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

摘要

In continuous casting of 16 percent 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 percent 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 approx 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.