The effect of dwell on thermomechanical fatigue in superaustenitic steel
Sanicro 25
Abstract
Superaustenitic steel Sanicro 25 has been subjected to in-phase and
out-of-phase thermomechanical fatigue cycles in the temperature range
from 250°C to 700°C. Both constant strain rate cycling and cycling with
10 minutes dwell at peak temperature were applied. The effect of the
dwells on the cyclic response, internal structure and damage mechanism
was studied. Cyclic hardening/softening curves, cyclic stress-strain
curves and fatigue life curves were evaluated. The transmission electron
microscopy was used to find modifications of the internal structure and
precipitation of the nanoparticles. 10 min dwell at maximum temperature
modified substantially the dislocation arrangement. Various
nanoparticles representing the obstacles for dislocation motion were
analysed and identified by energy dispersive X-ray spectroscopy in
scanning transmission electron microscope. The damage mechanism
operating under specific loading conditions was investigated on the
surface as well as in the interior of the cycled specimens. Scanning
electron microscopy combined with focused ion beam and electron
backscatter diffraction was adopted to reveal the respective mechanisms
responsible for crack nucleation and propagation. Effect of dwells on
fatigue behaviour, modification of internal structure and damage
mechanisms are analysed and discussed.