DUPLEX STAINLESS-STEEL FRACTURE SURFACE-ANALYSIS USING X-RAY FRACTOGRAPHY

The fatigue fracture surface of a duplex stainless steel was analyzed using x-ray fractography. A lower than average austenite content was o bserved at the fracture surface due to the transformation of austenite into deformation-induced martensite, The influence of fatigue cycling on the transformation was confined to a depth of about 30 mu m below the fracture surface, X-ray analyses of both the ferrite-martensite an d the austenite phases indicated residual stresses (sigma(r)) increasi ng with depth from the fracture surface and reaching a maximum some te ns of microns below the fracture surface. The lower sigma(r) observed at the fracture surface has been attributed to the stress relaxation e ffects caused by the new fracture surfaces created in the crack growth process, The observed decrease in full width at half maximum (FWHM) i n the ferrite-martensite phase was presumed to be due to the dynamic r ecovery effect that was likely to occur within the material close to t he crack tip as a consequence of fatigue cycling.