Production method of 8620H gear steel and 8620H gear steel

Abstract

The invention provides a production method of 8620H gear steel and the 8620H gear steel, and the production method of the 8620H gear steel comprises the following steps: (1) smelting: TiN nanoparticles are added into molten steel, and argon is introduced for dispersion; adding refining slag into the molten steel, and feeding a CaSi wire; (2) continuous casting: controlling a casting blank to enter a slow cooling pit by adopting electromagnetic braking and soft reduction; (3) rolling: sequentially carrying out rough rolling, finish rolling and finish rolling on the casting blank, and cooling after rolling; and (4) forging is conducted, specifically, the rolled piece is forged, and then carburizing treatment and gas quenching treatment are conducted. The 8620H gear steel disclosed by the invention is treated by a specific production process, shows excellent mechanical properties, meets high requirements of high-quality gear steel on purity and comprehensive mechanical properties, and has a wide application prospect.

Description

Technical Field

[0001] This application relates to the field of metal smelting technology, and in particular to a method for producing 8620H gear steel and 8620H gear steel. Background Technology

[0002] Gear steel is one of the key materials with high requirements among special alloy steels used in automobiles, railways, ships, and construction machinery. It is a manufacturing material for core components that ensure safety. Gear steel must not only have good strength, toughness, and wear resistance, but also withstand impact, bending, and contact stress during operation. At the same time, it is required to have small deformation, high precision in the processed gears, and low noise.

[0003] 8620H is an alloy steel round bar conforming to the ASTM A304 standard, primarily used in automotive gear manufacturing and machinery manufacturing. Its chemical composition includes carbon (C): 0.18–0.23%, silicon (Si): 0.15–0.35%, manganese (Mn): 0.70–0.90%, chromium (Cr): 0.40–0.60%, nickel (Ni): 0.40–0.70%, and molybdenum (Mo): 0.15–0.25%, etc. Its mechanical properties include tensile strength ≥980 MPa and yield strength ≥785 MPa. With the rapid technological development of the machinery industry, gears require longer service life and higher safety factors, placing higher demands on the performance and quality of gear steel.

[0004] CN101306435A discloses a method for producing gear steel. The steel composition (by weight percentage) is: carbon 0.10–0.35%, silicon 0.15–0.45%, manganese 0.60–1.50%, phosphorus ≤0.03%, sulfur ≤0.045%, chromium 0.80–1.50%, titanium 0.03–0.12%, aluminum 0.01–0.10%, nickel 0–0.30%, molybdenum 0–0.20%, copper 0–0.20%, nitrogen 0.004–0.015%, and iron as the balance. The process flow includes: converter primary refining → ladle refining or vacuum degassing furnace refining → continuous casting → continuous rolling. This method uses a converter instead of an electric furnace to produce gear steel, resulting in a short production cycle, low energy consumption, and minimal environmental pollution. Furthermore, its contact fatigue life is 1×10⁻⁶. 7 The current cycle is insufficient to meet the needs of users of high-quality gear steel. Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and its purpose is to provide a method for producing 8620H gear steel and 8620H gear steel.

[0006] Specifically, the first aspect of this application provides a method for producing 8620H gear steel, comprising the following steps: (1) Smelting: Add TiN nanoparticles to molten steel and disperse them by argon gas; then add refining slag to molten steel and feed in CaSi wire; (2) Continuous casting: Electromagnetic braking and light pressure are used to control the billet to enter the slow cooling pit; (3) Rolling: The billet is subjected to rough rolling, fine rolling and final rolling in sequence, and then cooled after rolling; (4) Forging: The rolled parts are forged, then carburized and gas quenched.

[0007] Further, the steel composition by mass percentage is C 0.19~0.21%, Si 0.23~0.27%, Mn 0.78~0.82%, Cr 0.53~0.57%, Ni 0.43~0.47%, Mo 0.16~0.18%, P≤0.020%, S 0.017~0.025%, Al 0.023~0.035%, Cu≤0.10%, N 0.0050~0.0090%, with the balance being Fe and unavoidable impurity elements.

