Constitutive equations for prediction of the flow behaviour of duplex stainless steels

The high temperature workability of a 2205 duplex stainless steel has been investigated by torsion testing between 950 and 1200 °C. The constitutive equations relating peak flow stress, temperature and strain rates were obtained, and the composite model, where austenite and ferrite are the hard and soft phases, respectively, was found to give an excellent description of the experimental data. The peculiar shape of the equivalent stress vs. equivalent strain flow curves has been discussed; a model based on the hypothesis that during torsion of wrought duplex stainless steels the load transfer from ferrite and austenite is delayed to a later stage of the straining process has been developed, and successfully used to describe the experimental data. Thus it was concluded that during the early stage of the tests the deformation is inhomogeneous, since strain accumulates in ferritic regions, while austenite is almost undeformed.