SynopsisThe mechanisms of deoxidation in the electroslag remelting process have been studied, with particular reference to the reactions involving calcium. ESR ingots made with varying deoxidation rates have been examined with respect to their bulk composition and oxide inclusion composition. We find that at high oxygen potentials (% FeO> 0.7 in the slag), reactions between slag FeO and the deoxidant predominate. At low oxygen potentials (% FeO C 0.2 in the slag) exchange reactions between deoxidant and the slag components control the inclusion composition. At intermediate oxygen potentials, the inclusion composition is strongly influenced by the Si02 content of the slag. The manufacture of low-oxygen, low-sulphur steels by ESR will hence require slaps with small contents of both Si02 and A1203.

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Solute-lean defects, commonly called white spots, are frequently found in superalloys. These defects limit the service life of components made from superalloys, and alloy producers have devoted intense study to their characterization and elimination. Recent work shows that solute lean defects can be classified as "discrete," "diffuse" and "mini," and can be further classified into" clean" and "dirty" white spots. More than one formation mechanism for white spots is exemplified by the chemical and morphological differences between discrete, diffuse and mini white spots. White spot detection depends on the thermomechanically developed precipitation of hardening phases, coupled with specific etches that preferentially react to microstructure differences. The white spot defect is indigenous to the vacuum arc remelting process, but defect formation can be minimized by careful process control.

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.

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