15CrA high-hardness carburizing, quenching, ice-cooling and tempering heat treatment process method

Abstract

The invention relates to the field of carburizing heat treatment processing, in particular to a 15CrA high-hardness carburizing, quenching, ice-cooling and tempering heat treatment process method. Methanol and propane are used as carburizing agents, namely methanol and propane are used as enriching agents, the carbon potential is controlled to be 1.15% C, a carbon determination method is used for comparing the consistency of an actual value and a display value of the carbon potential in a furnace, the accuracy of the carbon potential is ensured, and the accuracy of the carbon potential is improved. And carburizing is conducted at the temperature of 910 DEG C, then the hardness is adjusted through normalizing, and finally through quenching, ice-cooling and tempering, the high hardness HRC larger than or equal to 62 is obtained, and the depth of a carburized layer reaches 1.3-1.7 mm.

Description

Technical Field

[0001] The invention relates to the field of carburizing heat treatment processing, and in particular to a 15CrA high-hardness carburizing quenching ice-cold tempering heat treatment process method. Background Art

[0002] Carburizing heat treatment is a heat treatment process that places low-carbon steel or low-carbon alloy steel parts in a carburizing medium, heats them to the austenite state and keeps them warm, so that carbon atoms penetrate into the surface of the parts. Carburizing treatment can not only improve the surface hardness, strength, wear resistance and fatigue resistance of parts, but also maintain a certain strength and toughness in the core of the parts.

[0003] At present, during the carburizing treatment of 15CrA, due to the long cycle in the carburizing process, there are many factors that affect the hardness of the carburized layer, including temperature, carbon potential, cooling medium, and quenching, ice-cooling, 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 fail to meet the high hardness requirements. Therefore, it is necessary to propose a 15CrA high hardness carburizing quenching ice-cooling and tempering heat treatment process method to ensure that the material can meet the high hardness of the carburized layer depth of 1.3-1.7mm and the hardness value of HRC≥62 after carburizing. Summary of the invention

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

[0005] Technical solution:

[0006] A 15CrA high-hardness carburizing, quenching, ice-cooling and tempering heat treatment process method comprises 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, methanol is injected, and after the temperature is raised to 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;

[0009] 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 are reduced. After venting, the carburizing furnace continues to heat up. 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;

[0010] Step (4) increasing 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 carbon is fixed;

[0011] Step (5) after the strong permeation is completed, the propane introduction amount is reduced, and when the carbon potential drops rapidly to 0.85%C, the diffusion stage is entered;

[0012] After the diffusion in step (6) is completed, the carburized part is cooled;

[0013] Step (7) normalizing the carburized part at 900°C, keeping the temperature for 60 minutes, and air cooling;

[0014] Step (8) heat treatment quenching adopts a temperature of 870±10°C, a holding time of 90 to 120 min, and oil cooling;

[0015] Step (9) performs ice cooling treatment on the carburized part, the treatment temperature is -70±5°C, the heat preservation time is 4-5h, and air cooling;

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

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

[0018] (1.1) Hydrocarbon ultrasonic cleaning and degreasing, 15 minutes;

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

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

[0021] (1.4) Carbon-hydrogen ultrasonic cleaning for 10 minutes;

[0022] (1.5) Water spray, 5 minutes;

[0023] (1.6) Dry at 100℃ for 10min.

[0024] Further, 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, carburized parts are loaded into the furnace.

[0025] Furthermore, 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 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.

[0026] Further, 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 infiltration stage begins. The strong infiltration is kept 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. During the strong infiltration stage, positive pressure is ensured in the furnace.

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

[0028] Load the pre-weighed carbon-fixing sheet into the carbon-fixing port at the bottom of the carburizing furnace, and then load it 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 for weighing, 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.

[0029] Further, step (5) is specifically as follows: after the strong permeation is completed, compressed air is introduced, the propane introduction rate is reduced to 0 L / min, the methanol introduction rate is reduced to 2 L / h, the carbon potential is quickly reduced to 0.85% C, the temperature is maintained at 910°C, 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.

[0030] Further, 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, with a nitrogen flow rate of 40 L / min, and rapid cooling is maintained for 30 minutes.

[0031] Furthermore, 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.

