A segmented induction quenching method for carburized gear and carburized gear

Abstract

This invention discloses a segmented induction hardening method for carburized gears and the carburized gear itself, belonging to the field of induction hardening technology. It addresses the problem that existing whole-part quenching treatments for large-module, high-hardenability gears often result in excessive hardness in the uncarburized core area, and the lack of a corresponding induction hardening process. The method includes: S1, carburizing the gear; S2, furnace cooling the carburized gear; S3, high-temperature tempering of the entire gear; S4, segmented induction hardening of each gear tooth; S5, cooling the gear to room temperature; S6, cryogenic treatment of the entire gear; and S7, low-temperature tempering of the entire gear. This method overcomes the technical difficulty of induction hardening due to high surface carbon content after carburizing, resulting in a deep hardened layer, a smooth hardness gradient transition area, and controllable core hardness, which is beneficial for subsequent machining. It also results in a high yield, good strength-plasticity matching of the hardened layer, and excellent wear resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of induction quenching, and in particular relates to a segmented induction quenching method for a carburized gear and the carburized gear. Background Art

[0002] Heavy-duty gears transmit large power, have large impact forces, work in harsh conditions and have high safety requirements. Their service conditions require them to have excellent wear resistance, high contact fatigue strength and bending fatigue strength. With the improvement of the industry's manufacturing process, the module of the gear is much larger than the national standard maximum value of 50mm, and the effective hardened layer depth of carburizing and quenching is required to be more than 3mm. The general quenching process can no longer match the effective hardened layer depth and the heating layer thickness well. Especially for high-hardenability gear steel with high Ni content, the overall carburizing and quenching heats and cools the tooth and the core at the same time, causing the core to be hardened, and the hardness is too high, which increases the difficulty of subsequent machining. Therefore, the development of an induction quenching process for large-modulus carburized gears to obtain an excellent tooth surface strengthening layer while ensuring the machinability of the core is an urgent problem to be solved in the current heavy equipment manufacturing industry. Summary of the invention

[0003] In view of the above analysis, the present invention aims to provide a segmented induction quenching method for carburized gears and carburized gears, which solves the problem in the prior art that the whole-piece quenching treatment of large-modulus and high-hardenability gears easily causes the hardness of the non-carburized area in the core to exceed the standard, and there is no related induction quenching process.

[0004] The purpose of the present invention is mainly achieved through the following technical solutions:

[0005] In one aspect, the present invention provides a method for segmented induction hardening of a carburized gear, comprising the following steps:

[0006] S1. Carburizing the gear;

[0007] S2, cooling the carburized gear along with the furnace;

[0008] S3, subjecting the entire gear to high temperature tempering treatment;

[0009] S4, performing segmented induction hardening on the gear teeth one by one;

[0010] S5, cooling the gear to room temperature;

[0011] S6. Perform deep cryogenic treatment on the entire gear;

[0012] S7. Perform low temperature tempering treatment on the entire gear.

[0013] Furthermore, in S1, in the raw materials of the gear, the mass percentage of C is 0.13% to 0.19%, the mass percentage of Cr is 1.35% to 1.65%, and the mass percentage of Ni is more than 2%.

[0014] Further, in S4, the segmented induction hardening includes:

[0015] S401, quickly heating to 440-450°C, heating time t1;

[0016] S402, heating to between 650 and 700°C, heating time t2;

[0017] S403, slowly heating to a final quenching temperature between 750°C and 900°C, with a heating time of t3; t1≤t2≤t3.

[0018] Furthermore, in S4,

[0019] When the carburized layer depth is less than 1.5 mm, t1 = t2 = t3;

[0020] When the carburized layer depth is (1.5, 3] mm, t1:t2:t3=1:1.4~1.5:1.4~1.5;

[0021] When the carburized layer depth is (3, 4] mm, t1:t2:t3=1:1.4~1.5:1.9~2;

[0022] When the carburized layer depth is (4, 5] mm, t1:t2:t3=1:1.9~2:2.4~2.5;

[0023] When the depth of the carburized layer is greater than 5 mm, t1:t2:t3=1:2~2.3:2.5~2.8.

