Abstract: During continuous normalizing treatment of circular parts produced by forged SCr415H low-alloy steel, there were low hardness and mixed crystal defects. The physical objects forged at temperatures of 1150, 1200, and 1230 ℃ were used as tested materials, and specimens were cut from the tested materials for conventionally normalizing and normalizing with two-stage cooling. The normalizing heating temperatures were 870, 900, 950, and 1000 ℃, and the holding time was 90 min. After two-stage normalizing at temperatures of 950, 1000, and 1050 ℃ for 60 min, the specimens were taken out and transferred in a box furnace preheated to 870 ℃ and 900 ℃ for further holding for 30 min then air cooled. The results show that in view of the low hardness and mixed crystal defects of the SCr415H steel in actual production, hot working specifications with forging temperature of 1200 ℃ and normalizing heating temperature of 900 ℃ can be used for normal normalizing; the two-stage normalizing process parameters are forging temperature of 1200 ℃, first heating temperature of 1000 ℃, and second heating temperature of 870-900 ℃. Taking into account the production efficiency, furnace life and other production practices, the preferred hot working process is forging temperature of 1200 ℃, normalizing temperature of 900 ℃. Thus, the results of the study have important practical significance for guiding the forging and heat treatment production of SCr415H steel.

Key words: SCr415H steel, forging, normalizing, mixed crystal, hardness