Abstract: In order to eliminate the streamlined structure of the most severely distorted part from the core to 1/2 radius of the forged billet of 20CrMoH steel gear with a large forging ratio, the effects of different normalizing processes on the microstructure transformation and hardness change of the most severely distorted part were studied. The results show that when the heating temperature is 880-920 ℃ and the heating time exceeds 2 h, the isothermal temperature is above 600 ℃ and the holding time is 1 h, the microstructure heredity of the forged billet can be eliminated, and the deformation streamline can be eliminated. The ferrite grain size can reach grade 9, and the hardness can be greatly reduced from 249 HBW to 146-165 HBW. With the extension of heating and isothermal time, the normalizing effect do not increase significantly. When the heating time in the range of 880-920 ℃ is shortened to 1 h, the isothermal temperature needs to reach 630 ℃ to achieve the same effect, and more energy can be saved and production costs can be reduced.

Key words: 20CrMoH steel, normalizing, microstructure, hardness