Methods respectively for manufacturing hot-dip galvanized steel sheet and alloyed hot-dip galvanized steel sheet

Abstract

A method for manufacturing a hot-dip galvanized steel sheet according to one aspect of the present invention includes an annealing step of reduction-annealing a steel sheet having a Si content of 1.0% by mass or more and 3.0% by mass or less at a temperature equal to or higher than an A3 point of the steel sheet in an atmosphere having a dew point of −20° C. or higher; and a hot-dip galvanizing step of making the annealed steel sheet enter into a galvanizing bath to form a galvanized layer on a surface of the steel sheet, wherein a temperature of the steel sheet entering into the galvanizing bath is set to 390° C. or lower.

1 . A method for manufacturing a hot-dip galvanized steel sheet, the method comprising:
 an annealing step of reduction-annealing a steel sheet having a Si content of 1.0% by mass or more and 3.0% by mass or less at a temperature equal to or higher than an A3 point of the steel sheet in an atmosphere having a dew point of −20° C. or higher; and   a hot-dip galvanizing step of making the annealed steel sheet enter into a galvanizing bath to form a galvanized layer on a surface of the steel sheet,   wherein a temperature of the steel sheet entering into the galvanizing bath is set to 390° C. or lower.   
     
     
         2 . A method for manufacturing a hot-dip galvannealed steel sheet,
 the method comprising an alloying step of alloying the galvanized layer formed in the hot-dip galvanized steel sheet obtained by the method for manufacturing a hot-dip galvanized steel sheet according to  claim 1 .   
     
     
         3 . The method for manufacturing a hot-dip galvannealed steel sheet according to  claim 2 , wherein the hot-dip galvanizing step and the alloying step are performed using a continuous galvanizing line.