오스템퍼 처리한 구상흑연주철의 강인성에 미치는 전조직의 영향

The Effects of Se, CaCo and CaO Addition on the 1st Stage Graphitization of Malleable Cast Iron

Austempered ductile cast iron has been well known for their good toughness and strength. Generally these properties were improved by the various heat treatments and alloying elements. In this study, the effects of prior heat treatment history(near ferrite, near pearlite, near martensite) on the toughness and strength of the austempered ductile cast iron were studied experimentally and theoretically. All of the test specimens was austenitized at $900^{\circ}C$ for 1 h and austempered at $300^{\circ}C$, $350^{\circ}C$, $400^{\circ}C$, $450^{\circ}C$, respectively. The prior structure of near martensite in austempered ductile cast iron was not good in term of toughness and strength because the carbon content was apt to high in austenite during ausnitizing. It was found, on the other hand, that the ferrite matrix as prior structure had good combination of toughness and strenght. The best tensile strength and good toughness were obtained at $300^{\circ}C$, austemper in the prior structure of near ferrite, while $400^{\circ}C$ austemper in that of near pearlite and martensite.