FATIGUE FRACTURE SURFACE-FEATURES PREVALENT IN STEELS AT AMBIENT-TEMPERATURES

Assessed in this study are the relationships that were recorded between the magnitude of the environmental assisted crack (EAC), growth contribution and the fatigue fractographic details observed in steels under ambient conditions. Four discrete static failure modes were observed on the fatigue surfaces; they are primarily transgranular cleavage and intergranular decohesion with a few instances of fan-shaped growth and macrofacet formation. All static failure modes could be explained by Beacham's model for hydrogen assisted cracking. It was established that the extent of EAC growth was uniquely related to the amount of static failure mode and that the relationship agreed well with the predictions of Congleton's model for EAC growth expressed in terms of the ratio of crack growth rate (da/dN)* in environments of humid air and saline solution to da/dN in dry air for a given stress intensity factor range DELTAK.