The large gear ring is the outer working part of the welded heavy-duty gear. Due to the lack of internal support, the gear ring will have obvious dimensional and shape changes during the carburizing and quenching heat treatment, and the machining allowance of the carburized layer is small. Machining creates difficulties. The author makes the necessary analysis on the heat treatment distortion and preventive measures that appear in the production site.
Large gear ring structure and heat treatment technology requirements 111 gear ring structure and processing process The large gear ring has a tooth top outer circle size <2000~<2500mm, and the ring thickness is 240mm. The shape is basically symmetrical, and the quality is 4~5t. The transmission power is very large. The shifting is precise and the power transmission has a large impact phenomenon.
In order to prevent gear tooth root fracture, surface hardening lamination and tooth surface peeling, a deep carburizing of 510 to 515 mm is performed on the tooth surface to improve contact fatigue strength and bending fatigue strength.
Processing steps: 1 gear ring is generally forged with 20CrMnMo or 17CrNiMo6 steel ingot (3镦3 pull → punching → mandrel reaming) → normalization of the structure (normalizing tempering) → roughing → carburizing heat treatment.
2 Combine the gear ring with the ZG3102570 cast steel hub to form a large heavy-duty gear → stress relief annealing → weld flaw detection → finishing.
112 heat treatment characteristics (1) requires a long time tooth surface high temperature deep carburizing of the gear ring, high temperature tempering after air cooling, and then quenching and then tempering.
(2) The gear ring has a large heat capacity and a long heating and cooling time. The surface hardened layer can reach 15-20 mm (50 martensite and 50 non-martensitic) during quenching, and the central portion is not hardened. The heat treatment mainly controls the size of the top of the tooth and the distortion of the tooth surface to ensure the normal size and meshing accuracy of the tooth.
2 Distortion characteristics and analysis of large gear ring 211 The distortion characteristics of the large gear ring are compared with the dimensions of the two ring gears of the 20CrMnMo steel (the original size 2375mm, 2165mm and 2040mm) before and after quenching, each ring gear is 60°. Three dimensions were measured for the boundary line. It can be seen from the data that the heat treatment distortion is mainly caused by the large and small cone distortion of the carburizing process, and the outer ring length and the elliptical distortion of the ring in the quenching and tempering process.
Distortion analysis of 212 large gear ring and measures to prevent distortion (1) Taper: self-weight plus long-term high-temperature carburization causes creep, resulting in cone distortion after the carburizing of the gear ring.
(2) Degree of expansion: During the carburizing and air cooling stages, the heating and cooling rates are slow, and the front and back structures are roughly the same (the volume and shape changes caused by carburizing and residual stress are negligible). In addition to the taper deformation, the size of the gear ring is basically not changes happened. The outer ring grows mainly in the quenching process: 1 Although the hardened layer of the gear ring is limited, its surface area is very large, and the surface layer is free of smoke, which effectively protects the environment, improves the yield and production efficiency of the product, and reduces the worker's Labor intensity, saving energy.
The amount of metal converted to martensite is still large, and the volume expands after quenching. 2 During the quenching process, the area of ​​the outer and inner circles and the curvature of the circumference are different, and the directions of heat shrinkage and phase change expansion are opposite, and the radial force and tangential force of the outer ring of the ring gear are generated. 3 carburization reduces the Ms point of the tooth surface, and the austenite transformation of the outer layer to martensite is later than the inner surface. In the tempering process, the shrinkage caused by the transformation of the quenched martensite of the outer layer into the low-carbon martensite ε2 carbide cancels out the expansion caused by the retained austenite transformation, and no change in appearance is observed. As a result of the combination of the above factors, the top of the tooth will increase by 4 to 5 mm. The diameter of the gear ring and the thickness of the ring directly affect the expansion size. In actual production, for <2000~<2500mm gear ring, the thickness of the ring is generally set to 240mm. According to the empirical data, the expansion allowance of 4~5mm is reserved to ensure the accuracy.
(3) Ellipticity: uneven material, improper heating and cooling, resulting in uneven expansion and contraction during heat treatment, asymmetric distortion, forming an ellipse. Quenching takes the lower limit temperature and lowers the cooling rate below Ms to reduce the ellipticity.
It is best to use isothermal quenching of nitrate salt.
