| Rotating bending fatigue behavior of the smooth and pitted specimens of STS 316 stainless steel has been examined at room temperature, 538℃, 593℃ and 650℃. The experimental results are as follows: The endurance fatigue limits of the smooth and the pitted specimens are clearly appeared at all experimental temperature below 10^7 cycles. Particularly, the knees of S-N curves at 650℃ appear at about 10⁴cycles. As temperature increases, endurance fatigue limits of the pitted specimens decrease more than those of the smooth ones. Cracks on the smooth specimens initiate in overall sites of the smooth specimens and those on the pitted ones initiate on the pit. Cracks propagate in brittle fracture, ductile striation and dimple fracture successively, in transgranular fracture modes. On the well defined ductile striation stage of the pitted specimens, ductile striation spacings are 1-3㎛. These striation spacings in this range are expressed as a function of σ_max√(πa). (Received May 28, 1984) |
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