  Irradiation Assisted Stress Corrosion Cracking (IASCC) is a material
degradation phenomenon affecting austenitic stainless steels used in nuclear
Pressurized Water Reactors (PWR), leading to the initiation and propagation of
intergranular cracks. Such phenomenon belongs to the broader class of
InterGranular Stress Corrosion Cracking (IGSCC). A micromechanical analysis of
IGSCC of an irradiated austenitic stainless steel is performed in this study to
assess local cracking conditions. A 304L proton irradiated sample tested in PWR
environment and showing intergranular cracking is investigated. Serial
sectioning, Electron BackScatter Diffraction (EBSD) and a two-step misalignment
procedure are performed to reconstruct the 3D microstructure over an extended
volume, to assess statistically cracking criteria. A methodology is also
developed to compute Grain Boundary (GB) normal orientations based on the EBSD
measurements. The statistical analysis shows that cracking occurs
preferentially for GB normals aligned with the mechanical loading axis, but
also for low values of the Luster-Morris slip transmission parameter.
Micromechanical simulations based on the reconstructed 3D microstructure,
FFT-based solver and crystal plasticity constitutive equations modified to
account for slip transmission at grain boundaries are finally performed. These
simulations rationalize the correlation obtained experimentally into a single
stress-based criterion. The actual strengths and weaknesses of such
micromechanical approach are discussed.
