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The origin of inclusions in the electroslag remelting process

University of British Columbia

The aim of this work was to determine whether (ASTM E-45) D-type inclusions are a necessary component of ESR ingots. Therefore, experiments were undertaken to ascertain the origin of the inclusions. Pure iron (FVE) and electrolytic nickel were melted through CaF₂+CaO+Al₂0₃ slags, and the changes in the metal compositions (with respect to calcium, aluminum and oxygen) were measured. The composition changes could not be accounted for by simple chemical slag/metal reactions. Hence, electrochemical slag/metal reactions were inferred. These reactions were detected, and the accompanying rectification of the 60 Hz A.C. melting current was measured. It was thus concluded that both chemical and electrochemical slag metal reactions contribute to the final composition of the metal. The cooling and solidification paths of the various metal compositions were then studied. With the use of the classical nucleation theory it was found that the metal compositions after reacting with the slag, provide sufficient supersaturation for inclusion nucleation at the latter stages of solidification. As in the latter stages of solidification little time and material is available for inclusion growth it was concluded that small inclusions are to be expected in the ESR solidification mode. Since the chemical and electrochemical reactions are an inherent part of the electroslag process, we are able to conclude that small globular oxide inclusions are a necessary result of the normal method of electroslag melting.

Text

2010-01-23

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http://hdl.handle.net/2429/19081

Metals and Materials Engineering

University of British Columbia

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