High-fatigue-resistance heavy-duty gear steel and preparation method thereof

Abstract

The invention relates to high-fatigue-resistance heavy-duty gear steel and a preparation method thereof, and belongs to the technical field of metal materials. The preparation method comprises the following steps: S1, carrying out two-stage carburizing treatment on the steel for the heavy-duty gear at 970-975 DEG C; the two-stage carburizing treatment comprises a first strong carburizing period and a first diffusion period; s2, the steel for the heavy-duty gear is subjected to first high-temperature tempering treatment; s3, the steel for the heavy-duty gear is subjected to two-stage carbonitriding treatment and staged cooling treatment at the temperature of 835-855 DEG C; the two-stage carbonitriding treatment comprises a second strong nitriding period and a second diffusion period; s4, the steel for the heavy-duty gear is subjected to second high-temperature tempering treatment; s5, quenching treatment is conducted on the steel for the heavy-duty gear; and S6, the steel for the heavy-duty gear is subjected to cold treatment and low-temperature tempering treatment, and the high-fatigue-resistance steel for the heavy-duty gear is obtained. The surface hardness of the steel for the high-fatigue-resistance heavy-duty gear is 69 HRC to 72 HRC, the contact fatigue strength of a tooth surface is 1808 MPa to 1843 MPa, and the bending fatigue strength of a tooth root is 685 MPa to 736 MPa.

Description

Technical Field

[0001] The invention belongs to the technical field of metal materials, and in particular relates to a high fatigue resistance heavy-duty gear steel and a preparation method thereof. Background Art

[0002] At present, coal still accounts for more than 50% of my country's energy structure. In order to ensure the sustainable development of social coal supply and related industries, efficient coal mining operations are a necessary direction for the development of the current coal industry. Heavy-duty gears, key components of coal mining machines, need to withstand higher loads, higher speeds and more complex working environments during service, and are very prone to failure. In order to achieve the development of coal mining machines towards heavy, large and powerful directions, heavy-duty gears are required to have high strength, high toughness, high hardness, high wear resistance and high fatigue resistance, etc., especially high fatigue resistance is crucial to extend service life.

[0003] Invention patent CN118186309A discloses a steel for electric vehicle differential bevel gears with high contact fatigue strength and strong pitting resistance. The contact fatigue strength is improved by adding alloy elements to the steel, but the higher alloy element content will significantly increase the material cost. Invention patent CN109321739A discloses a heat treatment process for heavy-duty gears with large carburized layers. The effective hardened layer depth is increased by extending the carburizing time at conventional carburizing temperatures (915℃-945℃), but the effective hardened layer depth is still less than 5.50mm, resulting in limited improvement in fatigue resistance. Invention patents CN117758198A and CN117758199A respectively refine the structure through high-temperature carburizing + double quenching and high-temperature carburizing + quenching with different media, but the hardened layer depth is less than 5.00mm and the surface hardness is less than 65HRC, which also leads to limited improvement in fatigue resistance. Judging from the current application situation, the fatigue resistance and service life of heavy-duty gear steel still need to be improved, and a new heat treatment process method for heavy-duty gear steel with high fatigue resistance is urgently needed. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a high fatigue resistance heavy-duty gear steel and a preparation method thereof, which combines carburizing treatment and carbonitriding treatment to significantly increase the carbon concentration in the surface layer, promote the formation of a large number of large-sized carbides, and obtain a hardened layer with sufficient depth; the martensite stability is improved by introducing nitrogen atoms, and nitrogen-containing martensite with sufficient depth is obtained in the surface layer; an appropriate amount of residual austenite is retained to relieve fatigue stress, thereby significantly improving the fatigue resistance of heavy-duty gear steel.

