Particle and microstructural characteristics in the coarse-grained heat-affected zone of Al–Ti–Ca complex deoxidized steels

The particles and microstructures in the coarse-grained heat-affected zones of Al–Ti–Ca complex deoxidized steels with different Al content were investigated by in-situ observation, various analytical techniques and calculations. The results show that the inclusions in high Al steel consist of Al–Ca oxides containing small amounts of TiO x surrounded by an outer layer of MnS. In low Al steel, the inclusions consist of Al–Ca–Ti oxides with high TiO x content covered by an outer layer of MnS, and the high TiO x content in the inclusions can remarkably enhance the ability of the inclusions to promote acicular ferrite nucleation. The fine-grained microstructure obtained in the coarse-grained heat-affected zones of low Al steel is attributed to the pinning effect of the finer particles and the formation of a high density of acicular ferrite.