Carburizing heat treatment method for 25 # steel workpiece and workpiece

Abstract

The invention discloses a carburizing heat treatment method for a 25 # steel workpiece and the workpiece, and relates to the field of heat treatment. The carburizing heat treatment method for the 25 # steel workpiece comprises the following steps: carrying out controlled atmosphere carburizing on the 25 # steel workpiece, wherein the controlled atmosphere carburizing comprises five stages of exhausting and introducing carbon-containing gas to heat up, intensively carburizing, diffusing, cooling and purifying; the workpiece subjected to controlled atmosphere carburizing treatment is preheated at the temperature of 650-700 DEG C; quenching heating is conducted on the workpiece after preheating, the quenching heating temperature ranges from 840 DEG C to 860 DEG C, and after heating is completed, the workpiece is transferred into a solution alkali with the temperature ranging from 160 DEG C to 180 DEG C to be cooled; keeping the temperature of the workpiece below-50 DEG C for 4-5 hours; and finally, the workpiece is subjected to low-temperature tempering at 150-170 DEG C, discharged from the furnace and air-cooled to the room temperature. The carburizing heat treatment method for the 25 # steel workpiece can accurately control carbon potential, reduce heat treatment deformation of the workpiece, inhibit oxidation reaction to obtain a clean surface, and obtain the workpiece with preset carburizing layer depth and hardness.

Description

Technical Field

[0001] This application relates to the field of hot working, and more specifically, to a carburizing heat treatment method for a No. 25 steel workpiece and the workpiece itself. Background Technology

[0002] Carburizing is a heat treatment process in which a steel workpiece is heated to the austenitic state in a medium with sufficient carbon potential and held at that temperature to form a carbon-rich layer on its surface. After carburizing, quenching and low-temperature tempering can achieve high surface hardness, wear resistance, and fatigue strength, significantly improving the overall mechanical properties of the workpiece.

[0003] Traditional pit-type carburizing furnaces use a drip-injection kerosene carburizing method, which is technologically outdated and results in significant fluctuations in carbon potential, leading to deviations in carburized layer depth and hardness. A critical component of a certain type of power mechanism, the piston, made of 25# steel, operates under heavy loads and high wear resistance, requiring high quality and reliability. Current drip-injection kerosene carburizing and quenching processes cannot effectively guarantee carburizing quality and deformation control. Summary of the Invention

[0004] The purpose of this application is to provide a carburizing heat treatment method and workpiece for 25# steel workpieces. By accurately controlling the carbon potential, the heat treatment deformation of the workpiece is reduced, the oxidation reaction is suppressed to obtain a clean surface, and a workpiece with a preset carburized layer depth and hardness is obtained.

[0005] This application is implemented as follows: This application provides a carburizing heat treatment method for a No. 25 steel workpiece, which includes the following steps: Controlled atmosphere carburizing of 25 steel workpieces includes five steps: exhausting the gas, introducing carbon-containing gas and heating, strong carburizing, diffusion, cooling, and purification treatment. The workpiece after controlled atmosphere carburizing is preheated at 650℃~700℃. After preheating, the workpiece is quenched at a temperature of 840℃~860℃. After heating, it is cooled in a 160℃~180℃ alkali solution. The quenched workpiece is kept at -50℃ for 4 to 5 hours. After low-temperature tempering, the workpiece is removed from the furnace and air-cooled to room temperature.

[0006] In some alternative implementations, the process of introducing carbon-containing gas to raise the temperature includes the following steps: first, nitrogen is introduced to purge the gas in the bottom charge multi-purpose furnace, and after the furnace temperature is raised to 700°C, methanol and propane are introduced. After the temperature and carbon potential stabilize, the workpiece is put into the furnace.

[0007] In some alternative implementations, the flow rate of methanol is 1.0–1.2 L / h, and the flow rate of propane is 0.8–2.4 L / h.

[0008] In some alternative implementations, the strong infiltration includes the following steps: subjecting the workpiece to strong infiltration treatment at 900°C to 910°C and a carbon potential of 1.1 ± 0.05% for 7 to 7.5 hours.

[0009] In some alternative implementations, diffusion includes the following steps: subjecting the workpiece to diffusion treatment at 900°C to 910°C and a carbon potential of 0.8 ± 0.05% for 2.5 to 3 hours.

[0010] In some alternative implementations, the cooling process includes the following steps: after the diffusion stage, the workpiece is cooled in the furnace to 850°C to 870°C, and then air-cooled after exiting the furnace.

