A method for carburizing induction quenching of gear and gear

Abstract

The present invention discloses a method for carburizing induction quenching of gears and gears, belonging to the field of gear technology, and solves the problem that the existing large-module whole-piece quenching and deep-cold treatment consumes a lot of energy and easily causes the hardness of the non-carburized area in the core to exceed the standard, or the high carbon on the surface is prone to quenching cracks. The carburizing induction quenching method includes: step 1, carburizing the entire gear; step 2, then high-temperature tempering the entire gear; step 3, then surface induction quenching the single teeth of the gear one by one; step 4, then ice-cold treatment the single teeth of the gear one by one; step 5, low-temperature tempering the entire gear. The gear prepared by the method of the present invention has low core hardness, good wear resistance, and high yield.

Description

Technical Field

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

[0002] Large-module heavy-duty gears are widely used in the running parts of heavy equipment. The gear surfaces of heavy-duty gears are often carburized and quenched to meet wear resistance requirements. The effective hardened layer depth is required to be more than 3mm, and the hardness is required to be above 55HRC. The traditional manufacturing process requires carburizing, high-temperature tempering, whole-piece quenching, cryogenic treatment and low-temperature tempering. At the same time, the core hardness is required to be below HRC42 to ensure good machinability of the core. However, whole-piece quenching and cryogenic treatment of large-module gears consumes a lot of energy and is prone to causing problems such as excessive hardness in the uncarburized area of ​​the core, which restricts the improvement of production efficiency. Therefore, the development of surface induction quenching technology for large-module carburized gears to save energy and increase production capacity is an urgent problem that needs to be solved in the heavy equipment manufacturing industry. Summary of the Invention

[0003] In view of the above analysis, the present invention aims to provide a method for carburizing induction quenching of gears and gears, which solves the problems in the prior art that the quenching and cryogenic treatment of large-module gears as a whole consumes a lot of energy and easily causes large quenching deformation of the entire gear. At the same time, the uncarburized area in the core produces a martensite-bainite phase transformation due to the common overall quenching, resulting in excessive hardness, or the high carbon on the surface is prone to quenching cracks.

[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 carburizing and induction hardening a gear, the method comprising the following steps:

[0006] Step 1: Carburize the entire gear;

[0007] Step 2: High-temperature tempering the entire gear;

[0008] Step 3: Perform surface induction hardening treatment on the gear teeth one by one;

[0009] Step 4: Cool the gear teeth one by one.

[0010] Step 5: Perform low-temperature tempering treatment on the entire gear.

[0011] Furthermore, in step 3, when the surface of the single gear tooth is subjected to induction hardening treatment, the maximum surface temperature of the single gear tooth subjected to induction heating is below 860° C., and the induction heating time is within 10 minutes.

[0012] Furthermore, in step 3, during induction heating, the thickness h of the heating zone with a temperature lower limit of 700°C and the depth H of the carburized layer have the following corresponding relationship:

[0013] When 2mm≤H≤3mm, h=H-(0~0.5)mm;

[0014] When 3mm<H≤4mm, h=H-(0~0.25)mm;

[0015] When 4mm<H≤6mm, h=H+(0~0.5)mm.

[0016] Furthermore, in step 3, when the surface of a single gear tooth is subjected to induction hardening treatment, an induction hardening coolant is used to completely cool the gear tooth to room temperature.

[0017] Furthermore, in step 4, the single gear tooth is subjected to ice-cooling treatment, including: high-speed cold nitrogen deep cooling of the single tooth after induction quenching treatment, and the deep cooling temperature T and the maximum carbon content C on the surface of the carburized layer have the following relationship: when the maximum carbon content C on the surface is 0.8%, the deep cooling temperature T is -70°C; for every 0.1% increase in the maximum carbon content C on the surface, the deep cooling temperature T decreases by 20°C.

[0018] Furthermore, in step 4, the deep cooling time t, the carburized layer depth H, and the alloying element Ni content have the following relationship:

[0019] For alloy steel with a Ni content of 2%, when H is 2mm, the deep cooling time t is 1min; for every 1mm increase in H, the deep cooling time t increases by 1min; for every 1% increase in Ni content, the deep cooling time increases by 0.5min.

