The effect of the eutectic structure and the residual effect of impurities on the uncertainty in the eutectic temperatures of Fe–C and Co–C

Abstract

This paper deals with the evaluation of the uncertainty in the equilibrium value of the eutectic temperature of the eutectic systems Fe–C and Co–C in their pure state. The first step towards this is deriving the equilibrium value of the liquidus temperature of the actual impure system and its associated uncertainty, the second estimating the uncertainty in the correction for the effect of impurities. The derivation of liquidus temperature and its uncertainty from the observed melting behaviour forms the core of this study. It involves the extrapolation of the measured melting plateaus, obtained at finite growth rates of the preceding freezes, towards the plateau related to zero growth rate, i.e. to the state of structural thermodynamic equilibrium. The uncertainty in the correction for the effect of impurities will be evaluated by means of ‘the sum of individual estimates’ and ‘the overall maximum estimate’, earlier shown to be applicable to eutectic systems.