[0032] Beneficial effects:

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

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments of the present invention. It is obvious that the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0035] Figure 1 It is a schematic diagram of a manufactured part of the present invention;

[0036] Figure 2 The carburizing and cleaning flow chart of step (1) of the present invention;

[0037] Figure 3 Schematic diagram of the carburizing process of steps (2)(3)(4)(5)(6)(7) of the present invention;

[0038] Figure 4 The normalizing, quenching, ice-cooling and low-temperature tempering curves after carburizing in steps (8), (9), (10) and (11) of the present invention;

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

[0040] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0041] The features and illustrative embodiments of various aspects of the present invention will be described in detail below. In the detailed description below, many specific details are proposed to provide a comprehensive understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present invention by illustrating examples of the present invention. The present invention is by no means limited to any specific settings and methods proposed below, but covers any improvements, replacements and modifications of structures, methods, devices without departing from the spirit of the present invention. In the accompanying drawings and the following description, known structures and technologies are not shown to avoid unnecessary ambiguity in the present invention.

[0042] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other, and the embodiments can refer to and quote each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0043] The invention provides a 15CrA high-hardness carburizing quenching ice-cooling tempering heat treatment process method. By using methanol and propane as carburizing agents, that is, using methanol and propane as enriching agents, the carbon potential is controlled at 1.15%C, and the carbon determination method is used to compare the consistency between the actual value of the carbon potential in the furnace and the displayed value to ensure the accuracy of the carbon potential. Carburizing is performed at a temperature of 910°C, and then the hardness is adjusted by normalizing. Finally, a high hardness HRC≥62 is obtained by quenching, ice-cooling and tempering, and the depth of the carburized layer reaches 1.3-1.7mm. The overall idea includes the following technical contents:

[0044] 1) Use methanol as diluent, propane as enrichment agent, and oxygen probe to monitor carbon potential;

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

[0046] CO + H2 → C + H2O;

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

[0048] CH4→C+H2

[0049] 2) Use carbon potential exhaust carbon potential 0.05% C to keep warm for 5 minutes, strong carburizing potential 1.15% C to keep warm for 660 minutes, and diffusion carbon potential 0.85% C to keep warm for 60 minutes;

[0050] 3) During the carburizing process, the carbon determination method is used to compare the carbon potential value in the furnace to ensure that the carbon potential is stable and accurate;

[0051] 4) The carburizing temperature is selected to be 910℃, which can not only increase the carburizing speed, but also effectively reduce the formation of retained austenite;

[0052] 5) Carburizing cooling is protected by nitrogen atmosphere, with a nitrogen flow rate of 40L / min for 30min to prevent oxidation and decarburization during cooling;

[0053] 6) Normalizing after carburizing can not only adjust the hardness, but also refine the grains, improve the structure, eliminate internal stress and improve the mechanical properties;

[0054] 7) Final quenching, cryogenic treatment and low temperature tempering;

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

[0056] The first embodiment of the present invention is to provide a 15CrA high hardness carburizing quenching ice-cooling tempering heat treatment process method, which specifically includes the following steps:

[0057] (1) Clean the surface of the carburized part and make sure the carburized surface is clean; surface oil will prevent carbon atoms from penetrating, resulting in a decrease in the carburized layer and the appearance of soft spots. A clean carburized surface helps improve the carburizing quality;

[0058] (2) After the equipment is heated to 750°C, methanol is injected. After the temperature reaches 800°C, propane is introduced. After the equipment reaches 910°C and the carbon potential reaches 0.5%C, the parts are loaded into the furnace. Since methanol is not completely cracked at temperatures below 750°C, a large amount of carbon black is easily generated during use, and the product is unsafe, the higher the temperature, the more thorough the cracking. However, considering that the accumulation of carbon potential takes time, a lower temperature is selected to inject methanol while ensuring that a large amount of carbon black is not generated. 750°C was selected through experiments. The cracking temperature of propane is relatively high. As an enriching agent, propane contains more carbon atoms. It is not completely cracked at low temperatures, which is easy to cause a large amount of carbon deposits and affect the carburizing effect. The purpose of selecting 800°C is to ensure that it is completely cracked and to reduce the formation of carbon deposits.

