A heat treatment process method of 15CrA high-hardness carburizing-quenching-ice-quenching-tempering

Abstract

The present application relates to the field of carburizing heat treatment processing, in particular to a kind of 15CrA high hardness carburizing quenching ice cold tempering heat treatment process method, by with methanol, propane as carburant, namely with methanol, propane as enriching agent, carbon potential is controlled at 1.15% C, the consistency of actual value and display value of carbon potential in furnace is compared using carbon fixation method, to ensure the accuracy of carbon potential, carburizing is carried out at 910 DEG C temperature, then hardness is adjusted by normalizing, finally high hardness HRC≥62 is obtained by quenching, ice cold, tempering, and carburized layer depth reaches 1.3-1.7mm.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of carburizing heat treatment, in particular to a 15CrA high-hardness carburizing quenching ice-cold tempering heat treatment process. BACKGROUND

[0002] Carburizing heat treatment is a heat treatment process in which a low-carbon steel or low-carbon alloy steel part is placed in a carburizing medium, heated to austenite state and kept, so that carbon atoms are penetrated into the surface layer of the part. Carburizing treatment not only can improve the surface hardness, strength, wear resistance and fatigue resistance of the part, but also can maintain a certain strength and toughness in the core of the part.

[0003] Currently, during carburizing treatment of 15CrA, the cycle is long, and there are many factors affecting the hardness of the carburized layer, including temperature, carbon potential, cooling medium, and quenching, ice-cold, and tempering processes. If the process is not well controlled, it is easy to cause surface decarburization, insufficient carbon concentration, insufficient carburized layer, and ultimately cannot meet the requirements of high hardness. Therefore, a 15CrA high-hardness carburizing quenching ice-cold tempering heat treatment process is needed to ensure that the material after carburizing can meet the requirements of a carburized layer depth of 1.3-1.7 mm and a hardness value of HRC≥62. SUMMARY

[0004] The purpose of the present application is to provide a 15CrA high-hardness carburizing quenching ice-cold tempering heat treatment process. By using methanol and propane as carburizing agents, i.e. using methanol and propane as enriching agents, the carbon potential is controlled at 1.15%C, the consistency of the actual value and the displayed value of the carbon potential in the furnace is compared by using the carbon fixation method to ensure the accuracy of the carbon potential, carburizing is carried out at a temperature of 910°C, then the hardness is adjusted by normalizing, and finally high hardness HRC≥62 is obtained through quenching, ice-cold, and tempering, and the carburized layer depth reaches 1.3-1.7 mm.

[0005] Technical solution

[0006] A 15CrA high-hardness carburizing quenching ice-cold tempering heat treatment process, comprising the following steps:

[0007] Step (1) cleaning the surface of the carburized part;

[0008] Step (2) after the carburizing furnace is heated to 750°C, start injecting methanol, and after the temperature rises to 800°C, start passing in propane. When the carburizing furnace reaches a temperature of 910°C and the carbon potential reaches 0.5%C, the carburized part starts to be loaded into the furnace;

[0009] Step (3) after the part is loaded into the carburizing furnace, the carburizing furnace is rapidly exhausted. After exhaust, the carbon potential and temperature in the furnace decrease. After exhaust is completed, the carburizing furnace continues to heat up. When the equipment reaches a temperature of 910°C and the carbon potential is 0.5%C again, keep for 5 minutes;

[0010] Step (4) increase the input of methanol and propane, the carbon potential quickly reaches 1.15%C, the carburized workpiece enters the strong carburizing stage, and the carbon is determined in the strong carburizing stage;

[0011] Step (5) after the end of the strong carburizing, the input amount of propane is reduced, and when the carbon potential quickly decreases to 0.85%C, the diffusion stage is entered;

[0012] Step (6) after the end of the diffusion, the carburized workpiece is cooled;

[0013] Step (7) the carburized workpiece is normalized at 900℃ for 60min and air-cooled;

[0014] Step (8) the quenching temperature of the heat treatment is 870±10℃, the holding time is 90-120min, and the oil cooling is adopted;

[0015] Step (9) the carburized workpiece is subjected to ice cold treatment, the treatment temperature is -70±5℃, the holding time is 4-5h, and the air cooling is adopted;

[0016] Step (10) the low-temperature tempering temperature of the heat treatment is 150±10℃, the holding time is 4-5h, and the air cooling is adopted.

