DP銅のき裂伝ぱ抵抗に及ぼす微視組織の影響

抄録

Rotating bending fatigue tests of dual-phase steels having various microstructures were carried out in order to investigate the effect of microstructures on the crack growth resistance. The fatigue lives of plain specimens in dual-phase steels are nearly equal to each other under the same relative stress σ_a/σ_B, regardless of the differences in martensite morphology and grain sizes of the ferrite and the martensite at high stress levels, (where σ_a and σ_B are the nominal stress amplitude and the tensile strength of each material, respectively). This is explained from the fact that most of the fatigue life is consumed by the growth of small cracks which are controlled by the small-crack growth law, dl/dN∝σⁿ_al (l : crack length, n : constant), and the crack growth resistance is evaluated by σ_B of each material using this law.