18Cr2Ni4WA gear steel and preparation method thereof

Abstract

The invention relates to 18Cr2Ni4WA gear steel and a preparation method thereof, and belongs to the technical field of metal materials. The preparation method comprises the following steps that S1, raw materials of the 18Cr2Ni4WA gear steel are sequentially subjected to smelting, forging, normalizing, tempering, size machining and annealing, and a blank is obtained; s2, the blank is subjected to carburizing treatment, and the steel for the heavy-duty gear is obtained; s3, carrying out high-temperature tempering treatment on the steel for the heavy-duty gear; s4, the steel for the heavy-duty gear is subjected to carbonitriding treatment; and S5, the steel for the heavy-duty gear is subjected to cold treatment and low-temperature tempering treatment, and the 18Cr2Ni4WA gear steel is obtained. According to the 18Cr2Ni4WA gear steel, the effective hardened layer thickness ranges from 5.50 mm to 5.75 mm, the surface hardness ranges from 65 HRC to 68 HRC, the surface layer tensile strength ranges from 2146 MPa to 2185 MPa, the surface layer yield strength ranges from 1553 MPa to 1587 MPa, the percentage elongation after fracture ranges from 4.2% to 4.5%, and the impact energy ranges from 83 J to 88 J.

Description

Technical Field

[0001] The invention belongs to the technical field of metal materials, and in particular relates to 18Cr2Ni4WA gear steel and a preparation method thereof. Background Art

[0002] At present, coal-fired power still accounts for about half of the world's electricity generation, which makes the green transformation of the coal-fired power industry particularly critical. In the coal-fired power industry chain, the coal mining industry, as an important upstream industry, has made a significant contribution to achieving the carbon reduction goals of the coal-fired power industry. In coal mining operations, gears, as one of the core components, are subject to huge load impacts. Due to the harsh environment at the coal mining site, coal particles, dust and other particles are often attached to the surface of the gears. These particles not only cause abrasive wear, but also further aggravate the deterioration of the service conditions of the gears.

[0003] In order to meet this challenge, carburizing technology is widely used in the industry to improve the comprehensive performance of gear steel. Invention patent CN109321739A discloses a heat treatment process for heavy-duty gears with large carburization layers, which increases the effective hardened layer depth by heating the gears to 915℃-945℃ and carburizing and keeping them warm for 175h-232h. Invention patent CN113234998A discloses a Nb-Ti micro-alloyed high-temperature carburized gear steel and its manufacturing method, which solves the problem of austenite grain coarsening during high-temperature carburizing by micro-alloying the raw material Nb-Ti, shortens the carburizing heat treatment process time, and reduces energy consumption. Invention patent CN117758199A discloses a high-temperature carburizing and double quenching process method for heavy-duty gear steel, which refines the austenite grains by combining high-temperature carburizing with two quenchings. However, the carburizing process alone still cannot meet the requirements of 18Cr2Ni4WA gear steel for hardened layer thickness and surface toughness. It is urgent to develop a new economical and high-performance processing method to significantly increase the service life of 18Cr2Ni4WA gear steel. This will not only ensure the efficient and stable operation of coal mining operations, but also help promote the greening process of the coal-fired power industry and make positive contributions to achieving the goals of carbon peak and carbon neutrality. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides an 18Cr2Ni4WA gear steel and a preparation method thereof, which combines carburizing treatment and carbonitriding treatment, so that the carbon concentration in the surface layer of the 18Cr2Ni4WA gear steel is improved, and the higher carburizing concentration increases the volume fraction of carbides and the proportion of large-size carbides; nitrogen-containing martensite is formed on the surface, and the introduction of nitrogen atoms improves the stability of the martensite and improves the strength and toughness of the 18Cr2Ni4WA gear steel.