[0005] The first object of the present invention is to provide a method for preparing a steel for heavy-duty gears with high fatigue resistance, comprising the following steps:

[0006] S1. Carburizing the heavy-duty gear steel at 970° C.-975° C. in two stages; the two-stage carburizing treatment includes a first intensive carburizing period and a first diffusion period;

[0007] S2, subjecting the heavy-duty gear steel obtained in S1 to a first high-temperature tempering treatment;

[0008] S3, subjecting the heavy-duty gear steel obtained in S2 to a two-stage carbonitriding treatment at 835° C.-855° C. and a staged cooling treatment; the two-stage carbonitriding treatment includes a second strong permeation period and a second diffusion period;

[0009] S4, performing a second high temperature tempering treatment on the heavy-duty gear steel obtained in S3;

[0010] S5, quenching the heavy-duty gear steel obtained in S4;

[0011] S6. Perform cold treatment and low-temperature tempering treatment on the heavy-duty gear steel obtained in S5 to obtain the high fatigue resistance heavy-duty gear steel.

[0012] In one embodiment of the present invention, in S1, the element composition and mass percentage of the heavy-duty gear steel are: C 0.14%-0.16%, Si 0.17%-0.20%, Mn 0.53%-0.60%, P 0-0.006%, S 0-0.005%, Cr 1.37%-1.43%, Ni 4.39%-4.45%, W 0.83%-0.88%, and the remainder is other inevitable impurities and iron.

[0013] In one embodiment of the present invention, in S1, the carbon potential of the first strong infiltration period is 1.5wt%-1.6wt%, and the time is 48h-62h; the carbon potential of the first diffusion period is 0.9wt%-1.0wt%, and the time is 17h-25h.

[0014] In one embodiment of the present invention, in S3, the carbon potential of the second strong infiltration period is 1.1wt%-1.2wt%, the time is 15h-22h, and the ammonia flow rate is 5L / min-7L / min; the carbon potential of the second diffusion period is 0.9wt%-1.0wt%, the time is 5h-8h, and the ammonia flow rate is 5L / min-7L / min.

[0015] In one embodiment of the present invention, in S3, the staged cooling treatment includes two stages, the first stage is furnace cooling to 800°C-820°C; the second stage is air cooling to 10°C-30°C (room temperature).

[0016] In one embodiment of the present invention, in S2 and S4, the temperature of the first high temperature tempering treatment and the second high temperature tempering treatment are independently 650°C-665°C, the time is independently 3h-4.5h, and the number of times is independently 1-2 times.

[0017] In one embodiment of the present invention, in S2 and S4, the first high temperature tempering treatment and the second high temperature tempering treatment are both performed under nitrogen protection.

[0018] In one embodiment of the present invention, in S5, the quenching treatment temperature is 780°C-800°C, the holding time is 80min-100min, the carbon potential is 0.8wt%-0.9wt%, and the method is oil quenching.

[0019] In one embodiment of the present invention, in S6, the temperature of the cold treatment is -120°C to -110°C, and the time is 2h-3h.

[0020] In one embodiment of the present invention, in S6, the low temperature tempering treatment is performed at a temperature of 180°C-200°C and for a time of 3h-6h.

[0021] The second object of the present invention is to provide a high fatigue resistance heavy-duty gear steel prepared by the method described above.

[0022] The technical solution of the present invention has the following advantages over the prior art:

[0023] (1) The preparation method described in the present invention combines carburizing treatment and carbonitriding treatment to significantly increase the depth of the hardened layer and obtain an effective hardened layer with a depth of 6.60 mm to 6.85 mm, thereby overcoming the disadvantage that the depth of the hardened layer is insufficient in the carbonitriding process alone.

[0024] (2) The preparation method described in the present invention increases the temperature of carburizing treatment to allow carbon atoms to fully diffuse, significantly improves the carbon concentration in the surface layer, increases the volume fraction and average size of carbides, and improves the stability of martensite by introducing nitrogen atoms. Nitrogen-containing martensite with a depth of 1.3mm-1.5mm is obtained on the surface. The solid solution strengthening of carbon and nitrogen atoms and the precipitation strengthening of carbides effectively improve the hardness and fatigue resistance of the hardened layer, thus overcoming the disadvantage of insufficient surface hardness of the carburizing process alone.

