Laser quenching heat treatment method

Abstract

The invention relates to the technical field of laser quenching, in particular to a laser quenching heat treatment method which comprises the following steps: S1, normal-temperature phosphating; s2, dehydrogenation tempering is conducted, oil stains and rust on the tooth part and the inner hole of the gear subjected to normal-temperature phosphating are removed, and dehydrogenation treatment is conducted on the gear; s3, laser quenching is conducted, specifically, the target tooth surface of the gear teeth serves as a quenching surface, the opposite tooth surface serves as a cooling surface, and when laser quenching is conducted on the quenching surface, a cooling medium flows through the cooling surface to conduct auxiliary cooling; s4, low-temperature tempering is carried out, normal-temperature phosphating treatment is carried out on the surface of the gear to replace brushing of a light absorption material, auxiliary cooling is carried out while laser quenching is carried out, the requirement for the quenching critical cooling speed is met through the heat dissipation capacity of a cooling medium, and the problem that the heat dissipation efficiency of the gear is insufficient due to self heat dissipation is solved; and auxiliary cooling is performed on the opposite surface while laser quenching is performed on the quenching surface, so that the surface hardness of the part can be improved, and the hardness requirement of the gear is met.

Description

Technical Field

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

[0002] Laser quenching is a surface heat treatment technology that uses a laser beam to irradiate the surface of a material, rapidly heating the temperature above the phase transformation point, causing the internal structure of the material to transform, and then relying on the self-cooling of the material through heat conduction to achieve quenching. After laser quenching, the surface hardness of the material is significantly improved, greatly increasing the wear resistance and fatigue resistance of the material. Compared with traditional quenching methods, laser quenching produces a smaller heat-affected zone and minimal deformation of the material, making it suitable for processing parts with high precision requirements. Laser quenching is fast, reducing production costs.

[0003] Conventional laser quenching is to apply an absorptive coating to the quenching area, rapidly heating by absorbing laser energy, and relying on self-cooling for quenching. For complex-structured parts such as gears, on the one hand, the operation of applying the absorptive coating is difficult, the coating configuration is complex, it is prone to solidification after long-term placement, and manual coating cannot ensure a uniform and dense coating, affecting the quenching effect. On the other hand, relying on the self-cooling of the part cannot meet the requirements of the critical cooling rate for quenching. Ordinary absorptive coatings have no waterproof performance, and when water-cooling spraying is used on the quenching area, the absorptive coating will be washed away, affecting the quenching effect. At the same time, for the 17CrNiMo6 material used to manufacture gears, its characteristics determine that the surface hardness of the part after conventional laser quenching is generally 42HRC, which cannot meet the requirements of high quenching hardness. Summary of the Invention

[0004] The purpose of the present invention is to provide a laser quenching heat treatment method, enabling the gear to meet the requirements of high quenching hardness and the critical cooling rate for quenching.

[0005] To achieve the above purpose, the present invention provides a laser quenching heat treatment method, including the following steps:

[0006] S1: Normal temperature phosphating. The gear is surface-treated, then immersed in a phosphating tank filled with a phosphating agent for phosphating, and then completed the normal temperature phosphating of the gear after alkali washing, water washing, and drying.

[0007] S2: Dew hydrogen tempering. Remove the oil stains and rust on the tooth part and inner hole of the gear after normal temperature phosphating, and perform dew hydrogen treatment on the gear under the first preset condition.

[0008] S3: Laser quenching. Confirm the laser quenching parameters, and along the circumferential direction of the gear, laser quench each tooth of the gear at an interval of at least one tooth. Among them, the target tooth surface of the tooth is used as the quenching surface, and the opposite tooth surface is used as the cooling surface. While laser quenching is performed on the quenching surface, a cooling medium flows through the cooling surface for auxiliary cooling.

[0009] S4: Low-temperature tempering, perform low-temperature tempering on the gear under the second preset condition to complete the processing.

