Chemometric evaluation of inhomogeneity in thin metallic strips

Abstract

The development of high-quality metallic strips based on iron—silicon alloys aims at sufficiently homogeneous distribution of chemical components. In our case, the remaining small inhomogeneities of silicon were to be revealed and quantified preferably on two very different spatial scales: in the centimetre range along the surface and in the micrometre range across the thickness. The first task was solved by gravimetric analysis of 5 × 5 adjacent samples having large volumes which smooth microsegregations and depth inhomogeneities. Analysis of variance and linear regression applied to the obtained silicon concentrations revealed a weak but significant macroscopic trend along the strip. The second problem was tackled by electron microprobe line scans along the cross-section of the strip. Two effects were separated from the intensity response for silicon after correction by the sample current: a trend to signal decrease with time, which probably results from instrumental drift, and a peak-like depletion in the central region of the strip caused by macrosegregations. The drift was obtained by regression analysis of a long pseudo-line scan which simply joins four short single scans. The peak-shaped depletion was confirmed to be significant by retrospective use of the cumulative sum technique. Moreover, a coefficient of inhomogeneity based on that technique is shown to be useful as a semi-quantitative measure for the quality of the strips.