[0017] Further, step (1) cleaning the surface of the carburized workpiece specifically includes the following steps:

[0018] (1.1), hydrocarbon ultrasonic cleaning to remove oil, 15min;

[0019] (1.2), hot water washing, 60℃, 2min;

[0020] (1.3), cold water washing, 2min;

[0021] (1.4), hydrocarbon ultrasonic cleaning for 10min;

[0022] (1.5), water spraying, 5min;

[0023] (1.6), drying at 100℃ for 10min.

[0024] Further, step (2) is specifically: the carburizing furnace is heated to 750℃, then the methanol is injected, the injection speed of the methanol is 2L / h, when the temperature rises to 800℃, the propane is input, the input speed of the propane is 0.15L / min, and the carburizing furnace is heated to 910℃, then the carburized workpiece is put into the furnace after the carbon potential reaches 0.5%C.

[0025] Further, step (3) is specifically: when the carburized workpiece is loaded into the furnace, the existing carburizing atmosphere in the furnace is reduced, after loading, the furnace door is quickly closed, the carbon potential and temperature in the furnace quickly rise, when the equipment reaches the temperature 910℃ and the carbon potential 0.5%C again, the furnace is kept for 5 minutes, the furnace presents positive pressure, and the gas is quickly discharged, and the atmosphere in the furnace meets the carburizing condition.

[0026] Further, step (4) is specifically: after the exhaust is completed, the amount of propane is increased, the propane input speed is 0.25L / min, the methanol input speed is 2.5L / h, the carbon potential quickly reaches 1.15%C, the temperature is kept at 910℃, the strong carburizing stage is started, the strong carburizing is kept for 660 minutes, after the keeping, the propane input speed is reduced to 0.05L / min, the methanol is kept at 2.3L / h, and the strong carburizing stage guarantees the positive pressure in the furnace.

[0027] Further, the carbon setting in step (4) is specifically:

[0028] The carbon setting piece weighed in advance is loaded into the carbon setting port below the carburizing furnace, is loaded into the furnace through the carbon setting port of the carburizing furnace, is pulled down to the cooling pipe for cooling for 5 minutes after being kept for 30 minutes, the valve door of the cooling pipe is opened, then the carbon potential atmosphere discharged from the valve door is ignited, the flame is guaranteed not to be extinguished during the whole cooling process, the carbon setting piece is not oxidized and is protected by the carbon potential atmosphere during the cooling process, the carbon setting piece is taken out after being cooled, the carbon potential value of the carbon setting in the furnace is calculated, and the carbon potential value is compared with the carbon potential value monitored by the oxygen probe of the carburizing furnace.

[0029] Further, step (5) is specifically: after the strong carburizing is completed, compressed air is input, the propane input speed is reduced to 0L / min, the amount of methanol is reduced to 2L / h, the carbon potential quickly reaches 0.85%C, the temperature is kept at 910℃, the diffusion stage is started, and the diffusion is kept for 60 minutes, and the process guarantees the positive pressure in the furnace.

[0030] Further, step (6) is specifically: after the diffusion is completed, the carburized workpiece is transferred into the gas cooling tank, nitrogen is continuously input during the transferring process, the nitrogen flow is 40L / min, and the nitrogen is kept for 30 minutes for rapid cooling.

[0031] Further, after step (10) is completed, step (11) is further included, that is, the carburized layer depth of the workpiece meets 1.3-1.7mm, and the hardness value meets HRC≥62.

