Effect of phase boundary on nucleation and propagation of microcrack in nuclear grade Z3CN20-09M stainless steel

Abstract

In order to study the effect of the phase boundary between austenite and ferrite phases on the nucleation and propagation behaviours of microcracks in nuclear grade Z3CN20-09M stainless steel, an in situ scanning electron microscopy (SEM) tensile technique was used to study the deformation, nucleation and propagation of microcracks during tension. The fractography was subsequently observed by SEM. The results indicated that, during tension, the deformation first occurred in the austenitic grains followed by in the ferrite, and the microcracks were subsequently preferential formed at the phase boundary between austenite and ferrite phases. In the case of the phase boundary perpendicular to the loading direction, microcracks nucleated and subsequently propagated along the phase boundary. In the case of the phase boundary parallel to the loading direction, microcacks nucleated at the intersection of slip bands and the phase boundary and propagated perpendicularly to the phase boundary, resulting in deflection of the main crack. The phase boundary played a hindrance effect on crack propagation.