A Fractographic Study of Fatigue Fracture of AISI 4340 Steel

Abstract

If the topography of fracture surfaces represents the peculiar pattern to various reasons of fracture, the reason could be known by observing them in detail, and further the observation might bring out some information on the fracture mechanism. From the above point of view, we conducted a fractographic investigation on fatigue fracture surface under rotating bending and repeated tension tests. The appearance of the surfaces is apparently different due to their location observed and the stress level in rotating bending test. But the surface pattern from the repeated tension test seemed to be same in the range from the stress at the fatigue limit to rather large stress under which plastic deformation occurs and it closely depends upon the heat-treated structure. The impact fracture surface consists of austenite grains, dimple pattern that shows ductile fracture, and other complex patterns.