Experimental characterization of short crack nucleation and growth during cycling in lean duplex stainless steels

• During LCF of AL 2003, cracks nucleate along intrusion/extrusions in the ferrite.
• In the austenite cracks grow by combined slip or along favorable slip planes.
• The microcracks growth follows an exponential law.
• The growth rate of microcracks decreases in crystallographic barriers.
• During high cycle fatigue (HCF) cracks nucleate at grains boundaries.

Considering that many applications of Lean Duplex Stainless Steels (LDSSs) involve cyclic loading, the aim of this paper is to study short crack initiation and growth during low (LCF) and high cycle fatigue (HCF) in AL 2003 (UNS S32003). Electron Backscattered Diffraction (EBSD) analysis of plastically active grains allows to determinate the slip systems and their associated Schmid factor (SF). Additionally, the dislocation structure developed during cycling is observed by transmission electron microscopy (TEM). Whereas in HCF cracks nucleate at grains boundaries, during LCF cracks nucleate along intrusion/extrusions in ferritic grains and as they reach austenitic grains grow along active slip systems or by double slip system. Moreover, phase boundaries and grain boundaries act as effective barrier against crack propagation.