Abstract

HILDERS, O.A et al. Fracture morphology study of a duplex stainless steel isothermically aged at 475 ºc. Rev. Fac. Ing. UCV [online]. 2007, vol.22, n.1, pp.61-70. ISSN 0798-4065.

The tension fracture process at room temperature has been studied in a duplex stainless steel isothermically aged at 475 ºC between 1 and 120 h. The fracture surfaces were studied by means of scanning electron microscopy (SEM) and the fracture profiles by an Image Analyzer (IA). The Fractal Dimension of these surfaces was measured by the Slit Island Method, and their values were related with the mechanical properties. The micro-void coalescence mechanism of fracture was observed for the aging times ranged between 1 and 120 h, and intergranular microcracks were developed just for the aging condition of 120 h. The strength of the steel continuously increases with the aging time, and the ductility decreases. On the other hand, the Fractal Dimension increases from 1,09 (the as-received condition), to 1,30 (6,5 h of aging), which was related to the increased complexity of the micro-voids on the fracture surfaces. On the other hand, the Fractal Dimension decreases from 1,30 (6,5 h of aging), to 1,05 (120 h of aging). This behaviour was related to a smaller micro-void size, to the initial process of intergranular secondary cracking and to the smaller tortuosity of the corresponding fracture surfaces.

Keywords : duplex steels; fractography; fracture profile; fractal dimension; micro-void coalescence.