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

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.

Application of Statistics of Extreme Values for Inclusions in Stainless Steel on Different Stages of Steel Making Process

“…In the previous study, 17,18) it was concluded that the 3D investigation of inclusions and clusters on a surface of a film filter after the electrolytic extraction (EE-method) of steel samples is preferred for EVD analysis in comparison with the conventional 2D investigation. Especially, the EE-method provided more accurate data by investigation of undamaged clusters and elongated inclusions (such as sulfides).…”

“…An electrolytic extraction technique is one of successful methods for 3D investigation of inclusions on a surface of a film filter after extraction of a steel sample. 17,18) Especially for elongated sulfide inclusions, the 3D investigation is more accurate compared to a conventional two-dimensional (2D) investigation on a polished cross section of a steel sample. 18) In this study, the EVDs of inclusion sizes were obtained for both original and deformed inclusions in a 304 austenitic stainless steel on different stages of a steel making process.…”

“…17,18) Especially for elongated sulfide inclusions, the 3D investigation is more accurate compared to a conventional two-dimensional (2D) investigation on a polished cross section of a steel sample. 18) In this study, the EVDs of inclusion sizes were obtained for both original and deformed inclusions in a 304 austenitic stainless steel on different stages of a steel making process. More specifically, the EVDs for inclusions in molten steel, © 2011 ISIJ slab and rolled steel were compared.…”

Three Dimensional Evaluations of REM Clusters in Stainless Steel

“…According to previous studies, [10][11][12] a three dimensional (3D) observation is more preferable and accurate than a cross sectional observation in 2D, especially for clusters whose shapes are irregular. Therefore, in this study, the characteristics of REM clusters (such as morphology, composition, number and size) in stainless steel were investigated in 3D after electrolytic extraction of steel samples taken during: a pilot trial (PT) and an industrial heat (IH).…”

Determination of Size Distribution and Probable Maximum Size of Inclusions in AISI304 Stainless Steel

“…The PMS of inclusions can be predicted with sufficient accuracy in a certain area or volume by using an extreme value distribution (EVD) of inclusion sizes. 5) In the previous studies, 2,[6][7][8] the authors have applied this EVD method to several kinds of steel samples taken from a tundish, a continuously cast slab and a hot band for prediction of size for the largest inclusion in the final steel products. The three-dimensional (3D) observation of inclusions with different morphologies was tried by electrolytic extraction method for more precise estimation of the maximum size inclusions in steel samples.…”