High-strength hot-dip galvanized steel sheet having excellent plating surface quality and adhesion, and method of manufacturing the same

Abstract

Provided is a method of manufacturing a hot-dip galvanized steel sheet. According to an aspect of the present invention, the method may include preparing a base steel sheet, forming a iron (Fe)-plated layer on the prepared base steel sheet, oxidation heating the steel sheet having the Fe-plated layer formed thereon at a temperature ranging from 600° C. to 800° C., maintaining the heated steel sheet at a temperature ranging from 750° C. to 900° C. for 5 seconds or more in a reducing atmosphere with a dew point of between −30° C. to 5° C. including 20 ppm or less of oxygen, 1 vol % to 20 vol % of H2, and N2 as well as unavoidable gases as a remainder, cooling the maintained steel sheet, and plating the cooled steel sheet by dipping in a hot-dip galvanizing bath.

1 - 17 . (canceled) 
     
     
         18 . A method of manufacturing a hot-dip galvanized steel sheet, the method comprising:
 preparing a base steel sheet;   forming an iron (Fe)-plated layer on the prepared base steel sheet;   oxidation heating the steel sheet having the Fe-plated layer formed thereon at a temperature ranging from 600° C. to 800° C.;   maintaining the heated steel sheet at a temperature ranging from 750° C. to 900° C. for 5 seconds or more in a reducing atmosphere with a dew point of between −30° C. to 5° C. including 20 ppm or less of oxygen, 1 vol % to 20 vol % of H 2 , and N 2  as well as unavoidable gases as a remainder;   cooling the maintained steel sheet; and   plating the cooled steel sheet by dipping in a hot-dip galvanizing bath.   
     
     
         19 . The method of  claim 18 , wherein the base steel sheet comprises 0.3 wt % or less of carbon (C) and 1.0 wt % to 6.0 wt % of one or more of silicon (Si), manganese (Mn), and aluminum (Al). 
     
     
         20 . The method of  claim 18 , wherein the base steel sheet comprises 0.5 wt % or less of each one or more of chromium (Cr), nickel (Ni), copper (Cu), molybdenum (Mo), phosphorous (P), sulfur (S), antimony (Sb), titanium (Ti), niobium (Nb), and nitrogen (N). 
     
     
         21 . The method of  claim 18 , wherein a coating weight of the Fe-plated layer is in a range of 0.2 g/m 2  to 2 g/m 2 . 
     
     
         22 . The method of  claim 18 , wherein the Fe plating is performed by using an electroplating method. 
     
     
         23 . The method of  claim 18 , wherein the heating is performed in a direct flame furnace by controlling an air-fuel ratio, and
 the air-fuel ratio is controlled to be (1100/(C 0.09 ×T))+(100/T)≦air-fuel ratio≦(1450/(C 0.09 ×T))+(100/T), where C is a coating weight of the Fe-plated layer (mg/m 2 ) and T is a temperature (° C.) of the direct flame furnace.   
     
     
         24 . The method of  claim 18 , wherein the heating is performed in a radiant tube flame furnace in an atmosphere having 5 vol % or less of H 2  and 20 ppm or less of O 2  as well as N 2  as a remainder, and
 an oxygen content in an oxidation region in the radiant tube flame furnace is controlled to be (4000/(C 0.2 ×T 0.08 ))+(3500/T)≦oxygen content (ppm)≦(5800/(C 0.2 ×T 0.08 ))+(3850/T), where C is a coating weight of the Fe-plated layer (mg/m 2 ) and T is a temperature (° C.) of the radiant tube flame furnace.   
     
     
         25 . The method of  claim 18 , wherein a temperature of the hot-dip galvanizing bath is in a range of 440° C. to 480° C. 
     
     
         26 . The method of  claim 18 , further comprising heating the hot-dip galvanized steel sheet to a temperature ranging from 480° C. to 650° C., after the hot-dip galvanizing. 
     
     
         27 . A hot-dip galvanized steel sheet comprising:
 a base steel sheet; and   a reduced iron (Fe) layer formed on the base steel sheet and a hot-dip galvanized layer formed on the reduced Fe layer,   wherein a total amount of one or more of SiO 2  and Al 2 O 3  at an interface between the reduced Fe layer and the hot-dip galvanized layer in a direction of the base steel sheet is 0.01 g/m 2  or less, and   one or more of silicon (Si) oxide, manganese (Mn) oxide, aluminum (Al) oxide, and a complex oxide thereof having a maximum length of 1 μm or less in a longitudinal direction in a cross section are included within 1 μm from the interface between the reduced Fe layer and the hot-dip galvanized layer in a direction of the base steel sheet.   
     
