Micromechanics of Stress Corrosion Cracking of Single-Crystal Austenitic Type 321 Stainless Steel Under Mode II Loading

Stress corrosion cracking (SCC) of single-crystal type 321 (UNS S32100) stainless steel (SS) was investigated in 42% boiling magnesium chloride (MgCl₂) solution. Tests were performed under Mode II loading to study the SCC mechanism. Maximum normal stress and maximum shear stress were located at different positions on the notch surface in the Mode II notch specimens. Results showed SCC initiated at the maximum normal stress position. No SCC occurred at the maximum shear stress position. SCC initiated on the (111) plane and propagated on the normal stress plane. Slip bands appeared around the maximum normal stress position but not in the area around the main crack. Many microcracks ~ 2 μm long were observed on the slip bands. Their direction was inclined ~ 35° to the slip bands instead of along them. Nucleation resulted from interaction of dislocation pileup stress and local anodic dissolution. Multiple microcracknucleations increased stress around crack tips of the main and microcracks. Highly concentrated local stress from dislocation pileups increased the anodic dissolution rate locally.