Effects of Chromium on Continuous Cooling Transformation Behavior and Heat Treatment Characteristics for Low Alloyed Ductile Iron

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 0.5 mass%Cr to 3.5 mass%C r. The speci-mens were austenitized at 1223 K-900 s ， and the range of cooling time from AC3 to 773 K was about 3 s to 4000 s. The volume of crystallized carbide in the low a l1 0yed ductile iron containing 3.5 mass%Cr ranged from 25% to 28%. The ferrite transformation region in CCT diagrams for ductile irons containing Cr less than 1 mass% shifted to a longer cooling time ， and did not exist for duc ti1 e irons containing Cr more than 2 mass%. 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 0.5 mass%Cr. The martensite transformation region less than 2 mass%Cr moved to a lower temperature with an increase in Cr conten t. The hardness of quenched ductile irons containing 0.5 mass%Cr to 2 mass%Cr was about 630HVI0 and that of the ductile iron containing 3.5 mass%Cr was about 800HVI0. The effects of Cr on hardenability for low alloyed ductile irons were smal l.