[0005] The first object of the present invention is to provide a method for preparing 18Cr2Ni4WA gear steel, comprising the following steps:

[0006] S1. The raw material of 18Cr2Ni4WA gear steel is sequentially smelted, forged, normalized, tempered, dimensionally processed and annealed to obtain a blank; the chemical composition and mass percentage of the raw material of 18Cr2Ni4WA gear steel are: C 0.15%-0.18%, Cr 1.45%-1.63%, Si 0.22%-0.35%, Mn 0.37%-0.58%, W 0.82%-1.05%, Ni4.16%-4.25%, P 0-0.010%, S 0-0.008%, and the balance is other inevitable impurities and iron;

[0007] S2, carburizing the blank obtained in S1 to obtain steel for heavy-duty gears;

[0008] S3, subjecting the heavy-duty gear steel obtained in S2 to high-temperature tempering treatment;

[0009] S4, performing carbonitriding treatment on the heavy-duty gear steel obtained in S3;

[0010] S5. The heavy-duty gear steel obtained in S4 is subjected to cold treatment and low-temperature tempering treatment to obtain the 18Cr2Ni4WA gear steel.

[0011] In one embodiment of the present invention, in S1, the smelting temperature is 1510°C-1530°C; the smelting equipment is an electric arc furnace or a vacuum induction furnace.

[0012] In one embodiment of the present invention, in S1, the forging ratio of the forging is not less than 3.2.

[0013] In one embodiment of the present invention, in S1, the normalizing temperature is 940°C-980°C, and the time is 5h-10h; the tempering temperature is 650°C-690°C, and the time is 3h-7.5h; the annealing temperature is 200°C-400°C, and the time is 3h-5h.

[0014] In one embodiment of the present invention, in S2, the carburizing treatment is performed at a temperature of 915°C-935°C, a carbon potential of 1.2wt%-1.4wt%, and a time of 100h-205h.

[0015] In one embodiment of the present invention, in S3, the high temperature tempering treatment is performed at a temperature of 640°C-690°C, for a time of 3h-7.5h, and twice.

[0016] In one embodiment of the present invention, in S4, the carbonitriding treatment temperature is 830°C-920°C, the carbon potential is 1.0wt%-1.2wt%, the ammonia flow rate is 4L / min-6L / min, and the time is 10h-30h.

[0017] In one embodiment of the present invention, in S5, the temperature of the cold treatment is -100°C to -70°C, and the time is 2h-3h.

[0018] In one embodiment of the present invention, in S5, the low temperature tempering treatment is performed at a temperature of 180°C-250°C and for a time of 3h-8h.

[0019] The second object of the present invention is to provide an 18Cr2Ni4WA gear steel prepared by the method described above.

[0020] The technical solution of the present invention has the following advantages over the prior art:

[0021] (1) The preparation method of the present invention combines carburizing treatment and carbonitriding treatment, which can increase the carbon concentration of the surface layer and promote the formation of more carbides. In addition, the introduction of nitrogen atoms after the carburizing-carbonitriding composite treatment can enhance the stability of martensite. Nitrogen-containing martensite is formed on the surface of 18Cr2Ni4WA gear steel. The nitrogen atoms in the nitrogen-containing martensite have the effect of solid solution strengthening, causing lattice distortion, hindering dislocation movement, and improving the strength and hardness of the material.

[0022] (2) The preparation method of the present invention combines carburizing and carbonitriding, which overcomes the disadvantages of high hardness but shallow carburizing layer in carburizing alone and low surface hardness in carburizing alone. Direct oil cooling to room temperature after carbonitriding can obtain a full martensitic structure while simplifying the process flow, ensuring a high strength-toughness combination.

[0023] (3) The cold treatment temperature used in the preparation method described in the present invention is carefully designed according to the composition of the 18Cr2Ni4WA gear steel, with the purpose of ensuring that the austenite content in the hardened layer is precisely controlled within the range of 7%-10%, aiming to improve the plasticity and toughness of the hardened layer by retaining an appropriate amount of austenite, thereby extending the service life of the 18Cr2Ni4WA gear steel.