3 Gear ring production precautions and heat treatment process 311 Precautions (1) Whether the heating temperature is uniform or not directly affects the elliptical distortion and internal structure of the ring gear, ensuring uniform temperature throughout the ring gear on the inner ring of the furnace is particularly important, and requires thermocouples Temperature measurement should be accurate.
(2) To prevent warping of the ring gear due to unevenness, inclination, and the like. For quenching spreaders that have been severely deformed for a long period of time, the blocks should be leveled.
(3) When carburizing, a plurality of ring gears are often placed together, and the degree of distortion of the ring gear in the lower layer is much more serious than that of the upper ring gear. Therefore, it is necessary to stack the ring gears with light weight or high precision requirements in the upper layer.
(4) If long distance transfer is required from the quenching furnace to the oil tank, in order to prevent the temperature drop of the tooth part during the transfer process, it is necessary to pre-place the heat preservation cover during quenching and heating, remove the heat preservation cover before entering the liquid; or increase the furnace temperature before the furnace is discharged. At 20 ° C, keep warm for 10 min, to ensure the quenching temperature when entering the liquid.
(5) The quenching method has a great influence on the distortion, and it is sure to ensure vertical liquid inflow and maintain the uniformity of circumferential cooling.
(6) The inconsistent quenching cooling speed inside and outside the ring gear has a great influence on the distortion: the outer ring cooling is better than the inner ring with “x†type distortion; while the inner ring cooling is better than the outer ring with “O†type distortion. Therefore, the quenching tank should be large enough and the coolant circulation should be sufficient.
(7) Segregation by the low-temperature quenching component causes the low-carbon portion of the ferrite to be not completely dissolved in the austenite, and full forging can improve the uniformity of the composition.
(8) The expansion and contraction along the direction of the fiber structure and its cross-direction during the heat treatment process are very different, so the consistency of the fiber direction of the whole ring should be ensured as much as possible during the forging.
Heat treatment process of 312 large gear ring (1) Carburizing heat treatment Wash the gear ring oil with hot alkaline water, and apply anti-seepage agent to the parts (inner hole and upper and lower end faces) that do not need carburization. 930 ° C, gas carburizing, carbon potential 112 during strong infiltration, carbon potential 018 during diffusion, plus BH infiltration agent 10ml / min, carburizing 120h. Due to long-term high temperature carburization of 20CrMnMo or 17CrNiMo6 steel at 930 °C, grain length It is obvious that at the same time, the hollow part is bundled with other carburized gear shafts and the like, so it is not suitable to use direct quenching, and generally adopts a cooling method in which the forced air is radiated outward in the furnace, which is equivalent to air cooling, and eliminates the network carbide of the layer. Normalize internal organization. At this time, the carburized layer is 510 ~ 515mm deep.
(2) tempering at 680 °C for high temperature, so that the carbide containing Cr is etched out, the retained austenite is transformed, the network carbide of the layer is further broken, and the normalizing stress is eliminated, and the structure is prepared for quenching.
(3) The surface of the quenching tooth is coated with anti-decarburizing agent or protective atmosphere, heated to 650 ° C for 2 to 3 hours, heat preservation for 3 hours; 810 ° C to 830 ° C, heat preservation for 9 hours; 180 to 200 ° C, nitrate salt austempering (or N32 engine oil) , fully cycled, cooled 115h ~ 2h.
(4) Tempering at 200 °C for 16 h, 180 °C for 16 h, two tempering to transform retained austenite into martensite, fully transforming martensite into tempered martensite, and carbonizing the layered structure Material and alloy carbide strengthening to ensure tissue and dimensional stability.
4Rework for gear ring with excessive distortion, unprocessable ring gear, or metallographic structure and mechanical properties that are unqualified, need to be reheated for rework, in order to avoid distortion superposition, to ensure carburization depth and dimensional accuracy of tooth surface, first The large gear ring is the outer working part of the welded heavy-duty gear. Due to the lack of internal support, the gear ring will have obvious dimensional and shape changes during the carburizing and quenching heat treatment, and the machining allowance of the carburized layer is small. Machining creates difficulties. The author makes the necessary analysis on the heat treatment distortion and preventive measures that appear in the production site.
Large gear ring structure and heat treatment technology requirements 111 gear ring structure and processing process The large gear ring has a tooth top outer circle size <2000~<2500mm, and the ring thickness is 240mm. The shape is basically symmetrical, and the quality is 4~5t. The transmission power is very large. The shifting is precise and the power transmission has a large impact phenomenon.
