Damage and Crack Initiation Behavior of Duplex Stainless Steel during Cyclic Loading

Abstract

Two phase metals during cyclic loading can suffer from non-uniform load or strain sharing between the phases due to elastic/plastic anisotropy. This can strongly influence the fatigue damage and crack initiation behavior. In this study, the fatigue damage and crack initiation behavior of an austenitic-ferritic duplex stainless steel with anneal/quenched and aged conditions has been studied by both experimental investigations and simulation using multi-scale material modeling. It was found, both experimentally and via simulations, that the material damage and crack initiation start in the ferrite phase in the material with the anneal/quenched condition and in either the ferrite or austenite phase in the material with the aged condition, mainly in the weakest phase if the deformation hardening is considered.

Micromechanical interactions in a superduplex stainless steel subjected to low cycle fatigue loading

“…It then increases slightly at the saturation stage. Such phase‐dependent changes can be related to the different cyclic behaviour that the ferrite has a larger cyclic softening rate than the austenite 16 …”

“…On the other hand, the evolution of the residual microstresses involves microplasticity and the correlations between them are more complicated. For the current steel in its initial state, the austenite is prone to plastic deformation under tension because of its somewhat lower initial hardness 16 and larger tensile microstresses. Yielding occurs in the austenite rather earlier in the tensile phase of the loading cycle, leading to the large reduction of thermal residual phase stresses observed by the neutron diffraction measurements.…”

“…3, after the initial cyclic hardening stage which extends over 3 loading cycles, the steel becomes cyclic softened. The ferrite which has a higher softening rate eventually becomes the softer phase in the steel 16 . This change in the relative phase properties likely results in the tensile microstresses in the ferrite and compressive microstresses in the austenite in the specimen unloaded from 100 cycles.…”

Macro and micro mechanical in-situ characterization using synchrotron diffraction of architectured micro-composite duplex stainless steels

“…Indeed, the pearlite lamellae transfer the load more effectively to the cementite phase. In more recent works, the effect of volume fraction, morphology and phase distribution in dual-phase steel has been extensively reported in [18]- [21] Several authors used multi-scale modeling and in-situ and ex-situ experiments to analyze the different parameters cited above and in particular the load sharing and stress interaction between phases and consequently the micro stress-strain curves [22][23] [6], [12], [15]. However, this approach seems to be insufficient to explain the complex plastic interaction between the ferrite and the austenite in conventional DSS microstructures [2], [12].…”