High-cycle fatigue tests were conducted to investigate the effects of temperature, stress ratio (R), specimen orientation, welding and specimen size on the fatigue behavior of type 316L stainless steel. The high-cycle fatigue test results indicated that the fatigue limits significantly decreased when the stress ratio (R) decreased. The corresponding fatigue limits were reduced to lower values when tests were conducted at 300 C, compared to those obtained at room temperature. The fatigue behavior and fatigue limits of standard and subsize specimens were observed to be consistent at both room temperature and 300 C. The constant life diagram was established from the S-N curves acquired. The fatigue limit strongly depended on the materials strength, which was a function of specimen orientation, test temperature, and welding processes. The dimension of the fatigue damaged area on a fracture surface increased as the stress ratio decreased. In the case of R ¼ À1:0, the fatigue damaged region extended over the whole fracture surface. The subgrain boundaries after high-cycle fatigue tests were clearly demonstrated by their diffraction patterns, which were related to the dynamic recovery of multiple dislocations.

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Fatigue tests under constant amplitude load were conducted on compact tension specimens of SA533B3 steels with four levels of sulphur content at different temperatures. A modified capacitance type crack opening displacement (COD) gauge was shown to be suitable for fatigue crack length measurement at high temperatures. Test results obtained with different measurement techniques show good consistency. The observation that the Young's moduli measured at a strain rate of 4610 23 s 21 for the SA533B3 steels at 150 and 300uC do not decrease with increasing temperature seems to be related to the presence of dynamic strain aging. The fatigue crack growth rates at 150 and 300uC are about two and half times slower than those tested at 400uC because dynamic strain aging prevails at 150 and 300uC. Fractographic examination results suggest that inclusions embedded in secondary cracks enhanced the fatigue crack initiation rather than the fatigue crack growth.

The environmentally assisted cracking behavior of Inconel Alloy 52-A508 weldment under simulated BWR coolant conditions was studied. Fatigue and corrosion fatigue crack growth rates of the dissimilar metal weldments were observed to increase with crack extension under the nominally constant ÁK loading mode. It can be accounted for by an increase in the tensile residual stress and a decrease in the crack closure effect with the weld depth. The tensile residual stress measured by hole-drilling strain gauges increased with the weld depth. After PWHT at 621 C for 24 h, the fatigue crack growth rate in the weld did not show to increase with crack length advancement. The crack closure effects in the weld were verified to decrease with the crack increment measured by the strain gauges in front of the crack tip.

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