JB/T 7516-1994 Gear gas carburizing heat treatment process and its quality control
Some standard content:
Mechanical Industry Standard of the People's Republic of China
JB/T7516-94
Gas carburizing heat treatment process for gears
and its quality control
Published on October 25, 1994
Ministry of Machinery Industry of the People's Republic of China
Implementation on October 1, 1995
Mechanical Industry Standard of the People's Republic of China
Gas carburizing heat treatment process for gears
and its quality control
1 Subject content and scope of application
JB/T7516—94
This standard specifies the material selection, heat treatment equipment, process and quality control of gas carburizing heat treatment gears. This standard applies to gas carburizing, quenching and tempering treatment of steel gears. 2 Reference standards
GB1818
GB1979
GB3077
GB3480
GB4340
GB5216
GB6394
GB8539
GB9450
GB9452
GB10561
GB/T230
GB/T13299
JB/T6077
ZBG51 108
ZBJ36012
ZB/TJ17004
ZBT04 001
3 Gear materials
3.1 Material selection principles
Method for testing Rockwell hardness of metal surface
Rating chart of macrostructure defects of structural steel
Technical conditions for alloy structural steel
Method for calculating the load-bearing capacity of involute circular gearsMethod for testing Vickers hardness of metals
Technical conditions for structural steel with guaranteed permeability
Method for determining average grain size of metals
General provisions for quality inspection of gear materials and heat treatmentDetermination and verification of carburization rate and effective hardening layer depth of steel partsHeat treatment Method for determining effective heating zone of furnace
Microscopic evaluation method for non-metallic inclusions in steel
Method for testing Rockwell hardness of metal
Method for evaluating microstructure of steel
Gear quenching and tempering process and quality control
Technical conditions for anti-seepage coating
Heat treatment of steel parts in endothermic atmosphere
Gear flame and induction quenching process and quality controlMetallographic inspection of carburized gears for automobiles
3.1.1 The selected gear steel can meet the design requirements of product performance after various mechanical processing and gas carburizing heat treatment. 3.1.2 The material should be essentially fine-grained steel.
3.1.3 For gears with high reliability requirements and gears produced in large quantities, structural steel with guaranteed transparency should be used. 3.1.4 The hot processing performance and cutting processing performance of the material should meet the production requirements. 3.1.5 Consider the economy and supply situation.
3.2 Recommended steel for carburized gears
Select according to the use conditions and steel permeability. Unless otherwise specified, the recommended steels are shown in Table 1. Approved by the Ministry of Machinery Industry on October 25, 1994
Implementation on October 1, 1995
20CrMo
20CrMnTi
20CrMnMo
20MnVB
12CrNi3
15CrNi3
20CrNi2Mo
20Cr2Ni4A
18Cr2Ni4WA
3.3 Material metallurgical quality
JB/T 7516-94
Machine tool gears, light load gears
Automobiles, squeegees, machine tools, engineering machinery, construction equipment, locomotives and industrial gears for chemical, metallurgical, engineering machinery, locomotives, power stations, ships, aviation, short-distance gears and heavy load gears with large impact loads
3.3.1 The chemical composition, mechanical properties, general porosity, central porosity, segregation and surface quality of the materials shall comply with the provisions of GB3077 and GB1979. For materials not listed in GB3077, their technical conditions and dimensional accuracy of the materials shall be controlled by agreement between the two parties. The gear manufacturer shall have a steel quality guarantee and shall conduct random inspections and verifications.
3.3.2 The austenite grain size of the material shall be above grade 5, and there shall be no mixed product phenomenon. It shall be inspected according to GB6394. 3.3.3 The lustrous band of the material shall be within the range specified in GB5216. When there are special requirements, the range of the degree of separation at a certain distance from the end of the end specimen shall be determined by negotiation between the user and the steel mill.
