Characterization of a commercial superplastic stainless steel, SuperDux64

The superplastic properties of SuperDux64 have been characterized at temperatures ranging from 1173 to 1323 K and strain rate ranging from 10−4 to 10−1 s−1. The strain rate sensitivity value for SuperDux64 is about 0.5, suggesting that grain boundary sliding is the dominant deformation mechanism. The apparent activation energy in the superplastic region is approximately 450 kJ mol−1. Strain accommodation at grain triple junctions is accomplished by the preferential dynamic recrystallization in the soft phase (i.e., ferrite). The cavitation behavior of SuperDux64 was also studied. Cavitation was found to occur in distinct bands that corresponded to regions containing high concentrations of γ phase in the δ matrix. The roles of heterophase and homophase boundaries, and their effects on boundary sliding are discussed. Strain incompatibility at grain triple junctions (resulting from the differential strain rates between a hetero-boundary and homo-boundary) is also addressed.