Abstract
Direct austempering (DAT) process of spheroidal graphite cast iron has continuous heat cycle from casting to austempering of the iron. Namely, DAT process is successive producing system of austempered spheroidal graphite cast iron (ADI) in organic combination with casting, austenitizing and bainitizing heat cycle. The DAT process which was developed in this study was made up three parts of upright equipment ; graphite mold for casting, electric furnace for austenitizing and salt bath for bainitizing. The microstructure of ADI manufactured by DAT process was observed and investigated quantitatively under the various producing conditions of specimens. Much more nodule count of spheroidal graphite than the normal process was obtained by rapid solidification and austenitization, leading remarkable graphitization and austemperability. Even if the iron was manganese alloyed, the austemperability was practically unaffected by the fine-dispersion of the normal segregation in eutectic cellular boundary.
