The Effect of Heating Conditions on the Removal of Oxide Film on Steel Surface by the Inert Gas Fusion Method.

Abstract

This study was carried out to establish an analytical technique for accurate evaluation of bulk oxygen in ultra-clean steel using the inert gas fusion method without pre-cleaning such as electrolytic or chemical polishing. This method had a two-step heating pattern, one was a continuous heating stage to remove contamination, and another was a fixed high-temperature stage to analysis oxide inclusions. In this paper, reduction sites of oxide film and the effect of bulk carbon content are also discussed. The results obtained are as follows: (1) The separation of bulk oxygen and contaminant oxygen on the steel surface depended on the heating rate of the steel at heating stage I. The lower the rate was, the better the separation was. (2) The optimum heating rate of the steel was 1 K/s. (3) In the case of high-carbon chromium bearing steel which contained 3.4 ppm of oxygen (a calibration standard sample JSS GS-6a), approximately a half of its total oxygen content was estimated to consist of contaminant oxygen on the steel surface. This value was well compared to the measurement by the charged particle activation analysis method and was found to be reasonable. (4) It was found that both the carbon content in the steel and the feed of carbon from the crucible/steel contact surface affected the removal of oxide film.