[0032] Beneficial effects:

[0033] In the present application, by reasonably selecting the carburizing agent, carburizing carbon potential concentration, carburizing temperature, carbon fixation monitoring, normalizing and final quenching, ice cooling, tempering and other process parameters, the stability of carburizing and the technical difficulty of high hardness of carburized layer are effectively improved, the technical requirements of design drawings are met, and the smooth delivery of products is ensured. At the same time, it also breaks through the conventional process idea and explores a new process method for carburizing high hardness processing of such material parts. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0035] Figure 1 The figure is a schematic diagram of the part of the present application;

[0036] Figure 2 The figure is a carburizing cleaning flow chart of step (1) of the present application;

[0037] Figure 3 The figure is a carburizing process schematic diagram of steps (2), (3), (4), (5), (6) and (7) of the present application;

[0038] Figure 4 The figure is a carburizing normalizing, quenching, ice cooling treatment and low temperature tempering curve diagram of steps (8), (9), (10) and (11) of the present application;

[0039] Figure 5 The figure is a process flow chart of the present application. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0041] The features and illustrative embodiments of various aspects of the present application will be described below in detail. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without some or all of these specific details. The description of the embodiments is merely intended to provide a better understanding of the present application by showing examples of the present application. The present application is in no way limited to any specific set of details disclosed below, but covers any modifications, alternatives, and equivalents of structures, methods, devices falling within the spirit of the present application. In the drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessary obscurity of the present application.

[0042] It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict, and each embodiment can be referred to and cited by each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0043] The present application provides a 15CrA high-hardness carburizing quenching ice-cold tempering heat treatment process method, which controls the carbon potential at 1.15% C by using methanol and propane as carburizing agents, i.e., using methanol and propane as enriching agents, compares the consistency of the actual value and the displayed value of the carbon potential in the furnace by using the carbon fixation method, ensures the accuracy of the carbon potential, carries out carburizing at a temperature of 910°C, then adjusts the hardness by normalizing, and finally obtains high hardness HRC≥62 by quenching, ice-cold, and tempering, the carburizing layer depth reaches 1.3-1.7mm, and the overall idea includes the following technical contents:

[0044] 1) Using methanol as a diluent and propane as an enriching agent, and monitoring the carbon potential with an oxygen probe;

[0045] The reaction mode of methanol is: CH3OH→CO+2H2

[0046] CO+H2→C+H2O;

[0047] The reaction mode of propane is: C3H8→2C+2H2+CH4→C+2CH4

[0048] CH4→C+H2

[0049] 2) The carbon potential exhaust carbon potential is 0.05% C, the holding time is 5 minutes, the strong carburizing potential is 1.15% C, the holding time is 660 minutes, and the diffusion carbon potential is 0.85% C, the holding time is 60 minutes;

[0050] 3) The carbon fixation method is used to compare the carbon potential value in the furnace during the carburizing process to ensure the stability and accuracy of the carbon potential;

[0051] 4) The carburizing temperature is selected as 910°C, which can not only improve the carburizing speed, but also effectively reduce the formation of residual austenite;

[0052] 5), carburizing cooling adopts nitrogen atmosphere protection, nitrogen flow is 40L / min, 30min, prevents oxidation decarburization when cooling;

[0053] 6), normalizing after carburizing can adjust hardness, can refine grain, improves organization, eliminates internal stress, improves mechanical properties;

[0054] 7), final quenching, deep cooling treatment, low temperature tempering;

[0055] 8), final carburized layer depth reaches 1.3~1.8mm, hardness value satisfies HRC≥62.

[0056] The first embodiment of the application is to provide a kind of 15CrA high hardness carburizing quenching ice cold tempering heat treatment process method, specifically including the following steps:

[0057] (1) clean the surface of carburized parts, determine carburized surface clean;Surface dirt can cause carbon atoms unable to penetrate, resulting in carburized layer reduction, soft point appears, clean carburized surface helps to improve carburizing quality;

[0058] (2) equipment is heated to 750 DEG C, then start injecting methanol, after temperature rises to 800 DEG C, start to pass into propane, equipment to temperature 910 DEG C, carbon potential reaches 0.5% C, then start to load furnace;Because methanol is not completely incomplete at lower than 750 DEG C, cracking, using process is easy to cause a large amount of carbon black, and product is not safe, the higher the temperature is more thorough, but considering the accumulation of carbon potential needs time, therefore, in the effect of ensuring that a large amount of carbon black is not produced, select lower temperature to inject methanol, through test 750 DEG C is selected;Propane cracking temperature is higher, propane as enriching agent contains more carbon atoms, incomplete cracking at low temperature, easy to cause a large amount of carbon deposition, affect carburizing effect, select 800 DEG C, the purpose is to ensure that it is completely cracked, and less carbon deposition is formed;

