A high-temperature tempering and quenching matching method for carburized gears and carburized gears

Abstract

The application discloses a carburized gear high-temperature tempering and quenching temperature control matching method and a carburized gear, and belongs to the technical field of gears, and is used for solving the problem that the high-temperature tempering and quenching process parameters of the existing heavy load gear rely on experience, which can cause the mechanical properties of the gears prepared by different carburizing processes to fluctuate greatly, quenching cracks to appear, and the mechanical properties to be poor. The method comprises the following steps: performing high-temperature tempering on the whole gear after carburizing treatment; then performing quenching treatment on the whole gear; the high-temperature tempering temperature T1, the high-temperature tempering holding time t1 and the quenching temperature T2 and the quenching holding time t2 satisfy the following relationship: T1*lg(t1) = T2*lg(t2) + B, the units of T1 and T2 are ℃, the units of t1 and t2 are min, and the value of B is 100-120. The gear prepared by the method has high yield and excellent mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of gear technology, specifically relating to a method for matching the temperature control of high-temperature tempering and quenching of carburized gears, and the carburized gear itself. Background Technology

[0002] The performance indicators of key heavy-duty transmission components are crucial factors driving the development of heavy-duty aircraft for more complex and demanding service environments. Among these, heavy-duty gear transmissions require high wear resistance and fatigue resistance. Traditional manufacturing processes necessitate deep carburizing to strengthen the surface of heavy-duty gears. To ensure sufficient strength and toughness, high-temperature tempering followed by quenching and tempering is typically performed after carburizing. Despite years of practical development, the performance of carburized heavy-duty gears after traditional heat treatment still cannot meet the increasingly stringent operating conditions. Controlling carbide precipitation during high-temperature tempering and the solid solution saturation of martensite during quenching are the most critical heat treatment control factors. Therefore, a precise matching and control technology for high-temperature tempering and quenching processes is needed to achieve the optimal mechanical properties of the carburized layer in heavy-duty gears. Summary of the Invention

[0003] Based on the above analysis, the present invention aims to provide a method for matching the temperature control of high-temperature tempering and quenching of carburized gears, and a carburized gear, to solve the problem that the existing high-temperature tempering and quenching process parameters of heavy-duty gears rely on experience, which leads to large fluctuations in the mechanical properties of gears prepared by different carburizing processes, quenching cracks, and poor mechanical properties.

[0004] The objective of this invention is mainly achieved through the following technical solutions:

[0005] On one hand, the present invention provides a method for matching high-temperature tempering and quenching of carburized gears, the method comprising: subjecting the carburized gear as a whole to high-temperature tempering; and then subjecting the gear as a whole to quenching; wherein the high-temperature tempering temperature T1 and the high-temperature tempering holding time t1 satisfy the following relationship with the quenching temperature T2 and the quenching holding time t2:

[0006] T1×lg(t1)=T2×lg(t2)+B,

[0007] The units for T1 and T2 are ℃, the units for t1 and t2 are min, and B is an empirical coefficient with a value of 100 to 120.

[0008] Furthermore, the value of T2 ranges from 760 to 870℃.

[0009] Furthermore, the value of T1 ranges from 550 to 650℃.

[0010] Furthermore, when 550℃≤T1≤600℃, 15min≤t2≤25min; when 600℃<T1≤650℃, 20min<t2≤30min.

[0011] Furthermore, the high-temperature tempering time t1 is defined as starting from when the highest temperature on the outer side of the gear part reaches 50°C below T1 temperature, and continuing until it is cooled to 50°C below T1 temperature after being removed from the furnace.

[0012] Furthermore, t2 is defined as the period from when the surface of the gear reaches temperature T2 and the core reaches 30°C below temperature T2 until it is quenched after being removed from the furnace.

[0013] Furthermore, during quenching, when the temperature of the gear core reaches temperature T2, the temperature difference between the gear surface and T2 is less than 10℃.

[0014] Furthermore, the surface microstructure of the quenched gear consists of a martensitic matrix with a carbon content of no more than 0.5 wt%, retained austenite with a volume fraction of less than 5%, and diffusely distributed approximately spherical Fe3C type carbides.

