Electroslag-melted molybdenum

Abstract

The preparation of molybdenum ingots by electroslag melting is discussed, ingot characteristics are described, and results of mechanical testing of wrought products are compared with those from similar material prepared from arc-cast molybdenum. Thermochemical considerations limit the choice of slag materials to a few high-temperature oxides; of these, yttrium oxide was found to be best suited for use in molybdenum melting. The use of additives to the slag was found necessary to minimize the occurrence of excessive oxide films at ingot grain boundaries. Changes in ingot surface and structure were found to be responsive to changes in such melting variables as power input, electrode spacing, electrode polarity, and environmental pressure conditions. Pressure conditions, electrode polarity, and the slag additives carbon and yttrium, were found to influence the oxygen level and occurrence of extraneous oxide phases in the ingots. Excellent surface conditions are normally associated with the electroslag ingots; as a direct result, much less waste in conditioning ingots for fabrication was encountered than is normal for arc-cast ingots. Additional material economy results from the unusually low temperature at which the electroslag ingots can be fabricated. Sheet fabricated from the electroslag-melted ingots appears to have mechanical properties superior to those of sheet prepared from similar arc-cast ingots.