[0024] (4) The effective hardened layer thickness of the 18Cr2Ni4WA gear steel described in the present invention is 5.50mm-5.75mm, the surface hardness is 65HRC-68HRC, the surface tensile strength is 2146MPa-2185MPa, the surface yield strength is 1553MPa-1587MPa, the elongation after fracture is 4.2%-4.5%, and the impact energy is 83J-88J. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] 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:

[0026] Figure 1 This is an optical microscope image of the 18Cr2Ni4WA gear steel prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] Example 1

[0032] The 18Cr2Ni4WA gear steel and the preparation method thereof of this embodiment specifically include the following steps:

[0033] S1. The raw materials are prepared according to the following mass percentage composition: C 0.15%, Cr 1.63%, Si 0.22%, Mn 0.48%, W 1.05%, Ni 4.25%, P 0.010%, S 0.007%, and the rest are other inevitable impurities and iron, and are smelted into steel ingots by an electric arc furnace at a smelting temperature of 1510°C; the steel ingots are sequentially forged, normalized, tempered, dimensionally processed and annealed to form gear steel billets; the forging ratio is 3.2; the normalizing temperature is 940°C for 10 hours; the tempering temperature is 650°C for 7.5 hours; the annealing temperature is 200°C for 5 hours;

[0034] S2, carburizing the gear steel blank at a temperature of 915°C, a carbon potential of 1.4wt%, and a time of 205h, and cooling to room temperature after the carburizing treatment;

[0035] S3, perform two high temperature tempering treatments on the gear steel, i.e., heat to 640°C and keep it for 7.5h for the first tempering, and then heat to 640°C and keep it for 7.5h for the second tempering;

[0036] S4, performing carbonitriding treatment on the gear steel, wherein the carbonitriding treatment temperature is 830°C, the carbon potential is 1.2wt%, the ammonia flow rate is 6L / min, and the time is 30h. After the carbonitriding treatment, the gear steel is directly oil-cooled to room temperature;

[0037] S5. The gear steel is subjected to cold treatment and low-temperature tempering treatment in sequence to obtain 18Cr2Ni4WA gear steel; the cold treatment temperature is -70°C and the time is 3h; the low-temperature tempering temperature is 180°C and the time is 8h.

[0038] Example 2

[0039] The 18Cr2Ni4WA gear steel and the preparation method thereof of this embodiment specifically include the following steps:

[0040] S1. The raw materials are prepared according to the following mass percentage composition: C 0.18%, Cr 1.45%, Si 0.35%, Mn 0.37%, W 0.82%, Ni 4.16%, P 0.010%, S 0.008%, and the rest are other inevitable impurities and iron, and are smelted into steel ingots by a vacuum induction furnace at a smelting temperature of 1530°C; the steel ingots are sequentially forged, normalized, tempered, dimensionally processed and annealed to form gear steel billets; the forging ratio is 3.3; the normalizing temperature is 980°C for 5h; the tempering temperature is 690°C for 3h; the annealing temperature is 400°C for 3h;

[0041] S2, carburizing the gear steel blank at a temperature of 935°C, a carbon potential of 1.2wt%, and a time of 100h, and cooling to room temperature after the carburizing treatment;

[0042] S3, the gear steel is subjected to two high temperature tempering treatments, that is, heating to 690°C and keeping the temperature for 3 hours for the first tempering, and then heating to 690°C and keeping the temperature for 3 hours for the second tempering;

[0043] S4, performing carbonitriding treatment on the gear steel, wherein the carbonitriding treatment temperature is 920°C, the carbon potential is 1.0wt%, the ammonia flow rate is 4L / min, and the time is 10h. After the carbonitriding treatment, the gear steel is directly oil-cooled to room temperature;

[0044] S5. The gear steel is subjected to cold treatment and low-temperature tempering treatment in sequence to obtain 18Cr2Ni4WA gear steel; the cold treatment temperature is -100°C and the time is 2h; the low-temperature tempering temperature is 250°C and the time is 3h.

