The cold rolled steel sheet is the raw material of hot dip galvanized coils.
The surface roughness of the steel sheet is one of the essential characteristics of the surface quality of the cold-rolled strip, which not only affects the deformation behavior of the strip during stamping and the appearance after coating but also changes the corrosion resistance of the material.
Due to the poor corrosion resistance of cold-rolled steel sheets, cold-rolled steel sheets are rarely used directly as prepainted galvanized steel coil and hot dip galvanized coils. As a result, a large amount of emulsion, lubricating oil, hydraulic oil, and tiny solid particles such as residual iron, carbon powder, and dust generated during rolling remains on the surface.
In the annealing process, the easily oxidizable elements in the steel plate are often used to migrate to the surface of the steel plate to form oxides and aggregate on the surface. Therefore, the rolling and annealing link significantly impact the corrosion resistance of the steel plate. In contrast, the pickling and leveling links have less impact on the corrosion resistance of the steel plate. The corrosion of the steel plate is mainly an electrochemical process, and the corrosion resistance of the surface of the steel plate is mainly affected by the surface microstructure. The wet heat test star of the steel plate after rolling is better than that of the steel plate after annealing. The amount of emulsion remaining on the surface of the steel plate, the amount of rolling oil, and the amount of residual iron make the corrosion resistance of each position of the steel vary greatly. The surface cleanliness of cold-rolled sheets is affected by various factors in the process of raw materials, rolling, annealing, and storage, and directly affects its corrosion resistance.