[0059] (3) When loading the workpiece into the furnace, the furnace door needs to be opened, which will cause the carbon potential and temperature in the furnace to decrease. Therefore, after loading the workpiece into the furnace, the exhaust should be started quickly. When the equipment reaches the temperature of 910℃ again and the carbon potential is 0.5%C, it should be kept warm for 5 minutes. Before loading the furnace, the temperature and carbon potential in the furnace should be ensured first, which can increase the exhaust rate after the workpiece is loaded into the furnace, reduce the long-term heating of the workpiece in the air, and reduce the risk of oxidation and decarburization. The carburizing temperature of 15CrA material can be selected within the temperature range of 880~930℃. Selecting the highest temperature can accelerate the carburizing effect, but the long-term high temperature of the workpiece will increase the risk of deformation. Taking the lowest temperature can reduce the risk of deformation, but it also increases the carburizing time. Through experimental comparison, 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 oxidation of the parts during the heating process. If the carbon potential of the exhaust process is too high, 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, the carbon potential in the furnace will not achieve the purpose of atmosphere protection for a long time after the parts enter the furnace, resulting in oxidation and decarburization of the carburized parts. Therefore, through the experiment, a carbon potential of 0.5%C is selected for exhaust.

[0060] (4) Strong carburizing: After exhaust, increase the amount of methanol and propane introduced, the carbon potential quickly reaches 1.15%C, and enter the strong carburizing stage. The purpose is to obtain a high carbon concentration and a carburizing layer depth on the surface of the workpiece. Increasing the amount of carburizing agent methanol and propane introduced can make the furnace obtain a high carbon potential. The higher the carbon potential, the more helpful it is to increase the carburizing speed. However, when the carbon potential is too high, a large amount of carbon black will be generated in the furnace, and the equipment will have serious carbon deposition, which will cause large fluctuations in the carbon potential during the carburizing process and unstable control. At the same time, a large amount of carbon deposition will adhere to the surface of the workpiece, resulting in the inability of carbon atoms to penetrate, which in turn reduces the carburizing speed, carburizing layer depth and surface carbon concentration. Therefore, 1.15%C is selected for strong carburizing, which not only ensures the carburizing speed and carburizing layer depth, but also ensures the surface carbon concentration.

[0061] (5) Carbon determination: During the process of intensive carburizing, the accuracy of carbon potential is detected by the carbon determination method, and the consistency between the actual value of carbon potential in the furnace and the displayed value is compared; the carbon potential in the furnace is monitored by an oxygen probe, which may fail or deviate during use, resulting in inaccurate carburizing results. The carbon determination method is used to monitor the carbon potential in front of the furnace, eliminating the risk of inaccurate carbon potential;

[0062] (6) Diffusion. After the strong penetration is completed, the propane injection amount is reduced, the carbon potential quickly drops to 0.85%C, and the diffusion stage begins. The purpose is to obtain a carbon concentration gradient and a hardness gradient. Diffusion is to ensure that the workpiece has a relatively gentle penetration layer hardness gradient, which helps the penetration layer of the workpiece to be more tightly combined with the core, and is not easy to peel off during use. A low carbon potential will lead to insufficient carbon concentration on the surface of the penetration layer of the workpiece, and the final penetration layer hardness required by the workpiece cannot be achieved. A high carbon potential will lead to excessive carbon concentration on the surface of the penetration layer of the workpiece, and the level of carbides will exceed the standard, which is prone to brittle cracking during use.

[0063] (7) Nitrogen cooling: After the diffusion is completed, the workpiece is transferred to the air cooling tank and nitrogen is introduced for rapid cooling to prevent oxidation and decarburization. Nitrogen can prevent the workpiece from oxidizing at high temperatures and can form a protective oxide layer on the surface of the workpiece.

[0064] (8) Normalizing the workpiece at 900°C, keeping it warm for 60 minutes, and air cooling it can eliminate network carbides, refine grains, improve structure, and increase surface hardness. The deeper the carburized layer, the easier it is for the workpiece to produce network carbides, which will cause the risk of cracking. A lower normalizing temperature cannot achieve the purpose of eliminating network carbides, and a higher temperature will cause coarse grains of the material, which will affect the mechanical properties of the product. Therefore, 900°C is selected for normalizing, and the holding time is selected for 60 minutes according to the effective thickness of the material.

