Detailed phase diagram mapping : T-X data for solidi and liquidi of the alloy system manganese-carbon

Abstract The liquidus lines of the binary system Mn – C were studied, mainly by solubility determinations (at high carbon) and thermal analysis (at low carbon). The low carbon part of the liquidus was mapped in unprecedented detail. The poorly defined phase Mn4C1 – X is probably the highest melting manganese carbide (i. e. not Mn7C3). No (stable) peritectics exist below 1326 °C, but three eutectics were identified: one meta-stable and two stable. Also, transistion temperatures were identified for some Mn carbides, as well as γ-Mn (austenitic manganese), and δ-Mn (ferritic). Literature data were co-opted to quantify the enthalpy of melting for δ-Mn (8.3 ± 1.5 kJ · mol−1) which is 3 to 5 kJ lower than given by current tabulations and databases. Several transition temperatures within Mn – C (including the melting of pure δ-Mn) are markedly affected by even minor amounts of oxygen and nitrogen.