Some effects of yield strength on the stress corrosion cracking behaviour of low alloy steels in aqueous environments at ambient temperatures

Abstract

The present paper describes the results of a literature review on the effects of material yield strength on the threshold stress corrosion cracking (SCC) condition known as K 1SCC, of a series of low alloy steels in various aqueous environments at ambient temperatures. It has been shown that an increase in yield strength reduced the value of K 1SCC and that this effect was more significant over the lower yield strength range 600–1200 MPa; at higher yield strength levels the effects of yield strength were much less evident. A review of the results indicated that SCC transgranular fracture was seen at yield strength values below around 1200 MPa while above this value the fracture path was exclusively intergranular in nature. Note that the transition point between transgranular and intergranular SCC coincided with the point at which yield strength effects were much reduced. A series of models reported in the literature, which attempted to explain the effects of yield strength on K 1SCC in terms of a fracture mechanics framework were examined with the introduction of a critical distance concept. Finally, the predictions of a grain size effect on the point at which the fracture path changed from transgranular to intergranular were taken from one model and used to show that the large data scatter in the region where transgranular fracture was operative, viz., the lower yield strength region of 600–1200 MPa, could be the result of grain size variations between the different reported studies.