Damage Evolution and Crack Nucleation During High-Cycle Fatigue in Duplex Stainless Steel

M.C. MARINELLI ; U. KRUPP; M. KUEBBELER; I. ALVAREZ-ARMAS; S. HEREÑÚ

Oxford

Conferencia; ESIS TC2 (Micromechanisms); 2012

ESIS

For studying the damage evolution during High-Cycle Fatigue, stress-controlled cyclic tests were conducted on standard duplex stainless steel (DSS) in two different heat treatment conditions (annealed, 475°C-embrittled) and scanning electron microscopy (SEM) observations in combination with automated electron backscattered diffraction technique (EBSD) measurements were analyzed. These studies have revealed that the fatigue limit is substantially increased by the embrittling heat treatment. For both heat treatment conditions cyclic plastic activity usually begins firstly in the austenite phase. As cycling proceeds, plastic deformation is present in both phases in the annealed material while in the embrittled DSS only some ferritic grains show plastic deformation near the phase boundaries. Therefore, in the embrittled DSS microcracks nucleate at alpha/alpha and alpha/gamma boundaries and then propagate along slip markings formed successively in the austenitic and ferritic grains, while in the as received material they nucleate mostly along slip bands in the ferrite and in austenite. The experimental data have been used in combination with a numerical short-crack model to describe quantitatively the propagation behaviour of microstructurally short fatigue cracks.