Determination of Heat Treatment Process Parameters of the Milling Ball in Low Alloyed Bainite Ductile Iron

The effects of heat treatment process parameters of the step austempering in room-temperature machine oil on the structure and properties of the low alloy bainite ductile iron for milling ball have been studied. The optimum process parameters of austenitizing temperature were 930—950℃,the temperature for taking out of oil was 180—220℃,the time interval from oil to furnace was 60s,the isothermal temperature was 220—240℃, and the isothermal time was 1—1.5 h.The matrix microstrueture of the material consisted of lower bainite,a small amount of martensite,retained austenite and carbide.For the obtained milling ball and impact sample,the impact toughness was more than 14 J/cm~2 and hardness was 52—56 HRC.