A297HF耐熱鋼在氯離子環境下之腐蝕破裂行為研究

The Corrosion Cracking Behavior of A297HF Heat-Resistant Steel in Chloride Environment

本研究針對二種不同肥粒鐵含量之A297HF材料，於高氯鹽環境下，以電化學及慢應變速率腐蝕實驗，了解其破裂行為。結果發現在90℃以下之高氯鹽環境下，A297HF有良好的抗應力腐蝕特性，但溫度昇高將會使材料之抗孔蝕性降低。若在陽極極化的環境下，由於肥粒鐵與沃斯田鐵偶合造成肥粒鐵優先溶解，使得材料截面積縮小而造成應力破壞。在陰極極化的環境（-900mV vs. SCE）下，由於氫的產生，造成肥粒鐵的脆化，材料沿肥粒鐵相破斷。此時若材料內肥粒鐵相過多且形成網狀分佈，將加速材料之破壞，因此在此環境下使用之材料，其肥粒鐵相含量不宜過高。

The corrosion behaviors of two A397HF steels with different ferrite content have been studied by using electrochemical techniques and slow strain rate tests. The results show that both A297HF have good stress corrosion cracking resistance in 19000 ppm chloride solution at temperature below 90℃. At anodic potential, the ferrite was corroded by galvanic cell with austenite. This result in stress assistant cracking of the specimen in slow strain rate test. At potential below -900 mv (vs. S.C.E),fracture surface examination reveals that hydrogen embrittlement occurs in ferrite phase. Time to failure of A297HF decreases with increasing ferrite content.