Satoru Yamamoto1, Takeshi Yasuda2 and Yotaro Murakami1
1Department of Metallurgy Faculty of Engineering, Kyoto University, Kyoto
It was confirmed that graphite formed during annealng of white cast iron is nodularized by sulphur addition, and that the nodularizing effect of sulphur depends upon annealing temperature, annealing time, amount of additional sulphur, method of sulphur addition and C contents: (1) The morphology of graphite is changed with increasing annealing time from sphere to irregulr shape. (2) The nodularizing effect of sulphur shows a remarkable dependency upon the annealing temperatures. (3) The graphite-nodularization is accelerated by the increasing amount of additional sulphur. (4) Immersion of stick sulphur into melts is more effective for the nodularization of graphite than the addition of powder sulphur onto surface of melts. (5) In low carbon alloys, graphite is more easily nodularized by a small addition of sulphur.
These results can be explained by the assumption that graphite nodules are formed by the filling up of spherical cavities in the solid with graphite and these spherical cavities were due to sulphur-gas bubbles in the melt on solidification.
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