Daily routine quantitative assessment of microstructure of steel by image analysis

The daily routine assessment of microstructure of steel for production quality control at Hoogovens involves the determination of the inclusion content, carbide distribution, and ferrite grain structure. A special image analysis program has been developed for all three aspects of microstructure. To determine the inclusion content, a large number of fields have to be scanned. The image analysis is straightforward: thresholding of the grey image and measurement of the area and length of the separate inclusions. To determine the carbide distribution, the analysis of only a few representative fields will suffice. The image analysis is more complicated. Special grey morphological processing is applied to distinguish different types of carbides. To determine the ferrite grain structure, the number of fields to be assessed can also be limited. To produce an acceptable reconstruction of the grain boundaries even for difficult grain structures, complicated grey-level transformations are used. The central part of this algorithm is the so-called watershed operation.