Electron Beam Cold Hearth Refining of Investment Casting Superalloys in a Large Production EB Furnace

Abstract

Electron beam cold hearth remelting (EBCHR) is increasingly applied to the production of remelt stock for investment casting. In smaller EBCHR furnaces, remelt bars are cast one at a time. Because this method does not lend itself well to production in large EBCHR furnaces, this investigation evaluates a newly developed EB drum casting process and the characteristics of half-round remelt bars produced. Processing parameters investigated were casting rate, mold size and configuration, and hot topping procedure. Half-round EBCHR drum cast bars of IN100 and PWA1422 were evaluated for structure, chemical composition and oxide cleanliness using the electron beam button test (EBBT). Bars with good internal and surface integrity were produced applying combinations of hot topping and a surface glazing procedure. The results indicate that uniform chemical composition can be achieved within individual bars and within a heat. Oxide cleanliness was improved after EBCHR, but the greatest impact was made when the top surface of the bars were conditioned.