Periodicity of Carbon Element Distribution Along Casting Direction in Continuous-Casting Billet by Using Singular Spectrum Analysis

The periodicity of carbon element distributions along the casting direction in a continuous-casting billet was investigated quantitatively in this article after finding it in the preceding research. By using singular spectrum analysis (SSA), this study focuses on the changes of periodicity at different positions (centerline position, V-shaped segregation band, and columnar-to-equiaxed transformation position), at different data layouts (continuous or discrete) and at different scales (large scale or small scale). SSA is a frequency-domain mathematical method. Based on SSA, two values, the extracting average period value (Pea) and the extracting comprehensive harmonic extent (Eech), have been defined for investigating the periodic characteristics of time series, which reflects the influence of the segregation on the casting-direction quality stability (fluctuation frequency and disorder extent) of the billet. First, it is found that there are different periodic characteristics (period value and harmonic extent) at different positions as to the carbon element distribution along the casting direction in a continuous-casting billet, and the corresponding variation trend with position may be different at different data layouts or at different scales. Moreover, as to the studied element distributions, the variation trends of the period value with position in the same data layout results are the same, but it is different in the same scale results of different data layout; the variation trends of the harmonic extent with position in the same scale results are the same, but it is different in the same data layout results of a different scale. This point may reveal a universal phenomenon in the object of different data layouts and different scales. Hence, when the solidified element distribution, the related solidification process and the properties of steel product (especially about the fluctuation of quality) are investigated, special attentions should be paid to the data layout and the scale of the raw data.