工廠退火的600合金在室溫25℃，0.1M氯化鈉溶液中的疲勞裂縫生長速率受外加電位、負荷頻率及負荷比的引影響，在外加陰極電位(-1300mV(下標　SCE))下，疲勞裂縫生長速率隨負荷頻率的降低及負荷比的提高而增加，在低於0.1Hz的負荷頻率有裂縫生長加速的現象，且此現象隨負荷比的提高而變得更加顯著。負荷比的效應採用Walker的模式來說明，並推導出一保守的上限邊界。斷裂面顯示有二次裂縫存在及穿晶破裂模式，對於可能的氫促進破裂的機制有所探討。

The fatigue crack growth (FCG) rates of mill annealed Alloy 60 in 0.1M NaCl soluton, 25℃, were studied by a fracture mechanics test method. They were affected by the applied potential, load frequency and load ratio. At an applied cathodic potential of -1300mV (subscript SCE), the FCG rates increased with lowering the load frequency and with increasing the load ratio. The enhanced FCG rate was found in the lower load frequencies (≤0.1Hz) and was more significant with increasing the load ratio. The load ratio effects were successfully accounted for employment of the Walker model. The secondary cracks and transgranular fracture modes were observed on the fractured surfaces with applied cathodic potential. The possible hydrogen-assisted cracking mechanism on enhancing the FCG rates of Alloy 600 cathodically charged in 0.1M NaCl solution, 25℃, was discussed in this paper.