[0008] Preferably, the molten steel composition by mass percentage is C 0.20%, Si 0.25%, Mn 0.80%, Cr 0.55%, Ni 0.45%, Mo 0.17%, P≤0.020%, S 0.020%, Al 0.030%, Cu≤0.10%, N 0.0070%, with the balance being Fe and unavoidable impurity elements.

[0009] Furthermore, the refining slag is CaO-Al2O3-SiO2-MgO, wherein the mass ratio of CaO, Al2O3, SiO2, and MgO is 53-58:24-26:8-12:9-11.

[0010] Further, the argon pulse frequency in step (1) is 0.3-0.6 Hz, and / or The flow rate of argon gas is 15-20 NL / min.

[0011] Further, the electromagnetic braking in step (2) is to control the flow field with a magnetic field of 300-320A current and / or a light pressure of 5-7mm.

[0012] Further, the rough rolling temperature in step (3) is 1150℃→1050℃, and the deformation is ≥55%; and / or The finishing rolling temperature is 950℃→880℃, and the deformation is ≥75%; and / or The final rolling temperature is ≤850℃, and the deformation is ≥15%.

[0013] Furthermore, the cooling described in step (3) is water mist cooling, with a cooling rate of 30-35℃ / s.

[0014] Further, the carburizing treatment in step (4) includes three stages: pre-oxidation, carburizing, and homogenization. The pre-oxidation is carried out in air at a temperature of 440-460°C and / or for a time of 25-35 minutes; and / or The carburizing medium is propane, the carburizing temperature is 900-950℃, and / or the carburizing time is 4-6 hours; and / or The homogenization temperature is 830-860℃, and / or the homogenization time is 2-3 hours.

[0015] Furthermore, the gas quenching in step (4) uses a mixture of nitrogen and hydrogen gas, and the cooling rate of the gas quenching is 35-45℃ / s.

[0016] The second aspect of this application provides an 8620H gear steel, which is prepared by the production method of the 8620H gear steel.

[0017] The present invention has the following beneficial effects: The 8620H gear steel production method of this invention effectively improves the uniformity and refines the grain size of molten steel by adding TiN nanoparticles and dispersing them with argon gas, thereby enhancing the mechanical properties of the steel. The added refining slag, through optimized composition ratio, can more effectively remove impurities from the molten steel, improving its purity. Simultaneously, the feeding of CaSi wire not only deoxidizes and desulfurizes but also further improves the steel's microstructure. During continuous casting, the application of electromagnetic braking and light pressure effectively controls the internal and surface quality of the billet, reducing defects. Temperature control and deformation setting during rolling ensure the microstructure evolution of the steel during rolling, further enhancing its strength and toughness. Carburizing and gas quenching after forging further enhance the surface hardness and wear resistance of the steel while maintaining good core toughness, resulting in excellent comprehensive mechanical properties for the 8620H gear steel. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0019] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0020] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0021] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0022] An embodiment of the first aspect of the present invention provides a method for producing 8620H gear steel, comprising the following steps: (1) Smelting: Add TiN nanoparticles to molten steel and disperse them by argon gas; then add refining slag to molten steel and feed in CaSi wire; (2) Continuous casting: Electromagnetic braking and light pressure are used to control the billet to enter the slow cooling pit; (3) Rolling: The billet is subjected to rough rolling, fine rolling and final rolling in sequence, and then cooled after rolling; (4) Forging: The rolled parts are forged, then carburized and gas quenched.

[0023] The method for producing 8620H gear steel of this invention involves adding 0.004% TiN nanoparticles (50-100 nm in diameter) to molten steel and dispersing them using argon gas. This effectively improves the uniformity and refines the grain size of the molten steel, inhibits austenite grain coarsening, and thus enhances the mechanical properties of the steel. The added refining slag, through optimized composition, can more effectively remove impurities from the molten steel, improving its purity. Simultaneously, the feeding of a CaSi wire (1.5 m / t) not only deoxidizes and desulfurizes the steel... Furthermore, it can further improve the microstructure of steel; during continuous casting, the application of electromagnetic braking and light pressure effectively controls the internal and surface quality of the billet, reducing the generation of defects; temperature control and deformation setting during rolling ensure the microstructure evolution of steel during rolling, further improving the strength and toughness of steel; carburizing and gas quenching after forging further enhance the surface hardness and wear resistance of steel, while maintaining good toughness in the core, giving 8620H gear steel excellent comprehensive mechanical properties.

