非金属介在物を含む低炭素鋼の疲労強度に及ぼすあらかじめ引張加工の影響

抄録

The fatigue limits due to rotary bending for specially prepared mild steels containing silicate inclusions were obtained after the specimens were preworked by statical tensile deformations beyond the yield point.
The results obtained are as follows;
(1) Comparing with the results for annealed states, the fatigue limits decrease few percent for small strains, and increase for large strains of preworking. This tendency is similar to that obtained previously by Fukui and Sato for ordinary carbon steels, and the effect of the presence of inclusions can not be found.
(2) Accordingly, in the preworked soft steels studied in this investigation, the presence of inclusions appears to have little influence on the fatigue strength.
(3) 196-1 steel contains greater quantity of inclusions than the other steels. The fatigue limit of this steel, preworked to about 2% tensile strain by applying the tensile stress of 27.0kg/mm², falls by 10% as compared with that for the annealed state, and then recover the same value for preworking of 40kg/mm² stress and approximately 7% tensile strain.
(4) Since the fatigue cracks initiate at inclusions, the fracture surface of a specimen which was subjected to a high stress level is very rough, and numerous micro-cracks are found on the outer smooth surface of many specimens near the fractured section.