Superplastic Behaviour of δ/γ Duplex Stainless Steel

A δ-ferrite/γ-austenite duplex stainless steel was recrystallized by rolling at 673 K and subsequent annealing. The superplastic behaviour of alloy sheets prepared by above processing has been investigated in the temperature range from 1123 to 1273 K and over a range of strain rates 4.2 × 10-4 to 2.0 × 10-2s-1.The In σ vs. In ε curves were obtained and it was shown that the conditions obtaining the maximum strain-rate sensitivity index m changed from the constant strain rate at temperatures above 1223 K to the constant flow stress below 1223 K, so that the In σ vs. In ε curves were possible to divide into six regions according to the deformation behaviour.