Variation of phosphatability with chemical composition and surface roughness of steel sheet

The purpose of the present study is to investigate the effect of specific steel alloying elements, such as Cr, Ni, and Cu, and surface roughness of substrate on phosphatability of cold rolled sheet steel for drums. Phosphatability depends upon surface characteristics and can be estimated by using the electrochemical method and measuring the τ value, which is the time of exposure to the substrate Fe. In order to obtain good phosphatability, low contents of retained elements are desirable, although phosphatability can be improved indirectly by increasing the surface roughness of the steel sheet. Phosphatability of cold rolled steel sheet is also related to the treatment conditions in the phosphating bath. Increasing both the temperature and acceleration of the phosphating solution is desirable in order to obtain good quality.