[0020] Furthermore, in step 1, the carbon content of the outermost carburized layer of the gear after carburizing and cooling is 0.85-1.2%.

[0021] Furthermore, in step 1, the gear after carburizing treatment has a carbon content of 0.4% as a critical point, a carburized layer depth H of the gear is 2 to 6 mm, and a carburizing diffusion front depth is 4 to 8 mm.

[0022] Furthermore, in step 2, the high temperature tempering temperature ranges from 550 to 650° C., and the high temperature tempering holding time is 1.5 to 4 hours.

[0023] On the other hand, the present invention also provides a gear manufactured by the above method.

[0024] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0025] 1) The carburizing induction quenching method for gears provided by the present invention adopts single-tooth induction quenching + cryogenic treatment, and does not require quenching and cryogenic treatment of the entire gear, thereby reducing energy consumption and improving production efficiency. At the same time, it can ensure good mechanical processing performance of the gear core, and overcomes the existing heat treatment process for quenching and cryogenic treatment of large-module gears as a whole, which consumes a lot of energy and easily causes large quenching deformation of the entire gear. At the same time, the uncarburized area in the core produces martensite-bainite phase transformation due to the common overall quenching, and the hardness exceeds the standard, or the high carbon on the surface is prone to quenching cracks. While improving production efficiency, it has the good performance of controllable carburized layer structure and optimized strength-plasticity matching, and is particularly suitable for heat treatment of heavy-loaded gears.

[0026] 2) The carburizing induction quenching method for gears provided by the present invention precisely controls the induction heating temperature and heating zone thickness, combined with the control of cryogenic temperature and time, to ensure that the surface structure of the gears after low-temperature tempering treatment is composed of high-carbon tempered martensite with less than 20% retained austenite, the sub-surface layer (with a carbon content of approximately 0.4% to 0.6%) is composed of medium-carbon tempered martensite with tempered bainite and less than 25% retained austenite, and the core structure is composed of bainite with less than 40% retained austenite. After low-temperature tempering, the gear tooth surface hardness is 56 to 60 HRC, the effective hardened layer depth is ≥2mm, and the gear core and inner ring hardness is 30 to 36 HRC, meeting machinability requirements. Furthermore, due to the precise control of the induction heating temperature and time, the probability of cracks on the gear surface is greatly reduced, the probability of quenching cracks is greatly reduced, and the yield rate is high (for example, the yield rate reaches over 99%).

[0027] 3) The mechanical properties of the surface layer of the gear of the present invention are: tensile strength of more than 1750MPa (for example, 1750-1830MPa), 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 10% (for example, 10%-13%). The gear has excellent mechanical properties and excellent wear resistance.

[0028] 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

[0029] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like parts throughout the drawings.

[0030] Figure 1 Schematic diagram of the carburizing induction quenching method of the present invention;

[0031] Figure 2 Schematic diagram of the hardness gradient of the gear in Example 1 of the present invention. DETAILED DESCRIPTION

[0032] The preferred embodiments of the present invention will be described in detail below with reference to 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.

[0033] The present invention provides a method for carburizing and induction quenching of gears, comprising the following steps:

[0034] Step 1: Carburize the entire gear;

[0035] Step 2: Then perform high temperature tempering on the entire gear;

[0036] Step 3: Then perform surface induction hardening treatment on the gear teeth one by one;

[0037] Step 4: Then perform cold treatment on the gear teeth one by one;

[0038] Step 5: Perform low-temperature tempering treatment on the entire gear.

[0039] Specifically, the gear is made of high-nickel low-carbon alloy carburizing steel. In the material of the gear, the total mass percentage of Cr and Ni is greater than 5%, and the mass percentage of C is less than 0.2%.

[0040] 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 to 780 mm, and the module of the gear is 30 to 60 mm.

[0041] Specifically, in the above step 1, before the carburizing treatment, the gear inner ring and the reference end faces on both sides are also subjected to anti-carburizing treatment.

[0042] Specifically, in the above step 1, the process steps of the carburizing treatment include: adopting gaseous, liquid or solid carburizing and then cooling.

[0043] Specifically, in the above step 1, after carburizing, the carbide is cooled in the furnace or naturally cooled in the air.

