DEVELOPMENT OF AN INTEGRATED METHOD FOR FULLY CHARACTERIZING MULTIPHASE INCLUSIONS AND ITS APPLICATION TO CALCIUM-TREATED STEELS

An integrated technique for the full characterization of multiphase in clusions has been developed. It is based on the positioning of the bea m of a scanning electron microscope along the skeleton of each phase p resent in the inclusions. It requires the integration of the signals g enerated by the scanning electron microscope, the X-ray spectrometer, and the image analyzer. This technique was used to characterize inclus ions found in commercial heats of steel treated with calcium. An optim um Ca/S ratio of 0.70 allows modification of the mean shape factor of MnS inclusions, which then changes from 0.25 to 0.73. The optimum calc ium concentration in the sulfide phase is approximate to 15wt.%. An in crease of this value beyond 15wt.% does not translate into any change in the shape factor of the inclusions. Finally, an empirical model for the transformation of inclusions, as a result of the calcium treatmen t, is proposed. It specifies that Ca-aluminates act as nucleation site s for the solidification of (Mn,Ca)S inclusions. (C) Elsevier Science Inc., 1997.