Three kinds of steels; aluminum-killed, silicon-killed and rimmed steel, were tested. Some of the materials were heat treated before machining; the others, after machining. Tension-compression fatigue test were made on these materials under constant stress and manifold repeated stress at two stress levels.
Observations were made on the effect of heating treatment and also on the hardness which varied before and after the fatigue test.
The conclusions obtained are as follows;
(1) Almost all S-N curves obtained have their knees at 5×106 repetition of stress cycles. The fatigue strength of the low temperature quenched rimmed steel is higher than that of the annealed killed steell.
(2) The mean values Σn/N based on the Miner's law of alminum-killed and rimmed steels are larger than that of silicon killed steel.
(3) In the manifold tests at two stress levels, the mean value of the relative hardness before and after testing is larger at the test in hi-lo-hi-lo…type than in lo-hi-lo-hi…type. The mean values Σn/N based on the Miner's law are larger in the hi-lo-hi-lo…type program test than in the lo-hi-to-hi …type.