High temperature mechanical behaviour of δ–γ stainless steel

Abstract

The deformation behaviour of a duplex stainless steel has been investigated by tensile and torsion tests at temperatures ranging from 1000 to 1275°C. The microstructure of the as received material consists of elongated islands of austenitic grains in a more or less continuous ferrite matrix. This microstructure remains essentially constant during deformation by tensile strain rate change tests. Deformation occurs by a slip creep process in most of the range of strain rates tested (n = 5) with a transition to a grain boundary sliding mechanism in the lower stress regime. On the other hand, dynamic recrystallisation starts after a critical strain during torsion testing. The flow stress decreases to a steady state value associated with a fine and stable microstructure. The deformation behaviour is characterised by a stress exponent of about 2·5–3, which suggests a contribution to deformation of both, slip creep and grain boundary sliding mechanisms. An activation energy for deformation of 370 kJ mol^-1 was measured for both tensile and torsion tests. This value is similar to that reported for the activation energy for deformation of austenitic stainless steels.