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 chlor ide (MgCl2) solution. Tests were performed under Mode II loading to st udy the SCC mechanism Maximum normal stress and maximum shear stress w ere located at different positions on the notch surface in the Mode II notch specimens. Results showed SCC initiated at the maximum normal s tress position. No SCC occurred at the maximum shear stress position. SCC initiated on the (111) plane and propagated on the normal stress p lane. Slip bands appeared around the maximum normal stress position bu t not in the area around the main crack. Many microcracks similar to 2 mu m long were observed on the slip bands. Their direction was inclin ed similar to 35 degrees to the slip bands instead of along them. Nucl eation resulted from interaction of dislocation pileup stress and loca l anodic dissolution. Multiple microcrack-nucleations increased stress around crack tips of the main and microcracks. Highly concentrated lo cal stress from dislocation pileups Increased the anodic dissolution r ate locally.