Grain-growth-inhibiting effects of primary inclusion particles of ZrO 2 and MgO in Fe-10 mass pct Ni alloy
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I. INTRODUCTION
IF the dispersion of fine particles is possible in practice by introducing primary deoxidation products into a liquid steel, considerable influence on properties such as strength and toughness may be exerted via grain-coarsening and nucleation effects, such as pinning on austenite grain boundaries and the ability to nucleate acicular ferrite. In order to homogeneously introduce fine primary inclusions into a liquid steel, fundamental problems such as coalescence and separation of inclusions have to be solved. The present authors[1] carried out deoxidation experiments to obtain a uniform dispersion of primary inclusions of ZrO2 or MgO in an Fe-10 mass pct Ni alloy. As a result, it was found that the particles of ZrO2 or MgO, having a mean diameter of about 1 mm, could be homogeneously dispersed under experimental conditions that inhibit particle coalescence. The grain-growth-inhibiting effect by second-phase particles has been studied by a number of investigators, in particular, Hillert[2] and Gladman,[3] who refined Zener’s original calculation.[4] All these refinements give results close to Zener’s estimate. A detailed review of the various models for grain-growth inhibition has been provided by Rymm et al.[5] Although the validity of Zener’s assumption has been challenged on theoretical grounds and on the basis of experimental studies, the experimental verification of Zener’s prediction is very limited due to the difficulties of accurate analysis of the mean size and volume fraction of the dispersed particles. This problem was addressed in a previous study,[1] in which the content of insoluble elements or oxygen as primary inclusions, determined by chemical analysis, was
KIMIAKI SAKATA, Graduate Student, Department of Metallurgy, and HIDEAKI SUITO, Professor, Institute for Advanced Materials Processing, are with Tohoku University, Sendai 980-8577, Japan. Manuscript submitted February 17, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS A
found to have a good correlation to that estimated from the inclusion-size distribution. The major objective of this research is to study the effect of the deoxidation products of ZrO2 or MgO particles on austenite grain growth from measurements of the grain-size distribution at 1673 K in an Fe-10 mass pct Ni alloy. The reason for choosing this alloy was to compare it with the results obtained in an Fe–0.10 to 0.50 mass pct C alloy. This alloy can go through a peritectic reaction to form gFe during cooling and, subsequently, austenite grain growth starts to take place. Deoxidation experiments with Ce were also performed, and the effect of ZrO2, MgO, and Ce2O3 particles on the limiting grain size was investigated as a function of volume fraction of the particles. These results were compared with those obtained in the Mg and Ce[6] deoxidation experiments for an Fe-0.20 mass pct C-0.02 mass pct P alloy. II. EXPERIMENTAL A. Procedure 1. Experiment without deoxidation A charge (70 g) containing high-purity electrolytic iron (99.99 mass pct) and globular nickel (99.97 ma
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