The formation of non-metallic inclusions during steelmaking.

A comprehensive review of the literature on deoxidation and inclusion formation has been carried out, including the results of both laboratory experiments and full scale plant trials. The main areas for discussion have been:- (i) Nucleation of inclusions. (ii) Growth and elimination of inclusions. (iii) Effect of steelmaking variables on inclusion formation. (iv) Reoxidation of steel. (v) Steel-refractory interactions. The experimental work has comprised a number of planned investigations into the types of oxide inclusions present at various stages during the steelmaking, tapping and teeming of several qualities of steel made by basic electric arc and open-hearth processes. A series of trials aimed at improving steel cleanness have been carried out and it has been possible to study the effects of numerous process variables during steelmaking on the nature of the non-metallic inclusions in the liquid metal.It has been shown that despite a bath of steel being relatively free from inclusions prior to tapping, the entrainment of exogenous material (e.g. slag, reoxidation and refractory erosion products) during tapping and teeming can result in quality problems and/or reduced yield. Ladle refractory erosion is a major source of inclusions, particularly in higher manganese steels, and the practice of slag-metal mixing during tapping to effect desulphurisation has been shown to lead to slag-based inclusions in the ingot.The formation of alumina agglomerates in 25 t slab ingots of carbon-manganese-niobium steel has been studied. A steelmaking practice aimed at reducing the incidence of these agglomerates and improving ductility has been developed involving among other things, a full aluminium deoxidation practice, 70% Al[2]O[3] ladle refractories and argon shrouding of the teeming stream.An attempt has been made to account for the changes in the types of oxide inclusions throughout the steelmaking of each trial cast. Finally, brief consideration has been given to possible methods of further improving steel cleanness.