[0015] Furthermore, the Ni element in the gear material has a mass percentage of more than 3%, and the total mass percentage of strong carbide-forming elements is less than 3%.

[0016] The present invention also provides a carburized gear, which is prepared by the above-described method.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1) The high-temperature tempering and quenching temperature control matching method for carburized gears provided by this invention precisely controls the high-temperature tempering temperature and time, as well as the subsequent quenching temperature and holding time, to ensure that the surface layer after final quenching has a microstructure with good strength and toughness, namely, a martensitic matrix with a carbon content not exceeding 0.5 wt% + retained austenite with a volume fraction of less than 5% + dispersed approximately spherical Fe3C type carbides with a particle size of less than 200 nm. This ensures that the gear tooth surface hardness is 56–60 HRC, and the gear core and inner ring hardness is 30–40 HRC, meeting the requirements for machinability.

[0019] 2) The mechanical properties of the outermost layer (referring to the surface layer with a carbon content of 0.8-0.9% or more) of the gear of the present invention are: tensile strength of 1750 MPa or more (e.g., 1750-1800 MPa) and elongation of 5.5% or more (e.g., 5.5%-6.5%); the mechanical properties of the core layer with a carbon content of less than 0.4% are: tensile strength of 1150 MPa or more (e.g., 1790-1200 MPa) and elongation of 8.5% or more (e.g., 8.5%-9%). The gear has excellent mechanical properties; the gear yield is as high as 99% or more.

[0020] 3) In the method of the present invention, based on the carburizing process and alloy system of the gear, the matching relationship between high-temperature tempering temperature and tempering time is established, and precise control technology is proposed to maximize the solid solution strengthening of carbon elements in the carburized layer after subsequent quenching, while avoiding problems such as microcracks on the quenched surface caused by insufficient high-temperature tempering; and through the precise matching of high-temperature tempering and quenching process, the optimal value of mechanical properties of the carburized layer of the gear is achieved.

[0021] 4) By precisely controlling the high-temperature tempering temperature and tempering time, this invention can accurately control the time the parts are in the furnace, greatly improving production efficiency. It overcomes the problem of uncontrollable carbon content in the large carburized layer after quenching and austenitization of carburized parts in existing heat treatment processes. While improving production efficiency, it also has the good performance of controllable carburized layer structure and optimized strong plasticity matching, making it especially suitable for the industrial application of heavy-duty gears.

[0022] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of what is particularly pointed out in the written description and drawings. Attached Figure Description

[0023] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0024] Figure 1 This is a microstructure diagram of the gear after high-temperature tempering in Embodiment 1 of the present invention;

[0025] Figure 2 A schematic diagram of the gradient hardness distribution of the gear after high-temperature tempering in Embodiment 1 of the present invention;

[0026] Figure 3 The final microstructure of the carburized layer in Example 2 provided by the present invention. Detailed Implementation

[0027] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of the present invention and, together with the embodiments of the present invention, serve to illustrate the principles of the present invention.

[0028] Currently, high-temperature tempering and quenching after deep carburizing of heavy-duty gears generally rely on empirical process parameters, such as a high-temperature tempering temperature of 600–650℃ and a tempering time of 1–3 hours. However, empirical process parameters often lead to significant fluctuations in the mechanical properties of gears prepared by different carburizing processes, resulting in quenching cracks or failing to fully utilize the strengthening and toughening effects of carbon elements in the carburized layer. Therefore, after in-depth research, the inventors, based on the carburizing process and alloying system of heavy-duty gears, established the matching relationship between high-temperature tempering temperature and tempering time and quenching process parameters, and proposed precise control techniques to maximize the solid solution strengthening of carbon elements in the carburized layer after quenching, while avoiding problems such as micro-cracks on the quenched surface caused by insufficient high-temperature tempering; through precise matching of high-temperature tempering and quenching processes, the optimal mechanical properties of the carburized layer of heavy-duty gears can be achieved.

