SA533B鋼材於不同溶氧水媒環境中低週疲勞行為研究

The Low-Cycle Fatigue Behavior of SA533B Steel in Water Environments with Different Contents of Dissolved Oxygen

SA533B低合金鋼係核能電廠反應爐壓力槽之構造鋼材。本報告主要探討於300℃、10MPa循環流動水媒中壓力槽鋼材低週疲勞行為受水中溶氧量、應變振幅及鋼材硫含量等不同因素之影響情形。測試結果顯示，應變振幅效應可從純疲勞機械作用力、疲勞與腐蝕交互作用、低週疲勞限及週期硬化等不同之影響研討。腐蝕與疲勞交互作用最顯著的情況發生在飽和溶氧水媒中應變振幅為0.2%的施力狀況。鋼材之低週疲勞限深受測試環境變異之影響而變化。水中溶氧量不同促使鋼材低週疲勞壽命顯著的差異。300℃空氣中測試，鋼材具有最佳之低週疲勞抗性，推估與動態應變時效（DSA）有關。在本測試範圍內，鋼材硫含量對其疲勞壽命之影響不明顯。破斷觀察以瞭解破斷型態。

SA533B low-alloy steel is the material mainly used for the reactor pressure vessels (RPVs) of nuclear power plants. This report is focused on the effects of dissolved oxygen content in feed water, strain amplitude and sulfur content in steel on the low-cycle fatigue (LCF) behavior of SA533B RPV steel in circulating water environments at a pressure of 10 MPa and a temperature of 300 ℃. The test results show the effect of strain amplitude can be studied from the perspectives of mechanical force of fatigue, fatigue-corrosioin interaction, low-cycle fatigue limit and cyclic hardening. The most significant fatigue-corrosion interaction occurred in a water environment saturated with dissolved oxygen under a strain amplitude of 0.2%. The variation of low-cycle fatigue limit is deeply affected by the change of test environments. The low-cycle fatigue life of the RPV steel is obviously varied with the dissolved oxygen content in the water environment. The best low-cycle fatigue resistance of SA533B steel was observed with the specimens tested in air at 300 ℃, which could be related with the dynamic strain aging (DSA). No or little dependence of fatigue life on sulfur content in steel was noted under the present test conditions. The fracture appearance and morphology were examined and discussed.