High-strength galvanized steel sheet having excellent electrical resistance spot weldability, and method for producing same

Abstract

Provided is a galvanized steel sheet having excellent spot weldability; and a method for producing same. The galvanized steel sheet includes a base steel sheet and a zinc-based plating layer formed on the base steel sheet, wherein the surface layer of the base steel sheet may have a decarburization rate of at least 30% as represented by equation 1. [Equation 1]: Decarburization rate (%) of surface layer=(1−average carbon concentration in surface layer/bulk carbon concentration)*100, where the surface layer refers to a region extending to a depth of 35 μm from the surface of the base steel sheet.

1 . A galvanized steel sheet including a base steel sheet and a zinc-based plating layer formed on the base steel sheet,
 wherein a surface layer of the base steel sheet has a decarburization ratio of 30% or more, represented by equation 1 as below.
   Decarburization ratio(%)of surface layer=(1−average carbon concentration in surface layer/bulk carbon concentration)*100
 
   where the surface layer refers to a region up to a depth of 35 μm from the surface of the base steel sheet.   
     
     
         2 . The galvanized steel sheet of  claim 1 , wherein the decarburization ratio of the surface layer is 40% or more. 
     
     
         3 . The galvanized steel sheet of  claim 1 , wherein tensile strength of the steel sheet is 490 Mpa or more. 
     
     
         4 . The galvanized steel sheet of  claim 1 , wherein a coating amount of the zinc-based plating layer is 30-70 g/m 2 . 
     
     
         5 . The galvanized steel sheet of  claim 1 , wherein the zinc-based plating layer is a hot-dip galvannealed (GA) layer having a degree of alloying of 8-13 weight %. 
     
     
         6 . The galvanized steel sheet of  claim 1 , wherein the steel sheet has a composition including 0.05-1.5% of C, 2.0% or less of Si, 1.0-30% of Mn, 3% or less of S—Al (acid-soluble aluminum), 2.5% or less of Cr, 1% or less of Mo, 0.005% or less of B, 0.2% or less of Nb, 0.2% or less of Ti, 0.2% or less of V, 0.1% or less of Sb+Sn+Bi, and 0.01% or less of N. 
     
     
         7 . A method of manufacturing a galvanized steel sheet having excellent spot weldability, the method comprising:
 obtaining a hot-rolled steel sheet by hot-rolling a steel slab;   obtaining a hot-rolled steel sheet by coiling the hot-rolled steel sheet at a temperature of 590-750° C.;   heating an edge portion of the coiled hot-rolled steel sheet at 600-800° C. for 5 to 24 hours in a nitrogen atmosphere including 0.5-2% of oxygen;   obtaining a cold-rolled steel sheet by cold-rolling the hot-rolled steel sheet;   annealing the cold-rolled steel sheet in an atmosphere of a dew point of -10-30° C. at 650-900° C. while allowing the cold-rolled steel sheet to pass at a passing speed of 40-130 mpm; and   hot-dip galvanizing the annealed cold-rolled steel sheet.   
     
     
         8 . The method of  claim 7 , further comprising:
 performing a galvannealing heat treatment on the hot-dip galvanized cold-rolled steel sheet.   
     
     
         9 . The method of  claim 8 , wherein the galvannealing heat treatment is performed at a temperature of 480-560° C. 
     
     
         10 . The method of  claim 7 , wherein the steel slab has a composition including 0.05-1.5% of C, 2.0% or less of Si, 1.0-30% of Mn, 3% or less of S—Al (acid-soluble aluminum), 2.5% or less of Cr, 1% or less of Mo, 0.005% or less of B, 0.2% or less of Nb, 0.2% or less of Ti, 0.2% or less of V, 0.1% or less of Sb+Sn+Bi, and 0.01% or less of N. 
     
     
         11 . The galvanized steel sheet of  claim 2 , wherein the steel sheet has a composition including 0.05-1.5% of C, 2.0% or less of Si, 1.0-30% of Mn, 3% or less of S—Al (acid-soluble aluminum), 2.5% or less of Cr, 1% or less of Mo, 0.005% or less of B, 0.2% or less of Nb, 0.2% or less of Ti, 0.2% or less of V, 0.1% or less of Sb+Sn+Bi, and 0.01% or less of N. 
     
     
         12 . The galvanized steel sheet of  claim 3 , wherein the steel sheet has a composition including 0.05-1.5% of C, 2.0% or less of Si, 1.0-30% of Mn, 3% or less of S—Al (acid-soluble aluminum), 2.5% or less of Cr, 1% or less of Mo, 0.005% or less of B, 0.2% or less of Nb, 0.2% or less of Ti, 0.2% or less of V, 0.1% or less of Sb+Sn+Bi, and 0.01% or less of N. 
     
     
         13 . The galvanized steel sheet of  claim 4 , wherein the steel sheet has a composition including 0.05-1.5% of C, 2.0% or less of Si, 1.0-30% of Mn, 3% or less of S—Al (acid-soluble aluminum), 2.5% or less of Cr, 1% or less of Mo, 0.005% or less of B, 0.2% or less of Nb, 0.2% or less of Ti, 0.2% or less of V, 0.1% or less of Sb+Sn+Bi, and 0.01% or less of N. 
     
     
         14 . The galvanized steel sheet of  claim 5 , wherein the steel sheet has a composition including 0.05-1.5% of C, 2.0% or less of Si, 1.0-30% of Mn, 3% or less of S—Al (acid-soluble aluminum), 2.5% or less of Cr, 1% or less of Mo, 0.005% or less of B, 0.2% or less of Nb, 0.2% or less of Ti, 0.2% or less of V, 0.1% or less of Sb+Sn+Bi, and 0.01% or less of N. 
     
     
         15 . The method of  claim 8 , wherein the steel slab has a composition including 0.05-1.5% of C, 2.0% or less of Si, 1.0-30% of Mn, 3% or less of S—Al (acid-soluble aluminum), 2.5% or less of Cr, 1% or less of Mo, 0.005% or less of B, 0.2% or less of Nb, 0.2% or less of Ti, 0.2% or less of V, 0.1% or less of Sb+Sn+Bi, and 0.01% or less of N.