Effects of pH and specimen orientation on the corrosion fatigue behaviour of a duplex stainless steel in chloride solutions

Fatigue crack. growth (FCG) behavior of a duplex stainless steel (DSS) in 3.5% NaCl solution at room temperature has been studied following the documented standard practice ASTM E647. FCG tests were conducted using compact tension specimens which were fatigue loaded in an NITS servohydraulic machine. Two types of specimens having TL and LT, orientations were investigated. LT specimens showed higher rates of crack growth as compared to TL specimens in both air and 3.5% chloride solution. A substantial effect on FCG rates was observed for both the TL and LT specimens, in. neutral chloride solution in comparison to those in air. In the lower applied DeltaK region, FCG rates were found to be almost five times higher in the neutral chloride solution than those in air. Lowering of pH of the solution from 7 to I and 3 resulted in the decrease in the crack growth rates. No pitting was observed in the specimens during anodic polarization in 3.5% chloride solutions of pH 1, 3 and 7. Corrosion fatigue crack initiation and growth seemed to be due to the rupture of the passive film under cyclic loading and subsequent, anodic dissolution.