Effects of mean strain and tensile pre-strain on torsional fatigue behaviours of duplex stainless steel SAF2205

Abstract

Abstract. Effects of mean strain and tensile pre-strain were investigated on the torsional fatigue behaviours of duplex stainless steel SAF2205. Two equivalent strain amplitudes (0.5%,0.7 %), three strain ratios (-1, -0.5, -0.25) and 5% tensile pre-strain were chosen. Results indicated that the mean strain had no distinct influences on the torsional fatigue behaviours in terms of cyclic stress reponse and fatigue life while tensile pre-straining made a significant increase in cyclic stress response which was mainly attributed to the cross hardening derived from the loading sequence of monotonic tension preceding to cyclic torsion and led to a reduction in fatigue life. The failure mechanisms were revealed by scanning electron microscope characterized by microcracks initiation at the extrusions in ferrite and phase boundary inhibited further propagation. Additionally, the fractography of all fatigued specimens revealed a quasi-cleavage brittle mode with features of distinct tearing ridges and cleavage facets.

DMA2022 Microscopic mechanism of cyclic hardening/softening of a TRIP-aided duplex stainless steel

“…A lot of research [10][11][12][13] has been extensively done on the steel without TRIP effect under cyclic loading conditions and systematically analyzed the effects of various factors (loading rate, strain amplitude, temperature). Literature [14][15][16][17] studied non-TRIP-aided duplex stainless steel and found that the leading cause of cyclic hardening/softening is dislocation generation, movement, obstruction, and interaction. However, there are few studies on TRIP-aided duplex stainless steel's cyclic mechanical properties and microscopic mechanism.…”

“…They fund the formation of crossing ε-martensite and α'martensite at higher ε a can hinder the rearrangement of dislocations in ferrite. Li et al [14] carried out the asymmetric strain-controlled fatigue test of DSS SAF2205 TRIP-aided duplex stainless steel. It is found that the test steel exhibits secondary cyclic hardening.…”