COATED STEEL MATERIAL HAVING SUPERIOR CORROSION RESISTANCE AFTER PAINTING

摘要

PURPOSE:To obtain a coated steel material having extremely superior corrosion resistance after painting by coating the surface of a steel material with a porous iron-zinc coating layer as a lower layer and a silicate film contg. zinc powder and a rust preventive chromate pigment as an upper layer. CONSTITUTION:A steel material such as a steel sheet, die steel or a steel pipe is pretreated by blasting or other method to remove a black film formed during rolling. A porous coating layer consisting essentially of iron and zinc is formed on the surface of the pretreated steel material preferably by 2-50g/m<2>. The porosity of the layer is especially regulated to 5-50%. The layer is preferably formed by dry-projecting a material demonstrated by Japan Patent Publication No.59-9312. A silicate layer contg. zinc powder and a rust preventive chromate pigment is then formed on the coating layer. The pref. amt. of the zinc powder is 50-95wt%. The pref. amt. of the pigment is 1-25wt% and the pref. average particle size is about 0.05-0.5mum.