[0025] (3) The preparation method described in the present invention ensures that 4.1%-5.4% of residual austenite is obtained in the hardened layer by regulating the temperature of the cold treatment and the low-temperature tempering treatment, which can relieve fatigue stress, inhibit the nucleation and expansion of fatigue cracks, and will not cause a significant decrease in the hardness of the hardened layer, thereby effectively improving the fatigue resistance.

[0026] (4) The surface hardness of the high fatigue resistance heavy-duty gear steel described in the present invention is 69HRC-72HRC, the tooth surface contact fatigue strength is 1808MPa-1843MPa, and the tooth root bending fatigue strength is 685MPa-736MPa; compared with the heavy-duty gear steel prepared by the existing process, the fatigue resistance is improved by more than 20%. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0028] Figure 1 This is an optical microscope image of the surface of the high fatigue resistance heavy-duty gear steel prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with specific embodiments so that those skilled in the art can better understand the present invention and implement it. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. It should be understood that the specific embodiments are only used to explain the present invention, but the embodiments are not intended to limit the present invention.

[0030] In the present invention, unless otherwise explained, technical and scientific terms used in the present invention have the same meanings as commonly understood by those skilled in the art to which the present invention belongs.

[0031] In the present invention, unless otherwise stated, the term "and / or" used in the present invention includes any and all combinations of one or more of the associated listed items.

[0032] In the present invention, unless otherwise stated, the experimental methods used in the embodiments of the present invention are conventional methods unless otherwise stated, and the materials, reagents, etc. used are all commercially available unless otherwise stated.

[0033] In the present invention, unless otherwise specified, the element composition and mass percentage of the heavy-duty gear steel 18Cr2Ni4WA used in the embodiments of the present invention are C 0.15%, Si 0.19%, Mn 0.57%, P 0.003%, S 0.003%, Cr 1.40%, Ni 4.42%, W 0.85%, and the balance is other inevitable impurities and iron.

[0034] Example 1

[0035] The high fatigue resistance heavy-duty gear steel and the preparation method thereof of this embodiment specifically include the following steps:

[0036] S1. Carburizing heavy-duty gear steel 18Cr2Ni4WA at 970°C in two stages: intensive carburizing and diffusion carburizing. The carbon potential in the intensive carburizing stage is 1.6wt%, the time is 62h, and the carbon potential in the diffusion stage is 1.0wt%, the time is 25h. After carburizing, the steel is air-cooled to room temperature.

[0037] S2. Perform a high temperature tempering treatment on the heavy-duty gear steel 18Cr2Ni4WA at a temperature of 650°C for 4.5 hours, with nitrogen protection during the high temperature tempering treatment;

[0038] S3. The heavy-duty gear steel 18Cr2Ni4WA was subjected to a two-stage carbonitriding treatment at 835°C, namely, a strong infiltration period and a diffusion period. The carbon potential in the strong infiltration period was 1.2wt%, the time was 22h, and the ammonia flow rate was 7L / min. The carbon potential in the diffusion period was 1.0wt%, the time was 8h, and the ammonia flow rate was 7L / min. After the carbonitriding treatment, the steel was first cooled to 800°C in the furnace and then air-cooled to room temperature.

[0039] S4. Perform high temperature tempering treatment twice on the heavy-duty gear steel 18Cr2Ni4WA. The high temperature tempering treatment temperature is 650℃ and the time is 4.5h. Nitrogen protection is used during the high temperature tempering treatment.

[0040] S5. Heat the heavy-duty gear steel 18Cr2Ni4WA to 780°C and keep it at this temperature for 100 min. During the heat preservation process, the carbon potential is 0.9wt%, and then immediately oil quench it to room temperature;

[0041] S6. The heavy-duty gear steel 18Cr2Ni4WA is subjected to cold treatment and low-temperature tempering treatment in sequence to obtain high fatigue resistance heavy-duty gear steel. The cold treatment temperature is -110°C for 3 hours, and the low-temperature tempering temperature is 180°C for 6 hours.