[0024] Furthermore, in S4, when the single gear tooth is subjected to segmented induction quenching, an aqueous medium is used to completely cool the gear tooth to room temperature.

[0025] Furthermore, in S2, the surface microstructure of the gear after cooling is martensite+bainite+retained austenite with a volume percentage not exceeding 30%.

[0026] Furthermore, in S3, the high temperature tempering temperature ranges from 550°C to 700°C, and the high temperature tempering holding time is 0.5 to 24h.

[0027] Furthermore, in S6, the deep cooling temperature is -50°C to -150°C, and the deep cooling time is 1 to 24 hours.

[0028] Furthermore, in S7, the low temperature tempering temperature is 150-250° C., and the tempering time is 1-12 h.

[0029] On the other hand, the present invention also provides a gear, which is prepared by the above method.

[0030] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0031] 1) The segmented induction quenching method for carburized gears provided by the present invention does not require quenching of the entire gear, reduces energy consumption, improves production efficiency, and can overcome the technical difficulty that the gear is not conducive to induction quenching due to high carbon on the surface after carburization. The hardened layer is deep, the hardness gradient transition area is gentle, and the hardness of the core can be controlled, which is beneficial to subsequent machining, has a high yield rate, and the hardened layer has good strength and plasticity matching and excellent wear resistance. It overcomes the problems of existing heat treatment processes for quenching large modulus gears as a whole, which consumes a lot of energy and causes the hardness of the non-carburized core area to exceed the standard. While improving production efficiency, it has the good performance of controllable carburized layer structure and optimized strength and plasticity matching, and is particularly suitable for heat treatment of heavy-loaded gears.

[0032] 2) The segmented induction quenching method for carburized gears provided by the present invention can obtain an effective hardened layer depth that meets the requirements by combining the depth of the carburized layer and accurately controlling the temperature and time of each segment of induction heating, thereby ensuring good uniformity of the surface hardness of the gear and a smoother gradient transition area of ​​the hardness, which is very beneficial for the service of the large carburized layer and can improve strength and toughness and contact fatigue performance; the hardness of the core and inner ring of the gear is below 450HV1 (for example, below 440HV1), which meets the machining performance requirements; and compared with overall quenching, the method of the present invention greatly reduces the probability of cracks on the gear surface and the probability of quenching cracks by accurately controlling the temperature and time of each segment of induction heating, and has a high yield rate (for example, the yield rate reaches more than 99%).

[0033] 3) The mechanical properties of the surface layer of the carburized gear of the present invention (referring to the surface layer with a carbon content of more than 0.8%) are as follows: tensile strength is more than 1750MPa (for example, 1750-1850MPa), and elongation is more than 6% (for example, 6%-7.5%); the mechanical properties of the core with a carbon content of less than 0.4% are as follows: tensile strength is more than 1150MPa (for example, (1150-1200MPa), and elongation is more than 11%, for example, (11%-15%). The gear has excellent mechanical properties and excellent wear resistance.

[0034] Other features and advantages of the present invention will be described in the following description, and part of them will become obvious from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the contents particularly pointed out in the written description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings are only for the purpose of illustrating specific embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0036] Figure 1 Schematic diagram of the segmented induction quenching method of Example 1 of the present invention;

[0037] Figure 2 This is a surface structure diagram of the gear of Example 1 of the present invention;

[0038] Figure 3 This is a subsurface structure diagram of the gear of Example 1 of the present invention;

[0039] Figure 4 This is a core structure diagram of a gear according to Embodiment 1 of the present invention;

[0040] Figure 5 This is a schematic diagram of the hardness gradient of the gear of Example 1 of the present invention;

[0041] Figure 6 A schematic diagram of the hardness gradient of the gear of Comparative Example 1 of the present invention;

[0042] Figure 7 Schematic diagram of the hardness gradient of the gears of Example 1 and Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0043] Preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used to explain the principles of the present invention together with the embodiments of the present invention.

