Studies on the initiation and the propagation of fatigue crack in tempered- martensitic high strength steel

Observations by both a scanning electron microscope and a plastic replication method have been made at suitable intervals during the fatigue testing. There are three types of crack propagation- microcracks are caused by various mechanisms and propagate until final fracture occurs; the predominant growth of microcracks initiated from severe non- metallic inclusions until final fracture, and third type is an intermediate nature between the above two types.