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A new organic composite-coated steel sheet “Zincrometal-KII” has been developed. The steel sheet consists of a specially improved thin zinc rich paint on Zn-Ni alley electroplated layer of low coating weight. Corrosion resistance, formability and weldability were investigated. (1) In two cyclic corrosion tests, consisting of salt spray, salt water immersion, drying and humidity, red rust initiation time of the flat part in unpainted condition of KII was about one and half times longer and its thickness reduction was reduced into less than about two third as compared to the conventional organic coated steel.

A new organic composite-coated steel sheet with bake-hardenability has been developed. The steel sheet consists of Zn-Ni alloy electroplated layer, chromate and zinc powder free organic film. To obtain better formability (anti-powdering) and weldability, the thickness of the organic film is reduced to 0.8∼1.5µm (1.0∼2.0g/m2). The addition of bake-hardenability to this organic coated steel sheet was realized by controlling the amount of residual solute carbon in continuous annealed extra low carbon steels.