3.3.4 Non-metallic inclusions shall be inspected according to GB10561, and oxides and colonies shall not be greater than level 3. For gears with high reliability requirements, the purity of the material shall be guaranteed, and steel smelted by vacuum smelting, electroslag remelting or vacuum remelting shall be used. The oxygen content of the material shall be controlled below 20ppm, the hydrogen content shall be controlled below 5ppm, and the sulfur content shall be less than 0.015%. When there are special requirements, it shall be stipulated in the agreement between the two parties. 3.3.5 The banded structure of the material shall be inspected according to GB/T13299, and generally shall not be greater than level 3. 3.4 Forging quality
3.4.1 The humidity of the initial and final forging of gear forgings shall be strictly controlled. 3.4.2 During forging, the entire cross section of the bad material shall be uniformly deformed, and the forging ratio shall be in accordance with GB8539. If closed forging is adopted, the streamlines shall be basically distributed radially. For large shaft gears, follow the relevant industry regulations. 3.4.3 The forged parts shall not have cracks, folds, overheating and other internal defects, nor shall they have surface defects that cannot be removed by the final processing. 4 Technical requirements for heat treatment equipment
4.1 Carburizing equipment
4.1.1 Carburizing can adopt continuous gas carburizing furnace, sealed box furnace, pit gas carburizing furnace, etc. 4.1.2 Continuous gas carburizing furnace and sealed box furnace shall be able to maintain the required time at the set temperature in each stage of heating, heat preservation and cooling.
4.1.3 The temperature in the effective heating zone of continuous gas carburizing furnace, sealed box furnace and pit gas carburizing furnace shall be controlled within the preset value of ±10C. The effective heating zone shall be tested in accordance with the provisions of GB9452. 4.1.4 The carburizing heating equipment shall have a reasonable structure and be equipped with a device to make the gas and oxygen in the furnace flow evenly. The carburizing heating chamber shall have good sealing performance, and the carburizing raw material supply system shall be safe and reliable. 4.2 Port carburizing post-fire heating equipment
4.2.1 The temperature in the effective heating zone of heating equipment such as converters, sealed box furnaces and pit-type gas carburizing furnaces shall be controlled within ±10°C of the preset value.
JB/T7516-94
4.2.2 Induction heating equipment shall comply with the requirements of ZB/TJ17004. 4.2.3 When heating in a salt bath furnace, the salt bath shall not have corrosion, decarburization and other harmful effects on the gears. 4.3 Quenching cooling equipment and cooling medium
4.3.1 The rate of quenching cooling equipment shall have a controllable heating, cooling circulation system and stirring device. 4.3.2 The quenching cooling equipment shall be equipped with a fire-proof smoke exhaust device. 4.3.3 The cooling medium for heat treatment shall have the cooling capacity required for gear heat treatment and shall not be prone to aging. Its technical requirements shall comply with relevant standards. A management system for regular analysis and adjustment shall be established at the production site to ensure the heat treatment quality. 4.4 Cleaning equipment
The cleaning equipment shall have functions such as soaking, spraying, and oil-water separation. The cleaning liquid may be alkaline water with a temperature of 80~90℃, or a special cleaning agent.
4.5 Tempering equipment
4.5.1 Tempering may be carried out in a continuous or periodic furnace, and the temperature of the effective heating zone in the furnace shall be controlled within ±10℃ of the predetermined value. 4.5.2 The tempering equipment shall be equipped with an exhaust device. 4.6 Temperature measurement and control equipment
4.6.1 The carburizing heat treatment furnace and tempering furnace shall be equipped with temperature measurement and control, automatic recording and alarm devices, and the heat treatment cooling equipment shall be equipped with a temperature measurement and control device.
