The hot-dip galvanized steel coil has good corrosion resistance after passivation. With the enhancement of environmental awareness, trivalent chromium passivation or chromium-free passivation gradually replaces hexavalent chromium passivation, which becomes an important part of hot-dip galvanizing production.
However, with the trivalent chromium passivation solution, the outer ring of the steel coil occasionally has white rust corrosion. The analysis is believed to be caused by the thinner passivation film, the low PMT temperature and the excessive temperature difference between the steel coil and the environment during packaging.
Strictly control the temperature of the steel coil packaging. Before the steel coil is packaged, it must be in the room for a long enough time to make the temperature the same as the indoor temperature to prevent condensed water from appearing on the surface of the coil due to the temperature difference. At the same time, the steel coil must be kept dry on the front surface of the package.
Whether it is rust-proof paper, plastic film or outer packaging board, it must be packaged strictly according to requirements to enhance its sealing and prevent rain or moisture from entering during storage and transportation.
In summary, by optimizing the passivation drying process, reducing the coiling and packaging temperature and other measures, eliminating white rust defects in the outer ring of the coil, and ensuring product quality.