High Temperature Fatigue of Mild Steel under Varying Temperatures (1st Report)

The object of this investigation is to estimate the high temperature fatigue strength of mild steel under varying temperature by assuming the equivalent temperature Te as [numerical formula] where, N^^- is the number of cycle and α(N, T) is a weight function, depending upon the temperature and cycles . We made rotary-bending fatigue tests of two kinds of mild steel, SM41A as recieved and S12C annealed at 910℃ under various temperature conditions. The S-N curves obtained from the experiments under three simple models of cyclic temperature changes coinsided very well with the curves which we made from the stress versus temperature curves for each endurance strength of the material at the equivalent temperature Te, assuming α=1. We could also substantiate this result by refering to the microstructures of both specimens which were exposed to varying temperature and equivalent temperature under the same bending stress.