Short crack growth during low cycle fatigue in a Duplex Stainless Steel

M. BALBI; H. KNOBBE; S. HEREñU; M. KüBBELER; M.C. MARINELLI; U. KRUPP; I. ALVAREZ

Trondheim

Simposio; International Symposium on Fatigue Design & Material Defects; 2011

The damage evolution during low and high cycle fatigue in an embrittled duplex stainless steel ischaracterized in this paper. The results have shown that for low cycle fatigue, microcracks initiatealong the most favorable oriented slip planes with the highest the Schmid factor (SF). However,intergranular a/a boundaries are also a possible crack nucleation site. The propagation of the crack in the austenite follows slip planes of the highest SF.In the high cycle fatigue regime, the damage is generally initiated in the austenite by slip bandformation followed by crack nucleation either in á-á boundary or in a/g boundary in the intersection of slip bands in the austenite. Microcracks in the ferrite nucleate and propagate along slip planes with the highest SF but in the case of the austenite grains, this is not always the case; namely, a crack can follow first on a slip plane of low SF and after several cycles it certainly changes to another one with the highest factor. This behavior can be attributed to the high elastic anisotropy of the austenitic phase.Despite the differences in both fatigue regimes, phase boundary is an effective barrier against crack propagation because it delays the advance of the crack tip.