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

Abstract

Various characteristics were observed in the solidification macrostructure of ingots and continuously cast slabs treated with REM.
The results are as follows:
1) REM addition brings about diminition of macro-segregation, enlargement of equiaxed zone, and reduction of loose structure.
2) The starting position of the formation of the inverse V-segregation moves toward the center of ingot and the segregated area expands. The length of segregation line and the segregation ratio are reduced.
3) By autoradiographic observation, large differences in macrosolidification rate are not observed, however, mushy zone at the bottom of an ingot is formed earlier.
4) REM-oxides, sulphides, and oxysulphides are mainly precipitated in dendrite arms. The constituents of inclusions are varied by the methods of REM addition.
Non-metallic inclusions formed by REM addition seem to act as nucleation catalyst and thus improve not only the microstructure but also the macrostructure of the casts.