Heat treatment carburizing and quenching process

Abstract

The invention discloses a heat treatment carburizing and quenching process. The technical solution mainly comprises the following steps: a first stage of carbon absorption: the temperature in a furnace body is controlled at 900°C, a high carbon potential is adopted, and the high carbon potential refers to a carbon potential value higher than Cp1.15%; a second stage of carbon absorption: the furnace body temperature is maintained at 900°C, and the carbon potential value is maintained at Cp1.15%; diffusion: the furnace body temperature is maintained at 900°C, a low carbon potential is adopted, and the low carbon potential is lower than Cp1%; quenching: after the workpiece is kept warm, the workpiece is quenched by oil quenching; the maximum carbon absorption time in the first stage is x, the actual value of the carbon potential value adopted in the first stage is l, x≤(l-1.15)*400, and the unit of x is min; by adopting a short time of high carbon potential value for carburizing treatment, it can be ensured that the surface hardness is not too high, and the carburizing efficiency can be accelerated and the carburizing time can be shortened.

Description

Technical Field

[0001] The present invention relates to the technical field of carburizing treatment, and more particularly to a heat treatment carburizing and quenching process. Background Art

[0002] Carburizing is a method of metal surface treatment. Carburizing is mostly used for low-carbon steel or low-alloy steel. The specific method is to place the workpiece in an activated carbon medium. After heating and keeping it warm for a sufficient time, the activated carbon atoms decomposed by the carburizing medium will penetrate into the surface of the steel part, thereby obtaining high carbon on the surface and maintaining the original composition in the core. Through carburizing treatment, the surface layer of the workpiece has high hardness and wear resistance, while the center part of the workpiece still retains the toughness and plasticity of low-carbon steel.

[0003] In the prior art, when carburizing a workpiece, the carbon potential value in the furnace is usually controlled at about Cp1.1%. Too high a carbon potential value can easily lead to excessive hardness of the workpiece surface, thus requiring a lot of time for the carburizing process. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a heat treatment carburizing and quenching process, which adopts a short-time high carbon potential value for carburizing treatment, which can not only ensure that the surface hardness is not too high, but also accelerate the carburizing efficiency and shorten the carburizing time.

[0005] To achieve the above object, the present invention provides the following technical solution: a heat treatment carburizing and quenching process, comprising the following steps:

[0006] The first stage of carbon absorption: the temperature inside the furnace is controlled at 900℃, and the carbon potential value adopts high carbon potential, which means the carbon potential value is higher than Cp1.15%;

[0007] The second stage of carbon absorption: the furnace temperature is maintained at 900 degrees Celsius and the carbon potential value is maintained at Cp1.15%;

[0008] Diffusion: The furnace temperature is maintained at 900 degrees Celsius, and the carbon potential value adopts low carbon potential, which is lower than Cp1%;

[0009] Quenching: After the workpiece is kept warm, it is quenched by oil quenching;

[0010] The maximum carbon absorption time in the first stage is x, and the actual value of the carbon potential value used in the first stage is l, x≤(l-1.15)*400, and the unit of x is min.

[0011] By adopting the above technical solution and using a short period of high carbon potential for carburizing treatment, the efficiency of carburizing can be accelerated and the carburizing time can be shortened. The time of carbon absorption in the first stage can be controlled by the above formula, and the carburizing time can be reduced as the carbon potential value increases, thereby preventing the high carbon potential carburizing treatment from causing the hardness of the workpiece surface to be too high. By reducing the carbon potential value during diffusion interruption, the high carbon potential carburizing in the first stage can be further prevented from causing the hardness of the workpiece surface to be too high.

[0012] The present invention is further configured such that the difference between the carbon potential value during diffusion and Cp1% is equal to the difference between the carbon potential value during the first stage of carbon absorption and Cp1.15%.

[0013] By adopting the above technical solution, the carbon potential value in the diffusion stage is controlled according to the specific numerical value of the high carbon potential value, and the carbon potential value in the diffusion stage can be changed according to the change of the carbon potential value during the first stage of carbon absorption. This not only ensures that the diffusion stage time is shortened, but also prevents the high carbon potential value during the first stage of carbon absorption from causing the surface hardness of the workpiece to be too high.

