Abstract
The terne sheet coated with a Pb-Sn alloy by hot dipping is a metalcoated sheet steel of typical cathodic type, and there will exist a possiblity that pitting corrosion occours in the presence of pin-holes. Then, the authors studied on chemical conversion treatments of terne sheet, which brought about satis-factory results. It was found that the pitting corrosion was markedly prevented bya treatment with dilute phosphoric acid. As the result of the treatment, the corrosion resistance of terne sheet was remarkably promoted by the formation of conversion coated thin film. The results obtained were as follows: (1) The conversion coated film had water repellent property. (2) The constituents of the coated film were mainly Pb5 (OH) (PO4)3 and a little amount of Sn3 (PO4)2. (3) The promotion of corrosion resistance of the terne plate was due to the filling up of the pin-holes with these reaction products as well as its water-repellent property.
