Failure of steels caused by hydrogen induced microcracking

Abstract

A model of hydrogen induced microcracking in pressure vessel steels has been developed. It is assumed that the initiation of microcracks is caused by a localized increase in hydrogen concentration at inclusions. The propagation at these site initiated microcracks results in fisheye formation and is controlled by a local stress intensity factor and fracture resistance of the matrix. Stability of the hydrogen induced brittle microcrack is dictated by the relative increase of both these quantities. This criterion has been used for the estimation of fisheye crack size at the fracture surface as a function of temperature. The introduced dimensionless coefficient of fracture resistance increase rate grows as the temperature increases. Very good agreement of predicted fisheye crack size with experimental fractographic observations has been found.