PURPOSE: To obtain a steel plate for fuel tank of automobile high in corrosion resistance against the fuel and environment of salt damage and in mold workability by applying successively a tin layer, an electrotreated chromate film, an epoxy based coated film having a specific thickness.
CONSTITUTION: The steel plate containing, by % by weight, ≤0.002 C, 3-20 Cr, 0.005-0.10 acid soluble Al, if necessary, 0.03-0.05 one or more kind of Ti Nb, Zr, V in wt.% and balance Fe is coated with tin, is coated with the electrochromate film thereon and furthermore is coated with the epoxy coating film of 0.1-3μm. The steel plate containing ≥3% Cr is excellent in corrosion resistance and in a tin plating steel plate, the steel is one-sidely corroded because the potential of tin is more positive than the potential of steel. When the content of Cr is above 20%, mold workability and weldability is deteriorated and the mechanical strength and corrosion resistance of the steel are lowered with increase in C content. When Al content is less than lower limit, the generation ratio of surface defect of the steel is high and when above upper limit, the soundness of plating is lost. When the thickness of the epoxy based coating film is less than the lower limit, tin is dissolved and when above upper limit, effect of preventing the elusion of tin is saturated.
ASAKAWA KENICHI
YOSHIDA MAKOTO
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