304SS網板的腐蝕破裂

Corrosion Cracking of 304SS Expended Metal

本文探討304不銹鋼（304SS）網板使用於焦炭輸送帶走道發生破裂之原因。研究方法包括外觀觀察、成分分析、腐蝕生成物分析、草酸試驗、裂縫觀察、破斷面觀察及應力腐蝕模擬試驗，結果發現：304SS經冷加工為擴張網後，使得原始沃斯田鐵組織超過15%以上轉變成麻田散鐵組織，並伴隨大量殘留應力產生。另外，焦炭在輸送機及轉送塔現場需常灑水以抑制粉塵，網板上附著的焦炭累積很多的SO4=與Cl-腐蝕因子，304SS網板即在含SO4=與Cl-腐蝕因子及濕潤的環境中，由網板表面先產生蝕孔，破壞鈍化膜，同時殘留應力會誘發蝕孔尖端產生裂縫，在腐蝕及破裂的反覆作用下，發生穿晶應力腐蝕破裂。若將304SS網板經1050℃的固溶化處理，其抗應力腐蝕壽命可以大幅提高45倍以上。

This study is to analyze the fracture of a 304 stainless steel (304SS) expended metal, which had been used in the walkway under a coke conveyer. The experimental methods included visual observation, composition analysis, corrosion products analysis, oxalic acid test, cracks observation, fracture surface observation and stress corrosion cracking simulation test. The results revealed that more than 15% of the original 304SS austenitic matrix had transformed to martensitic, meanwhile, a lot of residual stress was induced after the expended metal was formed in the processing if heat treatment was not performed. Moreover, the coke in the fields of conveyer and transfer tower was sprayed water very often to reduce dust. It also accumulated a lot of corrosive SO4= , Cl- . In SO4= and Cl contain-ning wetting conditions, the expended metal surface was pitted, first, and the passivity film was destroyed, meanwhile, cracks was induced at the pitting tips by the residual stresses. Under the cyclic interaction of corrosion and cracking, 304SS expended metal finally was failed in the form of transgranular stress corrosion cracking. The life time of stress corrosion cracking resistance of 304SS expended metal can highly be improved to more than 45 times by a 1050℃ solution treatment.