Chapter 5 - Solidification structure

Abstract

This chapter reviews how the metal changes their state from liquid to solid, and how the solid develops its structure— together with its pore structure. The effect of a variety of nitrides and carbides on the nucleation of solid pure iron, from the liquid state results—gives useful evidence. The evidence states that the best nuclei are those with a lattice plane giving a good atomic match with a lattice plane in the nucleating solid. The grain structure that forms on solidification—may turn out to be the same as in the finished casting. It happens only in those cases where the metal is a single phase, from the freezing point down to room temperature. Some of its examples include: some austenitic stainless and some ferritic stainless. Even in these single-phase materials there is an opportunity for grain boundary migration—possibly for grain growth and recrystallization. The chapter concludes by discussing the shrinkage problems that lead to a set of void phenomena, sometimes appearing as porosity.