A New Induction Heating Floating-Zone Refining Furnace for Ultrapurification of Iron-Chromium Alloys

Abstract
A new induction heating floating-zone refining (IHFZR) furnace was designed and constructed using ultrahigh vacuum technology for the ultrapurification of base metals. The ultrahigh vacuum attainable in this furnace is so good as 1x10^-7} Pa that a base metal bar can be zone-melted in both ultrahigh vacuum and higher-purity gas atmosphere containing less residual gases. The outline of this IHFZR furnace and the results of its application to the purification of high-purity iron, Fe-18%Cr alloy and Fe-50%Cr alloy are described. After only two zone-leveling passes in dry hydrogen, oxygen easily decreases in concentration from over 60 mass ppm to a few mass ppm ; on the other hand, carbon decreases in concentration not so easily as oxygen but gradually. As a result, ultrahigh-purity Fe-18%Cr alloy with the concentration of C+N+O+S of 12 mass ppm and ultrahigh-purity Fe-50%Cr alloy with the concentration of C+N+O+S of 10 mass ppm were obtained after only two zone-leveling passes and ten zone-leveling passes in dry hydrogen, respectively.