[0024] In this embodiment, the steel composition by mass percentage is: C 0.19~0.21%, Si 0.23~0.27%, Mn 0.78~0.82%, Cr 0.53~0.57%, Ni 0.43~0.47%, Mo 0.16~0.18%, P≤0.020%, S 0.017~0.025%, Al 0.023~0.035%, Cu≤0.10%, N 0.0050~0.0090%, with the balance being Fe and unavoidable impurity elements.

[0025] In this embodiment, the refining slag is CaO-Al2O3-SiO2-MgO, wherein the mass ratio of CaO, Al2O3, SiO2, and MgO is 53-58:24-26:8-12:9-11, and the basicity R = 3.8. Preferably, the mass ratio of CaO, Al2O3, SiO2, and MgO is 55:25:10:10. By precisely controlling the mass ratio of CaO, Al2O3, SiO2, and MgO in the refining slag, the deoxidation, desulfurization, and removal of non-metallic inclusions of the refining slag can be optimized. In this embodiment, the mass ratio of the components in the refining slag is strictly controlled within a certain range to ensure optimal refining results.

[0026] In this embodiment, the argon pulse frequency in step (1) is 0.3-0.6 Hz, the argon flow rate is 15-20 NL / min, and the time is 20-30 min. The amount of TiN nanoparticles added is 0.004% of the mass of the molten steel, and their particle size is controlled within the range of 50-100 nm to ensure uniform dispersion of nanoparticles in the molten steel and to achieve a grain refinement effect. In addition, the selection of the argon pulse frequency and flow rate ensures effective dispersion of TiN nanoparticles while avoiding the potential decrease in molten steel quality due to excessive stirring.

[0027] In another preferred embodiment, a vacuum treatment (VD) can be employed, with the vacuum level controlled at ≤67 Pa and maintained for 25 minutes, to further remove hydrogen and nitrogen from the molten steel, reduce porosity and inclusions in the steel, and improve the quality and performance of the steel. Furthermore, the VD treatment can promote the uniform distribution of alloying elements in the molten steel, improving the microstructure uniformity and mechanical properties of the steel.

[0028] In this embodiment, the electromagnetic braking in step (2) uses a magnetic field with a current of 300-320A. This magnetic field strength can moderately control the flow of molten steel, reduce turbulence, and make the internal quality of the billet more uniform. The light reduction is 5-7mm, preferably 6mm. By moderately compressing the billet, the generation of defects such as internal shrinkage cavities and porosity is reduced, and it also helps to improve the surface quality of the billet. The billet is placed in a slow cooling pit and cooled to room temperature at a rate of 30-50℃ / h. This avoids internal stress and structural defects caused by excessively fast or slow cooling rates, thereby obtaining a more uniform and fine grain structure and improving the mechanical properties and toughness of the steel.

[0029] In this embodiment, the temperature of the rough rolling in step (3) is 1150℃→1050℃, and the deformation is ≥55% to break the as-cast structure; The finishing rolling temperature is 950℃→880℃, and the deformation is ≥75%, in order to refine the grains through dynamic recrystallization. The final rolling temperature is ≤850℃, and the deformation is ≥15%, so as to induce ferrite phase transformation by deformation.

[0030] During the rolling process, temperature control and deformation setting are crucial for ensuring the evolution of the steel's microstructure. The temperature gradually decreases and the deformation gradually increases during roughing, finishing, and final rolling. This process setting helps refine the steel's grains and improve its strength and toughness.

[0031] In this embodiment, the cooling in step (3) is water mist cooling, with a cooling rate of 30-35℃ / s. The coiling temperature is 500±10℃ to avoid bainite transformation. The cooling step ensures rapid cooling of the steel while avoiding the generation of internal stress and cracks caused by excessive cooling rate.