[0044] The present invention provides a segmented induction quenching method for carburized gears, comprising the following steps:

[0045] S1. Carburizing the gear;

[0046] S2, cooling the carburized gear along with the furnace;

[0047] S3, then the gear is subjected to high temperature tempering treatment as a whole;

[0048] S4, then perform segmented induction hardening on the gear teeth one by one;

[0049] S5, then cooling the gear to room temperature;

[0050] S6, then the gear is subjected to deep cryogenic treatment as a whole;

[0051] S7. Then the gear is subjected to low temperature tempering treatment as a whole.

[0052] Specifically, in the above S1, in the raw materials of the gear, the mass percentage of C is 0.13% to 0.19%, the mass percentage of Cr is 1.35% to 1.65%, and the mass percentage of Ni is more than 2%.

[0053] Specifically, the diameter of the inner ring of the gear is greater than 300 mm, the diameter of the pitch circle of the gear is 510-780 mm, and the module of the gear is 30-60 mm.

[0054] Specifically, in the above S1, before the carburizing treatment, the gear inner ring and the reference end faces on both sides are also subjected to anti-carburizing treatment.

[0055] Specifically, in the above S1, the carburizing treatment may be gaseous, liquid or solid carburizing.

[0056] Specifically, in the above S2, the carbon content of the outermost carburized layer of the gear after cooling is 0.8% to 1.5%.

[0057] Specifically, in the above S2, the gear after cooling has a carbon content of 0.4% as a critical point, a carburized layer depth of the gear of 1 to 6 mm, and a carburized diffusion front depth of 4 to 8 mm.

[0058] Specifically, in the above S2, the surface microstructure of the gear after cooling is martensite + bainite + retained austenite not exceeding 30% (volume percentage); the content of retained austenite at the position where the carbon content is 0.4% does not exceed 15%.

[0059] Specifically, in the above S3, the high temperature tempering temperature ranges from 550°C to 700°C, and the high temperature tempering holding time ranges from 0.5 to 24 hours.

[0060] Specifically, in the above S3, high temperature tempering can be performed twice. The holding time of high temperature tempering is determined according to the geometric size of the workpiece. The thicker the workpiece, the longer the holding time.

[0061] Specifically, in the above S4, the segmented induction hardening includes:

[0062] S401, quickly heating to 440-450°C, heating time t1;

[0063] S402, heating to between 650 and 700°C, heating time t2;

[0064] S403, slowly heating to a final quenching temperature between 750°C and 900°C, with a heating time of t3; t1≤t2≤t3.

[0065] Specifically, in the above S4, when the depth of the carburized layer is less than 1.5 mm, t1=t2=t3; when the depth of the carburized layer is (1.5, 3] mm, t1:t2:t3=1:1.4~1.5:1.4~1.5; when the depth of the carburized layer is (3, 4] mm, t1:t2:t3=1:1.4~1.5:1.9~2; when the depth of the carburized layer is (4, 5] mm, t1:t2:t3=1:1.9~2:2.4~2.5; when the depth of the carburized layer is greater than 5 mm, t1:t2:t3=1:2.0~2.3:2.5~2.8.

[0066] Specifically, in the above S4, when the single gear tooth is subjected to segmented induction quenching, an aqueous medium is used to completely cool the gear to room temperature.

[0067] Specifically, in S6 above, considering that the inappropriate cryogenic temperature and time will result in the surface hardness and performance of the gear failing to meet the technical requirements, the inventors, after in-depth research, controlled the cryogenic temperature to -50°C to -150°C and the cryogenic time to 1 to 24 hours.