[0045] Example 3

[0046] The 18Cr2Ni4WA gear steel and the preparation method thereof of this embodiment specifically include the following steps:

[0047] S1. The raw materials are prepared according to the following mass percentage composition: C 0.16%, Cr 1.54%, Si 0.27%, Mn 0.50%, W 0.93%, Ni 4.19%, P 0.008%, S 0.006%, and the rest are other inevitable impurities and iron, and are smelted into steel ingots by an electric arc furnace at a smelting temperature of 1520°C; the steel ingots are sequentially forged, normalized, tempered, dimensionally processed and annealed to form gear steel billets; the forging ratio is 3.2; the normalizing temperature is 960°C for 7.5h; the tempering temperature is 670°C for 5h; the annealing temperature is 300°C for 4h;

[0048] S2, carburizing the gear steel blank at a temperature of 930°C, a carbon potential of 1.3wt%, and a time of 153h, and cooling to room temperature after the carburizing treatment;

[0049] S3, perform two high temperature tempering treatments on the gear steel, i.e., heat to 660°C and keep it for 5 hours for the first tempering, and then heat to 660°C and keep it for 5 hours for the second tempering;

[0050] S4, performing carbonitriding treatment on the gear steel, wherein the carbonitriding treatment temperature is 880°C, the carbon potential is 1.1wt%, the ammonia flow rate is 5L / min, and the time is 20h, and the gear steel is directly oil-cooled to room temperature after the carbonitriding treatment;

[0051] S5. The gear steel is subjected to cold treatment and low-temperature tempering treatment in sequence to obtain 18Cr2Ni4WA gear steel; the cold treatment temperature is -90°C and the time is 2.5h; the low-temperature tempering temperature is 220°C and the time is 5.5h.

[0052] Example 4

[0053] The 18Cr2Ni4WA gear steel and the preparation method thereof of this embodiment specifically include the following steps:

[0054] S1. The raw materials are prepared according to the following mass percentage composition: C 0.17%, Cr 1.62%, Si 0.29%, Mn 0.43%, W 1.03%, Ni 4.22%, P 0.009%, S 0.006%, and the rest are other inevitable impurities and iron, and are smelted into steel ingots by a vacuum induction furnace at a smelting temperature of 1510°C; the steel ingots are forged, normalized, tempered, dimensioned and annealed in sequence to form gear steel billets; the forging ratio is 3.4; the normalizing temperature is 960°C for 10 hours; the tempering temperature is 690°C for 5.5 hours; the annealing temperature is 300°C for 5 hours;

[0055] S2, carburizing the gear steel blank at a temperature of 925°C, a carbon potential of 1.2wt%, and a time of 204h, and cooling to room temperature after carburizing;

[0056] S3, the gear steel is subjected to two high temperature tempering treatments, that is, heating to 660°C and keeping the temperature for 7.5 hours for the first tempering, and then heating to 660°C and keeping the temperature for 7.5 hours for the second tempering;

[0057] S4, performing carbonitriding treatment on the gear steel, wherein the carbonitriding treatment temperature is 880°C, the carbon potential is 1.2wt%, the ammonia flow rate is 6L / min, and the time is 30h. After the carbonitriding treatment, the gear steel is directly oil-cooled to room temperature;

[0058] S5. The gear steel is subjected to cold treatment and low-temperature tempering treatment in sequence to obtain 18Cr2Ni4WA gear steel; the cold treatment temperature is -100°C and the time is 3h; the low-temperature tempering treatment temperature is 220°C and the time is 8h.

