Precision part surface high-hardness chromizing coating process

Abstract

The invention relates to the technical field of surface coatings of precision parts, in particular to a high-hardness chromizing coating process for the surface of a precision part, which comprises the following steps: ultrasonically cleaning the precision part; detecting the workpiece to be chromized by using an energy disperse spectroscopy; the workpiece to be carburized is placed in a working area of a vacuum carburizing furnace to be subjected to vacuum carburizing heat treatment; preparing a chromizing agent; after the workpieces are arranged according to requirements, the workpieces are fully filled with a chromizing agent for chromizing; the loaded chromizing tank is moved into a vacuum atmosphere chromizing furnace for chromizing heat treatment; and the workpiece subjected to chromizing is cleaned. According to the method, the metal to be chromized is screened through carbon element detection, chromizing is conducted after the carburized layer is formed on the metal surface with the low carbon content through the vacuum carburizing technology, the limitation of the hard chromizing technology on metal materials is effectively solved, and the hardness, abrasion resistance, corrosion resistance and other performance of the metal are improved; vacuum sealing treatment is adopted, no harmful gas is discharged, and the green manufacturing standard is met.

Description

Technical Field

[0001] The invention relates to the technical field of surface coatings for precision parts, in particular to a high-hardness chromizing coating process for the surfaces of precision parts. Background Art

[0002] Precision components such as gears, bearings, and impeller blades are widely used in fields such as machinery manufacturing, transportation, and aerospace. Due to their complex shapes and structures and stringent machining requirements, these precision components require not only advanced CNC machining equipment and high-precision testing equipment, but also are often made from easily machined metals such as mild steel. However, these metals have low hardness, and components made from them are susceptible to wear over time, reducing their dimensional accuracy and even causing failure. Therefore, increasing the surface hardness of machined precision components through physical or chemical methods is an effective measure to extend their service life.

[0003] Chromizing coating technology is a common metal surface coating technology. It uses heating to penetrate chromium into the metal surface to form a chromium alloy layer, thereby improving the metal's hardness, wear resistance, corrosion resistance, and oxidation resistance. In chromizing technology, the carbon content of the metal is an important factor affecting the coating performance. Chromizing treatment of metals with low carbon content is soft chromizing, which mainly improves the metal's corrosion resistance and high-temperature oxidation resistance, but does not significantly increase the metal's hardness to improve the metal's wear resistance. If the carbon content of the chromized metal is high (generally ≥0.3%), the chromizing will improve the metal's corrosion resistance and its hardness will also increase significantly, reaching 1100-1800HV. It has outstanding wear resistance, corrosion resistance, and high-temperature oxidation resistance, and is suitable for occasions that require both wear resistance and corrosion resistance.

[0004] Existing chromizing processes have stringent requirements for the carbon content of materials (≥0.3%), making it impossible to directly hard-chromize low-carbon precision parts such as 20CrMnTi, resulting in insufficient hardness after chromizing (typically <900 HV). The traditional carburizing-chromizing process, which involves a separate step, results in an uneven carburizing layer due to oxidation issues and uses chemical chromizing agents that pollute the environment. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that the conventional carburizing-chromizing step-by-step process causes uneven carburizing layers due to oxidation problems, and the use of chemical carburizing agents pollutes the environment.

[0006] The technical solution adopted by the present invention to solve the technical problem is: a high-hardness chromizing coating process for the surface of precision parts, comprising the following steps:

[0007] Step 1: Place the precision parts in an ultrasonic cleaner, wash them with deionized water and anhydrous ethanol for 10 minutes in sequence to remove oil and rust on the metal surface, dry them in a dryer, and then grind and polish them to obtain the workpiece to be chromized;

[0008] Step 2: Use an energy dispersive spectrometer to detect the carbon content (C%) of the chromized workpiece. If the C% of the workpiece is greater than 0.3%, the workpiece is sent to a vacuum chromizing furnace for chromizing. If the C% is less than or equal to 0.3%, the workpiece is sent to a vacuum carburizing furnace for carburizing before chromizing.

[0009] Step 3: Place the workpiece to be carburized into the working area of the vacuum carburizing furnace for vacuum carburizing heat treatment;

[0010] Step 4: Prepare a chromizing agent by weighing the following materials by mass percentage: 50% chromium powder, 47% spherical alumina, and 3% ammonium chloride powder, with the particle size of the chromium powder and the spherical alumina being 200-300 mesh. Mix them evenly in a powder mixer and use them as the chromizing agent.

