The Influence of Microstructural Morphology and Prestrain on Fatigue Crack Propagation of Dual-phase Steels in the Near-threshold Region

摘要

The influence of microstructure and prestrain on fatigue crack propagation in the near threshold region was studied for dual-phase steels with different microstructural morphologies. The material with martensite phases dispersed in ferrite matrix exhibited a higher nominal stress intensity range and a lower crack propagation rate than those of material with a continuous marteniste phase around ferrite grains. Prestrain prior to fatigue testing resulted in a decrease of nominal stress intensity range in both materials. However there was a slight difference among all the materials in the effective stress intensity range. The microstructural morphology and prestrain exerted a great influence on crack path and that caused a large difference in crack closure. A quantitative correlation existed between crack closure level and surface roughness of fatigue fracture.