[0014] The present invention is further configured as follows: when the carbon absorption time in the first stage is 0, the carbon absorption time in the second stage is y, and the diffusion time is z;

[0015] When the carbon absorption time in the first stage is greater than 0, the carbon absorption time in the second stage is yx*2.5 and the diffusion time is zy*0.5.

[0016] By adopting the above technical solution, the carbon absorption time of the first stage is controlled according to the change of the carbon potential value during the carbon absorption in the first stage, and then the carbon absorption time and diffusion time of the second stage are converted according to the carbon absorption time of the first stage. Under the premise of ensuring the quality of the carburizing treatment, the time of carbon absorption and diffusion in the second stage can be shortened.

[0017] The present invention is further configured as follows: the workpiece to be heat treated is a gear having a module range of 2.75 mm to 4 mm and a hardened layer requirement of 0.6 mm to 1.0 mm;

[0018] The carbon potential value of the first stage carbon absorption is controlled at Cp1.3%, and the carbon absorption time is 60 minutes. The carbon absorption time of the second stage is 180 minutes, and the carbon potential value during diffusion is controlled at Cp0.85%.

[0019] The present invention is further configured to control the tolerance of the carbon potential value in each stage to be 0.05.

[0020] The present invention is further configured to provide carbon potential by introducing methanol, propane and nitrogen into the furnace body;

[0021] The introduction rate of methanol is 4000ml / min-6000ml / min, the introduction rate of propane is 4L / min-6L / min, and the introduction rate of nitrogen is 2600ml / min-4000ml / min.

[0022] The present invention is further configured as follows: before the first stage of carbon absorption, a heating step is performed to increase the temperature of the furnace body until the furnace body temperature reaches 900°C; when the furnace body temperature is increased to 800°C, methanol, propane and nitrogen are introduced until the carbon potential value in the furnace body reaches the carbon potential value requirement for the first stage of carbon absorption.

[0023] The present invention is further configured to include a cleaning step, in which between the heating steps, oil stains and iron filings on the surface of the workpiece are removed by spraying an alkaline solution and washing with clean water.

[0024] The present invention is further configured to include an anti-seepage step located between the cleaning step and the heating step;

[0025] The parts of the workpiece that do not need to be carburized are covered with an anti-seepage agent.

[0026] By adopting the above technical solution, the positions that do not require carburizing are covered by the anti-seepage agent, thereby preventing the positions that do not require carburizing from being accidentally carburized, which increases the difficulty of subsequent processing.

[0027] The present invention is further configured as follows: in the quenching step, the holding temperature of the workpiece is 820° C. and the holding time is 30 minutes.

[0028] In summary, the present invention has the following beneficial effects compared to the prior art:

[0029] 1. The present invention adopts a short-time high carbon potential value for carburizing treatment, which can accelerate the carburizing efficiency and shorten the carburizing time. The time of carbon absorption in the first stage is controlled by the above formula. As the carbon potential value increases, the carburizing time is reduced, thereby preventing the high carbon potential value carburizing treatment from causing the surface hardness of the workpiece to be too high;

[0030] 2. The present invention can further prevent excessive hardness of the workpiece surface caused by carburization with high carbon potential in the first stage by reducing the carbon potential value during diffusion interception;

[0031] 3. The present invention controls the carbon potential value in the diffusion stage according to the specific numerical value of the high carbon potential value, and can change the carbon potential value in the diffusion stage according to the change of the carbon potential value during the first stage of carbon absorption, thereby shortening the diffusion stage time and preventing the high carbon potential value during the first stage of carbon absorption from causing excessive hardness of the workpiece surface.

[0032] 4. The present invention controls the carbon absorption time of the first stage according to the change of the carbon potential value during the carbon absorption in the first stage, and then converts the carbon absorption time and diffusion time of the second stage according to the carbon absorption time of the first stage, thereby shortening the carbon absorption and diffusion time of the second stage while ensuring the quality of the carburizing treatment;

[0033] 5. The present invention covers the positions that do not require carburizing treatment by covering with an anti-seepage agent, thereby preventing positions that do not require carburizing from being accidentally carburized, thereby increasing the difficulty of subsequent processing. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is clearly and completely described below. Based on the embodiments in this application, other similar embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of this application. In addition, the directional words mentioned in the following embodiments, such as "up", "down", "left", "right", etc. are only reference directions. Therefore, the directional words used are used to illustrate rather than limit the invention.

