Investigation on machining induced surface and subsurface modifications on the stress corrosion crack growth behaviour of super duplex stainless steel

Highlights: • The tensile residual stress and surface defects influenced the crack direction and their orientation on the surface. • With an increase in exposure time, the secondary crack width grows at a faster rate than the primary crack width. • The austenite phase showed better crack resistance than ferrite, but microcracks were initiated in both the phases. - Abstract: After stress corrosion crack testing in a MgCl₂ environment, turned surface of super duplex stainless steel showed four types of cracks. The residual stress and surface defects such as feed marks and long grooves generated after machining played a significant role in the direction and orientation of these cracks. The generated cluster of cracks acted as a precursor to the formation of pits. The biaxial tensile stress in the surface promoted successive branching of cracks, which led to high crack density. The subsurface results showed that cracks passing perpendicular to feed marks found more detrimental than the other types.