On the Mechanism of Formation of Oxide Inclusions at the Addition of Deoxydizer

Abstract

By adding various deoxidizers to the liquid iron which was heated in the high frequency induction furnace, the dissolved state and growth of inclusions were observed at 1600°C. The results obtained are summarizedas follows.
1) Metallic chromium dissolved very slowly into the liquid iron. That is, the distribution of chromiumat the boundary between chromium and molten iron is considered a rate-determining step of this dissolution.
Inclusions were formed at a slower rate than the rate of dissolution, because they formed in the regionof 26%Cr.
2) Fe-Mn alloy dissolved into the liquid iron as a laminar flow. Inclusions of MnO are formed aroundfine particles of Al₂O₃ as nuclei in this flow.
3) Ti, Si and Al were made to dissolve into the liquid iron by stirring with thermal convection due to the heat of mixing at the boundary between the deoxidizer and the molten iron. Cloudy inclusions wereobserved for these deoxidizers in this case.
On the basis of the nucleation theory, these phenomena were considered and the conclusions were drawnas follows.
4) Homogeneous necleation occurred at the dissolving step for the elements Si, Ti and Al which had ahigh deoxidizing power and cloudy inclusions were formed at the initial period of deoxidation.
5) Contrary to the above, homogeneous nucleation did not occur for the elements Cr, and Mn whichhad a low deoxidizing power. These inclusions were formed through heterogeneous nucleation.