SA533壓力槽鋼材在高溫高壓水媒中之低週疲勞行為

Low-Cycle Fatigue Behavior of SA533 Reactor Pressure Vessel Steel in a High Temperature and High Pressure Water Environment

SA533低合金鋼係核能電廠反應爐壓力槽之構造鋼材。本報告主在探討應變振幅、水中溶氧量及低週疲勞頻率等不同參數對SA533壓力槽鋼材於300℃、10MPa循環流動水媒中低週疲勞行為之影響情形。測試結果顯示，隨著應變振幅之增加，鋼材低週疲勞壽命週期數明顯降低。疲勞頻率效應測試結果顯示，頻率越低者鋼材疲勞壽命週期數越短，其下降效應由快速顯著轉趨遲緩鈍化。水媒中溶氧量之多寡對鋼材低週疲勞壽命更具有決定性的影響力，降低溶氧量可抑低水媒環境中鋼材之疲勞劣化情形。另進行空氣與水媒中之低週疲勞比較測試，其結果明顯可見環境效應對鋼材疲勞劣化之影響程度。腐蝕與疲勞協同作用的結果，鋼材在飽和溶氧水媒中之疲勞壽命最短。掃描式電子顯微鏡（SEM）觀察破斷面，以瞭解破斷型態及探求水媒中疲勞劣化機制。

SA533 low-alloy steel is the material mainly used for the reactor pressure vessels (RPV) of nuclear power plants. This report is mainly focused on the effects of strain amplitude, dissolved oxygen content in feed water and fatigue frequency on the low-cycle fatigue (LCF) behavior of SA533 reactor pressure vessel steel in a high temperature, high pressure water environment. The test results show the fatigue life is significantly decreased with increasing the strain amplitude. The lower the fatigue frequency was applied, the shorter the specimen fatigue life was observed. The low-cycle fatigue life of the RPV steel is also significantly affected by the dissolved oxygen content in feed water. The degradation of SA533 steel in water environment could be effectively reduced by lowering the dissolved oxygen content. For a comparison purpose, some low-cycle fatigue tests were conducted in air environment. The steel specimens have the longest fatigue life when tested in air, but, in contrast, they were observed to have the shortest one when tested in the high temperature, high pressure water environment saturated with dissolved oxygen. From the above observations, it can be inferred that the fatigue-corrosion interaction plays a significant role in determining the fatigue life of SA533 RPV steel. The fracture appearance and morphology on the fracture surface were examined by scanning electron microscopy. The degradation mechanism was also discussed in this report.