     
         28 . A hot-dip galvanized steel sheet comprising:
 a base steel sheet; and   a reduced iron (Fe) layer formed on the base steel sheet and a hot-dip galvanized layer formed on the reduced Fe layer,   wherein a total amount of one or more of SiO 2  and Al 2 O 3  at an interface between the reduced Fe layer and the hot-dip galvanized layer in a direction of the base steel sheet is 0.01 g/m 2  or less, and   one or more of silicon (Si) oxide, manganese (Mn) oxide, aluminum Al oxide, and a complex oxide thereof having an average length greater than 0.05 μm and equal to or less than 0.7 μm in a longitudinal direction in a cross section are included within 1 μm from the interface between the reduced Fe layer and the hot-dip galvanized layer in a direction of the base steel sheet.   
     
     
         29 . A hot-dip galvanized steel sheet comprising:
 a base steel sheet; and   a reduced iron (Fe) layer formed on the base steel sheet and a hot-dip galvanized layer formed on the reduced Fe layer,   wherein a total amount of one or more of SiO 2  and Al 2 O 3  at an interface between the reduced Fe layer and the hot-dip galvanized layer in a direction of the base steel sheet is 0.01 g/m 2  or less, and   the amount of one or more oxides of silicon (Si) oxide, manganese (Mn) oxide, aluminum (Al) oxide, and a complex oxide thereof having a length greater than 1 μm in a cross section included within 1 μm from the interface between the reduced Fe layer and the hot-dip galvanized layer in a direction of the base steel sheet is 10% or less of the amount of total oxides.   
     
     
         30 . The hot-dip galvanized steel sheet of  claim 27 , wherein the oxides are dispersed in thickness and width directions. 
     
     
         31 . The hot-dip galvanized steel sheet of  claim 27 , wherein the base steel sheet comprises 0.3 wt % or less of carbon (C) and 1.0 wt % to 6.0 wt % of one or more of Si, Mn, and Al. 
     
     
         32 . The hot-dip galvanized steel sheet of  claim 27 , wherein the base steel sheet comprises 0.5 wt % or less of each one or more of chromium (Cr), nickel (Ni), copper (Cu), molybdenum (Mo), phosphorous (P), sulfur (S), antimony (Sb), titanium (Ti), niobium (Nb), and nitrogen (N). 
     
     
         33 . The hot-dip galvanized steel sheet of  claim 27 , wherein the oxides comprise Fe and metal having a change in Gibbs free energy (delta G) for 1 mole of oxygen during an oxidation reaction lower than that of Fe in an amount of 30 wt % or less. 
     
     
         34 . The hot-dip galvanized steel sheet of  claim 27 , wherein the hot-dip galvanized steel sheet is a galvannealed steel sheet and the hot-dip galvanized layer comprises 7 wt % to 13 wt % of Fe. 
     
     
         35 . The hot-dip galvanized steel sheet of  claim 28 , wherein the oxides are dispersed in thickness and width directions. 
     
     
         36 . The hot-dip galvanized steel sheet of  claim 28 , wherein the base steel sheet comprises 0.3 wt % or less of carbon (C) and 1.0 wt % to 6.0 wt % of one or more of Si, Mn, and Al. 
     
     
         37 . The hot-dip galvanized steel sheet of  claim 28 , wherein the base steel sheet comprises 0.5 wt % or less of each one or more of chromium (Cr), nickel (Ni), copper (Cu), molybdenum (Mo), phosphorous (P), sulfur (S), antimony (Sb), titanium (Ti), niobium (Nb), and nitrogen (N). 
     
     
         38 . The hot-dip galvanized steel sheet of  claim 28 , wherein the oxides comprise Fe and metal having a change in Gibbs free energy (delta G) for 1 mole of oxygen during an oxidation reaction lower than that of Fe in an amount of 30 wt % or less. 
     
     
         39 . The hot-dip galvanized steel sheet of  claim 28 , wherein the hot-dip galvanized steel sheet is a galvannealed steel sheet and the hot-dip galvanized layer comprises 7 wt % to 13 wt % of Fe.