In order to prevent gear tooth root fracture, surface hardening lamination and tooth surface peeling, a deep carburizing of 510 to 515 mm is performed on the tooth surface to improve contact fatigue strength and bending fatigue strength.
Processing steps: 1 gear ring is generally forged with 20CrMnMo or 17CrNiMo6 steel ingot (3镦3 pull → punching → mandrel reaming) → normalization of the structure (normalizing tempering) → roughing → carburizing heat treatment.
2 Combine the gear ring with the ZG3102570 cast steel hub to form a large heavy-duty gear → stress relief annealing → weld flaw detection → finishing.
112 heat treatment characteristics (1) requires a long time tooth surface high temperature deep carburizing of the gear ring, high temperature tempering after air cooling, and then quenching and then tempering.
(2) The gear ring has a large heat capacity and a long heating and cooling time. The surface hardened layer can reach 15-20 mm (50 martensite and 50 non-martensitic) during quenching, and the central portion is not hardened. The heat treatment mainly controls the size of the top of the tooth and the distortion of the tooth surface to ensure the normal size and meshing accuracy of the tooth.
2 Distortion characteristics and analysis of large gear ring 211 The distortion characteristics of the large gear ring are compared with the dimensions of the two ring gears of the 20CrMnMo steel (the original size 2375mm, 2165mm and 2040mm) before and after quenching, each ring gear is 60°. Three dimensions were measured for the dividing line and the results are shown. It can be seen from the data that the heat treatment distortion is mainly caused by the large and small cone distortion of the carburizing process, and the outer ring length and the elliptical distortion of the ring in the quenching and tempering process.
Distortion analysis of 212 large gear ring and measures to prevent distortion (1) Taper: self-weight plus long-term high-temperature carburization causes creep, resulting in cone distortion after the carburizing of the gear ring.
(2) Degree of expansion: During the carburizing and air cooling stages, the heating and cooling rates are slow, and the front and back structures are roughly the same (the volume and shape changes caused by carburizing and residual stress are negligible). In addition to the taper deformation, the size of the gear ring is basically not changes happened. The outer ring grows mainly in the quenching process: 1 Although the hardened layer of the gear ring is limited, its surface area is very large, and the surface layer is free of smoke, which effectively protects the environment, improves the yield and production efficiency of the product, and reduces the worker's Labor intensity, saving energy.
The amount of metal converted to martensite is still large, and the volume expands after quenching. 2 During the quenching process, the area of ​​the outer and inner circles and the curvature of the circumference are different, and the directions of heat shrinkage and phase change expansion are opposite, and the radial force and tangential force of the outer ring of the ring gear are generated. 3 carburization reduces the Ms point of the tooth surface, and the austenite transformation of the outer layer to martensite is later than the inner surface. In the tempering process, the shrinkage caused by the transformation of the quenched martensite of the outer layer into the low-carbon martensite ε2 carbide cancels out the expansion caused by the retained austenite transformation, and no change in appearance is observed. As a result of the combination of the above factors, the top of the tooth will increase by 4 to 5 mm. The diameter of the gear ring and the thickness of the ring directly affect the expansion size. In actual production, for <2000~<2500mm gear ring, the thickness of the ring is generally set to 240mm. According to the empirical data, the expansion allowance of 4~5mm is reserved to ensure the accuracy.
(3) Ellipticity: uneven material, improper heating and cooling, resulting in uneven expansion and contraction during heat treatment, asymmetric distortion, forming an ellipse. Quenching takes the lower limit temperature and lowers the cooling rate below Ms to reduce the ellipticity.
It is best to use isothermal quenching of nitrate salt.
3 Gear ring production precautions and heat treatment process 311 Precautions (1) Whether the heating temperature is uniform or not directly affects the elliptical distortion and internal structure of the ring gear, ensuring uniform temperature throughout the ring gear on the inner ring of the furnace is particularly important, and requires thermocouples Temperature measurement should be accurate.
(2) To prevent warping of the ring gear due to unevenness, inclination, and the like. For quenching spreaders that have been severely deformed for a long period of time, the blocks should be leveled.
(3) When carburizing, a plurality of ring gears are often placed together, and the degree of distortion of the ring gear in the lower layer is much more serious than that of the upper ring gear. Therefore, it is necessary to stack the ring gears with light weight or high precision requirements in the upper layer.
