DP鋼の微小疲労き裂の伝ぱ特性に及ぼす微視組織の影響

概要

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The influences of the martensite morphology on the characteristics of small fatigue crack growth were investigated under rotating bending using two kinds of dual-phase steels, Steel A which has a microstructure containing isolated martensite phases in a ferrite phase and Steel B which has a continuous martensite phase filled by ferrite phases. In the two steels, most of the fatigue life in plain specimens is occupied by the growth of small cracks less than 1 mm, and in the region corresponding to about 50 % of the total life, small crack growth is affected strongly by microstructures such as the ferrite grain boundary and martensite phase. Even in the region where the growth behaviors are affected by microstructures and the fluctuation of growth rate is remarkable, the average crack growth rate can be considered to be proportional to the crack length. That is, the resistance to the crack growth is approximately evaluated through the static strength. On the other hand, the fatigue limits in the steels are determined by each limit for crack growth which is affected by the microstructure. Consequently, there is a large difference between fatigue ratios (σ_W/σ_B) of the two steels (0.39 in Steel A, 0.49 in Steel B).
一般社団法人日本機械学会の論文
1991-12-25