Surface treated steel plate excellent in corrosion resitance electroconductivity and appearance of coating film

Abstract

PROBLEM TO BE SOLVED: To provide a surface-treated steel sheet having superior corrosion resistance in spite of containing no hexavalent chromium in a coating, and besides, having superior conductivity and coating film appearance.SOLUTION: The surface-treated steel sheet has a composite oxide coating on the surface of a galvanized or aluminized steel sheet, as the first layer, and an organic coating thereon as the second layer. The composite oxide coating includes (α) silica, (β) phosphoric acid and / or a phosphate compound, (γ) one or more metals selected among Mg, Mn and Al and (σ) a tetravalent vanadium compound, each in a predetermined amount. The organic coating includes a reaction product (X) of a film-forming organic resin (A) and an active-hydrogen-containing compound (B) formed of a hydrazine derivative (C), of which one part or all parts have active hydrogen; and a particular corrosion-preventing component (Y).

Description

technical field [0001] The present invention relates to a surface-treated steel sheet most suitable for use in automobiles, home appliances, building materials, and the like. In particular, it relates to an environment-friendly surface-treated steel sheet that does not contain hexavalent chromium that may have adverse effects on operators, users, or the environment when performing wastewater treatment and treatment products during manufacture. Background technique [0002] Among steel sheets for automobiles, steel sheets for home appliances, and steel sheets for building materials, chromate-treated steel sheets provided with a zinc or aluminum plating layer on the surface have been widely used. Chromate treatment is to improve its corrosion resistance (white rust resistance, red rust resistance), and a chromate layer is formed with a treatment solution mainly composed of hexavalent chromium. However, since the chromate treatment uses hexavalent chromium, which is a pollutio...

AI Technical Summary

Problems solved by technology

[0010] However, in the chromium-free technologies (1) to (3) above, in terms of potential barrier effect, even without relying on chromium, organic resins can be used to achieve a certain level, but in terms of self-healing effect, since it cannot be developed Self-healing effect of hexavalent chromium, so high corrosion resistance cannot be achieved

[0011] On the other hand, in the technique of (4) above, by adding a specific substance exhibiting a self-healing effect to the upper layer, it can be seen that the corrosion resistance is improved to some extent, but the effect is not necessarily sufficient.

This is because there is no hexavalent chromium in the film formed at the interface between the zinc plating layer and the upper layer, that is, the lower layer film, so the direct rust prevention effect due to self-healing properties cannot be obtained.

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