[0059] (3) The furnace door needs to be opened when the parts are loaded, which will cause the furnace carbon potential and temperature to decrease. Therefore, after the parts are loaded, the rapid exhaust should be started, and when the equipment reaches the temperature of 910℃ and the carbon potential of 0.5%C, the temperature should be maintained for 5 minutes. Before loading, the temperature and carbon potential in the furnace should be ensured, which can increase the exhaust rate after the parts are loaded, reduce the risk of oxidation and decarburization of the parts in the air for a long time, and select the highest temperature in the range of 880-930℃ for the carburizing temperature of 15CrA material. Selecting the highest temperature can accelerate the carburizing effect, but the long time of high temperature of the parts will increase the risk of deformation. Selecting the lowest temperature can reduce the risk of deformation, but it also increases the carburizing time. Through comparison and test, selecting 910℃ can effectively solve the risks of deformation and long carburizing time. The purpose of exhaust is to ensure the carbon potential in the furnace and prevent the parts from oxidizing during the heating process. If the carbon potential is too high during the exhaust process, it will take a long time to inject methanol and propane, which will cause waste of carburizing agent and equipment. However, if the carbon potential is too low, it will cause the carbon potential in the furnace to fail to reach the atmosphere protection purpose for a long time after the parts are loaded, resulting in oxidation and decarburization of the carburized parts. Therefore, through test, the carbon potential of 0.5%C is selected for exhaust.

[0060] (4) Strong carburizing: after the exhaust is completed, the injection of methanol and propane is increased, the carbon potential quickly reaches 1.15%C, and the strong carburizing stage is started. The purpose is to obtain high carbon concentration on the surface of the parts and the depth of the carburized layer. Increasing the injection amount of carburizing agent methanol and propane can obtain high carbon potential in the furnace. The higher the carbon potential, the higher the carburizing speed. However, when the carbon potential is too high, a large amount of carbon black will be produced in the furnace, the equipment will be seriously carbonized, the carbon potential will fluctuate greatly during the carburizing process, the control will be unstable, and a large amount of carbon will adhere to the surface of the parts, which will prevent carbon atoms from penetrating, thereby reducing the carburizing speed, the depth of the carburized layer, and the surface carbon concentration. Therefore, selecting 1.15%C for strong carburizing can ensure the carburizing speed and the depth of the carburized layer, and also ensure the surface carbon concentration.

[0061] (5) Carbon fixation: during the strong carburizing process, the carbon fixation method is used to detect the accuracy of the carbon potential, and the consistency of the actual value and the displayed value of the carbon potential in the furnace is compared. The carbon potential in the furnace is monitored by the oxygen probe, which may fail or deviate during use, resulting in inaccurate carburizing results. The use of the carbon fixation method for pre-furnace carbon potential monitoring eliminates the risk of inaccurate carbon potential.

[0062] (6) Diffusion, after the end of the strong penetration, the amount of propane is reduced, and the carbon potential is rapidly reduced to 0.85% C, and the diffusion stage is started. The purpose is to obtain carbon concentration gradient and hardness gradient; diffusion is to ensure that the workpiece has a relatively gentle penetration layer hardness gradient, which helps the workpiece penetration layer and the core to combine more closely, and is not easy to produce peeling phenomenon during use. Low carbon potential will lead to insufficient carbon concentration on the surface of the workpiece penetration layer, and the final penetration layer hardness of the workpiece cannot meet the requirements. High carbon potential will lead to excessive carbon concentration on the surface of the workpiece penetration layer, and the grade of carbide will be excessive, and brittle cracking will easily occur during use;

[0063] (7) Nitrogen cooling, after the end of diffusion, the workpiece is transferred to the gas cooling tank and nitrogen is introduced for rapid cooling to prevent oxidation and decarburization; nitrogen can prevent the workpiece from being oxidized at high temperature, and it can form a protective oxide layer on the surface of the workpiece;

