Fractographic Analysis in the Understanding of Corrosion Fatigue Mechanisms

Abstract

Fractographic analyses have been used to explain the cyclic crack growth behaviour of A533-B, D u a l W30, a C-Mn steel and type 304 stainless steel in simulated light water reactor environments at ambient temperature. Fractographic observations have offered an explanation for anomalous crack growth behaviour and have also indicated where microstructural or environmental variables dominate in producing certain fracture modes and crack growth rates. An understanding of the operative corrosion fatigue mechanisms has been formulated through these fractographic analyses. Environmental crack growth in the ferritic steels has been described by 9 model involving both anodic dissolution and hydrogen embrittlement. Conditions where only one of these mechanisms would dominate have been identified and limits to their effect postulated. A crystallographic mode of failure observed in the austenitic type 304 stainless steel has also been explained by a selective dissolution process.