[0035] The present invention will be further described below with reference to the embodiments.

[0036] Embodiment: A heat treatment carburizing and quenching process comprises the following steps:

[0037] The first stage of carbon absorption: the temperature inside the furnace is controlled at 900℃, and the carbon potential value adopts high carbon potential, which means the carbon potential value is higher than Cp1.15%;

[0038] The second stage of carbon absorption: the furnace temperature is maintained at 900 degrees Celsius and the carbon potential value is maintained at Cp1.15%;

[0039] Diffusion: The furnace temperature is maintained at 900 degrees Celsius, and the carbon potential value adopts low carbon potential, which is lower than Cp1%;

[0040] Quenching: After the workpiece is kept warm, it is quenched by oil quenching;

[0041] The maximum carbon absorption time in the first stage is x, and the actual value of the carbon potential value used in the first stage is l, x≤(l-1.15)*400, and the unit of x is min.

[0042] Carbon potential is a thermodynamic property of the atmosphere, which indicates a kind of equilibrium ability of the atmosphere. It is the ability of the atmosphere to balance the activated carbon atoms provided in the gas phase of the atmosphere with the carbon content in the austenite on the surface of the steel at the heat treatment heating temperature. The level of carbon potential is characterized by the carbon potential value. The higher the carbon potential value, the faster the carburizing treatment process, and the lower the carbon potential value, the slower the carburizing treatment process.

[0043] In the existing carburizing process, it usually includes two stages, namely the carbon absorption stage and the diffusion stage. The carbon potential value of the carbon absorption stage is controlled at about Cp1.1%. When the carbon potential value of the carbon absorption stage is too high, it is easy to cause the surface hardness of the workpiece to be too high, affecting the subsequent processing of the workpiece.

[0044] In this application, the carbon absorption stage is divided into two sections. In the first stage, a short period of high carbon potential value is used for carburizing treatment, which can speed up the carburizing efficiency and shorten the carburizing time. The time of the first stage of carbon absorption is controlled by the above formula. As the carbon potential value increases, the carburizing time is reduced to prevent the high carbon potential value carburizing treatment from causing the hardness of the workpiece surface to be too high; the second stage of carbon absorption uses a normal carbon potential value for long-term carburizing, so that the surface strength of the workpiece will not be too high in the second stage; by reducing the carbon potential value during diffusion interruption, it can further prevent the high carbon potential value carburizing in the first stage from causing the surface hardness of the workpiece to be too high.

[0045] Specifically, the difference between the carbon potential value during diffusion and Cp1% is equal to the difference between the carbon potential value during the first stage of carbon absorption and Cp1.15%. When a high carbon potential value is used for the first stage of carbon absorption, the carbon potential value of the diffusion chamber needs to be lowered to ensure that the surface hardness of the workpiece after the final carburizing is not too high. By ensuring that the difference between the carbon potential value during diffusion and Cp1% is equal to the difference between the carbon potential value during the first stage of carbon absorption and Cp1.15%, the carbon potential value during the diffusion step can be quickly converted when the carbon potential value is changed during the first stage of carbon absorption.

[0046] After adopting high carbon potential value in the first stage carbon absorption, the second stage carbon absorption time and diffusion time can be shortened compared with adopting carbon absorption and diffusion alone, and the technical requirements of the workpiece after carburizing can still be guaranteed after the reduction.

[0047] When the first-stage carbon absorption time is 0, the second-stage carbon absorption time is y, and the diffusion time is z. When the first-stage carbon absorption time is greater than 0, the second-stage carbon absorption time is yx*2.5, and the diffusion time is zy*0.5. The first-stage carbon absorption time is calculated based on the carbon potential value in the first-stage carbon absorption. After changing the carbon potential value in the first-stage carbon absorption, the second-stage carbon absorption time and diffusion time are both reduced relative to y and z. The above formula can quickly determine the actual second-stage carbon absorption time and diffusion time based on the first-stage carbon absorption time.

[0048] Specifically, this embodiment takes the carburizing treatment of a gear as an example for explanation, wherein the module of the gear is between 2.75 mm and 4 mm, and the thickness of the hardened layer is required to be between 0.6 mm and 1.0 mm.