[0064] (8) Normalize the workpiece at 900℃ for 60min and air cool to eliminate network carbide, refine the grain, improve the structure and increase the surface hardness; the deeper the carburized layer, the more likely the workpiece will produce network carbide, and the risk of cracking will occur. Lower normalizing temperature cannot eliminate network carbide, and higher temperature will lead to coarse grains of the material, which will affect the mechanical properties of the product. Therefore, 900℃ is selected for normalizing, and the holding time is 60min according to the effective thickness of the material;

[0065] (9) Quenching temperature for heat treatment is 870±10℃ for 90-120min, oil cooling; the quenching temperature of 15CrA material can be selected as 790-880℃. Lower temperature will not fully transform the structure, which will lead to lower hardness. Therefore, higher temperature 870℃ is selected for quenching to ensure high hardness after quenching;

[0066] (10) Ice cooling treatment temperature is -70±5℃ for 4-5h, air cooling; the purpose of ice cooling treatment is to eliminate residual austenite and accelerate the transformation of residual austenite to ensure the final hardness. For carburized workpieces with high surface hardness requirements, -60℃ to -80℃ can be used. Generally, the lower the temperature, the better the effect of eliminating residual austenite. However, -80℃ requires high equipment requirements for low temperature box. Through comparison test, -70℃ can meet the requirements. Therefore, -70℃ is selected for ice cooling treatment;

[0067] (11) low temperature tempering, 150±10℃ for 4-5h, air cooling; the lower the tempering temperature, the higher the hardness, but too low temperature will cause incomplete quenching stress relief, and for some parts, the service temperature and hydrogen removal temperature are higher, if the service temperature and hydrogen removal temperature are higher than the final tempering temperature of the parts, the hardness of the parts will decrease, so the tempering temperature should be as high as possible to ensure the hardness of the parts.

[0068] (12) the depth of the carburized layer of the parts is 1.3-1.7mm, and the hardness value is HRC≥62.

[0069] The second embodiment of the application is a 15CrA high-hardness carburizing and quenching and ice tempering heat treatment process, which comprises the following steps:

[0070] (1) the parts are cleaned as follows:

[0071] 1) carbon hydrogen ultrasonic cleaning to remove oil, 15min;

[0072] 2) hot water washing, 60℃, 2min;

[0073] 3) cold water washing, 2min;

[0074] 4) carbon hydrogen ultrasonic cleaning, 10min;

[0075] 5) water spraying, 5min;

[0076] 6) drying, 100℃, 10min;

[0077] (2) after the equipment is heated to 750℃, start injecting methanol 2L / h, when the temperature rises to 800℃, start injecting propane 0.15L / min, the equipment is heated to 910℃, and the carbon potential reaches 0.5%C, then the parts are loaded into the furnace; before loading, the temperature and carbon potential in the furnace should be ensured to improve the exhaust rate of the parts after loading;

[0078] 1) the furnace temperature rises to 750℃, and the equipment starts to inject diluent methanol;

[0079] 2) the furnace temperature rises to 800℃, and the equipment starts to inject enriching agent propane;

[0080] 3) when the furnace temperature rises to 910℃ and the carbon potential rises to 0.5%C, start loading;

[0081] (3) When the workpiece is loaded into the furnace, the existing carburizing atmosphere in the furnace will be reduced. After loading, the furnace door is quickly closed, and the carbon potential and temperature in the furnace will quickly rise. When the equipment reaches a temperature of 910°C and a carbon potential of 0.5%C again, the furnace is kept for 5 minutes, the furnace presents a positive pressure, and the gas has been quickly discharged, and the atmosphere in the furnace meets the carburizing conditions;

[0082] (4) After the exhaust is completed, the amount of propane introduced is increased to 0.25 L / min, the amount of methanol introduced is 2.5 L / h, the carbon potential quickly reaches 1.15%C, the temperature is kept at 910°C, and the strong carburizing stage is started. The strong carburizing is kept for 660 minutes, the amount of propane introduced is reduced to 0.05 L / min, and the amount of methanol is kept at 2.3 L / h, and the process ensures that the furnace is under positive pressure;