[0011] Step 5: The workpieces to be chromized as described in the inspection phase of Step 3 and / or the workpieces with C% greater than 0.3% as described in Step 2 are buried in a stainless steel open chromizing tank filled with chromizing agent. The workpieces are placed in the chromizing tank with the following requirements: the thickness of the chromizing agent on the lower surface of the workpiece b1 ≥ 25 mm, the thickness of the chromizing agent on the upper surface of the workpiece b2 ≥ 25 mm, and the spacing d between the workpieces ≥ 15 mm. After the workpieces are arranged as required, the chromizing agent is completely filled to the brim.

[0012] Step 6: Move the loaded chromizing tank into a vacuum atmosphere chromizing furnace for chromizing heat treatment;

[0013] Step 7: The chromized workpiece is cleaned. The processing flow is as follows: the workpiece is cleaned with deionized water and anhydrous ethanol in an ultrasonic cleaner for 10 minutes respectively, and then dried in a dryer. The treated workpiece is tested and recorded using a Vickers hardness tester and a scanning electron microscope (SEM) to detect and record the Vickers hardness HV and the depth h of the chromized layer on the surface of the workpiece.

[0014] Said step 3 includes the following four stages:

[0015] During the heating and holding stage, after checking and cleaning the vacuum carburizing furnace, turn on the power supply, open the exhaust valve to evacuate the furnace to below 10Pa, and increase the temperature of the carburizing furnace from room temperature to the preheating temperature T1 (600-700℃) at a heating rate of 25℃ / min. Keep it warm for 40 minutes, then increase the temperature to the carburizing temperature T2 (900-950℃) at a heating rate of 10℃ / min and keep it warm for 30 minutes.

[0016] The carburizing stage consists of a strong carburizing stage and a diffusion stage. During the strong carburizing stage, the charging valve is opened to introduce high-purity acetylene (C2H2) into the vacuum carburizing furnace after insulation. The high-purity acetylene flow rate is 10-15 L / min, the pressure in the furnace is 200-500 Pa, and the strong carburizing time is t1=15-20 min. During the diffusion stage, the charging valve is closed and the exhaust valve is opened to extract the gas in the furnace. After the extraction is completed, the charging valve is opened to fill in nitrogen and maintain the pressure below 100 Pa. The diffusion time is t2=5t1.

[0017] In the quenching and tempering stage, the carburizing furnace temperature is cooled from T2 to the quenching temperature T3 (800-850°C) at a cooling rate of 5°C / min. After holding for 30 minutes, the workpiece is quenched with 60°C oil for 30 minutes. After quenching, the workpiece is heated to the tempering temperature T4 (150-200°C) and tempered at low temperature for 30 minutes. The carburizing furnace power is turned off and the workpiece is placed in an inert gas environment to cool to room temperature before being taken out.

[0018] In the post-processing stage, the carburized workpiece is taken out from the vacuum carburizing furnace for post-processing.

[0019] The carburized workpiece processing process is as follows: cleaning with deionized water and anhydrous ethanol in an ultrasonic cleaner for 10 minutes, drying in a dryer, and grinding and polishing to obtain a workpiece to be chromized.

[0020] Said step 6 includes the following three stages:

[0021] During the heating and sealing stage, the chromizing tank containing the workpiece and the chromizing agent is placed in a vacuum chromizing furnace. After the power is turned on, the exhaust valve of the chromizing furnace is opened to evacuate the furnace to 0.133 Pa. The chromizing furnace is heated from room temperature to 450°C at a heating rate of 30°C / min and then kept warm for 1 hour. The chromizing tank is then taken out within 10 seconds, and the opening of the chromizing tank is sealed with a mixture of high-temperature refractory mud and water glass. The chromizing tank is then placed back into the chromizing furnace, and the inflation valve is opened to introduce nitrogen to maintain the furnace pressure at 0.02 MPa.

[0022] In the chromizing stage, the chromizing furnace is heated at a heating rate of 25°C / min to the chromizing temperature Ts (850-1000°C), and chromizing is started at this temperature, and the holding time is ts (6-10h);

[0023] In the cooling stage, the temperature of the chromizing furnace is lowered from Ts to the cooling temperature Tc = 160°C at a cooling rate of 50°C / min, and then the furnace door is opened to take out the chromizing tank. After removing the seal of the chromizing tank, the chromized workpiece is taken out and placed in an inert gas environment to cool to room temperature.

