PROCESS FOR GALVANIZING

摘要

A process for galvanizing by which hot-rolled steel sheets, cold-rolled steel sheets, and basis sheets having various compositions can be galvanized without bare spots, specifically, a process which comprises subjecting a basis sheet to surface cleaning and preplating with Ni, heating the resulting basis sheet rapidly in a non-oxidizing or reducing atmosphere to a sheet temperature of 430 to 500ºC at a temperature rise rate of 20°C/sec or above, and then subjecting the sheet to hot-dipping in a zinc plating bath, wherein the following requirements (a) to (d) are satisfied: (a) when the basis sheet is an acid-pickled hot-rolled steel sheet having an Si content of 0.2% or above, the build-up of Ni in the preplating is controlled to be 0.5g/m² or above, (b) when the basis sheet is an acid-pickled hot-rolled steel sheet having an Si content of less than 0.2 %, the build-up of Ni in the preplating is controlled to be 0.2g/m² or above, (c) when the basis sheet is an annealed cold-rolled steel sheet having an Si content of 0.2% or above, the build-up of Ni in the preplating is controlled to be 0.3g/m² or above, and (d) when the basis sheet is an annealed cold-rolled steel sheet having an Si content of less than 0.2%, the build-up of Ni in the preplating is controlled to be 0.05g/m² or above.