[0083] (5) Carbon fixation. The carbon fixation piece weighed in advance is loaded into the carbon fixation port below the equipment, introduced into the furnace through the carbon fixation port of the equipment, kept for 30 minutes, then pulled out of the furnace into the cooling pipe, the valve of the cooling pipe is opened, then ignited, and cooled for 5 minutes. The whole cooling process ensures that the flame does not go out, which proves that the carbon fixation piece is protected by carbon potential atmosphere during the cooling process and will not be oxidized. After cooling, it is taken out and weighed. Clean white gloves are required during the whole process to prevent the carbon fixation piece from being contaminated, and the weighing is not accurate. The consistency of the carbon potential value of the carbon fixation in the furnace and the carbon potential result displayed in the furnace is calculated;

[0084] (6) After the strong carburizing is completed, compressed air is introduced, the amount of propane introduced is reduced to 0 L / min, the amount of methanol introduced is reduced to 2 L / h, the carbon potential is quickly reduced to 0.85%C, the temperature is kept at 910°C, and the diffusion stage is started. The diffusion is kept for 60 minutes, and the process ensures that the furnace is under positive pressure;

[0085] (7) After the diffusion is completed, the workpiece is transferred into the gas cooling tank, and nitrogen is continuously introduced during the transfer process at a flow rate of 40 L / min for 30 minutes for rapid cooling to prevent oxidation and decarburization;

[0086] (8) The workpiece is normalized at a temperature of 900°C for 60 minutes and air cooled;

[0087] (9) The workpiece is quenched at a temperature of 870°C for 100 minutes and oil cooled;

[0088] (10) The workpiece is ice cooled at a temperature of -70°C for 4.5 hours and air cooled;

[0089] (11) The workpiece is heat treated and low temperature tempered at a temperature of 150°C for 4.5 hours and air cooled;

[0090] (12) The workpiece is detected for carburized layer depth, hardness HRC62.9, HRC63.1, HRC62.6, and meets the high hardness HRC≥62.

[0091] In the application, by reasonably selecting the carburizing agent, carburizing carbon potential concentration, carburizing temperature, carbon fixation monitoring, normalizing and final quenching, ice cooling, tempering and other process parameters, the stability of carburizing and the technical difficulty of high hardness of carburized layer are effectively improved, the technical requirements of design drawings are met, and the smooth delivery of products is ensured. At the same time, the conventional process idea is broken through, and a new process method for carburizing high hardness processing of such material parts is explored.

[0092] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of various equivalent modifications or replacements within the technical range disclosed by the present application, and these modifications or replacements should be covered within the protection scope of the present application.

Claims

1. A 15CrA high hardness carburizing quenching ice-cooling tempering heat treatment process, characterized in that: The following steps are involved: Step (1) cleaning the surface of the carburized part; Step (2) After the carburizing furnace is heated to 750°C, methanol is injected. After the temperature reaches 800°C, propane is introduced. After the carburizing furnace is heated to 910°C and the carbon potential reaches 0.5%C, the carburized parts are loaded into the furnace; Step (3) After the workpiece is loaded into the carburizing furnace, the carburizing furnace is quickly vented. After venting, the carbon potential and temperature in the furnace decrease. After venting, the carburizing furnace continues to heat up. When the equipment reaches a temperature of 910°C again and the carbon potential reaches 0.5%C, it is kept warm for 5 minutes; Step (4) increases the amount of methanol and propane introduced, the carbon potential quickly reaches 1.15%C, and the carburized part enters the strong carburization stage, during which carbonization is performed; Step (5) after the strong permeation is completed, the propane injection rate is reduced, and when the carbon potential drops rapidly to 0.85%C, the diffusion stage is entered; After the diffusion in step (6) is completed, the carburized part is cooled; Step (7) normalizing the carburized part at 900°C, keeping the temperature for 60 minutes, and air cooling; Step (8) heat treatment quenching adopts temperature 870±10℃ holding time 90~120min, oil cooling; Step (9) performing ice cooling treatment on the carburized part at a treatment temperature of -70±5°C for a holding time of 4 to 5 hours, followed by air cooling; Step (10) heat treatment low temperature tempering adopts 150±10℃ holding time 4~5h, air cooling.

2. The 15CrA high hardness carburizing, quenching, ice-cooling and tempering heat treatment process according to claim 1, characterized in that: Step (1) cleaning the surface of the carburized part specifically comprises the following steps: (1.1) Hydrocarbon ultrasonic cleaning and degreasing, 15 minutes; (1.2) Wash with hot water, 60℃, 2min; (1.3), cold water wash, 2min; (1.4), hydrocarbon ultrasonic cleaning for 10 minutes; (1.5), clean water spray, 5min; (1.6) Dry at 100℃ for 10 minutes.

