Static recrystallization behavior and mechanical properties of heterogeneous nanostructured duplex phase stainless steel

Abstract

Static recrystallization (SRX) behavior and tensile property of a 92% cold-rolled duplex phase stainless steel were investigated. Lamellae structure, in which austenite (£) and ferrite (¡) phases were complicatedly stacked, was developed by heavy cold rolling. The lamellae gradually changed to equi-axed fine grains during annealing at 1023 K and fully SRXed after 1.44 © 104 s (4 h). Because of precipitation and its impediment of grain-boundary migration, grain coarsening was strongly suppressed even by prolonged annealing to 2.59 © 105 s (72 h). While volume fraction of £ phase was about 30% before annealing, it drastically increased up to 90%. The transformed phase from £ to ¡ by heavy cold rolling re-transformed to stable equilibrium £ at 1023 K and occurrence of SRX. No softening took place even with the occurrence of SRX and exhibited quite high HV hardness of 5.9 GPa due to precipitation, which effectively suppressed grain growth. Tensile strength was barely changed before and after annealing and stayed about 1.5 GPa on average, while ductility rapidly decreased.