[0065] (9) Heat treatment quenching adopts a temperature of 870±10℃, a holding time of 90-120min, and oil cooling; the quenching temperature of 15CrA material can be selected from 790-880℃. The low temperature will not lead to sufficient microstructure transformation, which will result in low hardness. Therefore, a higher temperature of 870℃ is selected for quenching to ensure high hardness after quenching;

[0066] (10) Ice-cold treatment uses a temperature of -70±5℃, a holding time of 4 to 5 hours, and air cooling; the purpose of ice-cold treatment is to eliminate residual austenite, accelerate the transformation of residual austenite, and ensure the final hardness. For carburized parts 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℃ has higher requirements for low-temperature box equipment. Through experimental comparison, -70℃ can meet the requirements. Therefore, -70℃ is selected for ice-cold treatment;

[0067] (11) Heat treatment low temperature tempering adopts 150±10℃ holding time 4~5h, air cooling; generally, the lower the tempering temperature, the higher the hardness, but if the temperature is too low, the quenching stress will not be completely eliminated. At the same time, for some parts, the use temperature and surface treatment requirements of the dehydrogenation temperature are relatively high. If the subsequent use temperature and dehydrogenation temperature are higher than the final tempering temperature of the part, the hardness of the part will be reduced and the high hardness requirement cannot be guaranteed. Therefore, while ensuring the hardness of the part, the tempering temperature should be increased as much as possible, and 150℃ is selected for low temperature tempering.

[0068] (12) The carburized layer depth of the tested parts meets the requirement of 1.3-1.7 mm and the hardness value meets the requirement of HRC ≥ 62.

[0069] The second embodiment of the present invention is to propose a 15CrA high hardness carburizing quenching ice-cold tempering heat treatment process method, which comprises the following steps:

[0070] (1) Clean the workpiece in the following manner;

[0071] 1) Hydrocarbon ultrasonic cleaning and degreasing, 15 minutes;

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

[0073] 3) Wash with cold water for 2 minutes;

[0074] 4) Carbon hydrogen ultrasonic cleaning for 10 minutes;

[0075] 5) Spray with clean water for 5 minutes;

[0076] 6) Drying at 100°C for 10 minutes;

[0077] (2) After the equipment is heated to 750°C, methanol is injected at 2L / h. After the temperature reaches 800°C, propane is introduced at 0.15L / min. After the equipment reaches 910°C and the carbon potential reaches 0.5%C, the parts are loaded into the furnace. Before loading the furnace, the temperature and carbon potential in the furnace are ensured to increase the exhaust rate after the parts are loaded into the furnace.

[0078] 1) The furnace temperature rises to 750°C and the equipment starts to inject diluent methanol;

[0079] 2) The furnace temperature rises to 800°C and the equipment starts to inject propane as an enrichment agent;

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

[0081] (3) When the workpiece is loaded into the furnace, the furnace door is opened, and 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 rise rapidly. When the equipment reaches the 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;

[0082] (4) After exhaust, the propane flow rate was increased by 0.25 L / min and the methanol flow rate was increased by 2.5 L / h. The carbon potential quickly reached 1.15% C, the temperature was maintained at 910°C, and the strong permeation stage began. The strong permeation was kept warm for 660 minutes. After the insulation settlement, the propane flow rate was reduced to 0.05 L / min and the methanol was maintained at 2.3 L / h. During the process, the positive pressure in the furnace was maintained;

[0083] (5) Carbon determination: load the pre-weighed carbon determination sheet into the carbon determination port at the bottom of the equipment, and then load it into the furnace through the carbon determination port of the equipment. After keeping warm for 30 minutes, pull it down from the furnace to the cooling pipe, open the valve of the cooling pipe, and then ignite it. Cool for 5 minutes to ensure that the flame will not go out during the entire cooling process. This can prove that the carbon determination sheet will not be oxidized during the cooling process under the protection of the carbon potential atmosphere. After cooling, take it out and weigh it. Wear clean white gloves during the whole process to prevent contamination of the carbon determination sheet and inaccurate weighing. The calculated carbon potential value of the carbon determination in the furnace is consistent with the carbon potential result displayed in the furnace.