[0044] Specifically, in the above step 1, the carbon content of the outermost carburized layer of the gear after carburizing and cooling is 0.85-1.2%.

[0045] Specifically, in the above step 1, the gear after carburizing treatment has a carbon content of 0.4% as a critical point, a carburized layer depth H of the gear is 2 to 6 mm, and a carburizing diffusion front depth is 4 to 8 mm.

[0046] Specifically, in the above step 1, the surface microstructure of the gear after carburizing and cooling is martensite + retained austenite not exceeding 30% (volume percentage); the retained austenite content at the position where the carbon content is 0.4% does not exceed 5%.

[0047] Specifically, in step 2 above, the high-temperature tempering temperature ranges from 550°C to 650°C, and the holding time for high-temperature tempering is 0.5 to 20 hours. The holding time for high-temperature tempering is determined based on the geometric dimensions of the workpiece. The thicker the workpiece, the longer the holding time.

[0048] Specifically, in step 3 above, considering that the heating temperature is too high, the gear is prone to overburning, coarse structure, and cracks. Therefore, when a single gear tooth is subjected to surface induction hardening treatment, the maximum surface temperature of the gear tooth induction heating shall not exceed 860°C (for example, 800-860°C), and the induction heating time shall not exceed 10 minutes. The thickness h of the heating zone with 700°C as the lower temperature limit and the carburized layer depth H have the following corresponding relationship:

[0049] When 2mm≤H≤3mm, h=H-(0~0.5)mm;

[0050] When 3mm<H≤4mm, h=H-(0~0.25)mm;

[0051] When 4mm<H≤6mm, h=H+(0~0.5)mm.

[0052] Specifically, in the above step 3, when the surface of a single gear tooth is subjected to induction hardening treatment, the gear tooth is completely cooled to room temperature using an induction hardening coolant.

[0053] Specifically, in the above step 4, the step of subjecting the single gear tooth to ice-cooling treatment includes: subjecting the single gear tooth after the induction quenching treatment to high-speed cold nitrogen deep cooling.

[0054] Specifically, in step 4 above, considering that inappropriate cryogenic temperature and duration can result in the gear's surface hardness and performance failing to meet technical requirements, the inventors, after in-depth research, determined that the relationship between cryogenic temperature T and the maximum carbon content C on the carburized layer's surface is as follows: when the maximum carbon content C is 0.8%, the cryogenic temperature T is -70°C; for every 0.1% increase in the maximum carbon content C, the cryogenic temperature T decreases by 20°C.

[0055] Specifically, in the above step 4, the deep cooling time t, the carburized layer depth H, and the alloying element Ni content have the following relationship:

[0056] For alloy steel with a Ni content of 2%, when H is 2mm, the deep cooling time t is 1min; for every 1mm increase in H, the deep cooling time t increases by 1min; for every 1% increase in Ni content, the deep cooling time increases by 0.5min.

[0057] Specifically, in the above steps 3 and 4, after completing the induction quenching of a single tooth in step 3, the cryogenic treatment of step 4 can be performed on this single tooth immediately, without affecting the induction quenching of the next single tooth in step 3, and so on, to complete the induction quenching and cryogenic treatment of all single teeth.

[0058] Specifically, in the above step 5, the low-temperature tempering treatment of the entire gear requires that after all single teeth are deep-cooled, the entire gear is placed in the air for more than 0.5 hours until the surface temperature of all gears reaches room temperature, and then low-temperature tempering treatment is performed. The low-temperature tempering temperature is 150-200°C, and the tempering time is more than 1 hour.

[0059] Specifically, in step 5 above, 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. The tooth surface hardness of the gear after low-temperature tempering is 56 to 60 HRC, the effective hardened layer depth is ≥ 2mm, and the hardness of the gear core and inner ring is 30 to 36 HRC, meeting the machining performance requirements. Moreover, due to the precise control of the temperature and time of induction heating, the probability of cracks on the gear surface is greatly reduced, the probability of quenching cracks is greatly reduced, and the yield rate is high (for example, the yield rate reaches more than 99%).

[0060] Specifically, in the above step 5, the mechanical properties of the outermost 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, 1750-1830MPa), 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 10% (for example, 10%-13%). The gear has excellent mechanical properties and excellent wear resistance.