[0042] Example 2

[0043] The high fatigue resistance heavy-duty gear steel and the preparation method thereof of this embodiment specifically include the following steps:

[0044] S1. Carburizing heavy-duty gear steel 18Cr2Ni4WA at 975°C in two stages: intensive carburizing and diffusion carburizing. The carbon potential in the intensive carburizing stage is 1.5wt%, the time is 48h, and the carbon potential in the diffusion stage is 0.9wt%, the time is 17h. After carburizing, the steel is air-cooled to room temperature.

[0045] S2. Perform a high temperature tempering treatment on the heavy-duty gear steel 18Cr2Ni4WA at a temperature of 665°C for 3 hours, with nitrogen protection during the high temperature tempering treatment;

[0046] S3. Carry out carbonitriding treatment of heavy-duty gear steel 18Cr2Ni4WA at 855°C in two stages: intensive infiltration period and diffusion period. The carbon potential of the intensive infiltration period is 1.1wt%, the time is 15h, and the ammonia flow rate is 5L / min. The carbon potential of the diffusion period is 0.9wt%, the time is 5h, and the ammonia flow rate is 5L / min. After carbonitriding treatment, it is first cooled to 820°C in the furnace and then air-cooled to room temperature.

[0047] S4. Perform high temperature tempering treatment twice on the heavy-duty gear steel 18Cr2Ni4WA. The high temperature tempering treatment temperature is 665℃ and the time is 3h. Nitrogen protection is used during the high temperature tempering treatment.

[0048] S5. Heat the heavy-duty gear steel 18Cr2Ni4WA to 800°C and keep it at that temperature for 80 minutes. During the heat preservation process, the carbon potential is 0.8wt%, and then immediately oil quench it to room temperature;

[0049] S6. The heavy-duty gear steel 18Cr2Ni4WA is subjected to cold treatment and low-temperature tempering treatment in sequence to obtain high fatigue resistance heavy-duty gear steel. The cold treatment temperature is -120°C for 2 hours, and the low-temperature tempering temperature is 200°C for 3 hours.

[0050] Example 3

[0051] The high fatigue resistance heavy-duty gear steel and the preparation method thereof of this embodiment specifically include the following steps:

[0052] S1. Carburizing heavy-duty gear steel 18Cr2Ni4WA at 970°C in two stages: intensive carburizing and diffusion carburizing. The carbon potential in the intensive carburizing stage is 1.6wt%, the time is 55h, and the carbon potential in the diffusion stage is 1.0wt%, the time is 22h. After carburizing, the steel is air-cooled to room temperature.

[0053] S2. Perform a high temperature tempering treatment on the heavy-duty gear steel 18Cr2Ni4WA at a temperature of 660°C for 4 hours, with nitrogen protection during the high temperature tempering treatment;

[0054] S3. Carry out carbonitriding treatment of heavy-duty gear steel 18Cr2Ni4WA at 845°C in two stages: intensive infiltration period and diffusion period. The carbon potential of the intensive infiltration period is 1.2wt%, the time is 20h, and the ammonia flow rate is 6L / min. The carbon potential of the diffusion period is 1.0wt%, the time is 6h, and the ammonia flow rate is 6L / min. After carbonitriding treatment, it is first cooled to 810°C in the furnace and then air-cooled to room temperature.

[0055] S4. Perform high temperature tempering treatment twice on the heavy-duty gear steel 18Cr2Ni4WA. The high temperature tempering treatment temperature is 660℃ and the time is 4h. Nitrogen protection is used during the high temperature tempering treatment.