[0024] The beneficial effects of the present invention are:

[0025] (1) The present invention screens the metal to be chromized by carbon element detection, and uses a vacuum carburizing process to form a carburized layer on the metal surface with a low carbon content before chromizing. This effectively solves the limitations of hard chromizing technology on metal materials and improves the hardness, wear resistance, corrosion resistance and other properties of the metal;

[0026] (2) By using a vacuum heat treatment furnace for carburizing and chromizing, the problems of oxidation and decarburization existing in traditional carburizing and chromizing technologies can be effectively avoided, while the process parameters such as temperature, time, and pressure can be precisely controlled to ensure the quality and uniformity of the carburized layer;

[0027] (3) The heat treatment stage of this process adopts vacuum sealing treatment, without any harmful gas emissions, which complies with green manufacturing standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be further described below with reference to the accompanying drawings and examples.

[0029] Figure 1 This is a process flow chart of the high-hardness, wear-resistant, and corrosion-resistant chromizing coating of the present invention.

[0030] Figure 2 It is a schematic diagram of the internal filler of the chromizing tank in the chromizing process of the present invention. DETAILED DESCRIPTION

[0031] The present invention will now be described in further detail with reference to the accompanying drawings, which are simplified schematic diagrams that illustrate the basic structure of the present invention in a schematic manner.

[0032] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "connected" and "connection" should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integral connection; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediary. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0033] Figure 1 、 Figure 2 shown

[0034] Example 1:

[0035] The workpiece described in this embodiment is 20CrMnTi, has a carbon content of 0.17% to 0.23%, and has dimensions of 40×15×8 mm.

[0036] A high-hardness chromizing coating process for the surface of a precision component, using the workpiece described in this embodiment, includes the following steps:

[0037] Step 1: Place the processed precision parts in an ultrasonic cleaner and clean them with deionized water and anhydrous ethanol for 10 minutes to remove oil and rust on the metal surface. Dry them in a dryer and then polish them to obtain the workpiece to be chromed.

[0038] Step 2: Use an energy dispersive spectrometer to detect the carbon content C% of the workpiece to be chromized. If the C% of the workpiece is greater than 0.3%, the workpiece is sent to a vacuum chromizing furnace for chromizing. If the C% is less than or equal to 0.3%, the workpiece is sent to a vacuum carburizing furnace for carburizing before chromizing.

[0039] Step 3: Place the workpiece to be carburized into the working area of the vacuum carburizing furnace for vacuum carburizing heat treatment, which includes the following four stages;

[0040] During the heating and holding stage, after checking and cleaning the vacuum carburizing furnace, turn on the power supply, open the exhaust valve to evacuate the furnace to below 10Pa, and increase the temperature of the carburizing furnace from room temperature to the preheating temperature T1 = 650°C at a heating rate of 25°C / min. Keep it warm for 40 minutes, then increase the temperature to the carburizing temperature T2 = 950°C at a heating rate of 10°C / min and keep it warm for 30 minutes.

[0041] The carburizing stage consists of a strong carburizing stage and a diffusion stage. In the strong carburizing stage, the charging valve is opened to introduce high-purity acetylene (C2H2) into the vacuum carburizing furnace after insulation. The high-purity acetylene flow rate is 15L / min, the pressure in the furnace is 500Pa, and the strong carburizing time t1 is 20min; in the diffusion stage, the charging valve is closed and the exhaust valve is opened to extract the gas in the furnace. After the extraction is completed, the charging valve is opened to fill nitrogen and maintain the pressure below 100Pa. The diffusion time t2 is 100min;

[0042] In the quenching and tempering stage, the carburizing furnace temperature is cooled from T2 to the quenching temperature T3 = 850 ° C at a cooling rate of 5 ° C / min. After keeping warm for 30 minutes, the workpiece is quenched with 60 ° C oil for 30 minutes. After quenching, the workpiece is heated to the tempering temperature T4 = 160 ° C and then tempered at low temperature for 30 minutes. The carburizing furnace power is turned off, and the workpiece is taken out after air cooling to room temperature.

[0043] In the post-processing stage, the carburized workpiece is taken out of the vacuum carburizing furnace for post-processing. The processing flow is as follows: cleaning with deionized water and anhydrous ethanol in an ultrasonic cleaner for 10 minutes, drying in a dryer, and grinding and polishing to obtain the workpiece 2 to be chromized;

[0044] Step 4: Prepare chromizing agent 3 by weighing the following materials by mass percentage: 50% chromium powder, 47% alumina powder, and 3% ammonium chloride powder. The chromium powder and spherical alumina have a particle size of 200-300 mesh. Mix them evenly in a powder mixer to prepare chromizing agent 3.

