Heat treatment process for transmission gears
The heat treatment technology requirements of transmission gears are: tooth surface hardness 58~ 62 (HRC); Heart hardness 33 to 48 (HRC); The deformation amount is not more than 0.25mm; the surface layer of the metallographic organization is tempered martensite + uniformly distributed fine-grained carbide + a small amount of residual austenite, and the center of the metallographic organization is low-carbon martensite + a small amount of ferrite.
(1) Preliminary heat treatment of the blank: 20CrMnTi steel transmission gears are required to have high finish and good machinability when processing, so that the chips of the jacks are curled and band-like, reducing the load on the machine tool and prolonging the life of the tool. Therefore, after the normalizing treatment, the hardness should be between 179 and 217 (HB), and a uniformly distributed flake pearlite + ferrous cable body is obtained, which ensures the above requirements. Its normalizing process temperature is 950 ~ 970 °C, air cooling after permeation or air cooling or blowing, spray cooling, if the hardness is low, you can take the measure of water cooling and then air cooling.
(2) Carburizing of the gear: Considering the carburizing speed and deformation problem in the carburizing process, the general carburizing temperature is selected between 920 and 940 °C, and the carburizing insulation time depends on the required carburizing layer depth, and its actual depth is twice the required carburizing layer depth plus the unilateral grinding amount of the gear, so the carburizing time should be reasonably selected in the actual operation process.
(3) Final heat treatment of transmission gears: After heat treatment, the gear obtains a high hardness, high strength surface layer and a good toughness of the heart. According to the performance requirements of the gearbox gear and the characteristics of the material, the gear can be directly quenched after carburizing and the furnace temperature drops to 850 ~ 860 °C.
