Effect of Crucible Materials on the Bearing Steel During Vacuum-Melting

By using the chamotte-, high-alumina-, alumina-and magnesia-crucibles the bearing steel (JIS SUJ 2) was melted in vacuum, and the change in the degree of vacuum during melting, the change of the chemical composition of the melted steel and the structures of the used crucibles were observed. Then the interrelation between the crucibles and the melted steel was studied, and the results were obtained as follows: (1) When the steel was melted in vacuum in chamotte- or high-alumina-crucibles, the lowering of the degree of vacuum during melting was remarkable, and C in steel was markedly decreased more than the case of melting with other crucibles, while Al and Si in steel were increased. Moreover, it was observed that the SiO2 contained in the crucible was decreased on the inner surface in contact with the molten steel. (2) When the steel was melted in alumina-crucibles, C in steel was decreased, while Al in steel was increased. (3) When steel was melted in magnesia-crucibles, little lowering of the degree of vacuum during melting was observed and C was little decreased. In this case, however, the magnesia-crucibles cannot be used again because of cracks.