304L不銹鋼鹽霧應力腐蝕特性之研究

Stress Corrosion Cracking of 304L Stainless Steel in Salt-Spray Environment

本研究係將304L板材先敏化處理後進行滾軋製程，模擬不完全固溶之應力腐蝕特性，探討原始晶界碳化物析出，對後續輥軋加工試片抗應力腐蝕特性之影響。在80℃- 10% NaCl之加熱鹽霧環境中，五種不同處理條件（BMS、SCR、SHR、SCRS、SHRS）下試件之應力腐蝕龜裂與劣化機制；並探討304L不銹鋼粗大晶粒組織對其應力腐蝕破裂之影響。研究結果顯示：U型彎曲試件在鹽霧環境中進行144 hr測試後，晶粒粗大化之輥軋試件在裂縫起始時呈現穿晶破裂特徵，易從交叉滑移帶侵蝕並生成裂縫，粗晶敏化試件在裂縫起始時為穿晶破裂而後轉為沿晶破裂；而先經敏化再輥軋之試件，裂縫剛開始以沿晶和穿晶混和之型態出現，之後呈現階梯狀的破壞型態，兩次敏化之試件其沿晶破裂特徵更為明顯，但階梯狀破裂模式明顯減少。

In this work, 304L stainless steel (SS) was subjected to either sensitization treatment at 650 ℃ for 10hr or grain-coarsening treatment at 1150 ℃ for 1hr before rolling to 20% reduction in thickness. The effects of carbide precipitation and coarse grain size on the stress corrosion cracking (SCC) of the specimens were evaluated and compared to the base metal specimen. The susceptibility to SCC of distinct specimens was ranked by determine the total crack length of the U bent specimen at 80 ℃ for 144 hr in salt-spray environment. However, the sensitization before rolling could obviously raise the cracking susceptibility of the specimens in salt-spray environment. Moreover, the crack path was more likely to change from transgranular to intergranular for the sensitized specimens. It was noted that cracks tended to initiate at the intersection of slip bands in the cold-rolled specimens. The step-wise crack growth in all the specimens was associated with the crack growth along the slip bands or induced martensite therein.