冷加工與敏化對304L不銹鋼應力腐蝕性質之影響

Effect of Cold Work and Sensitization Treatment on the Stress Corrosion Cracking of 304L Stainless Steels

本研究針對304L不銹鋼探討冷加工與敏化熱處理對其顯微組織、機械性質及其於80℃之40 wt%氯化鎂溶液中之應力腐蝕特性之影響。實驗結果顯示，冷加工導致加工硬化伴隨材料缺陷增加，加工應變並促使應變誘發沃斯田鐵至麻田散鐵相變態。氯化鎂環境測試結果顯示，冷加工後因材料缺陷增加對氫原子之捕集位置，缺口拉伸強度下降量僅11%，較固溶處理試片之25%明顯降低。冷加工後再經敏化熱處理之試片，因於晶界附近生成應力誘發麻田散鐵相變態，提供氫原子較快速之擴散途徑，缺口拉伸強度下降量增加至27%，且破斷型貌由冷加工試片之準劈裂轉變成沿晶破裂。

The effect of cold work and sensitization treatment on the microstructure, mechanical property and stress corrosion cracking of 304L stainless steels in an 80 ℃ 40 wt% MgCl2 solution was investigated in this research. The results showed that cold work caused obvious work-hardening in the 304L stainless steel plate along with a great increase in defects, and it also enhanced strain-induced martensite in the steel. Increased trapping sites for hydrogen due to the defects resulted in a much lower NTS loss of the cold-rolled specimen (11%) than that of the solution-treated specimen (25%), tested in the MgCl2 solution. For the cold-worked and sensitized specimen, the strain-induced martensite formed near the grain boundary provided a short path for hydrogen diffusion and led to a larger NTS loss of 27%. In addition, the fracture morphologies of the cold worked specimen altered from quasi-cleavage to intergranular fracture.