[0059] Comparative Example 1

[0060] The process is basically the same as Example 1, except that the temperature of the cold treatment is adjusted to -60°C, and specifically comprises the following steps:

[0061] S1. The raw materials are prepared according to the following mass percentage composition: C 0.15%, Cr 1.63%, Si 0.22%, Mn 0.48%, W 1.05%, Ni 4.25%, P 0.010%, S 0.007%, and the rest are other inevitable impurities and iron, and are smelted into steel ingots by an electric arc furnace at a smelting temperature of 1510°C; the steel ingots are sequentially forged, normalized, tempered, dimensionally processed and annealed to form gear steel billets; the forging ratio is 3.2; the normalizing temperature is 940°C for 10 hours; the tempering temperature is 650°C for 7.5 hours; the annealing temperature is 200°C for 5 hours;

[0062] S2, carburizing the gear steel blank at a temperature of 915°C, a carbon potential of 1.4wt%, and a time of 205h, and cooling to room temperature after the carburizing treatment;

[0063] S3, perform two high temperature tempering treatments on the gear steel, i.e., heat to 640°C and keep it for 7.5h for the first tempering, and then heat to 640°C and keep it for 7.5h for the second tempering;

[0064] S4, performing carbonitriding treatment on the gear steel, wherein the carbonitriding treatment temperature is 830°C, the carbon potential is 1.2wt%, the ammonia flow rate is 6L / min, and the time is 30h. After the carbonitriding treatment, the gear steel is directly oil-cooled to room temperature;

[0065] S5. The gear steel is subjected to cold treatment and low-temperature tempering treatment in sequence to obtain 18Cr2Ni4WA gear steel; the cold treatment temperature is -60°C and the time is 3h; the low-temperature tempering temperature is 180°C and the time is 8h.

[0066] Comparative Example 2

[0067] The method is basically the same as Example 1, except that the mass percentage of Ni is adjusted to 3.67%, and specifically includes the following steps:

[0068] S1. The raw materials are prepared according to the following mass percentage composition: C 0.15%, Cr 1.63%, Si 0.22%, Mn 0.48%, W 1.05%, Ni 3.67%, P 0.010%, S 0.007%, and the rest are other inevitable impurities and iron, and are smelted into steel ingots by an electric arc furnace at a smelting temperature of 1510°C; the steel ingots are sequentially forged, normalized, tempered, dimensionally processed and annealed to form gear steel billets; the forging ratio is 3.2; the normalizing temperature is 940°C for 10 hours; the tempering temperature is 650°C for 7.5 hours; the annealing temperature is 200°C for 5 hours;

[0069] S2, carburizing the gear steel blank at a temperature of 915°C, a carbon potential of 1.4wt%, and a time of 205h, and cooling to room temperature after the carburizing treatment;

[0070] S3, perform two high temperature tempering treatments on the gear steel, i.e., heat to 640°C and keep it for 7.5h for the first tempering, and then heat to 640°C and keep it for 7.5h for the second tempering;

[0071] S4, performing carbonitriding treatment on the gear steel, wherein the carbonitriding treatment temperature is 830°C, the carbon potential is 1.2wt%, the ammonia flow rate is 6L / min, and the time is 30h. After the carbonitriding treatment, the gear steel is directly oil-cooled to room temperature;

[0072] S5. The gear steel is subjected to cold treatment and low-temperature tempering treatment in sequence to obtain 18Cr2Ni4WA gear steel; the cold treatment temperature is -70°C and the time is 3h; the low-temperature tempering temperature is 180°C and the time is 8h.

[0073] Comparative Example 3

[0074] The method is basically the same as Example 1, except that the temperature of the carburizing treatment is adjusted to 905° C., and specifically includes the following steps:

[0075] S1. The raw materials are prepared according to the following mass percentage composition: C 0.15%, Cr 1.63%, Si 0.22%, Mn 0.48%, W 1.05%, Ni 4.25%, P 0.010%, S 0.007%, and the rest are other inevitable impurities and iron, and are smelted into steel ingots by an electric arc furnace at a smelting temperature of 1510°C; the steel ingots are sequentially forged, normalized, tempered, dimensionally processed and annealed to form gear steel billets; the forging ratio is 3.2; the normalizing temperature is 940°C for 10 hours; the tempering temperature is 650°C for 7.5 hours; the annealing temperature is 200°C for 5 hours;