[0029] This invention provides a method for matching the high-temperature tempering and quenching temperature control of carburized gears. The method includes: subjecting the carburized gear to high-temperature tempering; and then quenching the gear. The high-temperature tempering temperature T1 and the high-temperature tempering holding time t1 are related to the quenching temperature T2 and the quenching holding time t2 as follows:

[0030] T1×lg(t1)=T2×lg(t2)+B,

[0031] The units for T1 and T2 are ℃, the units for t1 and t2 are min, and B is an empirical coefficient with a value of 100 to 120.

[0032] Specifically, the value of T2 is in the range of 760 to 870℃.

[0033] Specifically, the value of T1 is in the range of 500 to 650℃; when 550℃≤T1≤600℃, 15min≤t2≤25min; when 600℃<T1≤650℃, 20min<t2≤30min.

[0034] It should be noted that the above-mentioned high-temperature tempering time t1 is defined as starting from when the highest temperature on the outer side of the entire gear reaches 50°C below T1 temperature, and ending when it is cooled to 50°C below T1 temperature after being taken out of the furnace; the quenching and holding time t2 is defined as starting from when the surface of the gear reaches T2 temperature and the core reaches 30°C below T2 temperature, and ending when it is quenched after being taken out of the furnace.

[0035] It should be noted that during the above quenching process, when the temperature of the gear core reaches T2, the temperature of the gear surface must not exceed T2 by more than 10°C (i.e., the difference between the gear surface temperature and T2 is less than 10°C).

[0036] Specifically, the surface of the quenched gears obtained above has a microstructure with good strength and toughness, that is, the surface structure is a martensitic matrix with a carbon content of no more than 0.5 wt% + retained austenite with a volume fraction of less than 5% + diffusely distributed approximately spherical Fe3C type carbides with a particle size of less than 200 nm.

[0037] Specifically, during the high-temperature tempering process of the aforementioned gear assembly, the high-temperature tempering temperature T1, the tempering holding time t1, and the carburized layer depth h and the carbon content C of the outermost layer of the carburized layer satisfy the following relationship:

[0038] T1×lg(t1)=A×C×lg(h+10),

[0039] The unit of T1 is ℃, the unit of t1 is min, A is an empirical coefficient with a value of 1000 to 1200, the unit of C is wt% (i.e., if the outermost carbon content is 1wt%, then C is 1 here), and the unit of h is mm.

[0040] Specifically, the Ni alloying element content of the aforementioned gear material is more than 3% by mass, and the total mass percentage of strong carbide-forming elements such as Cr, V, and W is less than 3% by mass.

[0041] Specifically, the materials for the aforementioned gears can be 20CrMnTi, 18Cr2Ni4W, or 20CrMnMo, etc.

[0042] Specifically, the inner ring diameter of the aforementioned gear is 100–300 mm, the pitch circle diameter is 200–400 mm, and the module is a large module of 16 or more.

[0043] Specifically, prior to the aforementioned carburizing treatment, anti-carburizing treatment is also performed on the inner ring of the gear and the reference end faces on both sides.

[0044] Specifically, the above-mentioned carburizing process steps include: carburizing in gaseous, liquid, or solid state followed by cooling.

[0045] Specifically, the carburizing carbon potential of the above carburizing treatment is ≥1.0wt%.

[0046] Specifically, the aforementioned carburizing treatment includes post-carburizing cooling in the furnace or natural cooling in the air.

[0047] Specifically, the surface microstructure of the gear after carburizing and cooling is martensite plus no more than 30% (volume percentage) of retained austenite; the retained austenite content at the subsurface carbon content location is no more than 5% (volume percentage).

[0048] Specifically, for gears treated with carburizing, the carbon content is 0.4 wt% as the critical point, the effective depth of the carburized layer of the gear is ≥3 mm, the depth of the carburizing diffusion front is ≥5 mm, and the carbon content of the outermost part of the carburized layer is ≥1.0 wt%.

[0049] Specifically, the value of A conforms to the following principles:

[0050] When the Ni alloy content of the gear material is 3wt% and the total content of strong carbide-forming elements such as Cr, V, and W is 3wt%, the value of A is taken as 1020.