[0068] Specifically, in the above S7, the low-temperature tempering temperature is 150-250° C., and the tempering time is 1-12 hours.

[0069] Specifically, in the above S7, the surface structure of the gear after low-temperature tempering treatment is high-carbon tempered martensite + less than 20% retained austenite, the sub-surface (carbon content of about 0.4% to 0.6%) is medium-carbon tempered martensite + tempered bainite + less than 25% retained austenite, and the core structure is bainite + less than 40% retained austenite.

[0070] Specifically, in the above S7, the effective hardened layer depth of the gear after low temperature tempering treatment is 2 to 7 mm.

[0071] After low temperature tempering, the surface hardness of the gear is 805-880HV1, and the core hardness is below 450HV1 (for example, below 440HV1). The surface hardness of the gear is uniform, the gradient transition area of ​​the hardness is smoother, and the core hardness is low, which is conducive to the later processing of the core and solves the problem of difficult processing of the core. In addition, there are no cracks on the gear surface, and the yield rate is high (for example, the yield rate reaches more than 99%).

[0072] Specifically, in the above S7, the gear after low temperature tempering is tested by micro tensile test, and the mechanical properties of the surface layer of the gear after low temperature tempering (referring to the surface layer with a carbon content of more than 0.8%) are: tensile strength of more than 1750MPa (for example, 1750-1850MPa), elongation of more than 6% (for example, 6%-7.5%); the mechanical properties of the core with a carbon content of less than 0.4% are: tensile strength of more than 1150MPa (for example, (1150-1200MPa), elongation of more than 11%, for example, (11%-15%), the mechanical properties of the gear are excellent, and the wear resistance is excellent.

[0073] The present invention also provides a carburized gear, which is prepared by the above method.

[0074] Compared with the prior art, the segmented induction quenching method for carburized gears provided by the present invention can obtain an effective hardened layer depth that meets the requirements by combining the depth of the carburized layer and accurately controlling the temperature and time of each segment of induction heating, thereby ensuring good uniformity of the surface hardness of the gear and a smoother gradient transition area of ​​the hardness, which is very beneficial for the service of the large carburized layer and can improve strength and toughness and contact fatigue performance; the hardness of the core and inner ring of the gear meets the machining performance requirements; the method of the present invention can greatly reduce the probability of cracks on the gear surface and the probability of quenching cracks by accurately controlling the temperature and time of each segment of induction heating, and the gear surface is free of cracks with a high yield rate (for example, the yield rate reaches more than 99%).

[0075] Example 1

[0076] This embodiment provides a segmented induction quenching method for carburized gears and a carburized gear. The material of the gear in this embodiment is 18Cr2Ni4WA; Figure 1 It is a schematic diagram of the segmented induction hardening method of the gear. The module of the gear in this embodiment is 40 mm, the pitch circle diameter is 650 mm, and the diameter of the inner ring is 300 mm.

[0077] Before carburizing, the inner ring of the gear and the reference end faces on both sides are first treated with anti-carburizing treatment; then:

[0078] Step 1, the gear is carburized as a whole; then the gear is cooled as a whole in the furnace; the carburized layer depth is 3.7mm, and the maximum carbon content of the outer side of the carburized layer is 1.0%;

[0079] Step 2: Then the gear is subjected to high temperature tempering at 650°C for 3h;

[0080] Step 3, then perform segmented surface induction quenching treatment on the single teeth of the gear one by one: in the first stage, the heating time is 20s, and the highest induction heating temperature of the surface layer is 450℃; after the surface layer reaches the temperature, the second stage of induction heating begins immediately, the heating time is 30s, and the highest induction heating temperature of the surface layer is 670℃; in the third stage, the temperature is slowly increased to the final quenching temperature of 800℃ at low power, the heating time is 40s, and the cooling adopts an aqueous composite cooling medium;

[0081] Step 4: After the gear teeth have completed the segmented surface induction quenching treatment, the gear teeth are then cryogenically treated; the cryogenic temperature is -130°C and the cooling time is 60 minutes;

[0082] Step 5: Place the entire gear in the air for 1 hour until the temperature of all tooth surfaces reaches room temperature, and then perform low-temperature tempering at 175°C for 3 hours.

