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Abstract: Differential thermal analysis has been employed to achieve an accurate determination of the solidliquid equilibria for γ-Fe at temperatures between 1147 C and 1430 C and compositions in the range 1.5 to 4.42 wt pct C. Several small but significant changes to the established phase diagram have been proposed. In particular, the liquidus in the vicinity of the eutectic has been raised by approximately 15 C and the temperature of the graphite eutectic lowered to 1150.5 C. Consequently, the eutectic compositions have been increased to 4.39 and 4.42 wt pct C for the graphite and cementite eutectics, respectively. The possibility of some modification to the γ-solidus has also been suggested, and a revised phase diagram is presented.

The liquidus surface of the C-Cr-Fe system has been experimentally determined in the Fe-rich region —C ≤6 wt pct, Cr ≤40 wt pct —using a sensitive differential thermal analysis technique, along with optical and scanning electron microscopy and X-ray diffraction. Previous liquidus surfaces for this system have differed on the extent of the (Cr,Fe)23C6liquidus field, with one version reporting its existence at ∼20 wt pet Cr, and others finding that it did not occur at Cr levels of less than ∼60 wt pct. The present investigation provides evidence in favor of the second contention, with the (Cr,Fe)23C6field not being detected at Cr ≤40 wt pct. Changes are proposed to the accepted liquidus surface in respect of the compositions of the invariant reactions—L + αδFe ⇌γFe + (Cr,Fe)7C3andL+ (Cr,Fe)7C3⇌γFe + (Fe,Cr)3C —and of the monovariant eutectic valley—L⇌ γFe + (Cr,Fe)7C3.