[0051] For every increase in Ni content (0–0.5 wt%), the A value decreases by 5; for example, an increase in Ni content of 0.1 wt% results in a decrease in the A value of 5; an increase in Ni content of 0.6 wt% results in a decrease in the A value of 10; when the Ni content exceeds 5 wt%, the A value is taken as 1000.

[0052] For every decrease in the total content of strong carbide-forming elements such as Cr, V, and W (0–0.5 wt%), the A value increases by 4.

[0053] When the total content of strong carbide-forming elements such as Cr, V, and W is less than 0.5 wt%, the A value is taken as 1200.

[0054] Specifically, the high-temperature tempering temperature T1 ranges from 500 to 650℃, and the t1 ranges from 60 to 130 min. Furthermore, when 3mm ≤ h ≤ 3.5mm, 1.0wt% ≤ C% ≤ 1.1wt%; when 3.5mm < h ≤ 4mm, 1.1wt% < C% ≤ 1.15wt%; and when 4mm < h, 1.15wt% < C% ≤ 1.2wt%.

[0055] Specifically, the above t1 allows for a deviation of ±5 minutes.

[0056] Specifically, by precisely controlling the high-temperature tempering temperature T1 and the high-temperature tempering time t1, the microstructure of the carburized layer after high-temperature tempering is a uniform and fine spherical carbide and a tempered martensite matrix with a solid solution carbon content of no more than 0.2 wt%, and there is no continuous network of carbides along the grain boundaries; specifically, the size of the spherical carbide is less than 300 nm.

[0057] Specifically, the solid carbon content in the outermost layer of the tempered martensite matrix of the gear after high-temperature tempering is ≤0.2wt%; at a depth of 0.8h from the surface, the solid carbon content in the tempered martensite matrix is ​​≤0.1wt%.

[0058] Specifically, the surface hardness of the gear after high-temperature tempering is below HRC30, the hardness at the subsurface layer (0.8h) depth is below HRC28, and the hardness of the uncarburized core area is below HRC25.

[0059] Specifically, the above-mentioned method for matching the high-temperature tempering and quenching temperature control of carburized gears also includes: performing deep cryogenic treatment on the quenched gear as a whole; and then performing low-temperature tempering on the gear as a whole to obtain a carburized gear.

[0060] Specifically, the above-mentioned cryogenic treatment can use liquid nitrogen, with a cryogenic temperature of -50 to -150°C and a cooling time of 15 to 40 minutes.

[0061] Specifically, the temperature for the aforementioned low-temperature tempering is 150–190°C, and the tempering time is 40–120 min.

[0062] Specifically, the surface microstructure of the gear after low-temperature tempering consists of a martensitic matrix with a carbon content not exceeding 0.5 wt%, retained austenite with a volume fraction of less than 5%, and diffusely distributed, approximately spherical Fe3C-type carbides with a particle size of less than 200 nm. The surface hardness of the gear after low-temperature tempering is 56–60 HRC, and the hardness of the gear core and inner ring is 30–40 HRC, meeting the requirements for machinability.

[0063] Specifically, the mechanical properties of the outermost layer of the gear after low-temperature tempering (referring to the surface layer with a carbon content of 0.8-0.9% or more) are as follows: tensile strength of 1750 MPa or more (e.g., 1750-1800 MPa) and elongation of 5.5% or more (e.g., 5.5%-6.5%); the mechanical properties of the core layer with a carbon content of less than 0.4% are as follows: tensile strength of 1150 MPa or more (e.g., 1790-1200 MPa) and elongation of 8.5% or more (e.g., 8.5%-9%). The gear exhibits excellent mechanical properties.

[0064] The present invention also provides a carburized gear, which is prepared by the above-mentioned high-temperature tempering and quenching temperature control matching method for carburized gears.

[0065] Compared with existing technologies, the high-temperature tempering and quenching temperature control matching method for carburized gears provided by this invention precisely controls the high-temperature tempering temperature and time, as well as the subsequent quenching temperature and holding time, to ensure that the surface layer after final quenching has a microstructure with good strength and toughness. This microstructure consists of a martensitic matrix with a carbon content not exceeding 0.5 wt.%, retained austenite with a volume fraction less than 5%, and dispersed, approximately spherical Fe3C-type carbides with a particle size less than 200 nm. This ensures that the gear tooth surface hardness is 56–60 HRC, and the gear core and inner ring hardness is 30–40 HRC, meeting the requirements for machinability.

