Measurement of crack bridging stresses in environment-assisted cracking of duplex stainless by synchrotron diffraction

Crack propagation studies have been conducted in age-hardened Zeron 100 duplex stainless steel, which in the 475 degrees C embrittled condition exhibits environment-assisted cracking under cathodic conditions in aqueous 3.5% NaCl solution. Values of the threshold stress intensity for environment-assisted cracking, K-1SCC, measured by crack arrest, show R-curve behaviour. Diffraction experiments on the high-energy beamline ID15A at the European Synchrotron Radiation Facility (ESRF) were performed to measure the crystal lattice strains in ferrite and austenite in wedge open loaded (WOL) stress corrosion specimens. The observations demonstrate that significant crack bridging stresses develop in the wake of the crack. This is due to branching of the environment-assisted crack. Simple bridging models for the effect of the measured stresses are in agreement with the observed R-curve behaviour.