Surface-treated steel strip with improved welding capacity and coating properties and its production.

摘要

A zinc or zinc-alloy plated steel sheet having an improved weldability and plating properties, as well as a method for making the same is provided. Even when the substrate steel sheet is the one which is difficult to deposit a zinc or zinc-alloy layer by conventional methods, such as an extra low carbon steel sheet, the present invention enable a reliable production of a galvanized steel sheet suffering from no plating failure or insufficient adhesion as well as a reliable production of a galvannealed steel sheet suffering from no plating failure or streaking of the alloyed layer. The zinc or zinc-alloy plated steel sheet having improved weldability comprises an extra low carbon steel sheet, an iron-carbon plated layer or a carbon-rich layer generated by diffusion of the iron-carbon plated layer on at least one major surface of the extra low carbon steel sheet, and a zinc or zinc-alloy plated layer on the iron-carbon plated layer or the carbon-rich layer. The zinc or zinc-alloy plated steel sheet having improved weldability and/or plating properties is produced by depositing on the steel sheet an iron-carbon plated layer having a carbon content of from 0.01% by weight to 10% by weight to a coating weight of from 0.01 g/m2 to 10 g/m2, optionally annealing the iron-carbon plated steel sheet, and depositing a zinc or zinc-alloy plated layer, preferably by galvanizing or galvannealing, on the annealed steel sheet.