Micromechanical Aspects of Transgranular and Intergranular Failure Competition

Quantification of characteristics that govern intergranular fracture initiation and
propagation of this fracture micromechanism in competition with cleavage one is main aim of the
paper. A NiCr steel of commercial quality and the same steel with an increased content of impurity
elements, Sn and Sb, were used. Step cooling ageing was applied in order to induce intergranular
embrittlement. Standard and pre-cracked Charpy type specimens were both tested in three-point
bending to determine fracture toughness characteristics. In order to characterise the quantitative
differences in fracture surfaces roughness a fractal analysis was applied. A boundary level of fractal
dimension has been determined to be 1.12: fracture surface roughness with a higher value reflects
high level of intergranular embrittlement and thus fracture resistance degradation.