抄録
The low cycle fatigue tests were conducted on Type 304 stainless steel at 500°C and 550°C, where dynamic strain aging easily occurs, and the effect of strain waveform on the low cycle fatigue life was studied. As the strain waveforms, the triangular, slow-fast and fast-slow waveforms under the total strain range Δεt=1.0 or 0.5% with a tension going strain rate of 1 to 0.001%/s and compression going strain rate of 1 to 0.001%/s, were used.
The results of the present study are summarized as follows;
(1) The negative strain rate dependence due to dynamic strain aging was observed at the strain rate more than about 0.01%/s to 0.005%/s under both strain range Δεt=1% and 0.5% at 550°C. A similar tendency was also observed for the thermal aged material (650, 700°C×500-3000h, Δεt=1%), although hardening due to dynamic aging was low.
(2) The low cycle fatigue life was approximately dominated by the tension going strain rate. The increasing of intergranular fracture with decreasing the strain rate was caused by the creep effect in tension going period rather than the dynamic strain aging.
(3) The thermal aged material (700°C×3000h) had a longer fatigue life than the solution heat treated material, because the stress in tension was reduced due to the decreased dynamic strain aging.
