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

摘要

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 IXIO'M 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.