| Summary: | A comprehensive review of the literature concerning the various types of inclusions commonly encountered in commercial steels, has been carried out. The conditions of formation of both sulphide and oxide inclusions have been discussed, and in particular the effects of the various oxo- and sulpho-phillic elements which can be employed to modify the more usual inclusion populations. The effect of working on the inclusion morphology has also been reviewed with particular emphasis being given to the various factors which affect inclusion behaviour. The behaviour of the more common types of inclusions, during hot working, has also been reviewed. The experimental work has investigated the effects of deformation temperature and the degree of matrix strain on the morphology of various types of silicate inclusions, during hot rolling. The Relative Plasticities of plastic inclusions were determined and the mechanisms of fracture and dissemination of brittle non-plastic inclusions was investigated. It was shown that crystalline and glassy silicate inclusions behaved in a brittle or rigid manner at lower rolling temperatures, depending on the size of the inclusions and the reduction attempted, but that at some critical temperature the behaviour suddenly became 'plastic' or 'fluid'. This transition temperature was shown to be related to the solidus temperature, in the case of crystalline silicate inclusions, but was dependent on the temperature at which the viscosity of glassy silicate inclusions fell below some critical value. This latter temperature was often considerably less than the corresponding solidus temperature. The stability of the various types of glassy inclusions has also been investigated and it has been shown that in those cases where the glassy phases are unstable, complex non-equilibrium structures may develop on extended soaking at the working temperatures. The mechanisms of formation of aluminous inclusions, produced on deoxidation with aluminium, have been investigated and theories have been proposed to explain the various inclusion morphologies observed. The effect of hot rolling on the morphology of these inclusion clusters has been investigated and an explnation for the strings of small angular alumina particles, often observed in commercial products, has been outlined.
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