Effect of crystallization behavior of mold flux on slab surface quality of a Ti-bearing Fe–Cr–Ni super alloy cast by means of continuous casting process

A continuous casting technology of a Ti-bearing Fe–Cr–Ni super alloy (N08825) has been developed. Laboratory-scale experiments including thermal analysis, high-temperature tensile test, measurement of thermal properties and reaction between molten alloy and flux were first carried out to determine the basic casting conditions. Throughout the experiments, this alloy was found to have lower liquidus temperature than type 304 stainless steel and have relatively wide brittle range immediately after solidification was completed. Subsequently, 18 t small-scale production tests were conducted setting up a mild cooling condition to prevent cracks. Two types of mold fluxes, which were crystalline and glassy ones, were compared. The test results revealed that crystallization behavior of the mold fluxes significantly affected the slab surface quality. Longitudinal cracks and depressions, which were partly accompanied with bleedings, were formed with the glassy type. On the other hand, sound surface quality with very few defects was obtained with the crystalline type. The appropriate flux was chosen through the small-scale tests followed by the successful practice in 60 t full-scale mass production.