The conjugation of <Fe-(Mn, Fe) S-(Fe, Mn) S>, <Melt-Fe-(Fe, Mn) S> and <Melt-Fe-(Mn, Fe) S> in the Fe-Mn-S ternary system with up to 4% of manganese in iron phase, was investigated as the first approach to understand kinetics of sulfide formation in steel, and the compositions of all phases were determined in the temperature range from 670°C to 1500°C.
The results are summarized as follows:
(1) The three-phase conjugation among melt, iron and (Mn, Fe) S was observed in the temperature range from 1004°C to 1500°C.
(2) No evidence was found for the intersection of the eutectic line with the miscibility gap, proposed by Wentrup.
(3) The solubility of sulfur in iron abruptly decreased at 1371°C from 0.12% to 0.05% with the δ→γ transformation of iron.
(4) As a result of the peritecto-eutectic reaction, four phases of melt, iron, (Mn, Fe) S and (Fe, Mn) S coexisted at 1004°C.
(5) Below the peritecto-eutectic temperature, both three-phase conjugations of <Melt-Fe-(Fe, Mn) S> and <Fe-(Mn, Fe) S-(Fe, Mn) S> were stable. The former met Fe-FeS binary at 988°C, its eutectic temperature.