Influence of dynamic strain aging on the mechanical properties and microstructural evolution for Alloy 800H during hot deformation

Abstract

Two types of hot compression tests, namely, constant strain rate and strain rate jump, were carried out for Alloy 800 H within a wide temperature range of 450–900 °C and strain rate range of 0.001–1 s−1. Following the above tests, we studied the effect of dynamic strain aging (DSA) on the mechanical properties and microstructure features to reveal the underlying mechanism responsible for DSA. The results indicated that three kinds of serrated yielding behavior (Type A, B and C) can be observed in the stress-strain curves of the DSA regime. The DSA temperature (TDSA) is located in the temperature range of 500–750 °C at a strain rate of 0.001 s−1, in 550–790 °C at 0.01 s−1, and in 600–840 °C at 0.1 s−1. The activation energy for the appearance of negative strain rate sensitivity was calculated to be 194 kJ/mol, and pipe diffusion of substitutional solutes (i.e. Cr, Ni and Ti) is regarded as the mechanism of DSA. TEM observations further elucidated a tendency of linear microstructure within the DSA regime, which also restricts the cross-slip of dislocations and promotes the strain localization along deformation bands.