[0032] In this embodiment, when the rolled piece is forged in step (4), the final forging temperature is 950℃, and it is water-cooled to 650℃ and held for 40 minutes. The carburizing treatment includes three stages: pre-oxidation, carburizing, and homogenization. The pre-oxidation is carried out in air at a temperature of 440-460℃ for 25-35 minutes. This step can form a 5-10nm Fe3O4 layer to promote carburizing. The carburizing medium is propane, the carrier gas is N2, the carburizing temperature is 900-950℃, the carburizing time is 4-6h, and the carbon potential CP is 1.2%. This step is used to quickly establish a carbon gradient. The homogenization temperature is 830-860℃, the homogenization time is 2-3h, and the carbon potential CP is 0.85%. This step is used to optimize carbon distribution and reduce network carbides.

[0033] In this embodiment, the gas quenching in step (4) uses a mixture of nitrogen and hydrogen gas, wherein the volume ratio of nitrogen to hydrogen is 50:1, the cooling rate of gas quenching is 35-45℃ / s, and the pressure of gas quenching is 5 bar. Gas quenching is used to reduce deformation and improve the surface hardness of gear steel.

[0034] The second aspect of this application provides an 8620H gear steel, which is prepared by the production method of the 8620H gear steel.

[0035] By employing the steel composition and production method of this invention, the gear steel exhibits an oxygen content ≤0.0020%, a hydrogen content ≤0.0002%, and a low level of non-metallic inclusions, meeting the stringent purity requirements for high-quality gear steel. Furthermore, the 8620H gear steel prepared using this method possesses a tensile strength ≥1050MPa, a yield strength ≥880MPa, and a fatigue life ≥2×10⁻⁶. 7 Compared with existing technologies, the secondary cycle has significantly improved the overall mechanical properties, and can better meet the high-performance requirements of gear steel in the fields of automobiles, railways, ships, and engineering machinery.

[0036] Example 1 A method for producing 8620H gear steel includes the following steps: (1) Smelting: Add 0.004% TiN nanoparticles to the molten steel, disperse them by argon gas, the argon gas pulse frequency is 0.3Hz, the argon gas flow rate is 18NL / min, and the time is 25min; then add refining slag CaO-Al2O3-SiO2-MgO to the molten steel and feed CaSi wire; (2) Continuous casting: The magnetic field electromagnetic braking with a current of 310A is used to control the light reduction of 5mm and control the billet to enter the slow cooling pit, and cool it to room temperature at a rate of 30℃ / h; (3) Rolling: The billet is subjected to rough rolling, fine rolling and final rolling in sequence, and then cooled after rolling; The rough rolling temperature is 1150℃→1050℃, and the deformation is ≥55% to break the as-cast structure. The finishing rolling temperature is 950℃→880℃, and the deformation is ≥75%, in order to refine the grains through dynamic recrystallization. The final rolling temperature is ≤850℃ and the deformation is ≥15% to induce ferrite phase transformation through deformation. The cooling method is water mist cooling, with a cooling rate of 33°C / s; (4) Forging: The rolled parts are forged, then carburized and gas quenched; During forging, the final forging temperature is 950℃, followed by water cooling to 650℃ and holding at that temperature for 40 minutes. The carburizing process includes three stages: pre-oxidation, carburizing, and homogenization. The pre-oxidation is carried out in air at a temperature of 440°C for 35 minutes. This step can form a 5-10 nm Fe3O4 layer to promote carburizing. The carburizing medium is propane, the carrier gas is N2, the carburizing temperature is 920℃, the carburizing time is 5h, and the carbon potential CP is 1.2%. This step is used to quickly establish a carbon gradient. The homogenization temperature is 860℃, the homogenization time is 2h, and the carbon potential CP is 0.85%. This step is used to optimize carbon distribution and reduce network carbides. The gas quenching uses a mixture of nitrogen and hydrogen, with a volume ratio of nitrogen to hydrogen of 50:1. The cooling rate of the gas quenching is 45°C / s, and the pressure of the gas quenching is 5 bar. The gas quenching is used to reduce deformation and improve the surface hardness of the gear steel.