[0010] After surface treatment of the gear, the surface performance of the gear can be improved. Then, perform normal-temperature phosphating on the gear. The phosphating effect of the gear can be significantly improved through surface treatment. The phosphating time in the phosphating tank should be ≥2h. When performing alkali washing in the neutralizing tank, the time should be 5 - 10min. Drying is carried out using compressed air equipment. Compared with high-temperature phosphating, normal-temperature phosphating greatly saves energy consumption, does not require a professional equipment tank, and reduces production costs. Since high-temperature heating is not required, pollutant emissions during the production process are reduced, making it more environmentally friendly. It does not require complex heating equipment and temperature control devices, is easy to operate and manage, and is not restricted by the site and equipment. The normal-temperature phosphating reaction speed is fast, the processing time is relatively short, and the production efficiency is improved. For the phosphated gear, laser quenching can solve the problem of uneven and non-dense coating of light-absorbing materials on complex parts. On the other hand, during quenching, use a cooling medium to flow through the cooling surface for auxiliary cooling to solve the problem of low quenching hardness. During the quenching process, use the method of spacing at least one tooth to reduce thermal stress concentration, accurately control the heating trajectory and cooling rate of each tooth surface, so as to obtain a more consistent metallographic structure and optimize the cooling efficiency.

[0011] Among them, in the step S1, the surface treatment includes degreasing the gear with a cleaner in sequence, pickling the gear in a pickling tank with an acid solution, and finally washing the gear with water.

[0012] During the surface treatment process of the gear, each process is carried out at normal temperature. In the pickling process, the time should be ≥5min until there is no rust on the gear surface, and the water washing time is 5 - 10min.

[0013] Among them, the first preset condition is to heat to 170 ± 20°C, hold for 2 - 12 hours, and then air-cool after taking out of the furnace.

[0014] Because the diffusion rate of hydrogen in the metal is relatively slow. The dehydrogenation process is actually a process in which hydrogen atoms diffuse from the inside of the metal to the surface and then escape from the surface. The holding time is to allow hydrogen atoms to have enough time to complete the diffusion from the inside to the surface.

[0015] Among them, in the step S3, confirming the laser quenching parameters specifically includes the following steps:

[0016] S11: After processing the tooth profile specimen according to steps S1 - S2, perform laser trial quenching on the tooth profile specimen. After the hardness of the tooth profile specimen is qualified for inspection, use this laser parameter as the initial quenching parameter;

[0017] S12: Pre-quench the gear to be processed with the initial quenching parameters. After at least two teeth are pre-quenched, if there are no cracks detected by color penetrant inspection, confirm the initial quenching parameters as the laser quenching parameters;

[0018] S13: If cracks are detected by color penetrant inspection, the quenching quality of the specimen is unqualified. Repeat steps S11 - S12 and adjust the initial quenching parameters until the quenching quality of the specimen is qualified to determine the laser quenching parameters.

[0019] Before laser quenching the gear, first complete the normal temperature phosphating and dehydrogenation tempering treatments on the tooth profile specimen according to steps S1 - S2. Subsequently, conduct laser trial quenching on the tooth profile specimen. After the hardness of the tooth profile specimen is qualified, confirm the initial quenching parameters that meet the hardness requirements. Use the initial quenching parameters to pre-quench the gear. If the color inspection is qualified, use the initial quenching parameters as the laser quenching parameters to continue the overall quenching of each tooth of the gear.

[0020] Among them, the laser quenching parameters are: voltage 280 - 300V, current 6 - 6.5A, scanning speed 150 - 250mm / min, and spot size 10 - 30mm.

[0021] Among them, the spot formed by the laser scans along the tooth width direction on the target tooth surface as the quenching direction. The flow direction of the cooling medium is consistent with the quenching direction of the laser quenching, and the flow rate of the cooling medium is less than or equal to the laser scanning speed.

[0022] The cooling medium can be selected from water or machining cutting coolant. The flow rate of the cooling medium being lower than the laser scanning speed can improve the overall hardness of the gear. When the flow rate of the cooling medium is low, the heat exchange between the gear and the cooling medium is relatively slow, and the cooling speed of the gear also slows down. According to the supercooled austenite transformation theory, a slow cooling speed allows sufficient time for the supercooled austenite to undergo diffusion-type transformation to form structures such as pearlite or bainite, which have relatively low hardness. Increasing the flow rate of the cooling medium accelerates the heat transfer between the part surface and the cooling medium, and significantly increases the cooling speed. When the cooling speed exceeds the critical cooling speed of the steel, the supercooled austenite will rapidly transform into martensite structure, and martensite has high hardness, thus significantly increasing the overall hardness of the part.

[0023] Among them, the second preset condition is that the tempering time interval ≤ 4h, hold for 6h at a temperature of 170 ± 20°C, and air cool after furnace discharging.

