The effect of Aluminium nitride precipitation in relation to grain growth in Steels

Abstract

Existing information on the grain growth in metals and alloys has been briefly surveyed. In aluminium deoxidised steel, it has been established that there is range of residual aluminium concentration for maximum grain growth inhibition. Hypotheses based on Al2O3, residual aluminium, surface adsorption, aluminium sulphide and aluminium nitride as inhibitors of austenitic grain growth has been critically examined. The hypothesis on grain growth inhibition based on the presence of intergranular sulphide inclusions, Al2O3 particles is rejected. It has been shown that on soaking in nitrogen atmosphere intergranular precipitation of aluminium nitride occurred in steels with substantial residual aluminium contents. In nitrogen soaked specimens size and distribution of precipitated aluminium nitride altered with residual aluminium, tending to agglomerate at higher temperatures. It has been concluded that precipitation and re-solution of submicroscopic aluminium nitride in steels with optimum residual aluminium steels could account for the observed coarsening characteristics of steels.