[0076] S2, carburizing the gear steel blank at a temperature of 905°C, a carbon potential of 1.4wt%, and a time of 205h, and cooling to room temperature after the carburizing treatment;

[0077] S3, perform two high temperature tempering treatments on the gear steel, i.e., heat to 640°C and keep it for 7.5h for the first tempering, and then heat to 640°C and keep it for 7.5h for the second tempering;

[0078] S4, performing carbonitriding treatment on the gear steel, wherein the carbonitriding treatment temperature is 830°C, the carbon potential is 1.2wt%, the ammonia flow rate is 6L / min, and the time is 30h. After the carbonitriding treatment, the gear steel is directly oil-cooled to room temperature;

[0079] S5. The gear steel is subjected to cold treatment and low-temperature tempering treatment in sequence to obtain 18Cr2Ni4WA gear steel; the cold treatment temperature is -70°C and the time is 3h; the low-temperature tempering temperature is 180°C and the time is 8h.

[0080] Comparative Example 4

[0081] The method is basically the same as Example 1, except that the carbonitriding treatment is replaced by nitriding treatment, which specifically includes the following steps:

[0082] S1. The raw materials are prepared according to the following mass percentage composition: C 0.15%, Cr 1.63%, Si 0.22%, Mn 0.48%, W 1.05%, Ni 4.25%, P 0.010%, S 0.007%, and the rest are other inevitable impurities and iron, and are smelted into steel ingots by an electric arc furnace at a smelting temperature of 1510°C; the steel ingots are sequentially forged, normalized, tempered, dimensionally processed and annealed to form gear steel billets; the forging ratio is 3.2; the normalizing temperature is 940°C for 10 hours; the tempering temperature is 650°C for 7.5 hours; the annealing temperature is 200°C for 5 hours;

[0083] S2, carburizing the gear steel blank at a temperature of 915°C, a carbon potential of 1.4wt%, and a time of 205h, and cooling to room temperature after the carburizing treatment;

[0084] S3, perform two high temperature tempering treatments on the gear steel, i.e., heat to 640°C and keep it for 7.5h for the first tempering, and then heat to 640°C and keep it for 7.5h for the second tempering;

[0085] S4. Perform nitriding treatment on the gear steel. The nitriding temperature is 830°C, the ammonia flow rate is 6L / min, and the time is 30h. After the nitriding treatment, the gear steel is directly oil-cooled to room temperature.

[0086] S5. The gear steel is subjected to cold treatment and low-temperature tempering treatment in sequence to obtain 18Cr2Ni4WA gear steel; the cold treatment temperature is -70°C and the time is 3h; the low-temperature tempering temperature is 180°C and the time is 8h.

[0087] Comparative Example 5

[0088] The method is basically the same as Example 1, except that no carbonitriding treatment is performed between the high-temperature tempering treatment and the cold treatment. The gear steel is only heated to 830° C. and kept for 30 hours, and then directly oil-cooled to room temperature. Specifically, the following steps are included:

[0089] S1. The raw materials are prepared according to the following mass percentage composition: C 0.15%, Cr 1.63%, Si 0.22%, Mn 0.48%, W 1.05%, Ni 4.25%, P 0.010%, S 0.007%, and the rest are other inevitable impurities and iron, and are smelted into steel ingots by an electric arc furnace at a smelting temperature of 1510°C; the steel ingots are sequentially forged, normalized, tempered, dimensionally processed and annealed to form gear steel billets; the forging ratio is 3.2; the normalizing temperature is 940°C for 10 hours; the tempering temperature is 650°C for 7.5 hours; the annealing temperature is 200°C for 5 hours;

[0090] S2, carburizing the gear steel blank at a temperature of 915°C, a carbon potential of 1.4wt%, and a time of 205h, and cooling to room temperature after the carburizing treatment;

[0091] S3, perform two high temperature tempering treatments on the gear steel, i.e., heat to 640°C and keep it for 7.5h for the first tempering, and then heat to 640°C and keep it for 7.5h for the second tempering;

[0092] S4, heat the gear steel to 830℃ and keep it at that temperature for 30h, then directly oil cool it to room temperature;

[0093] S5. The gear steel is subjected to cold treatment and low-temperature tempering treatment in sequence to obtain 18Cr2Ni4WA gear steel; the cold treatment temperature is -70°C and the time is 3h; the low-temperature tempering temperature is 180°C and the time is 8h.

