浸炭表面硬化鋼における疲労き裂の発生, 進展および停留に及ぼす切欠き深さの効果

概要

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Rotating bending fatigue tests were performed on SCM21 casecarburized and hardened steel, and the effect of notch depth on the fatigue properties was examined by six types of notched specimens (the notch depth; t=0.2-6.4 mm, the notch root radius; p=0.08 mm). Furthermore, the effect of notch root radius on the fatigue Iimit of carburized steel was discussed using the author's data as well as others'. SCM 21 test pieces were carburized at 920℃, under 0.9% carbon potential atmosphere for 4 hrs. and oil-queched from 820℃. Tempering was carried out at 180℃ for 2 hrs. The results obtained are as follows. (1) The crack initiating fatigue limit is not influenced by the notch depth under the condition of t/ρ>10, but is influenced under the condition of t/ρ<lO. (2) The fatigue crack propagating stress (N=10^7 cycles) is nearly constant (31〜34 kg/mm^2) , when the effective crack length (l_<npc>+t) is 0.8-6.8 mm. This tendency reveals that the compressive residual stress in the surface layer increases with notch depth. (3) The non-propagating crack is not in existence under the condition of t/ρ>2.5 and its properties are not influenced by the notch depth under the condition of t/ρ<5, (4) The crack initiating fatigue limit is influenced by the notch root radius, and the notch factor is smaller than one-half of the theoretical stress concentration factor.
社団法人日本材料学会の論文
1977-06-15