4.6.2 Temperature measuring instruments and thermocouples should be calibrated regularly and should comply with the provisions of GB9452. 4.7 Equipment for measuring and controlling the atmosphere in the furnace
The hydrogen in the furnace can be measured and controlled by any method such as CO, infrared instrument, oxygen probe, resistance wire, dew point meter, carbon plate and gas analysis. The relevant equipment should be operated according to their respective instructions. The carbon potential control accuracy should be within ±0.05%. 5 Preparatory treatment before carburizing
5.1 Normalizing
5.1.1 The gear forgings after forging should be normalized. The normalizing temperature is generally 890~950℃. The holding time depends on the effective size of the forgings, the loading conditions and the type of furnace. The forgings should not be stacked for cooling after leaving the furnace. The surface should be spread out for air cooling or spray cooling. 5.1.2 For some alloy structural steels, when the normalizing and tempering process is used, the normalizing temperature is slightly higher than the carburizing temperature, and the tempering temperature is 600~680℃c.bzxZ.net
5.1.3 According to the characteristics of the steel and the specific conditions of silver production, the forging residual heat isothermal annealing or forging residual heat normalizing process can be used. 5.1.4 The hardness after normalizing or normalizing plus tempering should comply with the provisions of the process documents. The test parts can refer to JB/T6077; the hardness should be uniform, and the hardness difference of a single piece is ≤25HBS. The hardness difference of the same batch is ≤40HBS. 5.2 Isothermal annealing
For high-precision gears, in order to increase the uniformity of the pretreatment organization, an isothermal annealing process can be used. 5.3 Stress relief treatment
For gears with high requirements and gears with a module greater than 14mm, stress relief treatment or high-temperature tempering at 600~650℃ should be carried out after rough machining of the tooth shape.
6 Preparations before carburizing treatment
6.1 Flaw detection
For gears with high reliability requirements, ultrasonic or magnetic particle flaw detection should be carried out. Its technical indicators can be in accordance with GB8539 or the regulations of various industries. 6.2 Cleaning of the surface
The gears to be carburized and the lifting fixtures should be cleaned or placed in a furnace at 450-550℃ for gasification degreasing to remove surface oil, iron filings and other harmful debris.
6.3 Anti-seepage measures
JB/T 7516-94
For the parts of the gear that do not need to be carburized, the surface can be coated with anti-seepage paint. The anti-seepage paint should adhere firmly and should be easy to fall off after carburizing treatment, and it should have no harmful effect on the surface quality of the gear. Its technical indicators are in accordance with ZBG51108. Anti-seepage measures such as copper plating or reserved processing volume can also be used.
6.4 Lifting fixture
The lifting fixture should be designed according to the type of processing equipment and the structural characteristics of the gear. 6.4.1 The structure and size of the fixture should ensure that it has sufficient rigidity under high temperature conditions. The lifting fixture should not have a large distortion effect on the gear after repeated use, and must be replaced in time if necessary. 6.4.2 The fixture should ensure that all parts of the gear are heated and cooled evenly during the treatment process, that the carburizing gas and hydrogen flow evenly, and that the production operation is safe and convenient.
6.5 Furnace specimens
The material of the furnace specimens should be the same as that of the gear being treated, and its shape and size should be representative of the actual treatment of the gear. According to the requirements, any of the following forms can be adopted.
6.5.1 The profile specimen or tooth profile specimen should contain at least 3 gear teeth. The lower surface thickness below the tooth root is equal to half of the root round tooth thickness or is selected according to the gear module, and should generally be greater than 10mm: the tooth width is 2 to 3 times the root tooth thickness, as shown in Figure 1. 3
Tooth profile specimens
6.5.2 See Table 2 for the inspection specimens of the carbon layer.
See Table 3 for the inspection specimens of the core hardness and core structure. Die
>10~18
Due to the size of the rod specimen
diameter×length
16×35
25×50
diameter=1/2tooth thickness at tooth height, length-(2~3)×diameterTable 3
Size of round rod specimen
Diameter×length
32×76
56×130
76×180
90×205
When using a disc specimen, its thickness should be greater than 70% of the diameter of the corresponding round wrest specimen in Table 2 and Table 3, and the diameter should be greater than 3JB/T 7516-94
6.5.5 The diameter of the round rod specimen used for push gears can be determined by referring to Table 2 and Table 3 according to the module value in the middle of the tooth width. 6.5.6 The size of the sample for the carbon stripping diagram of the furnace is: d×l.25mm×100mm, 6.5.7 The number of samples for the furnace is determined according to the type of equipment and the furnace loading situation. The samples should be placed in the position that can represent the quality of the gear heat treatment. The mid-inspection samples of the periodic carbon furnace shall be implemented according to the regulations of each enterprise. 6.6 Selection of raw materials for carburizing
Select according to the type of heat treatment equipment, the characteristics of the carburizing raw materials and the supply situation. 6.6.1 The drip-type gas carburizing furnace can use any of special carburizing oil, kerosene, acetone, isopropanol, ethyl acetate, toluene, etc. as the carburizing agent, and methanol as the diluent.
