Cavity Sequences in Continuously Cast Billets: Part I. Analysis of Empirical Data

Voids in the core of continuously cast steel billets are accompanied by segregation and therefore can be a problem. Samples of round steel billets are analyzed in this work with respect to the dynamics of central porosity formation. Longitudinal radiographs of the samples have been digitized. The stream of porosities is represented as a time sequence. Statistical properties of the series are determined. Spectral analysis is used to produce autocorrelations and power spectra and, thus, to test for periodicities. Clustering of voids is studied. The distribution functions of interval lengths and void fractions are examined. A U-shaped relation is observed between interval lengths and interval void fractions. Techniques of nonlinear analysis are applied to quantify the degree of randomness and complexity of the signals.