[0066] The outermost layer of the gear of the present invention (referring to the outermost layer with a carbon content of 0.8 to 0.9% or more) has the following mechanical properties: tensile strength of 1750 MPa or more (e.g., 1750 to 1800 MPa) and elongation of 5.5% or more (e.g., 5.5% to 6.5%); the core layer with a carbon content of less than 0.4% has the following mechanical properties: tensile strength of 1150 MPa or more (e.g., 1790 to 1200 MPa) and elongation of 8.5% or more (e.g., 8.5% to 9%). The gear exhibits excellent mechanical properties.

[0067] In the method of this invention, based on the carburizing process and alloy system of the gear, a matching relationship between high-temperature tempering temperature and tempering time is established, and precise control techniques are proposed to maximize the solid solution strengthening of carbon elements in the carburized layer after subsequent quenching, while avoiding problems such as microcracks on the quenched surface caused by insufficient high-temperature tempering; and through precise matching of high-temperature tempering and quenching processes, the optimal mechanical properties of the gear carburized layer are achieved.

[0068] This invention, by precisely controlling the high-temperature tempering temperature and tempering time, can accurately control the time parts are in the furnace, greatly improving production efficiency. It overcomes the problem of uncontrollable carbon content in the large carburized layer after quenching and austenitization of carburized parts in existing heat treatment processes. While improving production efficiency, it also has the good properties of controllable carburized layer structure and optimized strength and plasticity matching, making it especially suitable for industrial applications of heavy-duty gears.

[0069] Example 1

[0070] This embodiment provides a method for matching the temperature control of high-temperature tempering and quenching of carburized gears, and a carburized gear. The gear material grade is 18Cr2Ni4WA, the diameter of the inner ring of the gear is 120mm, the diameter of the pitch circle is 260mm, the module is 20, and the depth of the carburized layer h is required to be 3.5mm.

[0071] In this embodiment, the Ni element in the gear material has a mass percentage of 4.5 wt%, the total mass percentage of strong carbide forming elements (Cr and W) is 2.5 wt%, A is 1009, and B is 110.

[0072] The preparation method is as follows:

[0073] Step 1: Carburize the entire gear. Before carburizing, anti-carburizing treatment is also performed on the inner ring of the gear and the reference end faces on both sides. The carburized gear is cooled in the furnace. The depth of the carburized layer h is 3.5 mm, and the maximum carbon content C of the outermost layer of the carburized layer is 1.0 wt%.

[0074] Step 2: Then, the entire gear is subjected to high-temperature tempering. The high-temperature tempering temperature T1 is 600℃ and the high-temperature tempering time t1 is 80min.

[0075] Step 3: Then, the gear is reheated and quenched at a temperature of 793℃ for quenching and a holding time of 20 minutes for quenching. After that, it is cooled to room temperature by spraying water-based coolant.

[0076] Step 4: Perform cryogenic treatment on the entire gear using liquid nitrogen; the cooling temperature is -100℃, and the cooling time is 20 minutes.

[0077] Step 5: Perform low-temperature tempering on the entire gear at 180℃ for 1 hour.

[0078] The microstructure of the gear surface after high-temperature tempering in this embodiment is as follows: Figure 1 As shown, the microstructure consists of a martensitic matrix with a carbon content of no more than 0.2 wt% and diffusely distributed approximately spherical Fe3C type carbides with a particle size of less than 300 nm, without intergranular network carbides.

[0079] Gradient hardness distribution after high-temperature tempering is as follows Figure 2 As shown, the surface hardness is HRC30, the hardness at a depth of 2.8mm in the subsurface layer is lower than HRC28, and the hardness of the uncarburized core area is lower than HRC25.