(4) If long distance transfer is required from the quenching furnace to the oil tank, in order to prevent the temperature drop of the tooth part during the transfer process, it is necessary to pre-place the heat preservation cover during quenching and heating, remove the heat preservation cover before entering the liquid; or increase the furnace temperature before the furnace is discharged. At 20 ° C, keep warm for 10 min, to ensure the quenching temperature when entering the liquid.
(5) The quenching method has a great influence on the distortion, and it is sure to ensure vertical liquid inflow and maintain the uniformity of circumferential cooling.
(6) The inconsistent quenching cooling speed inside and outside the ring gear has a great influence on the distortion: the outer ring cooling is better than the inner ring with “x†type distortion; while the inner ring cooling is better than the outer ring with “O†type distortion. Therefore, the quenching tank should be large enough and the coolant circulation should be sufficient.
(7) Segregation by the low-temperature quenching component causes the low-carbon portion of the ferrite to be not completely dissolved in the austenite, and full forging can improve the uniformity of the composition.
(8) The expansion and contraction along the direction of the fiber structure and its cross-direction during the heat treatment process are very different, so the consistency of the fiber direction of the whole ring should be ensured as much as possible during the forging.
Heat treatment process of 312 large gear ring (1) Carburizing heat treatment Wash the gear ring oil with hot alkaline water, and apply anti-seepage agent to the parts (inner hole and upper and lower end faces) that do not need carburization. 930 ° C, gas carburizing, carbon potential 112 during strong infiltration, carbon potential 018 during diffusion, plus BH infiltration agent 10ml / min, carburizing 120h. Due to long-term high temperature carburization of 20CrMnMo or 17CrNiMo6 steel at 930 °C, grain length It is obvious that at the same time, the hollow part is bundled with other carburized gear shafts and the like, so it is not suitable to use direct quenching, and generally adopts a cooling method in which the forced air is radiated outward in the furnace, which is equivalent to air cooling, and eliminates the network carbide of the layer. Normalize internal organization. At this time, the carburized layer is 510 ~ 515mm deep.
(2) tempering at 680 °C for high temperature, so that the carbide containing Cr is etched out, the retained austenite is transformed, the network carbide of the layer is further broken, and the normalizing stress is eliminated, and the structure is prepared for quenching.
(3) The surface of the quenching tooth is coated with anti-decarburizing agent or protective atmosphere, heated to 650 ° C for 2 to 3 hours, heat preservation for 3 hours; 810 ° C to 830 ° C, heat preservation for 9 hours; 180 to 200 ° C, nitrate salt austempering (or N32 engine oil) , fully cycled, cooled 115h ~ 2h.
(4) Tempering at 200 °C for 16 h, 180 °C for 16 h, two tempering to transform retained austenite into martensite, fully transforming martensite into tempered martensite, and carbonizing the layered structure Material and alloy carbide strengthening to ensure tissue and dimensional stability.
4 Rework for gears with excessive distortion, unworkable ring gear, or metallographic structure and mechanical properties that are unqualified, need to be reheated for rework, to avoid the superposition of distortion, to ensure the carburizing depth and the dimensional accuracy of the tooth surface.
5 Conclusion (1) The distortion of the large ring gear is the heat treatment distortion caused by the thermal stress caused by the distortion of the main and phase changes. As a result of the distortion, the outer circle of the top of the tooth expands outward by 4 to 5 mm, the inner hole is enlarged, and the height is lowered. The ellipticity is controlled mainly by preserving the margin to ensure the accuracy of the top of the tooth, low temperature quenching and lowering the cooling rate below Ms.
(2) Heat treatment distortion control of large ring gears involves all aspects of materials and design and manufacturing. Part design, forging and machining have a direct impact on the heat treatment distortion of the ring gear. Therefore, we should also solve the problem of heat treatment distortion of the ring gear from the aspects of part design, forging and machining.
There is a category of Other Auto Parts For Renault for Japanese Car.The Other Auto Parts For Renault are made of steel,and only for Japanese Car.
we also sell other parts for Renault,especially Automobile Sheet Metal Parts.
If you want Other Auto Parts ,please conduct us,we provide many kinds of automobile Sheet Metal Parts .
JUNCHENG AUTO firmly believe quality is first,our products are both of high quality and low price.
The automobile sheet metal parts both of high quality and low price are what we would provide.
Other Auto Parts For Japanese Car
Other Auto Parts For Japanese Car
JIANGSU JUNCHENG VEHICLE INDUSTRY CO.,LTD , http://www.junchengautopart.com