1988 Volume 74 Issue 8 Pages 1601-1608
A process has been developed to enhance the undercooling of molten carbon steel, by controlling the heterogeneous nucleation catalysts with addition of rare earth metal (REM). Molten steel of substantial mass, processed for the enhanced undercooling, was easily undercooled even with comparatively smaller cooling rates. A chemical analysis showed that REM components didn't exist in the ingot with REM addition except for the surface layer of the ingot. Furthermore, the number of nonmetallic inclusions decreased due to REM addition. It is considered that inclusions, which are active as nucleation catalyst, are attracted to the inner wall of alumina crucible used for the experiment by interreaction between REM components in the melt and the crucible wall and the active catalysts are removed from melt.
The microstructure of specimens after solidification was investigated in relation to the degrees of undercooling and recalescence. In the specimen solidified with significant amount of recalescence, nondendritic structure of homogeneous matrix with precipitated graphite particles was observed. On the other hand, dendrite morphology was observed in the specimen solidified with little amount of recalescence even though the melt was highly undercooled.