[0024] Perform low-temperature tempering under the second preset condition to significantly improve the anti-fatigue property, dimensional stability, and service reliability of the gear while maintaining high hardness after laser quenching.

[0025] Among them, each liter of the phosphating agent comprises the following raw materials: 50 - 80 g of manganese phosphate, 80 - 100 g of zinc nitrate, 0.2 - 1 g of sodium nitrite, 0.2 - 0.5 ml of hydrogen peroxide, and the balance is water.

[0026] A laser quenching heat treatment method of the present invention replaces painting an absorbent material with normal temperature phosphating treatment on the gear surface, and performs auxiliary cooling while performing laser quenching. The heat dissipation capacity of the cooling medium is used to meet the requirements of the critical cooling rate for quenching, avoiding the problem of insufficient heat dissipation efficiency of the gear by itself. At the same time, while performing laser quenching on the quenching surface, auxiliary cooling is performed on the opposite surface, which can also improve the surface hardness of the part, thereby meeting the hardness requirements of the gear. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0028] Figure 1 It is a schematic diagram of the synchronous process of laser quenching and cooling of a laser quenching heat treatment method of the present invention.

[0029] 1 - quenching surface, 2 - cooling surface. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] The following details the embodiments of the present invention. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention, but should not be construed as a limitation of the present invention.

[0031] The present invention provides a laser quenching heat treatment method, which comprises the following steps:

[0032] S1: Normal temperature phosphating. The gear is surface - treated, and then the gear is immersed in a phosphating tank filled with a phosphating agent for phosphating. Subsequently, after alkali washing, water washing and drying, the normal temperature phosphating of the gear is completed;

[0033] S2: Hydrogen - removal tempering. Remove the oil stain and rust on the tooth part and inner hole of the gear after normal temperature phosphating, and perform hydrogen - removal treatment on the gear under the first preset condition;

[0034] S3: Laser quenching. Confirm the laser quenching parameters. Along the circumferential direction of the gear, laser quench each tooth of the gear at intervals of at least one tooth. Among them, the target tooth surface of the tooth is used as the quenching surface, and the opposite tooth surface is used as the cooling surface. While laser quenching is performed on the quenching surface, the cooling medium flows through the cooling surface for auxiliary cooling;

[0035] S4: Low-temperature tempering. Perform low-temperature tempering on the gear under the second preset condition to complete the processing.

[0036] Further, in the step S1, the surface treatment includes degreasing the gear with a cleaner in sequence, pickling the gear in a pickling tank with acid solution, and finally washing the gear with water.

[0037] Further, the first preset condition is to heat to 170 ± 20 °C, hold for 2 - 12 hours, and air cool after taking out of the furnace.

[0038] Further, the confirmation of the laser quenching parameters in the step S3 specifically includes the following steps:

[0039] S11: After machining the tooth profile specimen according to steps S1 - S2, perform laser trial quenching on the tooth profile specimen. After the hardness of the tooth profile specimen is qualified for inspection, use this laser parameter as the initial quenching parameter;

[0040] S12: Pre-quench the gear to be processed with the initial quenching parameter. After at least 2 teeth are pre-quenched, if there is no crack in the dye penetrant inspection, confirm the initial quenching parameter as the laser quenching parameter;

[0041] S13: If there is a crack in the dye penetrant inspection and the quenching quality of the specimen is unqualified, repeat steps S11 - S12 and adjust the initial quenching parameter until the quenching quality of the specimen is qualified to determine the laser quenching parameter.

[0042] Further, the laser quenching parameters are voltage 280 - 300V, current 6 - 6.5A, scanning speed 150 - 250mm / min, and spot size 10 - 30mm.

[0043] Further, the spot formed by the laser scans along the tooth width direction on the target tooth surface as the quenching direction. The flowing direction of the cooling medium is the same as the quenching direction of the laser quenching, and the flow rate of the cooling medium is less than or equal to the laser scanning speed.

[0044] Further, the second preset condition is that the tempering time interval ≤ 4h, hold for 6h under the temperature condition of 170 ± 20 °C, and air cool after taking out of the furnace.

[0045] Further, each liter of the phosphating agent includes the following raw materials: 50 - 80g of Marcusson's salt, 80 - 100g of zinc nitrate, 0.2 - 1g of sodium nitrite, and 0.2 - 0.5ml of hydrogen peroxide.