[0083] The surface structure of the gear prepared in this embodiment is as follows: Figure 2 As shown, it is high carbon tempered martensite + about 10% retained austenite, and the subsurface structure is as follows Figure 3 As shown, it is medium carbon tempered martensite + tempered troostite + about 15 residual austenite, and the core structure is as follows Figure 4 As shown, it is bainite + about 30% retained austenite.

[0084] The hardness distribution of the gears prepared in this embodiment is as follows: Figure 5 As shown in the figure, the relationship between the distance L from the tooth surface and the hardness of the gear is as follows: 0≤L≤3mm, the hardness is 805~880HV1; 3<L≤5.5mm, the hardness is 435~810HV1; 5.5mm<L, the hardness is below 435HV1. The surface hardness of the gear is uniform, and the gradient transition area of ​​the hardness is smoother. The effective hardening layer depth of the gear is 4.5mm, and the hardness of the gear core and inner ring is below 440HV, which meets the machining performance requirements.

[0085] The mechanical properties of the surface layer of the gear prepared in this embodiment are as follows: tensile strength of about 1800 MPa, elongation of 6.5%; the mechanical properties of the core are as follows: tensile strength of about 1170 MPa, elongation of 11.5%; and the gears of this embodiment and the gears of comparative example 1 are both subjected to wear resistance tests, and the wear resistance is excellent. Compared with comparative example 1, the wear weight loss of the grinding pair in this embodiment can be reduced by 15%.

[0086] Example 2

[0087] This embodiment provides a segmented induction quenching method for a carburized gear and a carburized gear. The material of the gear in this embodiment is 18Cr2Ni4WA; the module of the gear in this embodiment is 40mm, the pitch circle diameter is 650mm, and the diameter of the inner ring is 300mm.

[0088] Before carburizing, the inner ring of the gear and the reference end faces on both sides are first treated with anti-carburizing treatment; then:

[0089] Step 1, the gear is carburized as a whole; then the gear is cooled as a whole in the furnace; the carburized layer depth is 4.2mm, and the maximum carbon content of the outer side of the carburized layer is 1.0%;

[0090] Step 2: Then the gear is subjected to high temperature tempering at 670°C for 2.5h;

[0091] Step 3, then perform segmented surface induction quenching treatment on the single gear teeth one by one: in the first stage, the heating time is 20s, and the highest induction heating temperature of the surface layer is 450℃; after the surface layer reaches the temperature, the second stage of induction heating begins immediately, the heating time is 40s, and the highest induction heating temperature of the surface layer is 690℃; in the third stage, the temperature is slowly increased to the final quenching temperature of 850℃ at low power, the heating time is 50s, and the cooling adopts an aqueous composite cooling medium;

[0092] Step 4: After the gear teeth have been subjected to the segmented surface induction hardening treatment, the gear teeth are subjected to a deep cooling treatment; the deep cooling temperature is -130°C and the cooling time is 90 minutes;

[0093] Step 5: Place the entire gear in the air for 1 hour until the temperature of all tooth surfaces reaches room temperature, and then perform low-temperature tempering at 210°C for 3 hours.

[0094] The surface structure of the gear prepared in this embodiment is high carbon tempered martensite + about 12% retained austenite, the sub-surface structure is medium carbon tempered martensite + tempered troostite + about 15% retained austenite, and the core structure is bainite + about 25% retained austenite.

[0095] The relationship between the distance L from the tooth surface and the hardness of the gear prepared in this embodiment is as follows: 0≤L≤3.7mm, the hardness is 805-880HV1; 3.7<L≤7mm, the hardness is 440-810HV1; 7mm<L, the hardness is below 440HV1. The surface hardness of the gear is uniform, and the gradient transition area of ​​the hardness is smoother. The effective hardening layer depth of the gear is 5mm, and the hardness of the gear core and inner ring is below 440HV, which meets the machining performance requirements.

