Microstructure associated with crack initiation during low-cycle fatigue in a low nitrogen duplex stainless steel

In the framework of an extensive investigation regarding crack initiation and propagation during low-cycle fatigue in Duplex Stainless Steels (DSS), the present study was focused on the fatigue surface damage in a low nitrogen DSS. The Coffin Manson curve is presented for DIN W Nr. 1.4460 DSS and compared with that of a high nitrogen steel. The surface damage has been observed by optical and electronic microscopy and analysed in relation to the underlying dislocation structure by transmission electron microscopy. The results for the present low nitrogen steel DIN W Nr. 1.4460 show that, at Δεt = 0.8 × 10−2, the preferred site for short crack initiation seems to be the intense slip marks formed mostly in the ferrite and less frequently in phase boundary. On the contrary, at Δεt = 1.2 × 10−2, short cracks form mostly in phase boundary.