[0056] S5. Heat the heavy-duty gear steel 18Cr2Ni4WA to 790°C and keep it at this temperature for 90 minutes. During the heat preservation process, the carbon potential is 0.8wt%, and then immediately oil quench it to room temperature;

[0057] S6. The heavy-duty gear steel 18Cr2Ni4WA is subjected to cold treatment and low-temperature tempering treatment in sequence to obtain high fatigue resistance heavy-duty gear steel. The cold treatment temperature is -120°C for 3 hours, and the low-temperature tempering temperature is 180°C for 4.5 hours.

[0058] Comparative Example 1

[0059] The method is basically the same as Example 1, except that the temperature of the two-stage carburizing treatment is adjusted to 960° C., and specifically includes the following steps:

[0060] S1. Carburizing heavy-duty gear steel 18Cr2Ni4WA at 960°C in two stages: intensive carburizing and diffusion carburizing. The carbon potential in the intensive carburizing stage is 1.6wt%, the time is 62h, and the carbon potential in the diffusion stage is 1.0wt%, the time is 25h. After carburizing, the steel is air-cooled to room temperature.

[0061] S2. Perform a high temperature tempering treatment on the heavy-duty gear steel 18Cr2Ni4WA at a temperature of 650°C for 4.5 hours, with nitrogen protection during the high temperature tempering treatment;

[0062] S3. The heavy-duty gear steel 18Cr2Ni4WA was subjected to a two-stage carbonitriding treatment at 835°C, namely, a strong infiltration period and a diffusion period. The carbon potential in the strong infiltration period was 1.2wt%, the time was 22h, and the ammonia flow rate was 7L / min. The carbon potential in the diffusion period was 1.0wt%, the time was 8h, and the ammonia flow rate was 7L / min. After the carbonitriding treatment, the steel was first cooled to 800°C in the furnace and then air-cooled to room temperature.

[0063] S4. Perform high temperature tempering treatment twice on the heavy-duty gear steel 18Cr2Ni4WA. The high temperature tempering treatment temperature is 650℃ and the time is 4.5h. Nitrogen protection is used during the high temperature tempering treatment.

[0064] S5. Heat the heavy-duty gear steel 18Cr2Ni4WA to 780°C and keep it at this temperature for 100 min. During the heat preservation process, the carbon potential is 0.9wt%, and then immediately oil quench it to room temperature;

[0065] S6. The heavy-duty gear steel 18Cr2Ni4WA is subjected to cold treatment and low-temperature tempering treatment in sequence to obtain high fatigue resistance heavy-duty gear steel. The cold treatment temperature is -110°C for 3 hours, and the low-temperature tempering temperature is 180°C for 6 hours.

[0066] Comparative Example 2

[0067] The method is basically the same as Example 1, except that the temperature of the cold treatment is adjusted to -100°C, and specifically comprises the following steps:

[0068] S1. Carburizing heavy-duty gear steel 18Cr2Ni4WA at 970°C in two stages: intensive carburizing and diffusion carburizing. The carbon potential in the intensive carburizing stage is 1.6wt%, the time is 62h, and the carbon potential in the diffusion stage is 1.0wt%, the time is 25h. After carburizing, the steel is air-cooled to room temperature.

[0069] S2. Perform a high temperature tempering treatment on the heavy-duty gear steel 18Cr2Ni4WA at a temperature of 650°C for 4.5 hours, with nitrogen protection during the high temperature tempering treatment;

[0070] S3. The heavy-duty gear steel 18Cr2Ni4WA was subjected to a two-stage carbonitriding treatment at 835°C, namely, a strong infiltration period and a diffusion period. The carbon potential in the strong infiltration period was 1.2wt%, the time was 22h, and the ammonia flow rate was 7L / min. The carbon potential in the diffusion period was 1.0wt%, the time was 8h, and the ammonia flow rate was 7L / min. After the carbonitriding treatment, the steel was first cooled to 800°C in the furnace and then air-cooled to room temperature.

