INVESTIGATION IN THE VACUUM MELTING OF HIGH-PURITY IRON IN MAGNESIA CRUCIBLES

Reaction between carbon and oxygen in melts of iron was studied, using crucibles made of electrically prefused magnesia, in a medium-frequency induction furnace of 10kg. capacity. It was found that the melts continually absorbed oxygen from the crucible, so that during the heat its oxygen content dropped to a minimum and then rose again. Under a furnace pressure of 10-4 (and in a few cases 10~(-1) mm Hg, the [％C].[0％] product fell between 6×10~(-6) and 3.5×10~(-5). By limiting the carbon content of the charged iron to 0.03—0.05％, with a C:O ratio of 2, a high-purity product containing less than 0.003％ oxygen and less than 0.006％ carbon was satisfactorily obtained. The melt-crucible reaction became less pronounced with each heat after a new crucible had been put into use. The oxygen content of the melt had a marked effect on its final nitrogen content. A high oxygen concentration retarded de-nitrogenation.