Development of a New Technique for the Simultaneous Determination of Soluble and Insoluble Oxygen Contents in Al-killed Steel

Abstract

Oxygen in Al-killed steel can be classi fied into two: soluble oxygen, which is chemically dissolved oxygen in steel and insoluble oxygen, which is the oxygen as a form of alumina (Al2O3). The current analytical technique usually reports total oxygen content (T.O.), which is the sum of the soluble oxygen content (S.O.) and the insoluble oxygen content (I.O.). In general, the cleanliness of steel has been evaluated by analyzing T.O. The present study proposed a new oxygen analysis technique that simultaneously detects the S.O. and I.O. in steel sample using the current inert gas fusion infrared absorptiometry, by separating signals of the S.O. and the I.O. Heating pattern, to carbothermically melt the sample, was changed from one step to two steps: a low-temperature holding for detecting S.O. and a high-temperature holding for detecting I.O. A number of Al-killed steels, sampled during the RH and the tundish processes were analyzed for S.O. and I.O. by the technique developed in the present study. The obtained I.O. representing the concentration of alumina inclusions was independently validated by counting inclusions using automated SEM. The mean diameter (MD) and the area fraction (AF) method were employed to calculate I.O. T.O. from the new technique was veri fied by that from the conventional technique. I.O. and T.O. were in good agreement with I.O. from the MD method, and T.O. from the conventional method, respectively. The newly proposed technique is found to be promising in the detailed oxygen analysis in steel samples and is expected to contribute to the development of a new index for steel cleanliness.