[0037] Example 2 A method for producing 8620H gear steel includes the following steps: (1) Smelting: Add 0.004% TiN nanoparticles to the molten steel, disperse them by argon gas, the argon gas pulse frequency is 0.6Hz, the argon gas flow rate is 15NL / min, and the time is 30min; then add refining slag CaO-Al2O3-SiO2-MgO to the molten steel and feed CaSi wire; (2) Continuous casting: The magnetic field electromagnetic braking with a current of 300A is used to control the light reduction of 7mm and control the billet to enter the slow cooling pit, and cool it to room temperature at a rate of 50℃ / h; (3) Rolling: The billet is subjected to rough rolling, fine rolling and final rolling in sequence, and then cooled after rolling; The rough rolling temperature is 1150℃→1050℃, and the deformation is ≥55% to break the as-cast structure. The finishing rolling temperature is 950℃→880℃, and the deformation is ≥75%, in order to refine the grains through dynamic recrystallization. The final rolling temperature is ≤850℃ and the deformation is ≥15% to induce ferrite phase transformation through deformation. The cooling method is water mist cooling, with a cooling rate of 30°C / s; (4) Forging: The rolled parts are forged, then carburized and gas quenched; During forging, the final forging temperature is 950℃, followed by water cooling to 650℃ and holding at that temperature for 40 minutes. The carburizing process includes three stages: pre-oxidation, carburizing, and homogenization. The pre-oxidation is carried out in air at a temperature of 460°C for 25 minutes. This step can form a 5-10 nm Fe3O4 layer to promote carburizing. The carburizing medium is propane, the carrier gas is N2, the carburizing temperature is 900℃, the carburizing time is 4h, and the carbon potential CP is 1.2%. This step is used to quickly establish a carbon gradient. The homogenization temperature is 850℃, the homogenization time is 2.5h, and the carbon potential CP is 0.85%. This step is used to optimize carbon distribution and reduce network carbides. The gas quenching uses a mixture of nitrogen and hydrogen, with a volume ratio of nitrogen to hydrogen of 50:1. The cooling rate of the gas quenching is 40°C / s, and the pressure of the gas quenching is 5 bar. The gas quenching is used to reduce deformation and improve the surface hardness of the gear steel.

[0038] Example 3 A method for producing 8620H gear steel includes the following steps: (1) Smelting: Add 0.004% TiN nanoparticles to the molten steel, disperse them by argon gas, the argon gas pulse frequency is 0.5Hz, the argon gas flow rate is 20NL / min, and the time is 20min; then add refining slag CaO-Al2O3-SiO2-MgO to the molten steel and feed CaSi wire; (2) Continuous casting: The magnetic field electromagnetic braking with a current of 320A is used to control the light reduction of 6mm and control the billet to enter the slow cooling pit, and cool it to room temperature at a rate of 40℃ / h; (3) Rolling: The billet is subjected to rough rolling, fine rolling and final rolling in sequence, and then cooled after rolling; The rough rolling temperature is 1150℃→1050℃, and the deformation is ≥55% to break the as-cast structure. The finishing rolling temperature is 950℃→880℃, and the deformation is ≥75%, in order to refine the grains through dynamic recrystallization. The final rolling temperature is ≤850℃ and the deformation is ≥15% to induce ferrite phase transformation through deformation. The cooling method is water mist cooling, with a cooling rate of 35°C / s; (4) Forging: The rolled parts are forged, then carburized and gas quenched; During forging, the final forging temperature is 950℃, followed by water cooling to 650℃ and holding at that temperature for 40 minutes. The carburizing process includes three stages: pre-oxidation, carburizing, and homogenization. The pre-oxidation is carried out in air at a temperature of 450°C for 30 minutes. This step can form a 5-10 nm Fe3O4 layer to promote carburizing. The carburizing medium is propane, the carrier gas is N2, the carburizing temperature is 950℃, the carburizing time is 6h, and the carbon potential CP is 1.2%. This step is used to quickly establish a carbon gradient. The homogenization temperature is 830℃, the homogenization time is 3h, and the carbon potential CP is 0.85%. This step is used to optimize carbon distribution and reduce network carbides. The gas quenching uses a mixture of nitrogen and hydrogen, with a volume ratio of nitrogen to hydrogen of 50:1. The cooling rate of the gas quenching is 35°C / s, and the pressure of the gas quenching is 5 bar. The gas quenching is used to reduce deformation and improve the surface hardness of the gear steel.