[0011] In some alternative implementations, the purification process includes the following steps: after the workpiece is removed from the furnace, nitrogen gas is introduced to flush the furnace chamber for 10 to 15 minutes.

[0012] In some alternative implementations, low-temperature tempering involves holding the workpiece at 150°C to 170°C for 3 to 4 hours.

[0013] This application also provides a workpiece that is processed using the carburizing heat treatment method described above for 25# steel workpieces.

[0014] In some alternative implementations, the workpiece has a diffusion layer depth of 1.1–1.4 mm and a diffusion layer hardness of HRC60–64. The beneficial effects of this application are as follows: The carburizing heat treatment method for 25# steel workpieces provided in this application includes the following steps: controlling atmosphere carburizing of the 25# steel workpiece, which includes five stages: exhausting and introducing carbon-containing gas for heating, strong carburizing, diffusion, cooling, and purification treatment; preheating the workpiece after controlling atmosphere carburizing at 650℃~700℃; quenching the workpiece after preheating at 840℃~860℃, and then cooling it in a 160℃~180℃ alkali solution; holding the quenched workpiece at -50℃ for 4h~5h; and air-cooling the workpiece to room temperature after low-temperature tempering. The carburizing heat treatment method for 25# steel workpieces provided in this application and the use of controlled atmosphere carburizing can accurately control the carbon potential, reduce the heat treatment deformation caused by rapid cooling in the low-temperature region, and inhibit oxidation reaction through low-temperature alkali cooling to obtain a clean surface, resulting in a workpiece with a preset carburized layer depth and hardness. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 A schematic flowchart of the carburizing heat treatment method for a No. 25 steel workpiece provided in the embodiments of this application; Figure 2 A schematic diagram of the carburizing process curve in the carburizing heat treatment method for the No. 25 steel workpiece provided in the embodiments of this application; Figure 3 A schematic diagram of the structure of the No. 25 steel workpiece in the carburizing heat treatment method provided in the embodiments of this application; Figure 4 Metallographic image of the carburized layer of a No. 25 steel workpiece obtained by the carburizing heat treatment method provided in the embodiments of this application; Figure 5 The metallographic structure test results of the carburized layer of the workpiece obtained by the carburizing heat treatment method of the No. 25 steel workpiece provided in the embodiments of this application; Figure 6 The hardness values ​​of different depths of the carburized layer of the workpiece are obtained by the carburizing heat treatment method of the No. 25 steel workpiece provided in the embodiments of this application. Figure 7 The straightness deformation at different dimensions of the carburized layer of the workpiece is obtained by the carburizing heat treatment method for the No. 25 steel workpiece provided in the embodiments of this application. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0018] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0019] The features and performance of the carburizing heat treatment method for No. 25 steel workpieces of this application will be further described in detail below with reference to the embodiments.

[0020] like Figure 1As shown in the figure, this application provides a carburizing heat treatment method for a No. 25 steel workpiece, which includes the following steps: Step 1: Controlled atmosphere carburizing of 25 steel workpieces is carried out in a bottom-charged multi-purpose furnace. The controlled atmosphere carburizing process includes five stages: exhaust gas introduction of carbon-containing gas for heating, strong carburizing, diffusion, cooling, and purification treatment. 1.1 The process of introducing carbon-containing gas to raise the temperature includes the following steps: First, nitrogen is introduced to purge the gas in the furnace from the bottom charge. After raising the furnace temperature to 700℃, methanol and propane are introduced. Once the temperature and carbon potential stabilize, the workpiece is introduced into the furnace. Optionally, the flow rate of methanol is 1.0–1.2 L / h, and the flow rate of propane is 0.8–2.4 L / h.

[0021] 1.2. Strong infiltration includes the following steps: subjecting the workpiece to strong infiltration treatment at 900℃~910℃ and a carbon potential of 1.1±0.05% for 7~7.5h.

[0022] 1.3. Diffusion includes the following steps: subjecting the workpiece to diffusion treatment at 900℃~910℃ and carbon potential of 0.8±0.05% for 2.5~3h.

[0023] 1.4 Cooling includes the following steps: After the diffusion stage is completed, the workpiece is cooled to 860°C in the furnace and then air-cooled after being removed from the furnace.

[0024] 1.5 The purification process includes the following steps: After the workpiece is taken out of the furnace, nitrogen gas is introduced to flush the furnace chamber for 10 to 15 minutes. Nitrogen gas is used to flush the furnace chamber to remove the waste gas in the furnace chamber and reduce the formation of carbon black.

