炭素鋼の疲労き裂伝ぱ挙動に及ぼす微視的組織の影響

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The fatigue crack growth behavior of four kinds of carbon steels (SB 42, S 35 C, S 55 C and SK 5) which have different microstructures formed by heat treatments was examined on the center-notched sheet specimens. Particular attention was given to the influence of microstructure on the fatigue crack growth near the threshold stress intensity ΔK_<th> and at the high ΔK region. The values of ΔK_<th> in the specimens with pearlite structure were higher than those with beinite and martensite structures. In the pearlite structure, the growth rate near the threshold region may not be always influenced by the cementite, because the fatigue crack tends to propagate in the ferrite or to grow along the ferrite-cementite boundary. ΔK_<th> and the crack growth resistance near the threshold region were found to be inversely proportional to the strength of the steels. The values ofΔK_<th> were correlated with the yield strength better than the ultimate tensile strength. The fatigue crack growth in the pearlite and beinite structures at the value of ΔK above 50 kgmm^<-3/2> was governed by striation formation. Hence, the growth rates in both structures were the same regardless of their differences in microstructure and mechanical properties. In the martensite structure, the crack growth at the high ΔK region was greatly influenced by the microstructure, and the growth rate markedly increased in comparison with that in the pearlite or beinite structure. This result was attributed to the occurrence of static fracture modes (intergranular, microvoid coalescence) during striation growth.
1980-10-15

著者

橘内良雄
産業安全研究所

炭素鋼の疲労き裂伝ぱ挙動に及ぼす微視的組織の影響

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