抄録
An experiment was conducted to clarify the mechanism of formation of eutectic graphite in cast irons induced by Ti. Fe-3.9% C-0.9% Si alloy specimens containing 0.16, 0.24, 0.44 and 0.82% Ti were melted at 1,370°C in electric resistant furnace and added S of 0.01-0.3%, and then solidified at the cooling rate of about 25°C/min. Weight of specimens was about 30g. S content in the form of Ti-sulfide and N content were analysed quantitatively and graphite structures were observed. Sulfur in melts were removed largely in the form of Ti4C2S2 by Ti addition. Even if comparatively a large amount of S remained in melts in a free form, eutectic graphite structure appeared when enough amount of free Ti was contained in melts during eutectic reaction. Nitrogen was removed as TiCN or TiN by Ti addition, but its effect on the graphite morphology was not significant. The eutectic graphite formation in cast iron is not caused by desulfurising or degassing effects which result by Ti addition, but it is due to the fact that enough free Ti is present in melts and it reacts with C during the eutectic reaction.
