Effect of Organic Film Composition on Performance of Organic Composite Coated Steel Sheet with Excellent Lubrication

There is an increasing demand for steel sheet that should be completely free from oiling and degreasing during the forming operation in order to improve working environment and hence global environment; In order to achieve this we studied a lubricated galvanized steel sheet, which has a thin organic film on the chromated upper layer.A lubricated galvanized steel sheet requires not only good lubricity but also good resistance to mechanical damage that causes deterioration of surface appearance. The reason why the appearance of the steel sheet deteriorated was investigated by considering that this is caused by sliding and deformation. The draw bead test which simulate both sliding and deformation components of forming process was used as a simulation testing method to study deterioration of the appearance.From the point of the improvement of resistance against mechanical damage, an organic film has high level of mechanical strength to reduce powdering by sliding, and has adequate softness that allows the film to follow to the press deformation well. The tensile strength and elongation of various films were also measured. On the basis of the test results, it is concluded that thermosetting polyurethane resin has good mechanical properties to provide excellent surface appearance.