Cold rolled steel sheet for hot-press forming having excellent surface quality, hot-press-formed member, and method for manufacturing same

Abstract

The present invention relates to a cold rolled steel sheet for hot-press forming, a hot-press-formed member, and a method for manufacturing same and, more specifically, to a cold rolled steel sheet for hot-press forming, having excellent surface quality, a hot-press-formed member, and a method for manufacturing same.

1 - 20 . (canceled) 
     
     
         21 . A cold-rolled steel sheet comprising: a base steel sheet and a first oxide layer formed on the base steel sheet,
 wherein the first oxide layer comprises two or more of Fe, Mn, Cr, and Si, and has a thickness of 5 to 500 nm.   
     
     
         22 . The cold-rolled steel sheet of  claim 21 , wherein the base steel sheet comprises, by wt %, 0.05 to 0.4% of C, 0.5 to 3.0% of Si, 0.3 to 5.0% of Cr, 0.01 to 4.0% of Mn, 0.001 to 0.4% of Al, 0.001 to 0.05% of P, 0.0001 to 0.02% of S, 0.001 to 0.02% of N, and a balance of Fe and other unavoidable impurities. 
     
     
         23 . The cold-rolled steel sheet of  claim 22 , wherein the base steel sheet comprises one or more of 0.001 to 0.4% of Ti, 0.001 to 0.4% of Nb, 0.001 to 0.4% of Zr, 0.001 to 0.4% of V, 0.0001 to 0.01% of B, 0.001 to 1.0% of Mo, 0.001 to 1.0% of W, 0.005 to 2.0% of Cu, 0.005 to 2.0% of Ni, 0.001 to 1.0% of Sb, 0.001 to 1.0% of Sn, and 0.0001 to 0.02% of REM. 
     
     
         24 . The cold-rolled steel sheet of  claim 21 , wherein a sum of contents of Si, Mn, and Cr in the first oxide layer is 30% or more in terms of wt %. 
     
     
         25 . The cold-rolled steel sheet of  claim 21 , wherein the cold-rolled steel sheet has a microstructure comprising 5 area % or more of ferrite and cementite. 
     
     
         26 . A member comprising: a base steel sheet; a first oxide layer formed on the base steel sheet; and a second oxide layer formed on the first oxide layer, wherein the first oxide layer comprises two or more of Fe, Mn, Cr, and Si, and the second oxide layer is formed of an Fe-based oxide and has a thickness of 0.1 to 10 μm. 
     
     
         27 . The member of  claim 26 , wherein the base steel sheet comprises, by wt %, 0.05 to 0.4% of C, 0.5 to 3.0% of Si, 0.3% or more and less than 5.0% of Cr, 0.01 to 4.0% of Mn, 0.001 to 0.4% of Al, 0.001 to 0.05% of P, 0.0001 to 0.02% of S, 0.001 to 0.02% of N, and a balance of Fe and other unavoidable impurities. 
     
     
         28 . The member of  claim 27 , wherein the base steel sheet comprises one or more of 0.001 to 0.4% of Ti, 0.001 to 0.4% of Nb, 0.001 to 0.4% of Zr, 0.001 to 0.4% of V, 0.0001 to 0.01% of B, 0.001 to 1.0% of Mo, 0.001 to 1.0% of W, 0.005 to 2.0% of Cu, 0.005 to 2.0% of Ni, 0.001 to 1.0% of Sb, 0.001 to 1.0% of Sn, and 0.0001 to 0.02% of REM. 
     
     
         29 . The member of  claim 26 , wherein a sum of contents of Si, Mn, and Cr in the second oxide layer is less than 30% in terms of wt %. 
     
     
         30 . The member of  claim 26 , wherein the member has a microstructure comprising martensite or bainite as a main phase. 
     
     
         31 . The member of  claim 26 , wherein a tensile strength of the member is 500 MPa or more. 
     
