超清浄メルティング・ストックの製造技術について

概要

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Production of super clean Ni base melting stocks were fundamentally investigated by using two vacuum induction furnaces having capacities of 50kg and 1ton.Under an usual MgO lining, it was possible to obtain about 10ppm of oxygen content, by limiting each titanium addition less than 2% of the melt and by lowering the bath temperature after the addition of active elements.Application of CaO lining enabled more effective deoxidation to attain oxygen levels less than 10ppm.Nitrogen content in the stocks can be removed to about 10ppm, by strict selection of charged materials, high temperature vacuum refining, reduction of air leakage and shortening interrupted time of vacuum evacuation.A thin wall mold and strong heat insulating hot top provided the melting stock with much better surface properties and decreased shrinkage cavities. As the result of these technical improvements, the overall quality of stocks are remarkably elevated.
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