6.6.2 During controlled atmosphere carburizing, the endothermic atmosphere raw gas is natural gas and liquefied petroleum gas, and its composition shall comply with the provisions of ZBJ36012. 6.6.3 The carburizing raw material should have a stable composition and low content of harmful impurities, and the vegetable content should be below 0.02%. It can be used after inspection and meeting the requirements. 6.7 Newly purchased equipment and new fixtures that have not been used for carburizing for a long time should be pre-carburized. 7 Process Control
7.1 Carburizing Process Specifications
7.1.1 Furnace Loading
7.1.1.1 Place the prepared gears and furnace samples on the lifting fixture. For thin-walled gears with medium and small modulus, a hanging or pad-type fixture should be used, and the gears with spline holes should be supported reasonably. 7.1.1.2 When the gears are installed on the fixture, there should be no overlap between the gear teeth, and sufficient space should be left between the working surfaces of the gear teeth. 7.1.1.3 The intermediate inspection sample of the parallel gas carburizing furnace can be placed in the sample hole after the gear is loaded into the furnace or after the exhaust is completed. 7.1.2 Exhaust
7.1.2.1 After the gears are loaded into the furnace, a large amount of methanol is dripped in when the temperature reaches above 750℃, and the carburizing agent is introduced after reaching 850℃. 7.1.2.2 When a pit-type gas carburizing furnace is used to treat gears that are prone to time change and have high reliability requirements, and when the furnace load is large, a segmented uniform temperature heating method should be adopted, and nitrogen should be introduced at the same time to start exhausting. Methanol is dripped in after the furnace temperature rises to 750℃. 7.1.2.3 When the furnace temperature reaches the set carburizing temperature and the carbon potential of the furnace gas reaches 0.8%, the exhaust is completed and the strong involvement stage is entered. 7.1.3 Carburizing temperature and time
The carburizing temperature is generally 890~930C. The carburizing time is determined by the characteristics of the steel, the depth requirements of the carburizing layer, the carburizing temperature, the characteristics of the carburizing raw materials, the furnace type and other conditions.
7.1.4 Diffusion
For gears that require a gentle carburizing layer gradient, diffusion should be carried out after the intensive carburizing. However, when the effective hardened layer depth is required to be less than 1mm, diffusion is not required.
7.1.4.1 When using a pit-type gas carburizing furnace, take out the intermediate inspection sample at the end of the intensive carburizing stage, check the carburizing layer depth, and transfer to the diffusion stage in a timely manner according to the technical requirements.
7.1.4.2 When transferring from the intensive carburizing stage to the diffusion stage, the temperature generally remains unchanged, and the proportion and amount of carburizing raw materials should be reasonably adjusted. If necessary, a gas that can quickly reduce the carbon potential in the furnace, such as nitrogen, air, etc., can be introduced. 7.1.4.3 When using a pit-type gas carburizing furnace, check the intermediate inspection sample at the end of the diffusion stage, and determine the actual diffusion time based on the required net layer depth and surface carbon content.