[0045] Step 5: The workpieces to be chromized 2 described in the inspection stage of Step 3 and / or the workpieces with C% greater than 0.3% described in Step 2 are buried in a stainless steel open chromizing tank 1 filled with a chromizing agent 3. The workpieces are placed in the chromizing tank 1 with the following requirements: the thickness b1 of the chromizing agent 3 on the lower surface of the workpiece is ≥ 25 mm, the thickness b2 of the chromizing agent 3 on the upper surface of the workpiece is ≥ 25 mm, and the spacing d between the workpieces is ≥ 15 mm. After the workpieces are arranged as required, the chromizing tank 1 is completely filled with the chromizing agent 3.

[0046] Step 6: The loaded chromizing tank 1 is moved into a vacuum atmosphere chromizing furnace for chromizing heat treatment, which includes the following three stages:

[0047] During the heating and sealing stage, the chromizing tank 1 containing the workpiece and the chromizing agent 3 is placed in a vacuum chromizing furnace. After the power is turned on, the exhaust valve of the chromizing furnace is opened to evacuate the furnace to 0.133 Pa. The chromizing furnace is heated from room temperature to 450°C at a heating rate of 30°C / min and then kept warm for 1 hour. The chromizing tank 1 is then taken out within 10 seconds, the opening of the chromizing tank 1 is sealed with a mixture of high-temperature refractory mud and water glass, and the chromizing tank 1 is returned to the chromizing furnace. The inflation valve is opened to introduce nitrogen to maintain the pressure in the furnace at 0.02 MPa.

[0048] In the chromizing stage, the chromizing furnace is heated at a heating rate of 25°C / min to a chromizing temperature Ts = 850°C, at which chromizing begins, and the holding time is ts = 6h;

[0049] In the cooling stage, the temperature of the chromizing furnace is lowered from Ts to a cooling temperature Tc = 160°C at a cooling rate of 50°C / min, and then the furnace door is opened to take out the chromizing tank 1. After removing the seal of the chromizing tank 1, the chromized workpiece is taken out and air-cooled to room temperature;

[0050] Step 7: The chromized workpiece is cleaned. The processing flow is as follows: the workpiece is cleaned with deionized water and anhydrous ethanol in an ultrasonic cleaner for 10 minutes and then dried in a dryer. The treated workpiece is tested and recorded using a Vickers hardness tester and a scanning electron microscope (SEM) to detect and record the Vickers hardness HV and the depth h of the chromized layer on the surface of the workpiece.

[0051] In this embodiment, in step 7, an ultrasonic cleaner is used to clean dirt on the surface of the workpiece, and then the workpiece is dried in a dryer. A hardness tester and an electron microscope are used to detect and record the surface hardness of the workpiece as 1159-1256 HV, and the depth of the chromized layer is 12-13 um.

[0052] Example 2:

[0053] This embodiment provides a high-hardness chromizing coating process for the surface of precision parts. The other aspects are the same as those of Example 1, except that the chromizing workpiece 2 used in this embodiment is 30CrMnTi with a carbon content of 0.24% to 0.30%.

[0054] In this embodiment, in step 7, an ultrasonic cleaner is used to clean dirt on the surface of the workpiece, and then the workpiece is dried in a dryer. A hardness tester and an electron microscope are used to detect and record the surface hardness of the workpiece as 1220-1253 HV and the depth of the chromized layer as 13-14 um.

[0055] Example 3:

[0056] This embodiment provides a high-hardness chromizing coating process for the surface of gold precision parts. The other aspects are the same as those of Example 1, except that in the chromizing stage of step 6 of this embodiment, the chromizing temperature Ts of the chromizing furnace is 950°C.

[0057] In this embodiment, in step 7, an ultrasonic cleaner is used to clean the dirt on the surface of the workpiece, and then a drying