[0061] The present invention also provides a gear, which is prepared by the above method.

[0062] Compared with the prior art, the carburizing induction quenching method for gears provided by the present invention, by precisely controlling the induction heating temperature and heating zone thickness, combined with the control of deep cooling temperature and time, ensures that the surface structure of the gears after low-temperature tempering treatment is high-carbon tempered martensite + less than 20% retained austenite, the sub-surface layer (carbon content of approximately 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. After low-temperature tempering, the tooth surface hardness of the gear is 56 to 60 HRC, the effective hardened layer depth is ≥ 2mm, and the hardness of the gear core and inner ring is 30 to 36 HRC, meeting the machinability requirements. Furthermore, due to the precise control of the induction heating temperature and time, the probability of cracks on the gear surface is greatly reduced, the probability of quenching cracks is greatly reduced, and the yield rate is high (for example, the yield rate reaches over 99%).

[0063] The carburizing induction quenching method for gears provided by the present invention adopts single-tooth induction quenching + deep cryogenic treatment, and does not require quenching and deep cryogenic treatment of the entire gear, thereby reducing energy consumption and improving production efficiency. At the same time, it can ensure good mechanical processing performance of the gear core, and overcomes the existing heat treatment process for quenching and deep cryogenic treatment of large-module gears as a whole, which consumes a lot of energy and easily causes large quenching deformation of the entire gear. At the same time, the uncarburized area of ​​the core produces martensite-bainite phase transformation due to the common overall quenching, and the hardness exceeds the standard, or the high carbon on the surface is prone to quenching cracks. While improving production efficiency, it has the good performance of controllable carburized layer structure and optimized strength-plasticity matching, and is particularly suitable for heat treatment of heavy-loaded gears.

[0064] The mechanical properties of the surface layer of the gear of the present invention are: tensile strength of more than 1750MPa (for example, 1750-1830MPa), 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 10% (for example, 10%-13%). The gear has excellent mechanical properties and excellent wear resistance.

[0065] Example 1

[0066] This embodiment provides a method for carburizing and induction hardening of a gear and a gear. The material of the gear in this embodiment is 18Cr2Ni4WA; Figure 1 The figure shows a schematic diagram of a method for carburizing and induction hardening a 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.

[0067] Before carburizing, the inner ring of the gear and the reference end faces on both sides are first subjected to anti-carburizing treatment; then:

[0068] Step 1: Carburize the entire gear; then cool the entire gear in the furnace; the carburized layer depth is 3.5 mm, the carburized diffusion front depth is 5.5 mm, and the maximum carbon content on the outer side of the carburized layer is 1.0%.

[0069] Step 2: Then perform high temperature tempering at 640°C for 3 hours on the entire gear;

[0070] Step 3: Then, the gear teeth are subjected to surface induction hardening treatment one by one; the maximum induction heating temperature is 810°C, the total heating time is 5 minutes, the thickness of the heating zone is 3.4mm, and the gear teeth are cooled to room temperature by spraying water;

[0071] Step 4: After induction heating of each single tooth, each single tooth is subjected to ice cooling treatment one by one; the cooling temperature is -110°C and the cooling time is 3.5 minutes;

[0072] The above steps 3 and 4 are carried out immediately before and at the same time;

[0073] Step 5: The gear after induction quenching is subjected to low-temperature tempering at a temperature of 180°C for 1 hour.

[0074] 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 bainite + about 15% retained austenite, and the core structure is bainite + about 25% retained austenite.

[0075] The hardness distribution of the gears prepared in this embodiment is as follows: Figure 2 As shown, the tooth surface hardness is 56-60HRC, the effective hardened layer depth is 3.5mm, and the hardness of the gear core and inner ring is 30-36HRC, which meets the machining performance requirements.

[0076] The mechanical properties of the gear produced in this example are: tensile strength of approximately 1760 MPa and elongation of 7% for the surface layer; tensile strength of approximately 1160 MPa and elongation of 11.5% for the core layer. Wear resistance tests on the gears in this example revealed excellent wear resistance. Compared to Comparative Example 1, this example reduces the wear weight loss of the grinding pair by 15%.

