Low cycle fatigue behaviour of duplex stainless steel: influence of isothermal aging treatment

The low-cycle fatigue behaviour of a duplex stainless steel was comparatively studied in standard heat-treated and isothermally aged (at 475 degrees C for 100 h) conditions by mechanical testing, scanning and transmission electron microscopy. It was established that fatigue life is longer in the aged condition as compared to the annealed condition at lower values of total strain amplitude delta epsilon/2 (delta epsilon/2 = 4.0 x 10-3 and 6.0 x 10-3) and becomes similar in annealed and aged conditions at delta epsilon/2 = 8.0 x 10-3. Fatigue resistance of the material converges with increase in delta epsilon/2 values as a result of rapid cyclic softening of the ferritic phase in the aged condition.