ALUMINUM EVAPORATION FROM TITANIUM-ALLOYS IN EB HEARTH MELTING PROCESS

In order to investigate Al evaporation behavior in the EBCHR process, Ti alloys were remelted in a 250 kW EB furnace. Ti alloys used in this experiment were Ti-64, Ti-811 and SP700, a newly developed Ti alloy at NKK. In this experiment, EB power was kept almost constant and round ingots with approximately 136 mm in diameter were cast at a different casting rate. During melting operation, in-situ temperature measurement was carried out by a two-color thermometer. For determining an Al evaporation site in this process, both feedstocks and metal in the hearth after melting operation were analyzed in detail together with ingots. It was found that the Al yield, the ratio of the final Al concentration to the initial Al concentration, increased with the casting rate. Under the present experimental condition, the Al evaporation reaction took place mainly in the hearth, which was found to be a complete mixing reactor. Based on the above experimental results, the rate equation of Al evaporation was considered by taking account of both reaction at the interface and mass transfer in the melt. Calculation explained the experimental results well when the time-averaged temperature in the hearth was in the range of 1 800 and 1 900-degrees-C, which was in a relatively good agreement with temperature measurement results.