[0025] Step 2: Preheat the workpiece after controlled atmosphere carburizing treatment at 650℃~700℃; Step 3: After preheating, quench the workpiece at a temperature of 840℃~860℃. After heating, cool it in a 160℃~180℃ alkali solution. Step 4: Keep the quenched workpiece at -50℃ or below for 4 to 5 hours; Step 5: After low-temperature tempering, remove the workpiece from the furnace and air-cool it to room temperature. Low-temperature tempering involves holding the workpiece at 150℃~170℃ for 3h~4h.

[0026] This application also provides a workpiece, which is processed by the above-mentioned carburizing heat treatment method for 25 steel workpieces. The carburizing layer depth of the workpiece is 1.1 to 1.4 mm, and the carburizing layer hardness is HRC60 to 64.

[0027] The carburizing heat treatment method for No. 25 steel workpieces provided in this application achieves accurate control of the carburizing process through controlled atmosphere carburizing. By adjusting the carbon concentration of the carbon-containing gases methanol and propane in the furnace, the carbon potential can be controlled more precisely than that of drip-type gas carburizing. At the same time, low-temperature alkaline cooling is used during workpiece quenching. The cooling rate in the high-temperature zone is greater than that of oil, while the cooling rate in the low-temperature zone is slowed down, reducing the heat treatment deformation of the workpiece caused by rapid cooling in the low-temperature zone. In addition, the low-temperature alkaline cooling of the workpiece can suppress the oxidation reaction, obtain a clean silver-gray surface, and obtain a workpiece with a preset carburized layer depth and hardness.

[0028] Example like Figure 1 and Figure 2 As shown in the figure, this application provides a carburizing heat treatment method for a No. 25 steel workpiece. The structure of the No. 25 steel workpiece is as follows: Figure 3 As shown, the carburizing heat treatment method for a No. 25 steel workpiece includes the following steps: Controlled atmosphere carburizing of 25# steel workpieces is carried out in a bottom-charged multi-purpose furnace. The controlled atmosphere carburizing process includes five stages: exhaust gas introduction of carbon-containing gas for heating, strong carburizing, diffusion, cooling, and purification treatment. Step 1, venting and heating with carbon-containing gas, includes the following steps: first, nitrogen is introduced and maintained for 5-8 minutes to exhaust the gas in the bottom charge of the multi-purpose furnace. After raising the furnace temperature to 700℃, methanol is introduced at a flow rate of 1.1L / h and propane is introduced at a flow rate of 1.6L / h. After the temperature reaches 900℃ and the carbon potential reaches 1.05%, the workpiece is put into the furnace.

[0029] Step 2, Intensive Infiltration, includes the following steps: subjecting the workpiece to intensive infiltration treatment at 905℃ and a carbon potential of 1.05% to 1.15% for 7 hours.

[0030] Step 3, diffusion, includes the following steps: subjecting the workpiece to diffusion treatment at 905℃ and a carbon potential of 0.75-0.85% for 2.5 hours.

[0031] Step 4, cooling includes the following steps: After the diffusion stage is completed, the workpiece is cooled to 860℃ in the furnace and then air-cooled after being removed from the furnace.

[0032] Step 5, purification treatment includes the following steps: After the workpiece is taken out of the furnace, nitrogen gas is introduced to flush the furnace chamber for 15 minutes.

[0033] Step 6: Preheating; The equipment is a box-type electric furnace. The preheating temperature of the workpiece is 670℃, and the holding time is 20 minutes. After the holding time is completed, the workpiece is transferred to quenching heating.

[0034] Step 7: Quenching; The equipment is a salt bath furnace. Before quenching, the salt bath furnace is deoxidized with 0.5 kg of deoxidizing agent. The quenching temperature is 850℃, and the holding time is 10 min. After the holding time, it is transferred to a 170℃ alkali solution for cooling for 8 min. Using low-temperature alkali cooling can effectively slow down the cooling rate of the workpiece in the low-temperature zone and reduce heat treatment deformation.

[0035] Step 8: Cold Treatment; The equipment is a cold treatment chamber, and the cold treatment temperature is -50℃. After reaching the temperature, the workpiece is packed into the chamber and held at that temperature for 270 minutes. After being removed from the chamber, it is slowly heated to room temperature before undergoing low-temperature tempering. The purpose of cold treatment is to promote the continued transformation of retained austenite into martensite at low temperatures, further improving the surface hardness of the diffusion layer. Due to the characteristics of the workpiece's shape and structure, the cold treatment temperature should not be too low to avoid cracking at sharp corners after cold treatment.

[0036] Step 9: Tempering; The equipment is an oven with a circulating fan. The tempering temperature is 160℃, the holding time is 210min, and the workpiece is air-cooled to room temperature after being removed from the oven to obtain heat treatment.

