The Effect of Carbon on the Composition of the Eutectic Conjugation in the Fe-Mn-S System and the Equilibrium of Sulfides in Solid Steels

Abstract

The effect of carbon on the eutectic conjugation of liquid, iron crystal, and (Mn, Fe) S in the Fe-Mn-S system was investigated in the range from the maximum temperature of eutectic line to peritecto-eutectic temperature. The effect of carbon and silicon on the composition of (Mn, Fe) S in <iron- (Mn, Fe) S> conjugation was also studied from 1450°C to 950°C. The results are as follows:
(1) The temperature of eutectic line is lowered and the eutectic line is dislocated towards the iron corner in the Fe-Mn-S diagram, as the carbon content of the iron crystal increases.
(2) The addition of carbon increases the manganese content of the iron crystal and (Mn, Fe) S in the eutectic conjugation, and decreases the sulfur content of the former.
As the temperature falls, both the tendencies of (1) and (2) gradually decay and are not recognised at all below 1250°C.
(3) The four-phase conjugation <liquid iron-liquid sulfide-iron crystal- (Mn, Fe) S> results from the intersection of the eutectic line with the miscibility gap, when the carbon content of the iron crystal exceeds 0.25%.
(4) The lower the temperature and the higher the manganese content of the iron matrix, the higher is the manganese content of (Mn, Fe) S in <iron- (Mn, Fe) S> conjugation. The composition of (Mn, Fe) S is hardly affected by the carbon and silicon contents of the iron matrix.