[0080] The surface of the quenched gear has a good microstructure with good strength and toughness. The surface structure consists of a martensitic matrix with a carbon content of no more than 0.5 wt%, a retained austenite with a volume fraction of less than 5%, and diffusely distributed approximately spherical Fe3C type carbides with a particle size of less than 200 nm.

[0081] The gear finally prepared in this embodiment has a surface microstructure consisting of a martensitic matrix with a carbon content not exceeding 0.5 wt%, retained austenite with a volume fraction of less than 5%, and diffusely distributed, approximately spherical Fe3C-type carbides with a particle size of less than 200 nm. The tooth surface hardness is 56–60 HRC, the effective hardened layer depth is 3.5 mm, and the hardness of the gear core and inner ring is 30–36 HRC, meeting the requirements for machinability.

[0082] The performance of the gear in this embodiment was tested using a micro-tensile test: the mechanical properties of the outermost layer of the gear in this embodiment (referring to the surface layer with a carbon content of 0.8-0.9% or more) were: tensile strength 1800 MPa, elongation 6.5%; the mechanical properties of the core with a carbon content of less than 0.4% were: tensile strength 1200 MPa, elongation 9%.

[0083] Example 2

[0084] This embodiment provides a method for matching the temperature control of high-temperature tempering and quenching of carburized gears, and a carburized gear. The gear material grade is 18Cr2Ni4WA, the diameter of the inner ring of the gear is 109mm, the diameter of the pitch circle is 360mm, the module is 40, and the depth of the carburized layer h is required to be 3.5mm.

[0085] In this embodiment, the Ni element in the gear material has a mass percentage of 4.5 wt%, the total mass percentage of strong carbide forming elements (Cr and W) is 2.5 wt%, A is 1009, and B is 105.

[0086] The preparation method is as follows:

[0087] Step 1: Carburize the entire gear. Before carburizing, anti-carburizing treatment is also performed on the inner ring of the gear and the reference end faces on both sides. The carburized gear is cooled in the furnace. The depth of the carburized layer h is 3.5 mm, and the maximum carbon content C of the outermost layer of the carburized layer is 1.0 wt%.

[0088] Step 2: Then, the entire gear is subjected to high-temperature tempering. The high-temperature tempering temperature T1 is 640℃ and the high-temperature tempering time t1 is 60min.

[0089] Step 3: Then the gear is reheated and quenched at a temperature of 760℃ for quenching and a holding time of 23 minutes for quenching. After that, it is cooled to room temperature by spraying water-based coolant.

[0090] Step 4: Cool the entire gear with liquid nitrogen; the cooling temperature is -100℃ and the cooling time is 20 minutes.

[0091] Step 5: Perform low-temperature tempering on the entire gear at 180℃ for 1 hour.

[0092] The surface structure of the gear finally prepared in this embodiment is as follows: Figure 3 As shown, the microstructure consists of a martensitic matrix with a carbon content of no more than 0.5 wt.%, a retained austenite with a volume fraction of less than 5%, and diffusely distributed, approximately spherical Fe3C-type carbides with a particle size of less than 200 nm.

[0093] The gear finally prepared in this embodiment has a tooth surface hardness of 56-60 HRC, an effective hardened layer depth of 3.5 mm, and a gear core and inner ring hardness of 35-40 HRC, which meets the requirements for machinability.

[0094] The performance of the gear in this embodiment was tested using a micro-tensile test: the mechanical properties of the outermost layer of the gear in this embodiment (referring to the surface layer with a carbon content of 0.8-0.9% or more) were: tensile strength 1750 MPa, elongation 5.5%; the mechanical properties of the core layer with a carbon content of less than 0.4% were: tensile strength 1190 MPa, elongation 8.5%.

[0095] During the preparation process of Examples 1-2, there were no microcracks on the quenched surface, and the gear yield (referring to the absence of product scrap due to problems such as cracks, network carbides, and excessive retained austenite) was as high as 99% or more. The gears prepared in these examples achieved the optimal mechanical properties of the gear carburized layer.