[0049] Specifically, the carbon potential value of the first stage carbon absorption is controlled at Cp1.3%, the carbon absorption time is 60 minutes, the carbon absorption time of the second stage carbon absorption is 180 minutes, the carbon potential value is controlled at Cp1.15%, the carbon potential value during diffusion is controlled at Cp0.85%, and the diffusion time is 60 minutes.

[0050] During actual operation, it is impossible to control the carbon potential value in the furnace at a certain precise value, and a tolerance needs to be set. Specifically, the tolerance is set to 0.05. Therefore, the carbon potential value of the first stage carbon absorption is controlled at Cp1.3%±0.05%, the carbon potential value of the second stage carbon absorption is controlled at Cp1.15%±0.05%, and the carbon potential value during diffusion is controlled at Cp0.85%±0.05%.

[0051] Using the traditional carburizing process, the carbon potential value during the carbon absorption phase is controlled at Cp1.1%±0.05% over a 330-minute period, and the carbon potential value during the diffusion phase is controlled at Cp0.9%±0.05% over a 90-minute period. Compared to the traditional process, this quenching process can save 120 minutes of carburizing time. After carburizing, the gears meet the technical requirements without excessive surface hardness.

[0052] Specifically, during carburizing treatment, carbon potential is provided by introducing methanol, propane and nitrogen into the furnace body; the introduction rate of methanol is 4000ml / min-6000ml / min, the introduction rate of propane is 4L / min-6L / min, and the introduction rate of nitrogen is 2600ml / min-4000ml / min.

[0053] Before the first stage of carbon absorption, a heating step is performed to increase the temperature of the furnace body until the furnace body temperature reaches 900°C. When the furnace body temperature is raised to 800°C, methanol, propane and nitrogen are introduced until the carbon potential value in the furnace body reaches the carbon potential value requirement for the first stage of carbon absorption.

[0054] After the first stage of carbon absorption is completed, the introduction rate of methanol, propane and nitrogen is reduced within the required range until the carbon potential in the furnace body reaches the carbon potential value required for the second stage of carbon absorption, and the entire carbon potential value reduction process is controlled to be completed within 15 minutes.

[0055] After the second stage of carbon absorption is completed, the introduction rate of methanol, propane and nitrogen is reduced within the required range until the carbon potential in the furnace body reaches the carbon potential value required in the diffusion stage, and the entire carbon potential value reduction process is controlled to be completed within 25 minutes.

[0056] Specifically, this embodiment also includes a cleaning step, which is performed between the heating steps. In the cleaning step, oil stains and iron filings on the surface of the workpiece are removed by spraying an alkaline solution and washing with clean water. Specifically, the cleaning step includes one alkali spray, one immersion, two immersions, two alkali sprays, clean spraying, and drying. Alkali spraying can remove oil stains and iron filings on the surface of the workpiece. When performing alkali spraying, a mixture of 4% alkaline solution with a pH value of 9, 3% anti-rust liquid, and 93% clean water is used. By adding anti-rust liquid to the alkali liquid, rust on the surface of the workpiece can be prevented during the alkali spraying process. Both the one-time immersion and the two-time immersion are to soak the workpiece in clean water, and the clean water soaking method removes the alkali solution on the surface of the workpiece. Clean spraying is to spray with clean water to remove the alkali solution on the surface of the workpiece by spraying with clean water.

[0057] During the drying process, the workpiece is dried by hot air, and the atmospheric pressure is controlled between 0.6MPa and 1MPa. By reducing the air pressure, the volatilization of moisture on the workpiece surface can be accelerated.

[0058] Specifically, the method further includes an anti-seepage step between the cleaning step and the heating step, wherein portions of the workpiece that do not require carburizing are covered with an anti-seepage agent. During the carburizing process, not all surfaces of the workpiece require carburizing. Carburizing portions that do not require carburizing increases the hardness of these portions, making machining more difficult when these portions are subsequently machined.

[0059] On exposed surfaces, direct application of an anti-seepage agent can complete the anti-seepage treatment. The thickness of the anti-seepage agent should be maintained at 0.2mm-0.3mm. For porous surfaces, after the anti-seepage treatment is completed, bolts are inserted into the holes to block carbon in the air and achieve anti-seepage treatment on the porous surface. When using an anti-seepage agent for anti-seepage treatment, it is necessary to ensure that the anti-seepage agent is completely dry before proceeding to the subsequent steps.