[0094] Test Example 1

[0095] The 18Cr2Ni4WA 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 7.8%, and the effective hardened layer depth is 5.50mm, which effectively improves the surface hardness and toughness.

[0096] Test Example 2

[0097] The retained austenite content, effective hardened layer depth, surface hardness, surface tensile properties (tensile strength, yield strength and elongation after fracture) and impact properties of the 18Cr2Ni4WA gear steel of Examples 1-4 and Comparative Examples 1-5 were tested:

[0098] Retained austenite content: Tested in accordance with the standard "YB / T 5338-2019 X-ray diffractometer method for quantitative determination of austenite in steel";

[0099] Effective hardened layer: Tested in accordance with the standard GB / T 9450-2005 Determination and verification of the depth of carburizing and quenching hardened layer of steel parts;

[0100] Surface hardness: Tested in accordance with GB / T 4340.1-2009 Metallic Materials Vickers Hardness Test Part 1: Test Methods;

[0101] Surface tensile properties: Tested in accordance with GB / T 228.1-2021 Metallic material tensile test Part 1: Room temperature test method;

[0102] Impact performance: Tested in accordance with GB / T 229-2020 Metal Materials Charpy Pendulum Impact Test Method.

[0103] Table 1 shows the relevant properties of the 18Cr2Ni4WA gear steel finally measured:

[0104] Table 1

[0105]

[0106] As can be seen from Table 1, the 18Cr2Ni4WA gear steel obtained in the embodiment has high surface hardness, surface tensile properties and impact properties, the surface hardness is 65HRC-68HRC, the surface tensile strength is 2146MPa-2185MPa, the surface yield strength is 1553MPa-1587MPa, the elongation after fracture is 4.2%-4.5%, and the impact energy is 83J-88J.

[0107] Comparison of Example 1 and Comparative Example 1 shows that the surface hardness, surface tensile strength, surface yield strength, elongation after fracture and impact energy of the gear steel in Comparative Example 1 are lower than those in Example 1. This is because the cold treatment temperature in Comparative Example 1 is higher than that in Example 1, resulting in a retained austenite content higher than 10%, which is not conducive to the improvement of the work hardening ability caused by dislocation entanglement and proliferation under higher stress levels, and is not conducive to the improvement of toughness and plasticity while reducing hardness and strength.

[0108] Comparing Example 1 and Comparative Example 2, it can be seen that the surface hardness, surface tensile strength, surface yield strength, elongation after fracture and impact energy of the gear steel in Comparative Example 2 are all lower than those in Example 1. This is because the mass percentage of Ni in Comparative Example 2 is lower than that in Example 1, the effects of Ni solid solution strengthening and improving hardenability are weakened, and the content of retained austenite is reduced, resulting in a simultaneous decrease in hardness, strength, plasticity and toughness.

[0109] Comparing Example 1 and Comparative Example 3, it can be seen that the surface hardness, surface tensile strength, surface yield strength, elongation after fracture and impact energy of the gear steel in Comparative Example 3 are all lower than those in Example 1. This is because the carburizing temperature in Comparative Example 3 is lower than that in Example 1, and the carbon atoms are not fully diffused, resulting in a decrease in the residual austenite content and the effective hardened layer depth, which in turn leads to a simultaneous decrease in hardness, strength, plasticity and toughness.

[0110] Comparison of Example 1 and Comparative Example 4 shows that the surface hardness, surface tensile strength, surface yield strength, elongation after fracture and impact energy of the gear steel in Comparative Example 4 are lower than those in Example 1. This is because the carbonitriding treatment is replaced by nitriding treatment in Comparative Example 4, and the carbon atoms are not fully diffused, resulting in a decrease in the content of retained austenite and the effective hardened layer depth, which in turn leads to a simultaneous decrease in hardness, strength, plasticity and toughness.