[0096] The mechanical properties of the surface layer of the gear prepared in this embodiment are as follows: tensile strength of about 1820 MPa, elongation of 6.5%; the mechanical properties of the core are as follows: tensile strength of about 1190 MPa, elongation of 11%; and the gear of this embodiment has excellent wear resistance. Compared with comparative example 1, the wear weight loss of the grinding pair in this embodiment can be reduced by 17%.

[0097] Example 3

[0098] This embodiment provides a segmented induction quenching method for a carburized gear and a carburized gear. The material of the gear in this embodiment is 18Cr2Ni4WA; the module of the gear in this embodiment is 40mm, the pitch circle diameter is 650mm, and the diameter of the inner ring is 300mm.

[0099] Before carburizing, the inner ring of the gear and the reference end faces on both sides are first treated with anti-carburizing treatment; then:

[0100] Step 1, the gear is carburized as a whole; then the gear is cooled as a whole in the furnace; the carburized layer depth is 5.2mm, and the maximum carbon content of the outer side of the carburized layer is 1.0%;

[0101] Step 2: Then the gear is subjected to high temperature tempering at 700°C for 2h;

[0102] Step 3, then perform segmented surface induction quenching treatment on the single gear teeth one by one: in the first stage, the heating time is 20s, and the highest induction heating temperature of the surface layer is 450℃; after the surface layer reaches the temperature, the second stage of induction heating begins immediately, the heating time is 44s, and the highest induction heating temperature of the surface layer is 700℃; in the third stage, the temperature is slowly increased to the final quenching temperature of 900℃ at low power, the heating time is 52s, and the cooling adopts an aqueous composite cooling medium;

[0103] Step 4: After the gear teeth have completed the segmented surface induction quenching treatment, the gear teeth are then cryogenically treated; the cryogenic temperature is -140°C and the cooling time is 70 minutes;

[0104] Step 5: Place the entire gear in the air for 1 hour until the temperature of all tooth surfaces reaches room temperature, and then perform low-temperature tempering at 200°C for 3 hours.

[0105] The surface structure of the gear prepared in this embodiment is high carbon tempered martensite + about 9% retained austenite, the sub-surface structure is medium carbon tempered martensite + tempered troostite + about 13% retained austenite, and the core structure is bainite + about 22% retained austenite.

[0106] The relationship between the distance L from the tooth surface and the hardness of the gear prepared in this embodiment is as follows: 0≤L≤4.2mm, the hardness is 805-880HV1; 4.2<L≤7.5mm, the hardness is 440-810HV1; 7.5mm<L, the hardness is below 440HV1. The surface hardness of the gear is uniform, and the gradient transition area of ​​the hardness is smoother. The effective hardening layer depth of the gear is 5.5mm, and the hardness of the gear core and inner ring is below 440HV1, which meets the machining performance requirements.

[0107] The mechanical properties of the surface layer of the gear prepared in this embodiment are as follows: tensile strength of about 1850MPa, elongation of 6%; the mechanical properties of the core are as follows: tensile strength of about 1200MPa, elongation of 11%; and the gear of this embodiment has excellent wear resistance. Compared with comparative example 1, the wear weight loss of the grinding pair in this embodiment can be reduced by 19%.

[0108] It can be seen from the microstructure and properties of Examples 1-3 that by adopting the method of the present invention, the gear has excellent mechanical properties, excellent wear resistance, the effective layer depth meets the requirements, and the core hardness is low, which is conducive to the later processing of the core. There are no cracks on the gear surface and the yield is high (for example, the yield reaches more than 99%).

