In Fig. 4.1, gears 5-8, 13 and 14 a

In Fig. 4.1, gears 5-8, 13 and 14 are subject to large impact force in transmission and frequently shift, so it is required that gears have high wear resistance, fatigue strength and core toughness. Therefore, 20Cr material is selected. The heat treatment process is carburizing + quenching + low temperature tempering. According to the working condition of machine tool gear, it belongs to heavy load gear, so the carburizing layer is 0.9 mm. After carburizing, the surface carbon content is increased, the surface hardness is required to be 58 (59) HRC, and the core hardness is up to 30-45 HRC, which ensures sufficient strength and toughness.