[0039] Example 4 A method for producing 8620H gear steel includes the following steps: (1) Smelting: Add 0.004% TiN nanoparticles to the molten steel, disperse them by argon gas, the argon gas pulse frequency is 0.5Hz, the argon gas flow rate is 16NL / min, and the time is 26min; then add refining slag CaO-Al2O3-SiO2-MgO to the molten steel and feed CaSi wire; (2) Continuous casting: The magnetic field electromagnetic braking with a current of 300A is used to control the light reduction of 6mm and control the billet to enter the slow cooling pit, and cool it to room temperature at a rate of 40℃ / h; (3) Rolling: The billet is subjected to rough rolling, fine rolling and final rolling in sequence, and then cooled after rolling; The rough rolling temperature is 1150℃→1050℃, and the deformation is ≥55% to break the as-cast structure. The finishing rolling temperature is 950℃→880℃, and the deformation is ≥75%, in order to refine the grains through dynamic recrystallization. The final rolling temperature is ≤850℃ and the deformation is ≥15% to induce ferrite phase transformation through deformation. The cooling method is water mist cooling, with a cooling rate of 35°C / s; (4) Forging: The rolled parts are forged, then carburized and gas quenched; During forging, the final forging temperature is 950℃, followed by water cooling to 650℃ and holding at that temperature for 40 minutes. The carburizing process includes three stages: pre-oxidation, carburizing, and homogenization. The pre-oxidation is carried out in air at a temperature of 450°C for 30 minutes. This step can form a 5-10 nm Fe3O4 layer to promote carburizing. The carburizing medium is propane, the carrier gas is N2, the carburizing temperature is 900℃, the carburizing time is 5h, and the carbon potential CP is 1.2%. This step is used to quickly establish a carbon gradient. The homogenization temperature is 850℃, the homogenization time is 3h, and the carbon potential CP is 0.85%. This step is used to optimize carbon distribution and reduce network carbides. The gas quenching uses a mixture of nitrogen and hydrogen, with a volume ratio of nitrogen to hydrogen of 50:1. The cooling rate of the gas quenching is 40°C / s, and the pressure of the gas quenching is 5 bar. The gas quenching is used to reduce deformation and improve the surface hardness of the gear steel.

[0040] Comparative Example 1 This comparative example is basically the same as Example 4, except that TiN nanoparticles were not added in step (1).

[0041] Comparative Example 2 This comparative example is basically the same as Example 4, except that the carburizing treatment in step (4) does not include the pre-oxidation and homogenization stages.

[0042] Comparative Example 3 This comparative example is basically the same as Example 4, except that the initial rolling temperature in step (3) is 980-1200℃ and the final rolling temperature is 800-900℃.

[0043] Comparative Example 4 This comparative example is basically the same as Example 4, except that in step (4), gas quenching is replaced with oil cooling, and the oil cooling rate is 20-30℃ / s.

[0044] Experimental Case The gear steels of Examples 1-4 and Comparative Examples 1-4 were subjected to performance testing. The contact fatigue specimens were carburized and gas-quenched before testing according to "YB-T 5345-2014 Metallic Materials Rolling Contact Fatigue Test Method". The test results are shown in the table below:

[0045] As can be seen from the table above, the 8620H gear steel of the present invention exhibits excellent mechanical properties after being processed by a specific production process. The gear steels in Examples 1 to 4 all have a contact fatigue life exceeding 2 × 10⁻⁶. 7After one cycle, the tensile strength is not less than 1050 MPa, and the yield strength is not less than 880 MPa. These values ​​are significantly better than those of the gear steel in the comparative example, demonstrating the significant effect of the method of the present invention in improving the overall performance of gear steel.

[0046] In Comparative Example 1, the gear steel without TiN nanoparticles showed a decrease in all performance indicators. This is because TiN effectively refines the grains, improving the material's strength and hardness. In Comparative Example 1 without TiN nanoparticles, the lack of this grain-refining effect resulted in a corresponding reduction in the mechanical properties of the gear steel, manifested as a decrease in contact fatigue life, tensile strength, and yield strength.

