σ相對2205雙相不銹鋼抗應力腐蝕破裂性質影響之研究

The Effect of σ phase on the Stress Corrosion Cracking Resistance of 2205 Duplex Stainless Steel

本研究主要探討σ相對2205雙相不銹鋼之機械及抗應力腐蝕性質的影響。2205雙相不銹鋼經800℃不同時間時效處理後，分別在空氣及沸騰氯化鎂環境中進行慢速拉伸試驗。實驗顯示2205雙相不銹鋼的硬度及抗拉強度均隨σ相的含量增加而增加，但延伸率則隨之減少。在沸騰的氯化鎂環境中，其延伸率亦隨σ相的增加而下降，顯示σ相析出會增加2205雙相不銹鋼的應力腐蝕破裂敏感性。經過時效處理之2205雙相不銹鋼，其應力腐蝕裂縫優先在經過共析反應之σ相區域內延伸。

The effect of σ phase on the mechanical and stress corrosion cracking behavior of 2205 duplex stainless steel was investigated. Tensile tests using slow strain rate testing (SSRT) were conducted in air and in boiling magnesium chloride solution for the steel specimens heat treated at 800℃ with different aging times. The experimental results showed that the hardness and the ultimate tensile strength (determined in air) increased, while the ductility decreased with increasing content of σ phase in 2205 duplex stainless steel. In boiling magnesium chloride solution, the percentage of elongation also decreased with increasing the content of σphase in the duplex stainless steel. The results indicated that the precipitation of σ phase would cause the increase of its susceptibility to stress corrosion cracking. The region where eutectoid reaction to form σ phase occurred was found to be the preferential path for the propagation of stress corrosion cracks.