PROCESS FOR PREPARING SURFACE-TREATED STEEL STRIPS ADAPTED FOR ELECTRIC RESISTANCE WELDING

摘要

Surface-treated steel strips suitable for electric resistance welding are prepared by forming a first layer of iron-nickel alloy on a steel strip, this first layer having a weight ratio of Ni/(Fe+Ni) in the range between 0.02 and 0.50 and a thickness of 10 to 5,000 angstroms, forming a second layer of tin or iron-tin-nickel alloy on the first layer by tin plating to a coating weight of 0.1 to 1 g/m2 of tin and optionally, causing the tin to reflow. A third layer is formed on the second layer by effecting an electrolytic chromate treatment, this third layer consisting essentially of metallic chromium and hydrated chromium oxide in a total amount of 5 to 20 mg/m2 calculated as elemental chromium. Preferably, the electrolytic chromate treatment is controlled so that at least 2 mg/m2 of metallic chromium is present in the third layer.