3. The 15CrA high hardness carburizing, quenching, ice-cooling and tempering heat treatment process according to claim 2, characterized in that: Step (2) is specifically as follows: after the carburizing furnace is heated to 750°C, methanol is injected at a rate of 2 L / h; after the temperature is raised to 800°C, propane is introduced at a rate of 0.15 L / min; after the carburizing furnace reaches 910°C and the carbon potential reaches 0.5%C, the carburized parts are loaded into the furnace.

4. The 15CrA high hardness carburizing, quenching, ice-cooling and tempering heat treatment process according to claim 3, characterized in that: Step (3) is specifically as follows: when the carburized parts are loaded into the furnace, the furnace door is opened, and the existing carburizing atmosphere in the furnace will be reduced. After loading the furnace, the furnace door is quickly closed, and the carbon potential and temperature in the furnace will rise rapidly. When the equipment reaches a temperature of 910°C again and the carbon potential is 0.5%C, it is kept warm for 5 minutes. The furnace presents a positive pressure, the gas has been quickly discharged, and the atmosphere in the furnace meets the carburizing conditions.

5. The 15CrA high hardness carburizing, quenching, ice-cooling and tempering heat treatment process according to claim 4, characterized in that: Step (4) is specifically as follows: after the exhaust is completed, the propane introduction rate is increased, the propane introduction rate is 0.25L / min, the methanol introduction rate is 2.5L / h, the carbon potential quickly reaches 1.15%C, the temperature is maintained at 910°C, and the strong permeation stage begins. The strong permeation is kept warm for 660min. After the insulation is completed, the propane introduction rate is reduced to 0.05L / min, and the methanol is kept at 2.3L / h. The positive pressure in the furnace is ensured during the strong permeation stage.

6. The 15CrA high hardness carburizing, quenching, ice-cooling and tempering heat treatment process according to claim 5, characterized in that: The carbon determination in step (4) is specifically: Place the pre-weighed carbon-fixing sheet into the carbon-fixing port at the bottom of the carburizing furnace, and then into the furnace through the carbon-fixing port. After keeping warm for 30 minutes, pull it down from the furnace to the cooling pipe and cool it for 5 minutes. At the same time, open the valve of the cooling pipe, and then ignite the carbon potential atmosphere discharged from the valve port to ensure that the flame will not go out during the entire cooling process. This can prove that the carbon-fixing sheet will not be oxidized during the cooling process due to the protection of the carbon potential atmosphere. After cooling, take out the carbon-fixing sheet and weigh it, calculate the carbon potential value in the furnace, and then compare it with the carbon potential value monitored by the oxygen probe of the carburizing furnace. If the comparison result meets the requirements, the carbon-fixing process is completed.

7. The 15CrA high hardness carburizing, quenching, ice-cooling and tempering heat treatment process according to claim 6, characterized in that: Step (5) is specifically as follows: after the strong permeation is completed, compressed air is introduced, the propane introduction rate is reduced to 0L / min, the methanol introduction rate is reduced to 2L / h, the carbon potential is quickly reduced to 0.85%C, the temperature is maintained at 910℃, and the diffusion stage begins. The diffusion and heat preservation are carried out for 60 minutes, and the positive pressure in the furnace is ensured during the process.

8. The 15CrA high hardness carburizing, quenching, ice-cooling and tempering heat treatment process according to claim 7, characterized in that: Step (6) is specifically as follows: after the diffusion is completed, the carburized workpiece is transferred to an air cooling tank, and nitrogen is continuously introduced during the transfer process at a nitrogen flow rate of 40 L / min, and rapid cooling is maintained for 30 minutes.

9. The 15CrA high hardness carburizing, quenching, ice-cooling and tempering heat treatment process according to claim 8, characterized in that: After step (10) is completed, step (11) is also included, that is, checking whether the carburized layer depth of the workpiece meets 1.3-1.7 mm and the hardness value meets HRC≥62.

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