[0084] (6) After the strong permeation is completed, compressed air is introduced, the propane introduction rate is reduced to 0 L / min, the methanol introduction rate is reduced to 2 L / h, the carbon potential is quickly reduced to 0.85% C, the temperature is maintained at 910°C, and the diffusion stage begins. The diffusion and heat preservation are carried out for 60 minutes. During the process, the positive pressure in the furnace is maintained;

[0085] (7) After the diffusion is completed, the workpiece is transferred to the air cooling tank. During the transfer process, nitrogen is continuously introduced at a flow rate of 40L / min. Rapid cooling is maintained for 30 minutes to prevent oxidation and decarburization.

[0086] (8) The workpiece is normalized at 900°C, kept at this temperature for 60 minutes, and air-cooled;

[0087] (9) Heat treatment quenching temperature is 870℃, holding time is 100min, oil cooling;

[0088] (10) The temperature for ice-cooling treatment was -70°C, the holding time was 4.5 h, and air cooling was used;

[0089] (11) Heat treatment low temperature tempering temperature selected 150 ℃ holding time 4.5h, air cooling;

[0090] (12) Detect the depth of carburized layer of workpiece 1. Hardness HRC62.9, HRC63.1, HRC62.6, meet the high hardness HRC ≥ 62.

[0091] In the present invention, by reasonably selecting the carburizing agent, carburizing carbon potential concentration, carburizing temperature, fixed carbon monitoring, normalizing, and final quenching, ice cooling, tempering and other process parameters, the stability of carburizing and the high hardness technical difficulty of the carburized layer are effectively improved, the technical requirements of the design drawings are met, and the smooth delivery of the product is guaranteed. At the same time, it also breaks through the conventional process thinking and explores a new process method for carburizing high hardness processing of such material parts.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the field can easily think of various equivalent modifications or substitutions within the technical scope disclosed by the present invention, and these modifications or substitutions should all be covered within the protection scope of the present invention.

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, and after the temperature is raised to 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 are reduced. After venting, the carburizing furnace continues to heat up. 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; Step (4) increasing 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 carbon is fixed; Step (5) after the strong permeation is completed, the propane introduction amount 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 a temperature of 870±10°C, a holding time of 90 to 120 min, and oil cooling; Step (9) performs ice cooling treatment on the carburized part, the treatment temperature is -70±5°C, the insulation time is 4 to 5 hours, and 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 tempering heat treatment process according to claim 1 is characterized in that: Step (1) cleaning the surface of the carburized part, specifically comprising 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) Carbon-hydrogen ultrasonic cleaning for 10 minutes; (1.5) Water spray, 5 minutes; (1.6) Dry at 100℃ for 10min.

3. The 15CrA high hardness carburizing quenching ice-cooling tempering heat treatment process according to claim 2 is 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, carburized parts are loaded into the furnace.

4. The 15CrA high hardness carburizing quenching ice-cooling tempering heat treatment process according to claim 3 is 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 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 tempering heat treatment process according to claim 4 is characterized in that: Step (4) specifically includes: after the exhaust is completed, the propane introduction rate is increased to 0.25 L / min, the methanol introduction rate is 2.5 L / h, the carbon potential quickly reaches 1.15% C, the temperature is maintained at 910°C, and the strong infiltration stage begins. The strong infiltration is kept for 660 minutes. After the insulation is completed, the propane introduction rate is reduced to 0.05 L / min, and the methanol is kept at 2.3 L / h. During the strong infiltration stage, positive pressure is ensured in the furnace.

6. The 15CrA high hardness carburizing quenching ice-cooling tempering heat treatment process according to claim 5 is characterized in that: The carbon determination in step (4) is specifically: Load the pre-weighed carbon-fixing sheet into the carbon-fixing port at the bottom of the carburizing furnace, and then load it 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 for weighing, 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 tempering heat treatment process according to claim 6 is 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 0 L / min, the methanol introduction rate is reduced to 2 L / h, the carbon potential is quickly reduced to 0.85% C, the temperature is maintained at 910°C, 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 tempering heat treatment process according to claim 7 is 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, with 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 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.

Images