Effect of aluminium nitride particles on hot ductility of steel

Abstract

The loss in hot ductility of the austenitic phase in carbon steels, attributable to the presence of aluminium nitride, has been shown to be dependent on the aluminium nitride particle size. Small particles result in poor ductility, while coarsening of the particles improves the ductility. A loss in hot ductility associated with aluminium nitride has also been shown to occur in a fully austenitic steel. Examination of samples quenched from the test temperature in the case of the austenitic alloys, combined with observations made on thermal etching of the carbon steels to allow the austenitic grain size to be measured, suggests that the influence of aluminium nitride can be explained in terms of austenitic grain-boundary pinning. Small particles which pin the austenitic grain boundaries cause correspondingly poor ductility. However, where the presence of coarse particles results in relatively easy grain-boundary migration, superior hot ductility occurs. The possible influence of aluminium nitride on recrystallization is discussed. It is also shown that where titanium treatment is used to avoid low ductility associated with aluminium nitride, the treatment will be fully effective only if the titanium nitride particle size is such that grain-boundary pinning is relatively weak.