[0096] Comparative Example 1

[0097] This comparative example provides a conventional carburized gear and its preparation method. The gear material and shape are the same as in Example 1. In this comparative example, the value of A is 1348. The heat treatment method includes the following steps:

[0098] Step 1: Carburize the entire gear. Before carburizing, anti-carburizing treatment is also performed on the inner ring of the gear and the reference end faces on both sides. The carburized gear is cooled in the furnace. The depth of the carburized layer h is 3.5 mm, and the maximum carbon content C of the outermost layer of the carburized layer is 1.0 wt%.

[0099] Step 2: Then, the entire gear is subjected to high-temperature tempering. The high-temperature tempering temperature T1 is 640℃ and the high-temperature tempering time t1 is 240min.

[0100] Step 3: Then, the gear is reheated and quenched at a temperature of 820℃ for quenching and a holding time of 20 minutes for quenching. After that, it is cooled to room temperature by spraying water-based coolant.

[0101] Step 4: Perform cryogenic treatment on the entire gear using liquid nitrogen; the cooling temperature is -100℃, and the cooling time is 20 minutes.

[0102] Step 5: Perform low-temperature tempering on the entire gear at 180℃ for 1 hour.

[0103] During the preparation process of this comparative example, microcracks sometimes appeared on the quenched surface, and the gear yield was about 85%. The tooth surface hardness of the gear prepared in this comparative example was 56-60 HRC, the effective hardened layer depth was 3.5 mm, and the hardness of the gear core and inner ring was 38-43 HRC. The mechanical properties of the outermost layer (referring to the surface layer with a carbon content of 0.8-0.9% or higher) of the gear in this comparative example were: tensile strength 1680 MPa, elongation 4.5%. The insufficient plasticity of this comparative example affected the fatigue performance of the gear.

[0104] The above description is only a preferred 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 conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for matching high-temperature tempering and quenching of carburized gears, characterized in that, The inner ring diameter of the gear is 100~300mm, the pitch circle diameter is 200~400mm, and the module is a large module of 16 or more. The method includes: subjecting the carburized gear to high-temperature tempering; then quenching the gear; the high-temperature tempering temperature T1 and the high-temperature tempering holding time t1 are related to the quenching temperature T2 and the quenching holding time t2 as follows: T1×lg(t1) =T2×lg(t2) +B, The units for T1 and T2 are ℃, the units for t1 and t2 are min, and B is an empirical coefficient with a value of 100~120. When 550℃≤T1≤600℃, 15min≤t2≤25min; when 600℃<T1≤650℃, 20min<t2≤30min. During the high-temperature tempering process of the gear as a whole, the high-temperature tempering temperature T1, the high-temperature tempering holding time t1, and the carburized layer depth h and the carbon content C of the outermost layer of the carburized layer satisfy the following relationship: T1×lg(t1)=A×C×lg(h+10), The unit of T1 is ℃, the unit of t1 is min, A is an empirical coefficient with a value of 1000~1200, the unit of C is wt%, and the unit of h is mm. The surface microstructure of the quenched gear consists of a martensitic matrix with a carbon content of no more than 0.5 wt%, a retained austenite with a volume fraction of less than 5%, and diffusely distributed approximately spherical Fe3C type carbides with a particle size of less than 200 nm.

2. The method according to claim 1, characterized in that, The value of T2 is in the range of 760~870℃.

3. The method according to claim 1, characterized in that, The value of T1 is in the range of 550~650℃.

4. The method according to claim 1, characterized in that, The high-temperature tempering holding time t1 is defined as starting from when the highest temperature on the outer side of the gear reaches 50°C below T1 and ending when it is cooled to 50°C below T1 after being removed from the furnace.

5. The method according to claim 4, characterized in that, The term t2 is defined as the period from when the surface of the gear reaches temperature T2 and the core reaches 30°C below temperature T2 until it is removed from the furnace and quenched.

6. The method according to claim 1, characterized in that, During the quenching process, when the temperature of the gear core reaches temperature T2, the temperature difference between the gear surface and T2 is less than 10°C.

7. The method according to any one of claims 1 to 6, characterized in that, The material of the gear contains more than 3% Ni by mass and less than 3% total mass of strong carbide-forming elements.

8. A carburized gear, characterized in that, The carburized gear is prepared by the method described in any one of claims 1 to 7.

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