Transfer of iron to Cu–Ni alloys from the lining of the vacuum induction furnace

Resumo

In Ni–Cu alloys, iron must be excluded in many cases. Iron may enter the alloy from the batch or the furnace lining. Since the Fe₂O₃ content in refractories may be as much as 2.5%, it is important to assess the increase in iron content in alloys on account of interaction with the furnace lining. In the present work, the influence of the Fe₂O₃ content in the crucible and the volume of the crucible on the iron content in the final alloy is studied. Thermodynamic analysis and experimental data indicate that the nickel and copper in Ni–Cu alloys may reduce iron that is present in the lining. When using low-iron batch, iron from the crucible is transferred almost completely to the melt. The increase in iron content in Ni–Cu alloys is investigated as a function of the capacity of the vacuum induction furnace and the Fe₂O₃ content in the periclase crucibles, with complete transfer of the iron from the lining to the melt. With increase in furnace capacity, less iron enters the melt from the crucible. With more than 200 kg of metal, the increase in iron concentration mainly depends not on the furnace capacity but on the Fe₂O₃ content in the refractory. In order to produce Ni–Cu alloys with <0.01% Fe, refractories with Fe₂O₃ content no higher than 0.5% must be used. To produce Ni‒Cu alloys with <0.05% Fe, the use of lining refractories with Fe₂O₃ content no higher than 2.5% is recommended.