Patent ID: 6368728
Filing Date: 2002-04-09
Classification: C23C,Y10T

Abstract:
A method of manufacturing a galvannealed steel sheet, comprising the steps of:applying hot-dip galvanizing to a steel sheet; subjecting said steel sheet to gas wiping for control of the coating weight; heating said steel sheet at a heating rate of at least about 10 Â° C./second to a maximum sheet temperature within a range of from about 470 to 550Â° C.; galvannealing said sheet at a temperature of the maximum sheet temperature or less, thereby obtaining a Znâ€”Fe galvannealing layer having an Al content XAl (wt %) of the galvannealing layer and the coating weight of said galvannealed steel sheet w (g/m2) substantially satisfying the following equation (1), 5&lE;WÃ—(XAlâˆ’0.12)&lE;15â€ƒâ€ƒ(1) maintaining an iron content in said galvannealing layer within the range of from about 7 to 12 wt %; wherein the total Al concentration NAl(wt %) and the total iron concentration Nfe(wt %) in the galvanizing bath upon hot-dip galvanizing substantially satisfy the following equation (2), and the incoming sheet temperature into the galvanizing bath tÂ° C. and the galvanizing bath temperature TÂ° C. satisfy the following equation (3): 0.08&lE;Nalâˆ’Nfe&lE;0.12â€ƒâ€ƒ(2) 0&lE;tâˆ’T&lE;50â€ƒâ€ƒ(3).