Some trials were carried out to produce spheroidal graphite cast iron by suspension of bubbles of gases such as H2, N2, C02, and Ar inside the molten cast irons. Two kinds of cast irons were used - a) a synthetic cast iron containing 3.8%C and 2.I%Si prepared from electrolytic iron, carbon, and high purity metallic Si, arid b) an ordinary cast iron containing 3.6%C, 2.6%Si, and 0.27% Ti. Three methods were employed to suspend gas bubbles inside molten cast irons - a) additions of Ce, La, Y, Ti, al!� Zr which contained large amounts of H2, b) precipitation of N2 bubbles from supersaturated molten cast iron, and c) direct injection of gas bubbles into the molten cast iron through extra fine porous plugs. The results of the present work are summarized as follows - I) Graphite nodules are obtained by the additions of Ce, La, Y, Ti, and Zr which have absorbed a large amount of H2. It is impossible to obtain graphite nodules by the additions of completely degassed Ce, La, Y, Ti, or Zr. 2) Graphite nodules are obtained by the suspension of N2 bubbles in the melts utilizing the pressure dependence of solubility of N2 in the melts. 3) Graphite nodules are obtained by direct injection of various other gases into melts through extra fine porous plugs. 4) Gas cavities and hollow graphite nodules are often observed which seem to be the result of incomplete filling up of gas bubbles with graphite. 5) Graphite nodules have a polycrystalline structure with the c axis of all crystallites pointing in a radial direction. 6) Some feat.ures of graphite nodules are explained based upon the gas bubble theory established in this work ..
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