[0047] In Comparative Example 2, the gear steel without pre-oxidation and homogenization stages in the carburizing treatment had lower contact fatigue life, tensile strength, and yield strength than that in Example 4. The Fe3O4 layer formed in the pre-oxidation stage can promote the carburizing process and make the carbon elements more evenly distributed in the gear steel; while the homogenization stage further optimizes the carbon distribution and reduces the formation of network carbides, thereby improving the mechanical properties and fatigue life of the gear steel.

[0048] In Comparative Example 3, the initial rolling temperature and the final rolling temperature were both too high, resulting in a larger grain size and a decrease in both strength and hardness of the material. This demonstrates that a suitable rolling temperature is crucial for obtaining high-performance gear steel.

[0049] In Comparative Example 4, air quenching was replaced with oil cooling. Although oil cooling can also achieve rapid cooling, its cooling rate is slower than that of air quenching, resulting in a higher content of residual austenite inside the gear steel, which affects the hardness and fatigue life of the gear steel.

[0050] In summary, the 8620H gear steel of this invention, through specific production processes, exhibits excellent mechanical properties, meeting the high requirements of high-quality gear steel for purity and comprehensive mechanical properties, and has broad application prospects.

[0051] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for producing 8620H gear steel, characterized in that, Includes the following steps: (1) Smelting: Add TiN nanoparticles to molten steel and disperse them by argon gas; then add refining slag to molten steel and feed in CaSi wire; (2) Continuous casting: Electromagnetic braking and light pressure are used to control the billet to enter the slow cooling pit; (3) Rolling: The billet is subjected to rough rolling, fine rolling and final rolling in sequence, and then cooled after rolling; (4) Forging: The rolled parts are forged, then carburized and gas quenched.

2. The method for producing 8620H gear steel according to claim 1, characterized in that, The molten steel composition by mass percentage is: C 0.19~0.21%, Si 0.23~0.27%, Mn 0.78~0.82%, Cr 0.53~0.57%, Ni 0.43~0.47%, Mo 0.16~0.18%, P≤0.020%, S 0.017~0.025%, Al 0.023~0.035%, Cu≤0.10%, N 0.0050~0.0090%, with the balance being Fe and unavoidable impurity elements.

3. The method for producing 8620H gear steel according to claim 1, characterized in that, The refining slag is CaO-Al2O3-SiO2-MgO, wherein the mass ratio of CaO, Al2O3, SiO2, and MgO is 53-58:24-26:8-12:9-11.

4. The method for producing 8620H gear steel according to claim 1, characterized in that, The argon pulse frequency in step (1) is 0.3-0.6 Hz, and / or The flow rate of argon gas is 15-20 NL / min.

5. The method for producing 8620H gear steel according to claim 1, characterized in that, The electromagnetic braking in step (2) is to control the flow field with a magnetic field of 300-320A current and / or a light pressure of 5-7mm.

6. The method for producing 8620H gear steel according to claim 1, characterized in that, The rough rolling temperature in step (3) is 1150℃→1050℃, and the deformation is ≥55%; and / or The finishing rolling temperature is 950℃→880℃, and the deformation is ≥75%; and / or The final rolling temperature is ≤850℃, and the deformation is ≥15%.

7. The method for producing 8620H gear steel according to claim 1, characterized in that, The cooling described in step (3) is water mist cooling, with a cooling rate of 30-35℃ / s.

8. The method for producing 8620H gear steel according to claim 1, characterized in that, The carburizing treatment in step (4) includes three stages: pre-oxidation, carburizing, and homogenization. The pre-oxidation is carried out in air at a temperature of 440-460℃ and / or for a time of 25-35 minutes; and / or The carburizing medium is propane, the carburizing temperature is 900-950℃, and / or the carburizing time is 4-6 hours; and / or The homogenization temperature is 830-860℃, and / or the homogenization time is 2-3 hours.

9. The method for producing 8620H gear steel according to claim 1, characterized in that, The gas quenching in step (4) uses a mixture of nitrogen and hydrogen gas, and the cooling rate of the gas quenching is 35-45℃ / s.

10. An 8620H gear steel, characterized in that, It is prepared by the production method of 8620H gear steel according to any one of claims 1-9.

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