[0077] Example 2

[0078] This embodiment provides a method for carburizing and induction hardening of a gear and a gear. The material of the gear in this embodiment is 18Cr2Ni4WA; Figure 1 The figure shows a schematic diagram of a method for carburizing and induction hardening a 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.

[0079] Before carburizing, the inner ring of the gear and the reference end faces on both sides are first subjected to anti-carburizing treatment; then:

[0080] Step 1: Carburize the entire gear; then cool the entire gear in the furnace; the carburized layer depth is 4.5 mm, the carburized diffusion front depth is 6.5 mm, and the maximum carbon content on the outer side of the carburized layer is 1.0%.

[0081] Step 2: Then perform high temperature tempering of the gear as a whole at 650°C for 2 hours;

[0082] Step 3: Then, the gear teeth are subjected to surface induction hardening treatment one by one; the maximum induction heating temperature is 840°C, the total heating time is 7 minutes, the thickness of the heating zone is 4.8mm, and the gear teeth are cooled to room temperature by spraying water;

[0083] Step 4: After induction heating of each single tooth, each single tooth is subjected to ice cooling treatment one by one; the cooling temperature is -110°C and the cooling time is 4.5 minutes;

[0084] The above steps 3 and 4 are carried out immediately before and at the same time;

[0085] Step 5: The gear after induction quenching is subjected to low-temperature tempering at a temperature of 170°C for 1 hour.

[0086] The surface structure of the gear prepared in this embodiment is high carbon tempered martensite + about 13% retained austenite, the sub-surface structure is medium carbon tempered martensite + tempered bainite + about 16% retained austenite, and the core structure is bainite + about 25% retained austenite.

[0087] The gear tooth surface hardness of the gear prepared in this embodiment is 57-60HRC, the effective hardened layer depth is 4.9mm, and the hardness of the gear core and inner ring is 31-36HRC, which meets the machining performance requirements.

[0088] The mechanical properties of the gear produced in this example are: tensile strength of approximately 1820 MPa and elongation of 6.5% for the surface layer; tensile strength of approximately 1190 MPa and elongation of 11% for the core layer. Wear resistance tests on the gears in this example revealed excellent wear resistance. Compared to Comparative Example 1, this example reduces the wear weight loss of the grinding pair by 17%.

[0089] Example 3

[0090] This embodiment provides a method for carburizing and induction hardening of a gear and a gear. The material of the gear in this embodiment is 18Cr2Ni4WA; Figure 1 The figure shows a schematic diagram of a method for carburizing and induction hardening a 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.

[0091] Before carburizing, the inner ring of the gear and the reference end faces on both sides are first subjected to anti-carburizing treatment; then:

[0092] Step 1: Carburize the entire gear; then cool the entire gear in the furnace; the carburized layer depth is 2.5 mm, the carburized diffusion front depth is 3.5 mm, and the maximum carbon content on the outer side of the carburized layer is 1.0%.

[0093] Step 2: Then perform high temperature tempering at 630°C for 3 hours on the entire gear;

[0094] Step 3: Then, the gear teeth are subjected to surface induction hardening treatment one by one; the maximum induction heating temperature is 800°C, the total heating time is 5 minutes, the thickness of the heating zone is 2.3mm, and the gear teeth are cooled to room temperature by spraying water;

[0095] Step 4: After induction heating of each single tooth, each single tooth is subjected to ice cooling treatment one by one; the cooling temperature is -110°C and the cooling time is 2.5 minutes;

[0096] The above steps 3 and 4 are carried out immediately before and at the same time;

[0097] Step 5: The gear after induction quenching is subjected to low-temperature tempering at a temperature of 160°C for 2 hours.

[0098] The surface structure of the gear prepared in this embodiment is high carbon tempered martensite + about 10% retained austenite, the sub-surface structure is medium carbon tempered martensite + tempered bainite + about 11% retained austenite, and the core structure is bainite + about 20% retained austenite.

[0099] The gear tooth surface hardness of the gear prepared in this embodiment is 57.5-60HRC, the effective hardened layer depth is 2.7mm, and the hardness of the gear core and inner ring is 32-36HRC, which meets the machining performance requirements.