[0046] The present invention mainly includes normal-temperature phosphating treatment and laser quenching process. Among them, normal-temperature phosphating is a pre-treatment process before laser quenching, replacing the brushing of light-absorbing coatings. The complete laser quenching process flow is: normal-temperature phosphating treatment, dehydrogenation tempering treatment, laser quenching, water-cooled auxiliary cooling, coloring flaw detection, and tempering treatment.

[0047] The process flow of the normal-temperature phosphating treatment process is: degreasing, pickling, water washing, phosphating, alkali washing, water washing, drying, and inspection.

[0048] Serial Number Process Name Equipment Temperature (°C) Time (min) 1 Degreasing Cleaning Agent Room Temperature 2 Pickling Pickling Tank Room Temperature ≥5 min until no rusting 3 Water Washing Water Tank Room Temperature 5-10 4 Phosphating Phosphating Tank Room Temperature ≥2h 5 Alkaline Washing Neutralization Tank Room Temperature 5-10 6 Water Washing Water Tank Room Temperature 5-10 7 Drying Compressed Air Room Temperature 10-30 8 Inspection / Room Temperature

[0049] In the present invention, the phosphating agent ratio is simple and easy to operate, only need to add according to the ratio each time. Compared with high-temperature phosphating, normal-temperature phosphating treatment greatly saves energy consumption, does not require a professional equipment tank, and reduces production costs. Since high-temperature heating is not required, pollutant emissions during the production process are reduced, which is more environmentally friendly. It does not require complex heating equipment and temperature control devices, is easy to operate and manage, and is not restricted by the site and equipment. The normal-temperature phosphating reaction speed is fast, the treatment time is relatively short, and the production efficiency is improved.

[0050] Dehydrogenation tempering treatment

[0051] After phosphating, the parts are cleaned, and the oil and rust on the teeth and inner holes are removed; dehydrogenation treatment: 170 ± 20 °C × 2 - 12 h, air cooling after furnace discharging.

[0052] Laser quenching:

[0053] Main parameters of laser quenching:

[0054]

[0055] First, perform tooth profile sample quenching, and send the quenched tooth profile sample for inspection. Only when the tooth profile sample is qualified can the initial quenching parameters be determined, and the first-piece quenching be carried out according to the initial quenching parameters; when the quenching quality of the sample is unqualified, re-heat treatment is allowed, and new initial quenching parameters are determined again.

[0056] Please refer to Figure 1 , where A - A' is the quenching direction. When performing the first-piece quenching, the part is pre-quenched for 2 teeth first, and only when there is no crack detected by coloring flaw detection can the initial quenching parameters be used as the laser quenching parameters to continue the overall quenching.

[0057] Tempering process:

[0058] After laser quenching, low-temperature tempering is carried out, and the tempering time interval ≤ 4 h; tempering process: 170 ± 20 °C × 6 h, air cooling after furnace discharging.

[0059] The specific embodiments are as follows:

[0060] Taking a gear made of 17CrNiMo6 with a module of 4 as a specimen, the required hardened layer depth is 0.8 - 1.4 mm, the required surface hardness is 44 - 55 HRC, and there should be no cracks after surface coloring flaw detection by laser quenching.

[0061] Four specimens, numbered 1# - 4# respectively, dehydrogenation tempering temperature 170°C * 12 h, laser quenching parameters: voltage 280 V, spot size 10 (mm), focal length 240 (mm) remain unchanged; tempering process: 170°C × 6 h / air cooling after furnace discharge remain unchanged.

[0062] Specimen 1#: Current 6.0 A, scanning speed 180 (mm / min), apply an absorbing coating on the tooth part before laser quenching;

[0063] Specimen 2#: Current 6.0 A, scanning speed 180 (mm / min), replace applying the absorbing coating with phosphating treatment on the tooth part before laser quenching;

[0064] Specimen 3#: Current 6.0 A, scanning speed 180 (mm / min), replace applying the absorbing coating with phosphating treatment on the tooth part before laser quenching, and use water cooling as an auxiliary cooling;

[0065] Specimen 4#: Current 6.5 A, scanning speed 250 (mm / min), replace applying the absorbing coating with phosphating treatment on the tooth part before laser quenching, and use water cooling as an auxiliary cooling;

[0066] The results are as follows:

[0067]

[0068] According to the test results, it can be seen that using phosphating + water cooling as an auxiliary cooling can greatly improve the surface hardness of the material, and the hardness and layer depth corresponding to the laser quenching parameters of Specimen 3# are the best when the surface of the part does not melt after quenching.

