Hydrogen-Induced Cracking and Stress Corrosion Cracking of Austenitic Stainless Steel under Mode III Loading

Hydrogen induced cracking (HIC) of austenitic stainless steel (SS) under mode III loading can occur during dynamic charging of hydrogen, and the normalized threshold stress was τ_HIC/τ_f = 0.62. The torsional angle, i.e., the torsional plastic deformation, enlarged continuously during dynamic charging under a constant torque until the specimen was twisted to failure. In the flat fracture surface of the delayed failure, however, secondary cracks propagated along the planes inclined at 45°. Stress corrosion cracking of austenitic SS in a boiling MgCl₂ solution can also occur under mode III loading, and the normalized threshold stress was τ_SCC/τ_f = 0.13. However, the cracks initiate and propagate along the planes inclined at 45° to torsional axis instead of the original notched torsional plane, where there is no shear stress but the maximum normal stress.