[0111] Comparing Examples 1-4 and Comparative Example 5, it can be seen that the surface hardness of the 18Cr2Ni4WA gear steel obtained in the examples is increased by 12.1%-17.2%, the surface tensile strength is increased by 12.8%-14.8%, the surface yield strength is increased by 18.4%-21.0%, the elongation after fracture is increased by 40.0%-50.0%, and the impact energy is increased by 16.9-24.0% compared with Comparative Example 5. This is because Examples 1-4 combine carburizing treatment and carbonitriding treatment, increase the surface carbon concentration to promote the formation of more carbides, introduce nitrogen atoms to enhance the stability of martensite, and accurately control the austenite content within the range of 7%-10%, ensuring a higher strength and toughness combination.

[0112] 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 18Cr2Ni4WA gear steel, characterized in that: The following steps are involved: S1. The raw material of 18Cr2Ni4WA gear steel is sequentially smelted, forged, normalized, tempered, dimensionally processed and annealed to obtain a blank; the chemical composition and mass percentage of the raw material of 18Cr2Ni4WA gear steel are as follows: C 0.15%-0.18%, Cr 1.45%-1.63%, Si 0.22%-0.35%, Mn 0.37%-0.58%, W 0.82%-1.05%, Ni 4.16%-4.25%, P 0-0.010%, S 0-0.008%, and the balance is other inevitable impurities and iron; S2, carburizing the blank obtained in S1 to obtain steel for heavy-duty gears; S3, subjecting the heavy-duty gear steel obtained in S2 to high-temperature tempering treatment; S4, performing carbonitriding treatment on the heavy-duty gear steel obtained in S3; S5. The heavy-duty gear steel obtained in S4 is subjected to cold treatment and low-temperature tempering treatment to obtain the 18Cr2Ni4WA gear steel.

2. The method for preparing 18Cr2Ni4WA gear steel according to claim 1, characterized in that: In S1, the smelting temperature is 1510°C-1530°C.

3. The method for preparing 18Cr2Ni4WA gear steel according to claim 1, characterized in that: In S1, the forging ratio of the forging is not less than 3.

2.

4. The method for preparing 18Cr2Ni4WA gear steel according to claim 1, characterized in that: In S1, the normalizing temperature is 940°C-980°C, and the time is 5h-10h; the tempering temperature is 650°C-690°C, and the time is 3h-7.5h; the annealing temperature is 200°C-400°C, and the time is 3h-5h.

5. The method for preparing 18Cr2Ni4WA gear steel according to claim 1, characterized in that: In S2, the carburizing treatment is performed at a temperature of 915°C-935°C, a carbon potential of 1.2wt%-1.4wt%, and a time of 100h-205h.

6. The method for preparing 18Cr2Ni4WA gear steel according to claim 1, characterized in that: In S3, the high temperature tempering treatment is performed at a temperature of 640°C-690°C, for a time of 3h-7.5h, and twice.

7. The method for preparing 18Cr2Ni4WA gear steel according to claim 1, characterized in that: In S4, the carbonitriding treatment is performed at a temperature of 830°C-920°C, a carbon potential of 1.0wt%-1.2wt%, an ammonia flow rate of 4L / min-6L / min, and a time of 10h-30h.

8. The method for preparing 18Cr2Ni4WA gear steel according to claim 1, characterized in that: In S5, the temperature of the cold treatment is -100°C to -70°C, and the time is 2h-3h.

9. The method for preparing 18Cr2Ni4WA gear steel according to claim 1, characterized in that: In S5, the low temperature tempering treatment is performed at a temperature of 180°C-250°C and for a time of 3h-8h.

10. A 18Cr2Ni4WA gear steel prepared by the method according to any one of claims 1 to 9.

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