[0069] In the present invention, phosphating treatment at room temperature is used on the gear surface instead of applying an absorbing material; the conventional method is to apply an absorbing coating on the quenching part of the gear and rely on the gear's own heat dissipation. Ordinary absorbing coatings have no waterproof performance, and when water cooling spray is used on the quenching part, the absorbing coating will be washed away, affecting the quenching effect. Water cooling is used as an auxiliary cooling during laser quenching; relying on the gear's own heat dissipation cannot meet the requirements of the critical cooling rate for quenching; through the auxiliary cooling of quenching coolant, the surface hardness of the part is improved. Dehydrogenation tempering treatment is carried out after phosphating; to prevent hydrogen atoms from penetrating into the interior of the metal material during phosphating, resulting in hydrogen embrittlement of the part, reducing the mechanical properties of the material, and affecting safety and service life.

[0070] The above-disclosed is only a preferred embodiment of the present invention. Of course, it cannot be used to limit the scope of the rights of the present invention. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the invention.

Claims

1. A laser quenching heat treatment method, characterized in that: The steps include: S1: Phosphating at room temperature, the gear surface is treated, and then the gear is immersed in a phosphating tank filled with a phosphating agent for phosphating, and then the gear is phosphated at room temperature after alkali washing, water washing and drying; S2: dehydrogenation tempering, to remove oil stains and rust from the gear teeth and inner holes after phosphating at room temperature, and to dehydrogenate the gear under the first preset conditions; S3: laser quenching, confirming the laser quenching parameters, laser quenching each gear tooth of the gear along the circumferential direction of the gear with an interval of at least one gear tooth, wherein the target tooth surface of the gear tooth is used as the quenching surface, and the opposite tooth surface is used as the cooling surface. While the quenching surface is laser quenched, the cooling medium flows through the cooling surface for auxiliary cooling; S4: Low temperature tempering, the gear is subjected to low temperature tempering under the second preset condition to complete the processing.

2. The laser quenching heat treatment method according to claim 1, characterized in that: In the step S1, the surface treatment includes successively using a cleaning agent to degrease the gear, using an acid solution to pickle the gear in a pickling tank, and finally washing the gear with water.

3. The laser quenching heat treatment method according to claim 1, characterized in that: The first preset condition is to heat to 170±20°C, keep warm for 2 to 12 hours, and then air-cool out of the furnace.

4. The laser quenching heat treatment method according to claim 1, characterized in that: Determining the laser quenching parameters in step S3 specifically includes the following steps: S11: After the tooth profile sample is processed according to steps S1 to S2, the tooth profile sample is subjected to laser test quenching. After the tooth profile sample is tested and the hardness is qualified, the laser parameters are used as initial quenching parameters; S12: Pre-quench the gear to be processed with the initial quenching parameters. After at least two gear teeth have been pre-quenched, if there are no cracks in the color flaw detection, it is confirmed that the initial quenching parameters are laser quenching parameters; S13: If cracks are found in the color flaw detection, the sample quenching quality is unqualified, and steps S11 to S12 are repeated and the initial quenching parameters are adjusted until the sample quenching quality is qualified to determine the laser quenching parameters.

5. The laser quenching heat treatment method according to claim 4, characterized in that: The laser quenching parameters are: voltage 280-300V, current 6-6.5A, scanning speed 150-250mm / min, and spot size 10-30mm.

6. The laser quenching heat treatment method according to any one of claims 4 to 5, characterized in that: The light spot formed by the laser is scanned on the target tooth surface along the tooth width direction as the quenching direction, the flow direction of the cooling medium is consistent with the quenching direction of the laser quenching, and the flow rate of the cooling medium is less than or equal to the laser scanning speed.

7. The laser quenching heat treatment method according to claim 1, characterized in that: The second preset condition is that the tempering time interval is ≤4h, the temperature is kept at 170±20℃ for 6h, and then air-cooled after being taken out of the furnace.

8. The laser quenching heat treatment method according to claim 1, characterized in that: Each liter of the phosphating agent includes the following raw materials: 50-80g of Marif salt, 80-100g of zinc nitrate, 0.2-1g of sodium nitrite, 0.2-0.5ml of hydrogen peroxide, and the balance of water.

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