[0058] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A high-hardness chromizing coating process for the surface of precision parts, characterized in that: The steps include: Step 1: Place the precision parts in an ultrasonic cleaning apparatus, wash with deionized water and anhydrous ethanol for 10 minutes to remove oil and rust on the metal surface, dry with a dryer, and then grind and polish to obtain a workpiece to be chromized (2); Step 2: Use an energy dispersive spectrometer to detect the carbon content C% of the workpiece to be chromized (2). If the C% of the workpiece is greater than 0.3%, the workpiece is sent to a vacuum chromizing furnace for chromizing; if the C% is less than or equal to 0.3%, the workpiece is sent to a vacuum carburizing furnace for carburizing before chromizing. Step 3: Place the workpiece to be carburized into the working area of the vacuum carburizing furnace for vacuum carburizing heat treatment; Step 4: Prepare a chromizing agent (3), weigh the following materials by mass percentage: 50% chromium powder, 47% spherical alumina, and 3% ammonium chloride powder, wherein the particle size of the chromium powder and the spherical alumina is 200-300 mesh, and stir them evenly in a powder mixer to prepare the chromizing agent (3); Step 5: burying the workpieces to be chromized (2) in the inspection stage of step 3 and / or the workpieces with C%>0.3% in step 2 into a stainless steel open chromizing tank (1) filled with a chromizing agent (3). The workpieces are placed in the chromizing tank (1) with the following requirements: the thickness b1 of the chromizing agent (3) on the lower surface of the workpiece is ≥25 mm, the thickness b2 of the chromizing agent (3) on the upper surface of the workpiece is ≥25 mm, and the spacing d between the workpieces is ≥15 mm. After the workpieces are arranged as required, they are completely filled with the chromizing agent (3). Step 6: moving the loaded chromizing tank (1) into a vacuum atmosphere chromizing furnace for chromizing heat treatment; Step 7: The chromized workpiece is cleaned. The processing flow is as follows: the workpiece is cleaned with deionized water and anhydrous ethanol in an ultrasonic cleaner for 10 minutes respectively, and then dried in a dryer. The treated workpiece is tested and recorded using a Vickers hardness tester and a scanning electron microscope (SEM) to detect and record the Vickers hardness HV and the depth h of the chromized layer on the surface of the workpiece.

2. A high-hardness chromizing coating process for the surface of precision parts according to claim 1, characterized in that: Said step 3 includes the following four stages: During the heating and holding stage, after checking and cleaning the vacuum carburizing furnace, turn on the power supply, open the exhaust valve to evacuate the furnace to below 10Pa, and increase the temperature of the carburizing furnace from room temperature to the preheating temperature T1 (600-700℃) at a heating rate of 25℃ / min. Keep it warm for 40 minutes, then increase the temperature to the carburizing temperature T2 (900-950℃) at a heating rate of 10℃ / min and keep it warm for 30 minutes. The carburizing stage consists of a strong carburizing stage and a diffusion stage. During the strong carburizing stage, the charging valve is opened to introduce high-purity acetylene (C2H2) into the vacuum carburizing furnace after insulation. The high-purity acetylene flow rate is 10-15 L / min, the pressure in the furnace is 200-500 Pa, and the strong carburizing time is t1=15-20 min. During the diffusion stage, the charging valve is closed and the exhaust valve is opened to extract the gas in the furnace. After the extraction is completed, the charging valve is opened to fill in nitrogen and maintain the pressure below 100 Pa. The diffusion time is t2=5t1. In the quenching and tempering stage, the carburizing furnace temperature is cooled from T2 to the quenching temperature T3 (800-850°C) at a cooling rate of 5°C / min. After holding for 30 minutes, the workpiece is quenched with 60°C oil for 30 minutes. After quenching, the workpiece is heated to the tempering temperature T4 (150-200°C) and tempered at low temperature for 30 minutes. The carburizing furnace power is turned off and the workpiece is placed in an inert gas environment to cool to room temperature before being taken out. In the post-processing stage, the carburized workpiece is taken out from the vacuum carburizing furnace for post-processing.

3. The high-hardness chromizing coating process for the surface of precision parts according to claim 2 is characterized by: The carburized workpiece processing process is as follows: cleaning with deionized water and anhydrous ethanol in an ultrasonic cleaner for 10 minutes, drying in a dryer, and grinding and polishing to obtain a workpiece to be chromized (2).

4. The high-hardness chromizing coating process for the surface of precision parts according to claim 1 is characterized by: Said step 6 includes the following three stages: During the heating and sealing stage, the chromizing tank (1) containing the workpiece and the chromizing agent (3) is placed in a vacuum chromizing furnace. After the power is turned on, the exhaust valve of the chromizing furnace is opened to evacuate the furnace to 0.133 Pa. The chromizing furnace is heated from room temperature to 450°C at a heating rate of 30°C / min and then kept warm for 1 hour. The chromizing tank (1) is then taken out within 10 seconds, the opening of the chromizing tank (1) is sealed with a mixture of high-temperature refractory mud and water glass, and the chromizing tank (1) is put back into the chromizing furnace. The inflation valve is opened to introduce nitrogen to maintain the pressure in the furnace at 0.02 MPa. In the chromizing stage, the chromizing furnace is heated at a heating rate of 25°C / min to the chromizing temperature Ts (850-1000°C), and chromizing is started at this temperature, and the holding time is ts (6-10h); In the cooling stage, the temperature of the chromizing furnace is lowered from Ts to a cooling temperature Tc=160°C at a cooling rate of 50°C / min, and then the furnace door is opened to take out the chromizing tank (1), and after removing the seal of the chromizing tank (1), the chromized workpiece is taken out and placed in an inert gas environment to cool to room temperature.

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