| The melting of Fe·C, Fe·C·Zr and Fe·C·Ca alloys in graphite crucible placed in vacuum was carried out at 1540℃, and then cooled down with the rate of 35℃/sec or more. To eliminate from the problems as many composition variables as possible, the samples used in these experiments consisted simply of pure iron and reactor grade graphite with pure nodulizing element. The results show that under these relatively simple and limited conditions, nodular graphite is produced by the addition of strong deoxidizing agent such as Zr or Ca in the critical concentration. This suggests that the spheroidization of graphite in the cast iron may partially be attributed to the deoxidation of the iron which may induce the supercooling of the melt. The experimental results also indicate that the spheroidizing tendency of graphite in cast iron was increased by rapid cooling and thereby higher degree of supercooling or supersaturation of the carbon in the melt or both. These factors, however, were aidding the improvement of the spheroidization of graphite but not decisive in the formation of nodular graphite. The most favourable factor seemed to be the increase of the interfacial energy between the liquid iron and graphite surface due to the adsorbtion of nodulizing element on the graphite surface. |
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