METHOD OF CONTINOUS ANNEALING/HOT-DIPPING OF STEEL SHEET CONTAINING SILICON AND APPARATUS FOR CONTINUOUS ANNEALING/HOT-DIPPING

摘要

The present invention provides, in a hot dip plating system having an annealing furnace for hot dip plating steel sheet containing Si, a continuous annealing and hot dip plating method and system causing internal oxidation without causing surface oxidation of the Si in the steel and avoiding a drop in the plating ability of the steel sheet and retardation of alloying, that is, a continuous annealing and hot dip plating method using an annealing furnace having, in order, a front heating zone, rear heating zone, soaking zone, and cooling zone and a hot dip plating bath, comprising heating or soaking the steel sheet at a steel sheet temperature of a temperature range of at least 300°C or more by indirect heating, making an atmosphere of the zones one comprised of hydrogen H: 1 to 10 vol% and a balance of nitrogen and unavoidable impurities, making a steel sheet peak temperature during heating at the front heating zone 550 to 750°C and making the dew point less than -25°C, making dew points of the following rear heating zone and soaking zone -30°C to 0°C, and making a dew point of the cooling zone less than - 25°C.