Ultra-purification of iron by three types of melting furnaces constructed using ultra-high vacuum technology

Abstract

For the ultra-purification of base metals a new arc melting furnace, a new induction-heating floating-zone melting furnace and a new cold-crucible induction melting furnace have been designed and constructed using ultra-high vacuum technology. The ultra-high vacuum attainable in this induction-heating floating-zone melting furnace is so good as 1×10 -7 Pa that an iron bar can be zone-melted not only in ultra-higher vacuum but also in higher purity gas atmosphere containing less residual gases than those in a conventionally used one. The high-purity electrolytic iron which had been developed by us has been purified by the combination of these melting furnaces. The concentration of C+N+O+S easily decreases from 14.4 mass ppm before zone-leveling to 2.9 mass ppm and 2.2 mass ppm after only four zone-leveling passes in dry hydrogen and further four zone-leveling passes in ultra-high vacuum, respectively, and each impurity concentration is below 1 mass ppm. Ultra-high vacuum is very important and effective for the ultra-purification of iron and also the other base metals and alloys.