THE SOLIDIFICATION CHARACTERISTICS OF AISI 304 STAINLESS STEEL BY TWIN ROLL STRIP CASTING PROCESS

摘要

Since the very early stage of solidification determines the surface quality of a cast strip, we have employed two major variables of melt superheat and casting speed to understand the solidification mode in the very early stage. The mechanism of longitudinal cracking on the surface of cast strips was also investigated. As the melt superheat lowered, the solidification microstructure of the as-cast strip was finer and showed a broader equiaxed zone. The microstructure of the cast strip with the low superheat melt was characterized by the large spherical particles of about 100 microns, which were bundled near the surface and mixed with columnar grains. When a strip with high nickel content was cast at low superheat, the primary austenitic solidification microstructure was shown at the very early solidification ahead of the columnar dendritic grains of the primary ferritic phase. The longitudinal facial cracks, which were found on the delayed solidified shell of the strip, can be explained by the hot cracking mechanism accompanying the formation of concentrated liquid film of low melting point preferably along grain boundaries.