Solidification Microstructure of Ingots and Continuously Cast Slabs Treated with Rare Earth Metal

Abstract

In order to evaluate theoretically and prove the effect of REM and Ca-sulphides on heterogeneous nucleation, investigations have been made to find how REM addition influences the solidication 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 arms are shorter, and they exist more in number.
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 hetrogeneous nucleation by REM addition in the region of comparatively small supercooling near liquid-solid interface.