Abstract
The purpose of this study is to clarify the continuous cooling transformation behavior and heat treatment characteristics for four kinds of ductile iron containing 0.5mass%Cr to 3.5mass%Cr. The specimens were austenitized at 1223K-900s, and the range of cooling time from Ac3 to 773K was about 3s to 4000s.
The volume of crystallized carbide in the low alloyed ductile iron containing 3.5mass%Cr ranged from 25% to 28%. The ferrite transformation region in CCT diagrams for ductile irons containing Cr less than 1mass% shifted to a longer cooling time, and did not exist for ductile irons containing Cr more than 2mass%. The pearlite transformation region in CCT diagrams shifted to a higher temperature and a shorter cooling time with increasing Cr content of ductile iron. The bainite transformation region existed only in CCT diagrams for ductile iron with 0.5mass%Cr. The martensite transformation region less than 2mass%Cr moved to a lower temperature with an increase in Cr content. The hardness of quenched ductile irons containing 0.5mass%Cr to 2mass%Cr was about 630HV10 and that of the ductile iron containing 3.5mass%Cr was about 800HV10. The effects of Cr on hardenability for low alloyed ductile irons were small.
