Thermodynamic Prediction of the Liquidus, Solidus, and Ae3 Temperatures, and Phase Compositions for Low-alloy Multicomponent Steels

The vast majority of steel weld deposits solidify under highly nonequilibrium cooling conditions. A consequence of this is the chemical segregation of substitutional alloying elements during solidification, a segregation that persists as the weld cools to ambient temperature. Solidification-induced segregation of interstitials is usually not a problem due to the ease with which they can diffuse and homogenize during cooling. The presence of substitutional element segregation can greatly influence the subsequent transformation of austenite into ferrite with reaction kinetics in general being accelerated in the solute-depleted regions. The formation of ferrite in these regions causes a redistribution of carbon into the remaining austenite whose hardenability is therefore increased. It has been demonstrated that such effects can have a major influence on the development of microstructure (Gretoft et al., 1986), and any method for alloy design must take them into proper consideration.