Effect of ferrite substructure on precipitation of Fe₃C at MnS in an ultra-low carbon steel

The effect of ferrite substructure on precipitation of Fe₃C at MnS in an Al-killed steel was studied. By heat treatment, dislocation density and grain size were varied under the presence of MnS particles. By the subsequent aging at 603 K and 703 K, the ratio of Fe₃C precipitates nucleating on MnS with respect to the total number of Fe₃C precipitates was lowered under the presence of a larger number of dislocations and grain boundaries. It was considered that a MnS particle is less effective than a dislocation, and is comparably effective with a grain boundary as a heterogeneous nucleation site of Fe₃C in ferrite.