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Chart-based techniques, such as ASTM E 45, have been used to rate inclusion types and content for more than half a century. Chart ratings are subject to considerable error, reproducibility among raters is poor, and they lack precision for today's steels with very low inclusion contents. Image analysis procedures, using ASTM E 1122, where the rating system has been modified to generate improved JK-chart ratings, are now being used widely. A new, alternate approach using stereological relationships for inclusion measurements is given by ASTM E 1245. In this method, the inclusions are separated by type (oxide vs. sulfide usually) and the volume fraction, number per unit area, average length, average area, and spacing are determined. E 1245 is easy to do by image analysis and is fast. In this paper, heats of 52100 bearing steel, made by different technologies, were rated using the current E 45/E 1122 method and by the method of the future, E 1245. The greater merit of the E 1245 method was demonstrated statistically by comparing the test results for the steels made by the different procedures.
automatic image analysis, bearing steels, nonmetallic inclusions, oxides, sulfides, stereology
Vander Voort, GF
Director, Buehler Ltd., Lake Bluff, IL