Phase morphology and fatigue cracks nucleation in UNS S32750 Plate

MC MARINELLI; JW SIGNORELLI; R BOLMARO; I ALVAREZ

Grado and Aquilea

Conferencia; 7th World Duplex 2007 Conference; 2007

AIM- Assoziazione Italiana de Metallurgia

The low cycle fatigue behaviour of rolling UNS S32750 duplex stainless steel plates was characterized at E=0.8x10E(-2) for specimens cut parallel and perpendicular to the rolling direction. The fatigue results indicate that specimens oriented parallel to the rolling direction reach the longest fatigue lives and microstructural observation has revealed that the plastic deformation nucleation generally initiate in the austenite and propagate to the ferrite. In the other direction, the deformation does not flow from one phase to the other but instead deformation lines are distributed in both phases. Anisotropy effects were observed in relation with the material orientation although no important differences have been observed in the relative values of the Taylor factor between austenite and ferrite along (2.18/2.07) or perpendicular (2.19/2.08) to the rolling direction. Variations in the morphology of the microstructure and particularly in the phase size seem to alter the distribution of the slip lines. This parameter is assumed to be intimately associated with plastic deformation. Thus, the experimental findings have been analyzed in terms of the modified Hall-Petch relation for multiphase materials.