THE EFFECTS OF MICROSTRUCTURE AND FRACTURE SURFACE ROUGHNESS ON NEAR THRESHOLD FATIGUE CRACK PROPAGATION CHARACTERISTICS OF A TWO‐PHASE CAST STAINLESS STEEL

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Abstract
In this study, the effects of stress ratio, microstructure and fracture surface roughness on the fatigue properties of a two‐phase cast stainless steel were investigated. This behaviour was examined by means of the fracture mechanics approach and fractography. The fatigue crack growth rate decreased with decreasing stress ratio. The stress ratio markedly influenced the fatigue crack growth rate as ΔK approached the ΔKth value. The roughness of the fracture surface was greater in the as‐cast material than in the heat‐treated material. Analysis of the crack growth data using ΔKeff showed that the effect of R ratio could be explained but that the effect of microstructure on crack growth rate could not.