铸铁材料在海洋环境中的腐蚀特征

Corrosion Characteristics of Cast Iron in Marine Environment

“南海I号”沉船出水了大量铁锅文物,在海洋深处的淤泥埋藏环境中,呈现出特殊的腐蚀形态。铁锅残片分析表明,铁锅为过共晶白口铸铁组织,为多层锈蚀形态,外层完全腐蚀矿化,内芯仍保留有较好的铁质基体,中间过渡层为一定程度腐蚀区。锈蚀产物结构复杂,过渡层有大量的微观裂隙,裂隙向材质内芯发展。裂隙在发展过程中,由单层的Fe3O4层向γ-FeOOH、γ-Fe2O3、α-FeOOH等混合锈蚀产物层转化,进一步引发裂隙应力增加,推进裂隙发展。

A large number of iron pot cultural relics were found in the water of the “Nanhai I” sunken ship, which showed a special corrosion form in the silt burial environment in the depths of the ocean. The analysis of iron pot fragments shows that the iron pot is hypereutectic white cast iron, which is in the form of multi-layer corrosion, the outer layer is completely corroded and mineralized, the inner core still retains a good iron matrix, and the intermediate transition layer is a corrosion area to a certain extent. The structure of corrosion products is complex, there are a large number of micro-cracks in the transition layer, and the cracks develop to the inner core of the material. In the process of fracture expansion, the structure of all corrosion products changes constantly. Fe3O4 layer can be changed to mixed components of γ-FeOOH, γ-Fe2O3, and α-FeOOH. It leads to the increase of crack stress and expansion of crack dimension