Effect of FeSi additive in dual-chamber sample cup on thermal analysis characteristic values and vermiculating rate of compacted graphite iron

Thermal analysis plays a key role in the online inspection of molten iron quality. Different solidification process of molten iron can be reflected by thermal analysis curves, and silicon is one of important elements affecting the solidification of molten iron. In this study, FeSi75 was added in one chamber of the dual-chamber sample cup, and the influences of FeSi75 additive on the characteristic values of thermal analysis curves and vermiculating rate were investigated. The results show that with the increase of FeSi75, the start temperature of austenite formation T_AL firstly decreases and then increases, but the start temperature of eutectic growth T_SEF, the lowest eutectic temperature T_EU, temperature at maximum eutectic reaction rate T_EM, and highest eutectic temperature T_ER keep always an increase. The temperature at final solidification point T_ES has little change. The FeSi75 additive has different influences on the vermiculating rate of molten iron with different vermiculation, and the vermiculating rate increases for lower vermiculation molten iron while decreases for higher one. According to the thermal analysis curves obtained by a dual-chamber sample cup with 0.30wt.% FeSi75 additive in one chamber, the vermiculating rate of molten iron can be evaluated by comparing the characteristic values of these curves. The time difference Δt_ER corresponding to the highest eutectic temperature T_ER has a closer relationship with the vermiculating rate, and a parabolic regression curve between the time difference Δt_ER and vermiculating rate η has been obtained within the range of 65% to 95%, which is suitable for the qualified melt.