[0071] S4. Perform high temperature tempering treatment twice on the heavy-duty gear steel 18Cr2Ni4WA. The high temperature tempering treatment temperature is 650℃ and the time is 4.5h. Nitrogen protection is used during the high temperature tempering treatment.

[0072] S5. Heat the heavy-duty gear steel 18Cr2Ni4WA to 780°C and keep it at this temperature for 100 min. During the heat preservation process, the carbon potential is 0.9wt%, and then immediately oil quench it to room temperature;

[0073] S6. The heavy-duty gear steel 18Cr2Ni4WA is subjected to cold treatment and low-temperature tempering treatment in sequence to obtain high fatigue resistance heavy-duty gear steel. The cold treatment temperature is -100°C for 3 hours, and the low-temperature tempering temperature is 180°C for 6 hours.

[0074] Comparative Example 3

[0075] The method is basically the same as Example 1, except that the temperature of the low-temperature tempering treatment is adjusted to 220° C., and specifically includes the following steps:

[0076] S1. Carburizing heavy-duty gear steel 18Cr2Ni4WA at 970°C in two stages: intensive carburizing and diffusion carburizing. The carbon potential in the intensive carburizing stage is 1.6wt%, the time is 62h, and the carbon potential in the diffusion stage is 1.0wt%, the time is 25h. After carburizing, the steel is air-cooled to room temperature.

[0077] S2. Perform a high temperature tempering treatment on the heavy-duty gear steel 18Cr2Ni4WA at a temperature of 650°C for 4.5 hours, with nitrogen protection during the high temperature tempering treatment;

[0078] S3. The heavy-duty gear steel 18Cr2Ni4WA was subjected to a two-stage carbonitriding treatment at 835°C, namely, a strong infiltration period and a diffusion period. The carbon potential in the strong infiltration period was 1.2wt%, the time was 22h, and the ammonia flow rate was 7L / min. The carbon potential in the diffusion period was 1.0wt%, the time was 8h, and the ammonia flow rate was 7L / min. After the carbonitriding treatment, the steel was first cooled to 800°C in the furnace and then air-cooled to room temperature.

[0079] S4. Perform high temperature tempering treatment twice on the heavy-duty gear steel 18Cr2Ni4WA. The high temperature tempering treatment temperature is 650℃ and the time is 4.5h. Nitrogen protection is used during the high temperature tempering treatment.

[0080] S5. Heat the heavy-duty gear steel 18Cr2Ni4WA to 780°C and keep it at this temperature for 100 min. During the heat preservation process, the carbon potential is 0.9wt%, and then immediately oil quench it to room temperature;

[0081] S6. The heavy-duty gear steel 18Cr2Ni4WA is subjected to cold treatment and low-temperature tempering treatment in sequence to obtain high fatigue resistance heavy-duty gear steel. The cold treatment temperature is -110°C for 3 hours, and the low-temperature tempering temperature is 220°C for 6 hours.

[0082] Comparative Example 4

[0083] The method is basically the same as Example 1, except that no two-stage carbonitriding treatment and staged cooling treatment are performed between the first high-temperature tempering treatment and the second high-temperature tempering treatment. Specifically, the method comprises the following steps:

[0084] S1. Carburizing heavy-duty gear steel 18Cr2Ni4WA at 970°C in two stages: intensive carburizing and diffusion carburizing. The carbon potential in the intensive carburizing stage is 1.6wt%, the time is 62h, and the carbon potential in the diffusion stage is 1.0wt%, the time is 25h. After carburizing, the steel is air-cooled to room temperature.

