Stress corrosion cracking failures in duplex stainless steels are uncommon, but they are particularly expensive when offshore components require repair or recovery from the seabed. The increased use of duplex stainless steels in thick walled pipelines, pressure vessels and large forgings creates a need for a fracture mechanics approach to brittle fracture and stress corrosion cracking. It is necessary to identify microstructures which are susceptible to crack propagation.

Brittle crack propagation in duplex stainless steels can be modelled using a critical shear stress/critical distance fracture criteria, i.e. a critical yielding volume. The effect of temperature, yield strength and ferrite grain size on fracture toughness have been successfully modelled. Stress corrosion cracking under cathodic polarisation has now been studied, and is found to occur by a related mechanism. A microstructural model for stress corrosion cracking resistance can be developed.