7.1.5 Principles of carbon potential control
7.1.5.1 Carbon potential control during the intensive carburizing period In general, under the premise that no carbon black appears and the carbide level on the workpiece surface is allowed, the carbon potential in the furnace during the intensive carburizing period should be the highest to obtain the fastest carburizing rate. 7.1.5.2 Carbon potential control during the diffusion period The carbon potential in the furnace is generally determined by the carbon concentration on the surface of the workpiece that meets the design requirements. 7.1.5.3 When there is microcomputer control, it should be able to automatically measure and control according to the design requirements of the carbon concentration distribution of the gear carburizing layer. 7.1.6 Cooling treatment
Different cooling treatments are used after carburizing according to the material and process requirements. Gears that need to be quenched directly can be cooled to 8405~860℃ in the carburizing furnace and kept warm for 0.5~1h before being put into the quenching medium for cooling; gears that need to be reheated can be cooled to 820~880℃ in the carburizing furnace and kept warm for a proper time before being moved to the cooling device for cooling, and anti-oxidation and decarburization measures should be taken. Gears can be air-cooled only when they are cooled to below 350℃: air cooling can be used when there is a large processing allowance on the tooth surface; materials with high nickel content can be cooled to 150~200℃ and then high-temperature tempering. 7.2 Quenching process specification
7.2.1 Direct quenching
After gas carburizing, the gear is cooled to 840~860℃ in the carburizing furnace and kept warm for 0.5~1h, and then put into the quenching medium for cooling. The gears treated by the pit gas carburizing furnace should be put into the quenching medium as soon as possible after leaving the furnace to avoid the formation of heterogeneous band structure on the surface. 7.2.2 Reheating quenching
For gears that need to be machined after carburizing or need to be precooled after carburizing due to the characteristics of steel materials, and need to undergo 1~2 high-temperature tempering or spheroidizing annealing, reheating quenching should be carried out.
7.2.2.1 One-time heating quenching The general heating temperature is 820~860C. For gears carburized in a continuous gas carburizing furnace or a sealed box furnace, they are cooled to 600℃ in the cooling device to refine the grains, and then reheated to the quenching temperature. 7.2.2.2 Secondary annealing The first annealing temperature is 860~880℃, and then annealing is performed after heat preservation. After cooling to room temperature, the second annealing is performed. The second heating temperature is 780~800℃, and the cooling method is the same as before. 7.3 Cleaning
Gears and lifting fixtures can be cleaned only after they have been annealed and cooled to an appropriate temperature. 7.4 Tempering process specifications
7.4.1 After cleaning, the gears should be tempered at low temperature in time, and the interval should not exceed 4 hours. The tempering temperature should be determined according to the hardness and steel type required by the drawing technology, which is generally 160-220℃ and the tempering time is 24 hours. For large gears with high nickel-chromium steel, they should be fully tempered, generally for 10-20 hours. 7.4.2 For high-altitude gears, stress relief tempering should be carried out after grinding, the temperature should be 140-160℃, and the insulation time should be not less than 2 hours. 7.4.3 For steels with high alloy element content, one or two high-temperature tempering should be carried out before reheating and quenching after carburizing and slow cooling, and the tempering temperature should be 600-700C, and the time for each time should be 2-6 hours. 7.5 Cold treatment
Generally, gears are not cold treated. For gears with high requirements for accuracy and reliability, cold treatment is only carried out when there is too much residual austenite in the carburized surface structure and the final hardness is required to be above 58HRC. 7.5.1 The gears should be subjected to low-temperature tempering before and after cold treatment to avoid micro cracks. 7.5.2 The cold treatment temperature is 70-80℃ and the time is 2h. The time for large gears should be appropriately extended. 7.5.3 After cold treatment, the gears should be allowed to return to room temperature and then subjected to low-temperature tempering, but the interval should not exceed 4h. 7.6 Sandblasting or shot peening
After heat treatment, the gears should be sandblasted or shot peened as required. 8 Quality control and inspection methods
8.1: Furnace sample inspection
8.1.1 Surface hardness
8.1.1.1 Select Rockwell, surface Rockwell and other hardness testers according to the effective hardened layer depth. The selection method is shown in Table 4 or according to the regulations of each industry, and the inspection is carried out according to the regulations of GB/T230 or GB1818. The hardness value shall meet the technical requirements of the drawing. Table 4
Effective hardened layer depth mm
>0. 3~0. 5
Hardness measurement category
Hardness range
When the drawing requires the measurement of surface hardness, use a Vickers hardness tester to measure at 0.05~0.10mm from the surface on the specimen surface. The measurement method is in accordance with GB4340. For gears that need to be ground after carburizing, the surface hardness should be measured from the specimen surface to the depth of the machining allowance on one side of the gear teeth.