[0085] S2. Perform a high temperature tempering treatment on the heavy-duty gear steel 18Cr2Ni4WA at a temperature of 650°C for 4.5 hours, with nitrogen protection during the high temperature tempering treatment;

[0086] S3. Perform a high temperature tempering treatment on the heavy-duty gear steel 18Cr2Ni4WA at a temperature of 650°C for 4.5 hours, with nitrogen protection during the high temperature tempering treatment;

[0087] S4, heating the heavy-duty gear steel 18Cr2Ni4WA to 780°C and keeping the temperature for 100 min, during which the carbon potential is 0.9wt%, and then immediately oil quenching to room temperature;

[0088] S5. The heavy-duty gear steel 18Cr2Ni4WA is subjected to cold treatment and low-temperature tempering treatment in sequence to obtain high fatigue resistance heavy-duty gear steel. The cold treatment temperature is -110°C for 3 hours, and the low-temperature tempering temperature is 180°C for 6 hours.

[0089] Test Example 1

[0090] The high fatigue resistance heavy-duty gear steel of Example 1 was characterized, and the results are as follows: Figure 1 As shown. Figure 1 It can be seen that the surface structure is composed of martensite, retained austenite and carbide. The content of retained austenite is 5.4%, the effective hardened layer depth is 6.60mm, and the depth of nitrogen-containing martensite is 1.3mm, which effectively improves the fatigue resistance.

[0091] Test Example 2

[0092] The retained austenite content, effective hardened layer depth, surface nitrogen-containing martensite depth, surface hardness and fatigue resistance (tooth surface contact fatigue strength and tooth root bending fatigue strength) of the heavy-duty gear steels of Examples 1-3 and Comparative Examples 1-4 were tested:

[0093] Retained austenite content: Tested in accordance with the standard "YB / T 5338-2019 X-ray diffractometer method for quantitative determination of austenite in steel";

[0094] Effective hardened layer depth and surface nitrogen-containing martensite depth: refer to the standard test of "GB / T 9450-2005 Determination and verification of carburizing and quenching hardened layer depth of steel parts";

[0095] Surface hardness: Tested in accordance with GB / T 4340.1-2009 Metallic Materials Vickers Hardness Test Part 1: Test Methods;

[0096] Fatigue resistance: Tested in accordance with the standards "GB / T 14229-2021 Gear contact fatigue strength test method" and "GB / T14230-1993 Gear bending fatigue strength test method".

[0097] Table 1 shows the final measured properties of the heavy-duty gear steel:

[0098] Table 1

[0099]

[0100] It can be seen from Table 1 that the high fatigue resistance heavy-duty gear steel obtained in the embodiment has good fatigue resistance, the tooth surface contact fatigue strength is 1808MPa-1843MPa, and the tooth root bending fatigue strength is 685MPa-736MPa.

[0101] Comparing Example 1 with Comparative Example 1, it can be seen that the tooth surface contact fatigue strength and tooth root bending fatigue strength of the heavy-duty gear steel in Comparative Example 1 are lower than those in Example 1. This is because the temperature of the two-stage carburizing treatment in Comparative Example 1 is lower than that in Example 1, resulting in a high content of retained austenite, a low effective hardened layer depth and a low surface hardness, which significantly reduces the fatigue resistance.

[0102] Comparing Example 1 and Comparative Example 2, it can be seen that the tooth surface contact fatigue strength and tooth root bending fatigue strength of the heavy-duty gear steel in Comparative Example 2 are lower than those in Example 1. This is because the cold treatment temperature in Comparative Example 2 is higher than that in Example 1, resulting in a higher content of retained austenite and lower surface hardness, which significantly reduces the fatigue resistance.

[0103] Comparing Example 1 and Comparative Example 3, it can be seen that the tooth surface contact fatigue strength and tooth root bending fatigue strength of the heavy-duty gear steel in Comparative Example 3 are lower than those in Example 1. This is because the temperature of the low-temperature tempering treatment in Comparative Example 3 is higher than that in Example 1, resulting in low residual austenite content and surface hardness, which leads to a significant decrease in fatigue resistance.

