抄録
The author has studied the inhibitory effects of elements such as Se, Te, Ti, Al, B, Cu, As, Sn, Sb, Pb and Bi on the formation of spheroidal graphite to clarify the mechanism of preventation of graphite spheroidization. In this report, the inhibitory effects of these elements on the solidification process were discussed and summarized.
Elements such as S, Se, Te, Pb and Bi consume Mg which is necessary to form spheroidal graphite, while Ti, Al, B, Cu, As, Sn and Sb do not. Harmful elements which have little or no solubility in molten iron and have small equilibrium distribution coefficients in austenite are more inhibitory than others. Elements such as S, Se and Te form vermicular, undercooled and flaky graphite with increased addition, while Ti, Al, B, Cu, As, Sn and Sb form degenerated graphite. Elements such as Pb and Bi form degenerated graphite when the amount is small but form vermicular, undercooled and flaky graphite when the content is high.
Granular and thread-like degenerated graphite form at the austenite cell boundary at the last stage, quasi-spheroidal and vermicular graphite form at the austenite grain boundary at the middle stage and aggregated graphite form at the first stage of eutectic solidification. The formation of vermicular, undercooled and flaky graphite on the addition of S, Se, Te, Pb and Bi, is caused by the consumption of Mg by these elements, and the formation of degenerated graphites such as granular, thread-like, vermicular and quasi-spheroidal ones on the addition of Ti, Al, B, Cu, As, Sn, Sb, Pb and Bi, is caused by the concentration of these elements at the austenite grain and cell boundaries during eutectic solidification. Elements such as B, Cu, As, Sn, Sb, Pb and Bi improve the shape of the primary graphite within a certain range of addition. The harmful elements can be classified into the following three groups depending on the type of inhibition, i. e. the Mg-consume type (S, Se, Te), the boundary concentrating type (Ti, Al, B, Cu, As, Sn, Sb) and the mixed type (Pb, Bi).
