Hot deformation characteristics of 2205 duplex stainless steel based on the behavior of constituent phases

High temperature behavior of 2205 duplex stainless steel was studied by considering behavior of each constituent phase. The specimens were subjected to hot compression tests at temperatures of 800–1100 °C and strain rates ranging from 0.001 to 1 s⁻¹ at intervals of an order of magnitude. The flow stress analysis showed that hot working empirical constants are different at low and high temperatures. The strain rate sensitivity m was determined and found to change from 0.12 to 0.21 for a temperature rise from 800 °C to 1100 °C. The apparent activation energy Q was calculated as 554 and 310 kJ/mol for low and high temperature, respectively. The validity of constitutive equation of hyperbolic sine function was studied and stress exponent, n, was assessed to be 4.2. Assuming the hyperbolic sine function for determination of strain rate and application of the rule of mixture, the interaction coefficients of δ-ferrite, P, and austenite, R, were estimated at different hot working regimes. It was found that the interaction coefficients are functions of Zener–Hollomon parameter Z and obey the formulas P = 1.4Z^−0.08 and R = 0.76Z^0.005. Therefore, it was concluded that at low Z values δ-ferrite almost accommodates strain and dynamic recovery is the prominent restoration process which may even inhibit dynamic recrystallization in austenite. Otherwise, at high Z, austenite controls the deformation mechanism of material and dynamic recrystallization leads in finer microstructure.