Morphological Classification of Inclusions in Steel by Image Processing of Micrograph

摘要

The inclusions in stainless steel are of different shapes on a micrograph: circle, triangle, square, bar and so on. A new method to identify the shape of an inclusion was developed with the aid of image processing equipment. Two morphological parameters of y = L~2/(4Aπ) and x=πD~2/(4A) were selected. On a two dimensional diagram of x and y, the respective area of each shape was determined theoretically and experimentally. The inclusions in specimen taken from molten steel, CC slab and rolled sheet were examined on optical micrographs of 1000 magnification and classified using this diagram. The inclusions in molten steel were more than 96% circular, those in CC slab, about 90% circular and those in rolled sheet, 80% circular. In the last specimen, squares accounted for about 10% and bars, 7%. The inclusions were analyzed by EPMA. The circular inclusions were mostly of oxide, whereas the elongated inclusions were of MnS based complex. Sizes of the circular inclusions were also determined, and the mean diameter in molten steel, CC slab and rolled sheet was 1.4, 2.0 and 1.0μm, respectively.