Hot Ductility and Microstructure in Slab Shell of Low Ni Austenitic Stainless Steel

Abstract

Hot ductility in slab shell of two types of low Ni austenitic stainless steels was investigated via tensile test. Results showed that, reduction of area (RA) in Cr17Mn6Ni4Cu2N decreased gradually from surface to inside. However, RA in Cr15Mn9Cu2NiN shell surface was low, and increased from surface to inside. Analysis suggested that, the difference of RA between the two steels due to the different solidification process. In the shell of former steel, δ ferrite solidifies as the primary phase, then transforms into austenite. The space between primary arms increases from surface to inside, leading to the decrease of hot ductility. In the latter steel, δ ferrite does not solidify entirely as the primary phase because of the high cooling rate, but austenite solidifies directly from the retained liquid between δ ferrite dendrites. The change of solidification mode is most obviously in slab surface, which decreases its hot ductility.