In order to theoretically evaluate and show the effect of REM and Casulfides on heterogeneous nucleation, investigations have been made to find how REM addition influences the solidification microstructure of ingots and continuously cast slabs.
Some characteristics of REM-added steel compared with ordinary steel are as follows; (1) Primary dendrite arm spacing is narrower. (2) Primary dendrite arm length is shorter. (3) The growth direction of dendrite arms is less oriented. (4) The micro-segregation of C, S, P, Si and Mn is less.
It is concluded that new primary dendrite arms are generated due to the heterogeneous nucleation by REM addition in the region of comparatively small supercooling near liquid-solid interface.