8.1.1.3 For the uniformity requirements of surface hardness, see GB8539.8.1.2 Core hardness
The core hardness value is generally required to be 3045HRC, which can be selected by the designer according to the use conditions of the gear. 8.1.2.1 For the determination position of the hardness of the core of the toothed specimen, refer to GB8539. 8.1.2.2 When using a round bar specimen, cut a 10mm thick specimen in the middle of the length of the test bar and measure it at the center of the cross-section of the specimen. The relationship between the specimen size and the modulus shall comply with Table 3.
8.1.3 Effective hardened layer depth
8.1.3.1 For gears that need to be processed after carburizing and quenching, the carburizing process layer depth shall be the depth marked on the drawing plus the machining allowance on one side of the gear tooth.
8.1.3.2 The determination of the effective hardened layer depth shall be based on the hardness method. The determination position shall be based on the provisions of GB8539, and the determination method shall be based on the provisions of GB9450 and GB4340. It may also be based on the provisions of the service industry or the agreement between the manufacturer and the user. 8.1.3.3 When using the metallographic method and the fracture method to detect the depth of the carburized layer, the relationship with the effective hardened layer depth determined by the hardness method shall be found in advance to ensure that the finished gear meets the technical requirements of the drawing.
8.1.3.4 The recommended value of the effective hardened layer depth of carburized gears is shown in Appendix A (reference). 8.1.3.5 When the drawing requires the determination of the effective hardened layer depth of the tooth root, it should be measured inward on the normal section of the tooth profile sample. 8.1.3.6 If the effective hardened layer depth of the furnace sample does not meet the technical requirements, at least one more gear shall be sampled from the batch for dissection and measurement, and the measurement result shall prevail.
8.1.4 Carbon content of the surface layer
8.1.4.1 The carbon content of the surface layer is the average carbon content from the surface to a depth of 0.10mm. 8.1.4.2 If there are no special requirements, the carbon content of the surface layer is generally controlled within the range of 0.8% to 1.0%, and in principle shall not be lower than the eutectoid carbon content of the corresponding steel.
8.1.4.3 The carbon content of the surface layer can be determined by chemical analysis of the sample brake layer, or by metallographic determination or analysis by direct reading spectrometer. 8.1.4.4 When various carbon control technologies are used to control the carburizing process, the relationship between the surface carbon content and the carbon potential of various steel materials during carburizing should be found in advance.
8.1.4.5 When new products are trial-produced or process debugging is carried out, the surface carbon content should be inspected. In mass production, if there are no gas oxygen control measures during the carburizing process, the surface carbon content should be inspected regularly. 8.1.5 Surface structure
8.1.5.1 Retained austenite shall be evaluated according to the metallographic inspection level chart of each industry. General gears should be controlled below 30%, and high-precision gears should be controlled below 20%. For gears with machining allowances, the internal control standards for the assessment parts shall be specified. 8.1.5.2 Martensite shall be evaluated according to the metallographic inspection level chart of each industry. For toothed specimens, the severe field of view near the pitch circle shall be used as the basis for judgment.
