Effect of Alloying Elements and Heat Treatment Temperatures on the Retained Austenite of Austempered Ductile iron

오스템퍼드구상흑연주철(球牀黑鉛鑄鐵)의 잔류(殘留)오스테나이트 조직(組織)에 미치는 합금원소(合金元素) 및 열처리온도(熱處理溫度)의 영향(影響)에 관한 연구(硏究)

Retained austenite in matrix of austempered ductile iron has been well-known as a parameter in controlling mechanical properties, but investigation to obtain quantitative relationship with mechanical properties lack. Therefore, this study executed austempering treatment at various temperatures on ductile iron alloyed with Mo, Ni, Cu. In consequence, microstructure of retained austenite transformed coarse, and quantity increased according as austempering temperature increased. After heat-treatment, microstructure of specimen alloyed with Ni was fine, and toughness improved. At austempering temperature up to $400^{\circ}C$, carbide precipitation started in retained austenite. In consequence, afforded cause of hardness increase, a lot of increase did not arise for coarse structure.