Abstract
The precipitation of aluminium nitride on as-cast grain boundaries can be a major cause of intergranular fracture in aluminium-killed-steel castings. It has long been known that AIN can exist in two idiomorphic forms (plates and dendrites) and it had been implied that both are precipitated in the solid state. In this paper directional-solidification studies, which were performed using a 0·30C-1·50Mn- 0.17Al-0·017N steel, are described. The results show that the dendritic form of AIN precipitates from the residual liquid during solidification, and this has been modelled using available solubility data. It has been demonstrated that AIN precipitation can occur in the solute-enriched liquid at a late stage of solidification, even in cases where the bulk AI and N contents are relatively low.
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