8.1.5.3 Carbides shall be evaluated according to the metallographic inspection level chart of each industry. When using the ZBT04001 carbide rating chart, if the sample has no obvious carbides at 400 times, but the surface hardness and carbon content of the sample are qualified, and the surface structure is not in a hypoeutectoid state, it can be rated as level 1. 8.1.5.4 After the surface decarburized sample is lightly corroded by 4% nitric acid solution, it is placed under a microscope and magnified 400 times for observation. For tooth-shaped samples, focus on checking the root fillet. The depth of the decarburized layer should not exceed 0.02mm or be controlled according to the GB8539 classification. 8.1.5.5 After the surface non-martensitic sample is lightly corroded by 4% nitric acid alcohol solution, it is placed under a microscope and magnified 400 times for observation. For tooth-shaped samples, the pitch circle and the root fillet are tested and controlled according to the GB8539 classification. 8.1.6 Core structure
Inspect according to the regulations of each industry or the agreement between the manufacturer and the user. 8.1.7 Hardness drop to the surface, hardness drop to the core When the drawing requires the measurement of hardness drop to the surface and hardness drop to the core, refer to GB8539 or follow the regulations of each industry. 8.1.8 Impact performance of the core
JB/T7516-94
When the user has requirements, take the material from the round bar sample or the tooth sample with the furnace, process it into an impact sample, and carry out the impact test. 8.2 Gear heat treatment quality inspection
8.2.1 Appearance
After heat treatment, the surface of the gear shall not have defects such as oxide scale, bruises, sharpness, rust, etc. 8.2.2 Tooth surface hardness
8.2.2.1 The number of random inspections shall be specified according to the importance of the gear, batch and furnace type. 8.2.2.2 The measurement position shall be based on the tooth surface, and the tooth item or end face can also be measured, but the difference between its hardness and the tooth surface hardness shall be considered. The measuring points are required to be distributed on three gear teeth about 120° apart. Generally, there shall be no less than 2 points on each gear tooth, and the hardness value shall meet the technical requirements of the drawing. 8.2.2.3 The hardness tester shall be stable, reliable and reproducible. When a tooth surface hardness tester is used to test the tooth surface, the probe shall be placed vertically on the tooth surface; when a Rockwell hardness tester is used to test the tooth top, the tested part shall be polished with sandpaper, and the surface roughness shall meet the requirements of GB/T230, and it shall be placed steadily during measurement; when a chain cutter is used to check the hardness of the tooth top and tooth root, the file shall be a standard chain cutter, and when a Shore hardness tester or Leeb hardness tester D-type punch device is used for testing, the effective hardening layer depth of the gear must be greater than 0.8mm. 8.2.2.4 For gears that cannot be tested with a hardness tester, the measured value of the furnace sample shall generally prevail. 8.2.2.5 When the hardness does not meet the technical requirements, double sampling shall be conducted. If it still does not meet the requirements, it shall be repaired or scrapped according to the specific situation. 8.2.3 Effective hardened layer depth
8.2.3.1 When various carbon control technologies are used to control the carburizing process and the production quality is stable, the test results of the furnace samples can be used as the basis. The sampling inspection cycle can be determined according to the specific situation.
8.2.3.2 For mass-produced gears, when there are no control measures for the carburizing atmosphere, if the sample is qualified, one gear should be sampled and dissected and measured every week. The inspection method is the same as Article 8.1.3. 8.2.4 The surface structure, core hardness, and core structure are generally based on the test results of the furnace samples. The factory can determine the inspection items and inspection cycle of the dissected gears according to the specific situation. The inspection method is between Articles 8.1.5, 8.1.2, and 8.1.6. 8.2.5 Cracks
8.2.5.1 After heat treatment and grinding, gears with high reliability requirements should be inspected 100%, and general gears should be inspected randomly. Cracks are generally not allowed on the surface after grinding.
8.2.5.2 The inspection method for cracks can be any of the following. Such as magnetic particle inspection, ultrasonic inspection, fluorescent penetration and dye penetration inspection.
8.2.5.3 Inspection of microcracks after cold treatment Observe the furnace sample with a microscope at 400 times magnification. Within the rectangular range of 0.30mm×0.25mm, there shall be no more than 10 microcracks with a length greater than 1 grain. 8.2.6 Distortion
8.2.6.1 The distortion after heat treatment should be controlled within the range of relevant technical requirements. 8.2.6.2 During mass production, the sampling items and number of pieces shall comply with the technical requirements of the product drawings. 8.2.6.3 Gears produced in single pieces shall be regularly sampled. 9 Record content
Gear material, quantity, part number, furnace number; carburizing heat treatment process and process parameters: inspection items, parts and results;
Name or code of heat treatment operator and inspector; e.
Operation and inspection date.
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