Solid-state nucleation of acicular ferrite on minerals added to molten steel

A technique has been developed for making samples of steel with controlled additions of powdered mineral phases. Alloys made using this technique have been studied from the point of view of the acicular ferrite microstructure, which forms when ferrite plates nucleate heterogeneously on non-metallic inclusions. It is observed that titanium oxide particles are most efficient in nucleating acicular ferrite. It is suspected that nucleation is enhanced around these particles because of their chemical interaction with surrounding steel, causing localized depletion in either carbon or manganese. Such local depletion zones thermodynamically stabilize the ferrite phase over the parent austenite, thus causing nucleation. Copyright (C) 1997 Acta Metallurgica Inc.