Effect of alloying elements M (M=C, Te, Mn, Cr, Si, Ti, Zr, and Ce) on supersaturation during aluminum deoxidation of Fe
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I.
INTRODUCTION
IT has been confirmed theoretically and experimentally that when powerful deoxidizers such as Al, Zr, etc. are employed, inclusions are likely to be formed under conditions of high supersaturation. If alloying elements are simultaneously present in supersaturated solution, the appearance of supersaturation is considered to be affected for nucleus formation.[1,2,3] In a previous article,[4] the supersaturated oxygen activities in the Fe-0.0017 to 0.41 mass pct Al-M (M 5 C, Te, Mn, Cr, Si, Ti, Zr, and Ce) melts were measured at 1873 K by using mullite-tube type and ZrO2-9 mol pct MgO-plug type probes. As a result, it was found that the supersaturated oxygen activities obtained from the electromotive force (EMF) measurements decreased with an increase in the contents of the alloying elements for a given Al content, and the decrement was related to the stability of the alloying element oxide. In the present article, the effect of the alloying elements on the supersaturation of alumina precipitation is discussed based on the contents of analyzed aluminum and oxygen in the Fe-Al-M alloys obtained in previous experiments of galvanic cell measurements. II.
EXPERIMENTAL
The experiments were carried out at 1873 K under a purified Ar atmosphere using an Al2O3 crucible containing 120 g of the Fe-0.0017 to 0.41 mass pct Al-M (M 5 C, Te, Mn, Cr, Si, Ti, Zr, and Ce) alloys. The melt was initially stirred for 2 minutes using an Al2O3 rod, and then was left for at least 1 hour without stirring. After the EMF measurements, the crucible containing the sample was pulled out of the furnace and quenched rapidly in a He gas stream, followed by water quenching. Total O contents in
GUANGQIANG LI, Research Student, and HIDEAKI SUITO, Professor, are with the Institute for Advanced Materials Processing, Tohoku University, Sendai 980, Japan. Manuscript submitted May 6, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS B
the quenched samples were determined by inert gas fusioninfrared absorptiometry. Detailed descriptions of the experimental apparatus, method, and chemical analyses have been given already in a previous article.[4]
III.
RESULTS AND DISCUSSION
A. Aluminum-Oxygen Relation The contents of the acid-insoluble alloying element M (M 5 Ti and Zr) and Al on a mass ppm basis are plotted against the total Al contents in the upper and lower diagrams of Figure 1, respectively. However, the acid-insoluble Ce could not be determined due to the dissolution of Ce-containing inclusions by the acid. Acid-insoluble Al contents for a given total Al level tend to be slightly higher than those in previous experiments[5] of the Fe-0.005 to 0.21 mass pct Al alloys, which are represented by a shaded area. Total Al (M) content represents the sum of the acid-soluble and acid-insoluble Al (M) concentrations, which correspond to the dissolved Al (M) in metal and Al (M)-containing inclusions, respectively. It was assumed in the present study that the inclusions precipitated during solidification. The validity of this assumption is explaine
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