[0109] Comparative Example 1

[0110] This comparative example provides a method for overall quenching of a gear and a gear. The material and structure of the gear in this comparative example are the same as those in Example 1. The overall quenching method in this comparative example is the same as step 1-step 2 of Example 1, except that:

[0111] Step 3, quench the gear as a whole; the quenching temperature is 800°C, the holding time is 20 minutes, and then the gear is cooled to room temperature by spraying water coolant;

[0112] Step 4: cryogenically treat the entire gear with liquid nitrogen; the cooling temperature is -130°C and the cooling time is 60 minutes;

[0113] Step 5: Low-temperature tempering of the entire gear at a tempering temperature of 175°C for 3 hours.

[0114] The hardness distribution of the gears in this comparative example is as follows: Figure 6 As shown, the hardness curves of this comparative example and Example 1 are put in one figure, as shown in FIG. Figure 7 As shown in the figure, the solid part is the hardness of Example 1, and the hollow part is the hardness of Comparative Example 1. It can be seen that the present invention adopts a suitable segmented induction quenching process to obtain a smoother hardness gradient, which is very beneficial for the service of gears with deeper infiltration layers, and can improve toughness and contact fatigue performance. In addition, the core hardness of the gear of the present invention is below 440HV1, which is lower than that of the overall furnace quenching, which is more conducive to the later processing of the core and solves the problem of difficult processing of the core.

[0115] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for segmented induction hardening of carburized gears, characterized in that: The steps include: S1. Carburizing the gear; S2, cooling the carburized gear along with the furnace; S3, subjecting the entire gear to high temperature tempering treatment; S4, performing segmented induction hardening on the gear teeth one by one; S5, cooling the gear to room temperature; S6. Perform deep cryogenic treatment on the entire gear; S7, performing low temperature tempering treatment on the entire gear; In S4, the segmented induction hardening includes: S401, quickly heating to 440-450°C, heating time t1; S402, heating to between 650 and 700°C, heating time t2; S403, slowly heating to a final quenching temperature between 750°C and 900°C, with a heating time of t3; t1≤t2≤t3; In S4, When the carburized layer depth is less than 1.5 mm, t1 = t2 = t3; When the carburized layer depth is (1.5, 3] mm, t1:t2:t3=1:1.4~1.5:1.4~1.5; When the carburized layer depth is (3, 4] mm, t1:t2:t3=1:1.4~1.5:1.9~2; When the carburized layer depth is (4, 5] mm, t1:t2:t3=1:1.9~2:2.4~2.5; When the depth of the carburized layer is greater than 5mm, t1:t2:t3=1:2~2.3:2.5~2.

8.

2. The segmented induction hardening method according to claim 1, characterized in that: In S1, in the raw materials of the gear, the mass percentage of C is 0.13% to 0.19%, the mass percentage of Cr is 1.35% to 1.65%, and the mass percentage of Ni is more than 2%.

3. The segmented induction hardening method according to claim 1, characterized in that: In S4, when the gear single tooth is subjected to segmented induction quenching, an aqueous medium is used to completely cool the gear to room temperature.

4. The segmented induction hardening method according to claim 1, characterized in that: In S2, the surface microstructure of the gear after cooling is martensite+bainite+retained austenite with a volume percentage not exceeding 30%.

5. The segmented induction hardening method according to claim 1, characterized in that: In S3, the high temperature tempering temperature ranges from 550°C to 700°C, and the high temperature tempering holding time ranges from 0.5 to 24 hours.

6. The segmented induction hardening method according to claim 1, characterized in that: In the step S6, the deep cooling temperature is -50°C to -150°C, and the deep cooling time is 1 to 24 hours.

7. The segmented induction hardening method according to any one of claims 1 to 6, characterized in that: In S7, the low-temperature tempering temperature is 150-250° C., and the tempering time is 1-12 hours.

8. A carburized gear, characterized in that: The carburized gear is prepared by the segmented induction quenching method according to any one of claims 1 to 7.

Images