

1.

5. The method according to claim 1, characterized in that, The gas pressure for the low-temperature ion nitriding is 250 Pa to 600 Pa, the time for the low-temperature ion nitriding is 5 h to 20 h, and the voltage for the low-temperature ion nitriding treatment is -550 V to -500 V.

6. The method according to claim 5, characterized in that, In step c, the AerMet100 steel sample is heated to 410℃~440℃, the pressure is first reduced to -480V~-450V, the gas pressure is increased to 250Pa~600Pa, the flow ratio of hydrogen to nitrogen is reduced to 0.3:1~3:1, and then the pressure is reduced to -550V~-500V for the second time. The heating rate is 1°C / min to 5°C / min, the first depressurization rate is 5V / min to 10V / min, the pressure increase rate is 20Pa / min to 50Pa / min, and the second depressurization rate is 5V / min to 10V / min.

7. The method according to claim 1, characterized in that, Before step c, the AerMet100 steel sample is also ground, and the roughness of the ground AerMet100 steel sample is 0.01 μm to 0.8 μm.

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