Continuous annealing hot dip plating method and continuous annealing hot dip plating apparatus for steel sheet containing Si

摘要

The present invention, in a hot dipping apparatus having an annealing furnace for hot dipping a steel sheet containing Si, causes internal oxidation without causing surface oxidation of Si in the steel, and lowers the plateability and alloying of the steel sheet. In a continuous annealing hot dip plating method using an annealing furnace and a hot dip plating bath having a heating zone first stage, a heating zone latter stage, a retentive zone, and a cooling zone in order. The heating or heat retention of the steel plate in the region where the steel plate temperature is at least 300 ° C. is indirect heating, and the furnace atmosphere of each zone is an atmosphere composed of hydrogen H: 1 to 10 vol%, the balance nitrogen and inevitable impurities. The temperature reached by the steel sheet during heating in the pre-tropical zone is set to 550 ° C. or higher and 750 ° C. or lower, and the dew point is set to less than −25 ° C. ° C. and 0 ℃ inclusive, performing annealing under the condition that the dew point less than -25 ° C. in the cooling zone.