[0060] In order to prevent the anti-seepage agent from falling off from the surface of the workpiece, it is necessary to clamp it through a tooling, press the tooling plate surface tightly against the anti-seepage agent coating, and use the tooling fixture to prevent the anti-seepage agent from falling off.

[0061] Specifically, during the quenching step, the workpiece is kept at a temperature of 820° C. in the furnace for 30 minutes. During quenching, oil is used as the quenching medium.

[0062] Specifically, when processing gears, a tempering operation is also included. During the tempering operation, the holding temperature is 190℃±10℃ for 50 minutes, and then the gear workpiece is air-cooled to room temperature.

[0063] After tempering, the gears are shot blasted by a shot blasting machine to improve the surface finish of the workpiece. After that, the gears are soaked in anti-rust liquid and packaged for shipment.

[0064] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiment. All technical solutions based on the concept of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A heat treatment carburizing and quenching process, characterized in that: The following steps are involved: The first stage of carbon absorption: the temperature inside the furnace is controlled at 900℃, and the carbon potential value adopts high carbon potential, which means the carbon potential value is higher than Cp1.15%; The second stage of carbon absorption: the furnace temperature is maintained at 900 degrees Celsius and the carbon potential value is maintained at Cp1.15%; Diffusion: The furnace temperature is maintained at 900 degrees Celsius, and the carbon potential value adopts low carbon potential, which is lower than Cp1%; Quenching: After the workpiece is kept warm, it is quenched by oil quenching; The maximum carbon absorption time in the first stage is x, and the actual value of the carbon potential value used in the first stage is l, x≤(l-1.15)*400, and the unit of x is min; The difference between the carbon potential value during diffusion and Cp1% is equal to the difference between the carbon potential value during the first stage of carbon absorption and Cp1.15%; When the carbon absorption time of the first stage is 0, the carbon absorption time of the second stage is y and the diffusion time is z; When the carbon absorption time in the first stage is greater than 0, the carbon absorption time in the second stage is yx*2.5 and the diffusion time is zy*0.

5.

2. The heat treatment carburizing and quenching process according to claim 1, characterized in that: The workpieces processed by heat treatment are gears with a module range of 2.75mm to 4mm and a hardened layer requirement of 0.6mm-1.0mm; The carbon potential value of the first stage carbon absorption is controlled at Cp1.3%, the carbon absorption time is 60min, the second stage carbon absorption time is 180min, and the carbon potential value during diffusion is controlled at Cp0.85%.

3. The heat treatment carburizing and quenching process according to claim 2, characterized in that: The tolerance of controlling the carbon potential value at each stage is 0.

05.

4. The heat treatment carburizing and quenching process according to claim 1, characterized in that: Carbon potential is provided by introducing methanol, propane and nitrogen into the furnace body; The introduction rate of methanol is 4000 ml / min-6000 ml / min, the introduction rate of propane is 4 L / min-6 L / min, and the introduction rate of nitrogen is 2600 ml / min-4000 ml / min.

5. The heat treatment carburizing and quenching process according to claim 4, characterized in that: Before the first stage of carbon absorption, a heating step is performed to increase the temperature of the furnace body until the furnace body temperature reaches 900°C. When the furnace body temperature is raised to 800°C, methanol, propane and nitrogen are introduced until the carbon potential value in the furnace body reaches the carbon potential value requirement for the first stage of carbon absorption.

6. The heat treatment carburizing and quenching process according to claim 5, characterized in that: The method further comprises a cleaning step, which is performed between the heating steps. In the cleaning step, oil stains and iron chips on the surface of the workpiece are removed by spraying an alkaline solution and washing with clean water.

7. The heat treatment carburizing and quenching process according to claim 6, characterized in that: Also included is an anti-seepage step between the cleaning step and the temperature raising step; The parts of the workpiece that do not need to be carburized are covered with an anti-seepage agent.

8. The heat treatment carburizing and quenching process according to claim 1, characterized in that: During the quenching step, the workpiece is kept at a temperature of 820°C for 30 minutes.