Analysis of Largest Sulfide Inclusions in Low Carbon Steel by Using Statistics of Extreme Values

Abstract

Abstract The statistics of extreme values was applied for the determination of the largest sulfide inclusions with different morphology in low carbon steel samples by using both two‐dimensional (2D) observations on the polished cross section and three‐dimensional (3D) observations on a surface of a film filter after electrolytic extraction of the samples. It was found that the globular, rod‐like and dendritic sulfides in the molten steel sample as well as the elongated sulfides in the rolled steel sample can be successfully extracted from the both samples, and analyzed precisely by using extreme value analysis in 3D. Based on the geometrical considerations of the probability for measurement of the true length of rod‐like and elongated inclusions on a cross section, it was found that this probability for inclusions decreases dramatically with an increasing real aspect ratio value of them. Particularly for the determination of the true length for elongated inclusions in the rolled steel sample by 2D investigations on a metal cross section, it is required to be cut investigating section of steel sample within ± 1 degree against rolling direction. Therefore, a 3D observation is considered to be more preferable and accurate than the conventional cross sectional observation in 2D, due to the possibility for the measurements of the real size of them.