ABSTRACT
Although castings rarely solid under equilibrium conditions,phase diagrams can be of considerable value for predicting the microstructural changes that occur during and after solidificalion. Unfortunately, experimentally determined phase diagrams are generally only available for simple binary and ternary alloy systems, which rarely correspond closely to industrial alloys,which may contain 10 or more elements. In recent years, va-rious thermodynamics-based computer models have been developed, which enable phase diagrams to be predicted for multicomponent alloys, but, to date, their application to ferrous alloys has been mainly restricted to steels. In the present work, the existing modeling work has been ex-tended to make it suitable for cast irons containing the following elements: Fe, C, Si, Mn, P, Ni, Cr,Mo, Cu, Nb, V, Ti, N and Mg.
This paper briefly outlines the principles involved in phase diagram modeling and provides examples of their practical application to cast irons. This includes prediction of precipitalion hardening in cast irons and of the effects of using titaniumcontaining steel scrap in the manufacture of flake and spheroi-dal graphite cast irons. It has been possible to predict the competition between the formation of different carbides and graphite, the influence of the principal elements on the various carbide-graphite reactions, and the segregation developed during solidification and the formation of pinholes. The use of phase diagram modeling to predict physical property data for use in solidification modeling is also described.
INTRODUCTION
Phase diagrams are an important tool for metallurgists since they allow predictions to be made of the amounts and compositions of the phases that are present in a material at a given temperature under equilibrium conditions, and provide valuable information to help understand nonequi-librium processes. Their value is, however, limited by the fact that they are often only available for simple binary and ternary alloy systems, which rarely correspond closely to industrial alloys, which can often contain 10 or more elements. The effort required to produce phase diagrams for multicomponent systems is very large, and, in practice, phase equilibria are usually only determined for specific alloys, sometimes with variations for a specific element, for example C in a tool steel.
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