Mechanical characterization and evaluation of pitting corrosion resistance of a superferritic stainless steel model alloy 25Cr-6Mo-5Ni

The mechanical properties and corrosion resistance of annealed superferritic stainless steel model alloy 25Cr-6Mo-5Ni were investigated in 0.6 M NaCl solution. The microstructure consisted of a ferrite matrix and eutectoid phase with a lamellar structure distributed at grain boundaries and within the ferrite grains with a spherical morphology. Tensile and impact results suggested brittle behavior of the model alloy. Fractography analysis revealed typical cleavage facets, river patterns and micro-cracks at grain boundaries and across the ferrite grains. Pitting corrosion began within the eutectoid phase, which contains in chrome depletion zones. Electrochemical impedance spectroscopy measurements suggest that the breakdown of passive films was more susceptible in the eutectoid phase.