[0100] The mechanical properties of the gear produced in this example are: tensile strength of approximately 1750 MPa and elongation of 7.5% for the surface layer; tensile strength of approximately 1150 MPa and elongation of 12.5% ​​for the core layer. Wear resistance tests on the gears in this example revealed excellent wear resistance. Compared to Comparative Example 1, this example reduces the wear weight loss of the grinding pair by 14%.

[0101] The microstructures and properties of Examples 1-3 show that the carburizing induction quenching method of the present invention can produce gears with excellent mechanical properties and wear resistance, with no cracks on the gear surface and a high yield rate (e.g., a yield rate of over 99%).

[0102] Comparative Example 1

[0103] 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 steps 1 and 2 of Example 1, except that:

[0104] Step 3: quench the gear as a whole; the quenching temperature is 810°C, the holding time is 30 minutes, and then the gear is cooled to room temperature by spraying water coolant;

[0105] Step 4: cryogenically treat the entire gear with liquid nitrogen; the cooling temperature is -130°C and the cooling time is 60 minutes;

[0106] Step 5: Temper the gear as a whole at a low temperature of 180°C for 1 hour.

[0107] The tooth surface hardness of the gear in this comparative example is 58.5~61HRC, the effective hardened layer depth is 3.6mm, the hardness of the gear core and inner ring is 40~44HRC, the core does not meet the machining performance requirements, and is prone to cracking during quenching, and the yield rate is less than 90%.

[0108] The mechanical properties of the surface layer of the gear prepared in this comparative example are: tensile strength of about 1850 MPa, elongation of 5%; the mechanical properties of the core are: tensile strength of about 1350 MPa, elongation of 8.5%; and the wear resistance is worse than that of Example 1.

[0109] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for carburizing and induction hardening of gears, characterized in that: The carburizing induction quenching method comprises the following steps: Step 1: Carburize the entire gear; Step 2: High-temperature tempering the entire gear; Step 3: Perform surface induction hardening treatment on the gear teeth one by one; Step 4: Cryogenically treat the gear teeth one by one; Step 5: Perform low-temperature tempering treatment on the entire gear; 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; the module of the gear is 30-60 mm; In step 3, when the surface of the single gear tooth is subjected to induction hardening treatment, the surface temperature of the single gear tooth is induction heated to 800-860° C., and the induction heating time is within 10 minutes; In step 3, during induction heating, the thickness h of the heating zone with a temperature lower limit of 700° C. and the depth H of the carburized layer have the following corresponding relationship: When 2mm≤H≤3mm, h=H-(0~0.5)mm; When 3mm<H≤4mm, h=H-(0~0.25)mm; When 4mm<H≤6mm, h=H+(0~0.5)mm; In step 4, the cryogenic treatment of the single gear tooth includes: performing high-speed cold nitrogen cryogenic treatment on the single gear after induction quenching, and the cryogenic temperature T and the maximum carbon content C on the surface of the carburized layer have the following relationship: when the maximum carbon content C on the surface is 0.8%, the cryogenic temperature T is -70°C; when the maximum carbon content C on the surface increases by 0.1%, the cryogenic temperature T decreases by 20°C; The relationship between deep cooling time t, carburized layer depth H and alloying element Ni content is as follows: For alloy steel with a Ni content of 2%, when H is 2 mm, the deep cooling time t is 1 min; for every 1 mm increase in H, the deep cooling time t increases by 1 min; for every 1% increase in Ni content, the deep cooling time increases by 0.5 min.

2. The carburizing induction quenching method according to claim 1, characterized in that: In step 3, when the surface of a single gear tooth is subjected to induction hardening treatment, the gear tooth is completely cooled to room temperature using an induction hardening coolant.

3. The carburizing induction quenching method according to claim 1, characterized in that: In step 1, the carbon content of the outermost carburized layer of the gear after carburizing and cooling is 0.85-1.2%.

4. The carburizing induction quenching method according to claim 1, characterized in that: In the step 1, the gear after carburizing treatment has a carbon content of 0.4% as a critical point, a carburized layer depth H of the gear is 2-6 mm, and a carburizing diffusion front depth is 4-8 mm.

5. The carburizing induction quenching method according to claim 1, characterized in that: In step 2, the high-temperature tempering temperature ranges from 550° C. to 650° C., and the high-temperature tempering holding time ranges from 1.5 to 4 hours.

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