抄録
In order to study the development of the fatigue strength of steel due to the induction hardening, it is necessary to investigate the effect of tempering upon the fatigue limits σw1, σw2 and the condition of crack propagation.
This paper contains the experimental results and the considerations concerning the induction hardened steel specimens (0.16%C) with V-notch, tempered at several kinds of temperatures.
The data and considerations may be summarized as follows;
(1) The fatigue limit σw1 has little change, while σw2 decreases rapidly with increase of tempering temperature. This fact shows the fact that the initial crack of specimens tempered at high temperature develops easily to final fracture.
This is closely related with the experimental results concerning the residual compressive stress-release due to the tempering at the V-notch root.
(2) At σ=30kg/mm2 stress level the curves of crack depths to stress cycles of specimens with two different tempering conditions (no-tempered and tempered at 300°C) completely coincide.
At higher stress level σ=50kg/mm2, however, the rate of the crack propagations of the tempered specimens is larger than that of the non-tempered ones, while the stress cycles before crack formation remain almost the same under both conditions.
(3) Based upon the above facts, the effects of the residual compressive stress at the crack tip upon the crack propagation have been discussed.
