碳鋼與耐候鋼在多風都市八年半之大氣腐蝕行為研究

A Study of 8 1/2-year Atmospheric Corrosion of Carbon and Weathering Steels in a Windy Urban Area

本研究是探討碳鋼、耐候鋼及熱浸鍍鋅碳鋼在多風都市經八年半的大氣腐蝕行為。研究方法包括實際曝露試驗與腐蝕生成物分析（SEM／EDS與XRD）。結果顯示裸露鋼材的大氣腐蝕速率滿足C = AtB之定律（C與t分別表腐蝕量與時間，A與B為常數），且耐候鋼不僅在未生成銹層以前反應比碳鋼低，而且在生成銹層後，其保護性也較佳。碳鋼的腐蝕生成物組成為FeOOH與保護性較差的Fe3O4，耐候鋼則祇有FeOOH而沒有Fe3O4，故耐蝕性較佳。至於熱浸鍍鋅碳鋼，雖然腐蝕速率未滿足上述之定律，但其經八年半的大氣曝露後，僅η相有輕微腐蝕現象，中間層ζ及δ相均尚未腐蝕，故此鋼材在多風都市環境的使用壽命應仍很長。

This study is to investigate the 8 1/2-year atmospheric corrosion behaviors of carbon steel, weathering steel, and hot-dip galvanized carbon steel in a windy urban area. The experimental methods included actual exposure test and analyses of corrosion products(SEM/EDS and XRD). The results revealed that the corrosion rates of bare steels obeyed the law C = AtB (C and t represent corrosion amount and time, respectively, while A and B are constants). The weathering steel not only possessed lower initial reaction rate, but also possessed better protective rust than carbon steel. The corrosion product of carbon steel was composed of FeOOH and less protective Fe3O4. However, that of weathering steel was composed of FeOOH and no Fe3O4 was observed at all. Therefore, its corrosion resistance was better. The corrosion of hot-dip galvanized carbon steel did not obey the above rate law. However, only η-phase of the hot-dip layer had been slightly attacked during the 8 1/2-year exposure. The intermediate ζ and δ phases were not corroded at all. Therefore, the life time of this steel in windy urban area is predicted to be very long.