Low frequency cyclic stresses are experienced by the materials in a number of applications. Effect of low frequency cyclic stresses on stress corrosion cracking (SCC) of duplex stainless steel (DSS) 2205 was investigated in this study. Previous work has suggested that the two phases (austenite and ferrite) of DSSs have different residual stresses, and different SCC susceptibilities in acidic chloride and caustic white liquor (WL) environments. To understand the effect of low frequency fatigue on SCC initiation and propagation, tests were performed on the as-received DSS 2205 in two different environments where SCC could occur: 26 wt% NaCl at room temperature and WL at 170 °C. Test results on as-received material showed that cyclic stresses facilitate crack initiation. Intermetallic precipitates and austenite phase were the preferential sites for cracks to initiate in chloride and WL environments, respectively. The effects of fatigue parameters like stress ratio and maximum stress level of the cyclic stresses were also characterized.
Duplex Stainless Steels are dual phase metallic materials. They are composed of approximately equal volume amount of austenitic (?) phase and ferritic (a) phase. They exhibit superior mechanical properties and a high corrosion resistance as compared to other grades, such as carbon steels and austenitic stainless steels. Structures may experience low frequency loads under various scenarios. For example, for offshore structures, changes of wind and wave directions.1 Another source of high stress-low frequency loads in ships is slamming. According to Aertssen, a peak crash-stress of 110% yield stress for mild steel was found to occur 2 or 3 times per hour, which is a frequency less than 0.001 Hz.2 Some studies showed that below 10-2 Hz and under constant amplitude loading, the crack growth rate increased by a factor of 2 for every 10-fold reduction in frequency.1
