Hot working and restoration mechanisms in duplex stainless steels

The strength and ductility behaviour of duplex stainless steel 23Cr-4Ni was investigated by means of continuous torsion tests in the temperature range of 1000 to 1200 °C and at strain rates of 0.1, 1 and 5 s^-1. The peak stresses of flow curves at various temperatures were analyzed in terms of α/γ ratio and of phase strength. The ductility was dependent on temperature and practically not affected by strain rate. Dynamic restoration processes produce recovered structure in ferrite and recrystallization in austenite both reducing the stress concentration at interfaces. The dependence of flow stress data on temperature and strain rate fitted a sinh equation; the activation energy of deformation and of α → γ transition was 460 kJ/mol. The microstructure analysis showed that deformation affects the soft ferritic phase at the beginning and is then transferred to strong austenite phase. The fracture under all test conditions appeared nucleated and propagating along α-γ interfaces.