[0037] like Figure 4 The image shows the metallographic structure of the heat-treated workpiece. The microstructure was tested according to HB5492—2011 "Grading and Evaluation of Metallographic Structure of Carburized and Carbonitrided Parts in Aerospace Steel". The required metallographic structure is: carbides grade 1-7, martensite and retained austenite grade 1-4, and core microstructure grade 1-4. The carburized layer depth was determined according to HB5493—1991 "Method for Determination of Carburized and Carbonitrided Layer Depth in Aerospace Steel Parts", with a required value of 1.1-1.4 mm. Figure 5 The results are from the metallographic structure analysis of the workpiece.

[0038] The hardness values ​​of different depths of the carburized layer on the workpiece are measured. The required hardness value of the carburized layer is HRC60~64 (HV698~795). Figure 6 This represents the hardness gradient value at the carburized layer of the workpiece.

[0039] Measure the straightness deformation at φ26mm and φ8mm on the workpiece. Figure 7 These represent the straightness deformation values ​​at two dimensions.

[0040] The above test results show that the carburizing heat treatment method for the No. 25 steel workpiece according to the embodiments of this application achieves the required carburized layer depth and hardness, with a relatively gentle hardness gradient and a metallographic structure that meets the grade evaluation requirements. Precise control of the carburized layer depth is achieved by adjusting the carbon concentration of the gas in the furnace. Heat treatment deformation of the workpiece is reduced by preheating before quenching and low-temperature alkaline cooling during quenching. Cold treatment further reduces the residual austenite content and increases the hardness of the carburized layer, ensuring the stability of the carburizing quality of the No. 25 steel.

[0041] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A carburizing heat treatment method for a No. 25 steel workpiece, characterized in that, It includes the following steps: Controlled atmosphere carburizing of 25 steel workpieces includes five stages: exhaust gas introduction of carbon-containing gas for heating, strong carburizing, diffusion, cooling, and purification treatment. The workpiece after controlled atmosphere carburizing is preheated at 650℃~700℃. After preheating, the workpiece is quenched at a temperature of 840℃~860℃. After heating, it is cooled in a 160℃~180℃ alkali solution. The quenched workpiece is kept at -50℃ for 4 to 5 hours. After low-temperature tempering, the workpiece is removed from the furnace and air-cooled to room temperature.

2. The carburizing heat treatment method for a No. 25 steel workpiece according to claim 1, characterized in that, The process of introducing carbon-containing gas to raise the temperature includes the following steps: first, nitrogen is introduced to expel the gas in the bottom-charged multi-purpose furnace, and after the furnace temperature is raised to 700°C, methanol and propane are introduced. After the temperature and carbon potential stabilize, the workpiece is put into the furnace.

3. The carburizing heat treatment method for a No. 25 steel workpiece according to claim 2, characterized in that, The flow rate of methanol is 1.0–1.2 L / h, and the flow rate of propane is 0.8–2.4 L / h.

4. The carburizing heat treatment method for a No. 25 steel workpiece according to claim 1, characterized in that, The strong infiltration process includes the following steps: subjecting the workpiece to strong infiltration treatment at 900℃~910℃ and a carbon potential of 1.1±0.05% for 7~7.5h.

5. The carburizing heat treatment method for a No. 25 steel workpiece according to claim 1, characterized in that, Diffusion includes the following steps: The workpiece is subjected to diffusion treatment at 900℃~910℃ and a carbon potential of 0.8±0.05% for 2.5~3h.

6. The carburizing heat treatment method for a No. 25 steel workpiece according to claim 1, characterized in that, Cooling down includes the following steps: After the diffusion stage, the workpiece is cooled in the furnace to 850℃~870℃ and then air-cooled after exiting the furnace.

7. The carburizing heat treatment method for a No. 25 steel workpiece according to claim 1, characterized in that, The purification process includes the following steps: After the workpiece is taken out of the furnace, nitrogen gas is introduced to flush the furnace chamber for 10 to 15 minutes.

8. The carburizing heat treatment method for a No. 25 steel workpiece according to claim 1, characterized in that, The low-temperature tempering involves holding the workpiece at 150℃~170℃ for 3h~4h.

9. A workpiece, characterized in that, It is processed using the carburizing heat treatment method for 25 steel workpieces as described in any one of claims 1 to 8.

10. The workpiece according to claim 9, characterized in that, Its infiltration depth is 1.1–1.4 mm, and the hardness of the infiltration layer is HRC60–64.

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