CONTROL OF COLUMNAR-TO-EQUIAXED TRANSITION IN CONTINUOUS CASTING OF 16% Cr STAINLESS STEEL

Abstract

In continuous casting of 16%Cr ferritic stainless steel, columnar grains undesirably forming among equiaxed
grains make non-uniform microstructure and degrade ridging property. Since this phenomenon results from
the change of solidification condition during continuous casting, we focused on Cellular-to-Equiaxed Transition
(CET) in continuous casting of 16%Cr ferritic stainless steel to control the microstructure of as-cast slab.
In order to find the CET condition, we carried out the one dimensional heat transfer analysis of the melt, and
predicted the CET condition by Hunt’s model. It was revealed that the secondary columnar grains usually formed
at 0.5~0.8 solid fractions, and the formation of them resulted from a steep increase of G/V1/2 value as the
melt was getting out of EMS field; however the increase of G/V1/2 was readily controlled by changing EMS
pattern and the secondary cooling intensity. In result, secondary columnar grains were eliminated by optimizing
the upper and lower EMS intensity, and increasing secondary cooling intensity. We also investigated
the effect of solidification parameters including superheat and casting speed as CET condition in continuous
casting process, and the results were also discussed by the terms of thermal condition of melt.