A NEW INDUCTION-HEATING FLOATING-ZONE REFINING FURNACE FOR ULTRAPURIFICATION OF IRON-CHROMIUM ALLOYS

A new induction heating floating-zone refining (IHFZR) furnace was des igned and constructed using ultrahigh vacuum technology for the ultrap urification of base metals. The ultrahigh vacuum attainable in this fu rnace is so good as 1x10(-7}) Pa that a base metal bar can be zone-mel ted in both ultrahigh vacuum and higher-purity gas atmosphere containi ng less residual gases. The outline of this IHFZR furnace and the resu lts 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-levelin g passes in dry hydrogen, oxygen easily decreases in concentration fro m over 60 mass ppm to a few mass ppm; on the other hand, carbon decrea ses in concentration not so easily as oxygen but gradually. As a resul t, ultrahigh-purity Fe-18%Cr alloy with the concentration of C+N+O+S o f 12 mass ppm and ultrahigh-purity Fe-50%Cr alloy with the concentrati on of C+N+O+S of 10 mass ppm were obtained after only two zone-levelin g passes and ten zone-leveling passes in dry hydrogen, respectively.