Alloyed Hot-Dip Galvanized Steel Sheet and Method of Producing the Same

Abstract

An alloyed hot-dip galvanized steel sheet has a composition containing about 0.05 to about 0.25 wt % of C, about 0.5 wt % or less of Si, about 1 to about 3 wt % of Mn, about 0.1 wt % or less of P, about 0.01 wt % or less of S, about 0.1 to about 2 wt % of Al, and less than about 0.005 wt % of N, and satisfying the relations, Si+Al≧0.6 wt %, (0.0006×Al) wt %≦N≦(0.0058−0.0026×Al) wt %, and Al≦(1.25×C 0.5 −0.57×Si+0.625×Mn) wt %, the balance including Fe and inevitable impurities. The alloyed hot-dip galvanized steel sheet can be obtained without passing through a complicated process, has excellent surface appearance and anti-secondary work embrittlement and high strength, and is thus suitable for application to an automobile steel sheet.

1 . An alloyed hot-dip galvanized steel sheet comprising a composition containing about 0.05 to about 0.25 wt % of C, about 0.5 wt % or less of Si, about 1 to about 3 wt % of Mn, about 0.1 wt % or less of P, about 0.01 wt % or less of S, about 0.1 to about 2 wt % of Al, and less than about 0.005 wt % of N, and satisfying the relations, Si+Al≧0.6 wt %, (0.0006×Al) wt %≦N≦(0.0058−0.0026×Al) wt %, and Al≦(1.25×C 0.5 −0.57×Si+0.625×Mn) wt %, the balance including Fe and inevitable impurities. 
     
     
         2 . The alloyed hot-dip galvanized steel sheet according to  claim 1 , wherein the composition further contains at least one element selected from the group consisting of about 1 wt % or less of Cr, about 1 wt % or less of V, and about 1 wt % or less of Mo. 
     
     
         3 . The alloyed hot-dip galvanized steel sheet according to  claim 1 , wherein the composition further contains at least one element selected from the group consisting of about 0.1 wt % or less of Ti, about 0.1 wt % or less of Nb, about 0.005 wt % or less of B, and about 1 wt % or less of Ni. 
     
     
         4 . The alloyed hot-dip galvanized steel sheet according to  claim 2 , wherein the composition further contains at least one element selected from the group consisting of about 0.1 wt % or less of Ti, about 0.1 wt % or less of Nb, about 0.005 wt % or less of B, and about 1 wt % or less of Ni. 
     
     
         5 . The alloyed hot-dip galvanized steel sheet according to  claim 1 , wherein the composition further contains at least one element selected from the group consisting of Ca and REM in a total of about 0.01 wt % or less. 
     
     
         6 . The alloyed hot-dip galvanized steel sheet according to  claim 2 , wherein the composition further contains at least one element selected from the group consisting of Ca and REM in a total of about 0.01 wt % or less. 
     
     
         7 . The alloyed hot-dip galvanized steel sheet according to  claim 3 , wherein the composition further contains at least one element selected from the group consisting of Ca and REM in a total of about 0.01 wt % or less. 
     
     
         8 . The alloyed hot-dip galvanized steel sheet according to  claim 4 , wherein the composition further contains at least one element selected from the group consisting of Ca and REM in a total of about 0.01 wt % or less. 
     
     
         9 . The alloyed hot-dip galvanized steel sheet according to  claim 1 , wherein the steel sheet has a metal structure containing a residual austenite phase at a volume ratio of about 3 to about 20%. 
     
     
         10 . A method of producing an alloyed hot-dip galvanized steel sheet, the method comprising casting, hot-rolling, and cold-rolling steel for a steel sheet having the composition according to  claim 1 , holding the steel at about 730° C. to about 900° C. for about 60 to about 300 seconds, cooling the steel at about 3 to about 100° C./s, further holding the steel at about 350° C. to about 600° C. for about 30 to about 250 seconds, hot-dip galvanizing the steel, and then alloying the steel at about 470° C. to about 600° C.