METHOD FOR MANUFACTURING HIGH QUALITY GA COLD ROLLED STEEL SHEET

摘要

PURPOSE: A method for manufacturing a GA (galvannealed) steel sheet having superior powdering resistance and surface quality is provided which cools an alloying heat treated plated steel sheet to a temperature of 300 deg.C in a cooling rate of 150 to 350 deg.C using an endothermic reactant solution having superior severity of quench instead of water. CONSTITUTION: In a method for manufacturing a hot galvanizing steel sheet comprising the processes of plating the steel sheet by passing a cold rolled base steel sheet through a plating vessel (210); and cooling the alloying heat treated steel sheet after alloying heat treating by heating the plated steel sheet, the method for manufacturing a high quality GA (galvannealed) steel sheet comprises the process of ultra rapidly cooling the plated steel sheet (201) to a temperature of 300 deg.C or less in a cooling rate of 50 to 350 deg.C/sec by spraying an endothermic reactant solution on the alloying heat treated plated steel sheet.