[0104] Comparing Examples 1-3 and Comparative Example 4, it can be seen that the tooth surface contact fatigue strength and tooth root bending fatigue strength of the heavy-duty gear steel prepared in the examples are both increased by more than 20%, and the fatigue resistance is greatly improved. This is because Examples 1-3 combine carburizing treatment and carbonitriding treatment, significantly increase the effective hardened layer depth, and introduce nitrogen atoms to obtain nitrogen-containing martensite with a depth of 1.3mm-1.5mm in the surface layer, significantly increase the surface hardness, and obtain 4.1%-5.4% of residual austenite, effectively improving the fatigue resistance.

[0105] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for preparing high fatigue resistance heavy-duty gear steel, characterized in that: The following steps are involved: S1. Carburizing the heavy-duty gear steel at 970° C.-975° C. in two stages; the two-stage carburizing treatment includes a first intensive carburizing period and a first diffusion period; S2, subjecting the heavy-duty gear steel obtained in S1 to a first high-temperature tempering treatment; S3, subjecting the heavy-duty gear steel obtained in S2 to a two-stage carbonitriding treatment at 835° C.-855° C. and a staged cooling treatment; the two-stage carbonitriding treatment includes a second strong permeation period and a second diffusion period; S4, performing a second high temperature tempering treatment on the heavy-duty gear steel obtained in S3; S5, quenching the heavy-duty gear steel obtained in S4; S6. Perform cold treatment and low-temperature tempering treatment on the heavy-duty gear steel obtained in S5 to obtain the high fatigue resistance heavy-duty gear steel.

2. The method for preparing high fatigue resistance heavy-duty gear steel according to claim 1, characterized in that: In S1, the element composition and mass percentage of the heavy-duty gear steel are: C 0.14%-0.16%, Si 0.17%-0.20%, Mn 0.53%-0.60%, P 0-0.006%, S 0-0.005%, Cr 1.37%-1.43%, Ni 4.39%-4.45%, W0.83%-0.88%, and the remainder is other inevitable impurities and iron.

3. The method for preparing high fatigue resistance heavy-duty gear steel according to claim 1, characterized in that: In S1, the carbon potential of the first strong infiltration period is 1.5wt%-1.6wt%, and the time is 48h-62h; the carbon potential of the first diffusion period is 0.9wt%-1.0wt%, and the time is 17h-25h.

4. The method for preparing high fatigue resistance heavy-duty gear steel according to claim 1, characterized in that: In S3, the carbon potential of the second strong penetration period is 1.1wt%-1.2wt%, the time is 15h-22h, and the ammonia flow rate is 5L / min-7L / min; The carbon potential of the second diffusion period is 0.9wt%-1.0wt%, the time is 5h-8h, and the ammonia flow rate is 5L / min-7L / min.

5. The method for preparing high fatigue resistance heavy-duty gear steel according to claim 1, characterized in that: In S3, the staged cooling treatment includes two stages. The first stage is furnace cooling to 800°C-820°C; the second stage is air cooling to 10°C-30°C.

6. The method for preparing high fatigue resistance heavy-duty gear steel according to claim 1, characterized in that: In S2 and S4, the temperatures of the first high temperature tempering treatment and the second high temperature tempering treatment are independently 650° C.-665° C., the time is independently 3 h-4.5 h, and the number of times is independently 1-2 times.

7. The method for preparing high fatigue resistance heavy-duty gear steel according to claim 1, characterized in that: In S5, the quenching treatment temperature is 780°C-800°C, the holding time is 80min-100min, the carbon potential is 0.8wt%-0.9wt%, and the method is oil quenching.

8. The method for preparing high fatigue resistance heavy-duty gear steel according to claim 1, characterized in that: In S6, the temperature of the cold treatment is -120°C to -110°C, and the time is 2h-3h.

9. The method for preparing high fatigue resistance heavy-duty gear steel according to claim 1, characterized in that: In S6, the low temperature tempering treatment is performed at a temperature of 180°C-200°C and for a time of 3h-6h.

10. A steel for heavy-duty gears with high fatigue resistance prepared by the method according to any one of claims 1 to 9.

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