Grain size and low-cycle fatigue life under hold-time conditions in FeCrNi austenites

Abstract

Low-cycle fatigue tests with one minute tension hold-times have been performed at 593 °C on Fe20Cr15Ni alloy specimens having grain diameters from 15 μm to 150 μm. Fatigue life is found to pass through a maximum at a grain size of about 40 μm. At finer grain sizes, lifetime appears to be controlled by the initiation of wedge-type cracks at grain boundaries on the surface and within the sample. At intermediate grain sizes, lifetime is controlled by crack initiation and by intergranular crack propagation in a combined viscous-fatigue mode. At the coarsest grain size, lifetime is reduced drastically and appears to be limited by the rapid propagation and link up of wedge-type cracks along grain boundaries.