Thermodynamic prediction of the ae3 temperature of steels with additions of Mn, Si, Ni, Cr, Mo, Cu

Abstract

Published binary phase diagrams and activity data for iron and binary and ternary alloys have been used to evaluate the general linear series expansion of the activity coefficient and the standard free energy changes and these have been employed in turn for the accurate thermodynamic determination of the Ae3 temperature in steels with additions of Mn, Si, Ni, Cr, Mo, and Cu. A computer program accurate for total additions up to 7.0 wt pct and an analytic formula accurate for total additions up to 2.5 wt pct have been developed. The predicted Ae3 temperatures compare favorably with observations on over 200 steels from international compendia. It is demonstrated that existing linear regression formulae are incorrect and that for low alloy additions they should be replaced by linear expressions with carbon concentration dependent coefficients.