STEEL MATERIAL WITH HEAVILY ANTICORROSIVE COATING EXCELLENT IN CATHODIC PEELING RESISTANCE

摘要

PURPOSE: To provide a steel material with heavily anticorrosive coating having desired cathodic peeling resistance and extremely excellent in cathodic peeling resistance at high temp. CONSTITUTION: A chromate layer is formed on the surface of a steel material by 100-1,000mg/m<2> (expressed in terms of total Cr) with a chromating agent partially reduced at >=80 deg.C or <=65 deg.C so that the weight ratio of trivalent Cr to total Cr is regulated to 0.1-0.7 and contg. 2.0-7.0 times (weight) as much vapor-phase silica having 2-4 hydroxyl groups per 1nm<2> specific surface area as total Cr. A primer layer. contg. 1.5-5.0mol/kg epoxide and 10-200g/kg acid pigment or basic pigment is formed on the chromate layer and an org. resin layer is further formed on the primer layer.