本研究探討A533-B和A508鋼材分別在常溫和高溫大氣環境中的疲勞裂縫成長特性。A533-B鋼材主要是在室溫下進行破壞韌性和疲勞裂縫成長速率測試，以研究鋼板滾軋加工方位、平均應力效應及環境溫度效應對A533-B破裂性質的影響。A508鋼材則是探討其鍛造加工方位、硫含量對高溫疲勞裂縫成長速率的影響，並進一步測試裂縫瑕疵在A508鋼材與Alloy 82或Alloy 52銲材之銲道交界附近的裂縫成長速率。 硫含量0.035 wt%之A533-B鋼材實驗結果顯示，裂縫平行滾軋方向(平行方位)的破壞韌性只有垂直滾軋方向(垂直方位)的38.8 %，平行方位裂縫成長速率對應力強度因子幅(DK)變化有較敏銳的反應，且其裂縫成長速率也比較快。在平均應力效應方面，以應力比0.05的疲勞裂縫成長速率為比較基準之下，應力比0.2約為應力比0.05的1.2倍，應力比0.4和0.6則都是約為1.35倍，故當應力比提高到0.6時，其平均應力效應明顯下降。另外，研究結果顯示室溫與300℃的裂縫成長速率極為接近，無明顯的溫度效應。 A508鋼材於300℃空氣中進行疲勞裂縫成長速率實驗結果顯示，在裂縫平行鍛造方向的條件下，高硫含量(0.015 wt% S)鋼材之裂縫成長速率約為低硫含量(0.005 wt% S)鋼材的1.23?1.53倍；而鍛造方位對疲勞裂縫成長速率則無顯著的影響。另針對A508異材金屬銲道以固定DK施力模式之疲勞裂縫成長速率測試中，銲道與母材交界附近呈現4個具有不同裂縫成長速率的區域，分別為銲材熔融區(Filler Fusion Zone)、稀釋區(Dilution Zone)、熱影響區(HAZ)及A508母材區，其中稀釋區的裂縫成長速率最緩慢。 The purpose of this thesis was to investigate the fatigue crack growth behavior of A533-B steel and A508 steel in air at room temperature and 300℃. Fracture toughness and fatigue crack growth rate tests were conducted on A533-B steel specimens with different orientations under various mean stresses. Fatigue crack growth rate tests were also performed on A508 steels with different specimen orientations and sulfur contents. Efforts were focused on the fatigue crack growth rate measurements of dissimilar metal weldments, Alloy82-A508 and Alloy 52-A508, under a nominally constant DK loading control. The experimental results of A533-B steel with sulfur content 0.035 wt% showed that the fracture toughness of the specimen with a crack in the rolling direction is only 38.8% of that perpendicular to the rolling direction. The fatigue crack growth rate is faster in the rolling direction than that in a direction perpendicular to the rolling direction. For the mean stress effect, the fatigue crack growth rate at a stress ratio of 0.2 was 1.2 times that at a stress ratio of 0.05, while the crack growth rates at stress ratios 0.4 and 0.6 were 1.35 times that at a stress ratio of 0.05. Therefore, the mean stress effects became saturated when the stress ratio was increased up to 0.6. In addition, the fatigue crack growth rates at room temperature and 300℃ were almost identical. Within the test temperatures, no significant temperature effects on the fatigue crack growth rate were observed for A533-B steel. The fatigue crack growth rate for A508 steel with sulfur content 0.015 wt% was 1.23~1.53 times that with sulfur content 0.005 wt% at 300℃. Little or no significant specimen orientation effect on the fatigue crack growth rate was observed. For the dissimilar metal weldment tested under the nominally constant DK loading control, four distinct crack growth rates were identified on the a-N curve, which corresponded to fusion zone, dilution zone, heat-affected zone and A508 base metal, respectively. Among these four zones, the dilution zone showed the slowest fatigue crack growth rate.