     
         32 . A manufacturing method of a cold-rolled steel sheet, comprising:
 reheating a steel slab;   hot rolling the reheated steel slab;   cooling and coiling the hot-rolled steel sheet;   cold rolling the coiled steel sheet; and   performing continuous annealing on the cold-rolled steel sheet,   wherein during the continuous annealing, a temperature increase rate at an atmosphere temperature of room temperature to 700° C. is 3.0 to 20.0° C./s, a temperature increase rate at an atmosphere temperature of 700 to 800° C. is 0.08 to 1.5° C./s, a temperature increase rate at an atmosphere temperature of 800 to 900° C. is 0.01 to 1.5° C./s, and a temperature increase rate at an atmosphere temperature of 900 to 1,000° C. is 0.01 to 1.0° C./s.   
     
     
         33 . The manufacturing method of  claim 32 , wherein the steel slab comprises, by wt %, 0.05 to 0.4% of C, 0.5 to 3.0% of Si, 0.3 to 5.0% of Cr, 0.01 to 4.0% of Mn, 0.001 to 0.4% of Al, 0.001 to 0.05% of P, 0.0001 to 0.02% of S, 0.001 to 0.02% of N, and a balance of Fe and other unavoidable impurities. 
     
     
         34 . The manufacturing method of  claim 33 , wherein the steel slab comprises one or more of 0.001 to 0.4% of Ti, 0.001 to 0.4% of Nb, 0.001 to 0.4% of Zr, 0.001 to 0.4% of V, 0.0001 to 0.01% of B, 0.001 to 1.0% of Mo, 0.001 to 1.0% of W, 0.005 to 2.0% of Cu, 0.005 to 2.0% of Ni, 0.001 to 1.0% of Sb, 0.001 to 1.0% of Sn, and 0.0001 to 0.02% of REM. 
     
     
         35 . The manufacturing method of  claim 32 , wherein the reheating is performed in a temperature range of 1,000 to 1,300° C.,
 the hot rolling is performed at a finish rolling temperature of Ar3 to 1,000° C., 
 the coiling is performed in a temperature range of Ms to 750° C., and 
 the cold rolling is performed at a reduction ratio of 30 to 80%. 
 
     
     
         36 . The manufacturing method of  claim 32 , wherein the continuous annealing is performed in a steel sheet temperature range of 700 to 900° C., and a continuous annealing time is 1 to 1,000 seconds. 
     
     
         37 . A manufacturing method of a member, comprising:
 performing a heat treatment on the cold-rolled steel sheet of  claim 32 ; and   performing hot press forming on the heat-treated steel sheet and then cooling the hot press formed steel sheet,   wherein during the heat treatment, an A value defined in the following Relational Expression 1 is 0.6 to 1.0:   
       
         
           
             
               
                 
                   
                     A 
                     = 
                     
                       
                         
                           ( 
                           
                             T 
                             + 
                             
                               0.2 
                                  
                               t 
                             
                           
                           ) 
                         
                         / 
                         1 
                       
                       
                         , 
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                       210 
                     
                   
                 
                 
                   
                     [ 
                     
                       Relational 
                       ⁢ 
                           
                       Expression 
                       ⁢ 
                           
                       1 
                     
                     ] 
                   
                 
               
             
           
         
         where T represents a heating temperature and a unit thereof is ° C., and t represents a total heating time and a unit thereof is a second. 
       
     
     
         38 . The manufacturing method of  claim 37 , wherein during the heat treatment, the heating is performed to the heating temperature at an atmosphere temperature increase rate of 1 to 1,000° C./s. 
     
     
         39 . The manufacturing method of  claim 37 , wherein during the heat treatment, the heating temperature is 700 to 1,000° C., and the heating time is 150 to 1,000 seconds. 
     
     
         40 . The manufacturing method of  claim 37 , wherein after the hot press forming, during the cooling, the cooling is performed to an Mf temperature or lower at a cooling rate of 10 to 1,000° C./s.