Initiation and propagation of short cracks in austenitic-ferritic duplex steel

Austenitic-ferritic duplex stainless steels are widely used for applications, where both excellent strength and high corrosion resistance are required. In the current study, high cycle fatigue experiments were performed on the austenitic-ferritic duplex stainless steel 1.4462 in order to investigate short crack initiation and propagation. It is shown that the most frequent crack initiation sites are grain boundaries between ferritic grains followed by slip bands in austenite and phase boundaries. Taking into account the elastic anisotropy of the austenitic phase, the surprisingly high fraction of cracks formed along slip bands in austenite can be explained with the texture and microstructure of the material. Analyzing the correlation between crack propagation rate and crack length, it is found that in both phases, the transition crack length between the regimes of microstructurally and mechanically short cracks correlates with the mean grain elongation under the average angle between crack path and loading axis. Additionally, the dependence of the crack propagation rate on the distance between crack tip and opposing grain or phase boundary, i.e. the barrier effect of these boundaries for short crack propagation, could be measured. The results obtained expand the knowledge about short crack behavior in the investigated material, which is a key parameter for the lifetime in the high cycle fatigue regime.