Effect of austenite content on the embrittlement of duplex stainless steels by cathodic polarisation

The application of stainless steels in corrosive environments under conditions that may give rise to hydrogen generation, particularly where cathodic protection is imposed, introduces the possibility of loss of ductility due to hydrogen pick-up. The behaviour of duplex stainless steels containing 35.5 and 50.2% austenite was therefore assessed by tensile straining smooth specimens at 2 x 10(-6) / s whilst cathodically polarised in a hot solution of 0.6 M sodium chloride (pH = 6.5). The results clearly indicate a lower susceptibility to hydrogen embrittlement in the steel containing most austenite. It also became clear that the severe conditions imposed by the application of cathodic potentials can produce greater embrittlement than that resulting from thermal charging with hydrogen or straining in a hydrogen atmosphere This confirms a dependence upon hydrogen fugacity that depends upon the potential applied in cathodic polarisation and the acidity (pH) of the environment. The effect of chloride concentration and the formation of epsilon - martensite in the austenite on the fracture process are briefly discussed.