Steel sheet

Abstract

A steel sheet according to an aspect of the present invention includes a predetermined chemical composition; in which a metallographic structure in a ¼ t portion contains residual austenite of 4 volume % to 70 volume %; [Mn]γ/[Mn]ave>1.5 is satisfied in the ¼ t portion; fγs/fγ≤0.30 and [C]×[Mn]≥0.15 are satisfied in the ¼ t portion.

1 . A steel sheet comprising, by unit mass %,
 C: 0.03% to 0.40%,   Si: 0.01% to 5.00%,   Mn: 0.50% to 12.00%,   Al: 0.001% to 5.000%,   P: 0.150% or less,   S: 0.0300% or less,   N: 0.0100% or less,   O: 0.0100% or less,   Cr: 0% to 5.00%,   Mo: 0% to 5.00%,   Ni: 0% to 5.00%,   Cu: 0% to 5.00%,   Nb: 0% to 0.500%,   Ti: 0% to 0.500%,   V: 0% to 0.500%,   W: 0% to 0.500%,   B: 0% to 0.0030%,   Ca: 0% to 0.0500%,   Mg: 0% to 0.0500%,   Zr: 0% to 0.0500%,   REM: 0% to 0.0500%,   Sb: 0% to 0.0500%,   Sn: 0% to 0.0500%,   As: 0% to 0.0500%,   Te: 0% to 0.0500%, and   a remainder including Fe and impurities,   wherein a metallographic structure in a ¼ t portion contains residual austenite of 4 volume % to 70 volume %,   an average Mn concentration [Mn] γ  in the residual austenite by unit mass % satisfies Expression 1 with respect to an average Mn concentration [Mn] ave  of the entire ¼ t portion by unit mass %, in the ¼ t portion,   a volume fraction f γs  of the residual austenite having an aspect ratio of 2.0 or less and a volume fraction f γ  of all the residual austenite satisfy Expression 2, in the ¼ t portion, and   a C content [C] and a Mn content [Mn] by unit mass % satisfy Expression 3.
   [Mn] γ /[Mn] ave >1.5  (Expression 1)
 
     f   γs   /f   γ ≤0.30  (Expression 2)
 
   [C]×[Mn]≥0.15  (Expression 3)
 
   
     
     
         2 . The steel sheet according to  claim 1 , comprising, by unit mass %,
 Mn: 3.50% to 12.00%.   
     
     
         3 . The steel sheet according to  claim 1 , comprising, by unit mass %, one or more selected from the group consisting of
 Cr: 0.01% to 5.00%,   Mo: 0.01% to 5.00%,   Ni: 0.01% to 5.00%,   Cu: 0.01% to 5.00%,   Nb: 0.005% to 0.500%,   Ti: 0.005% to 0.500%,   V: 0.005% to 0.500%,   W: 0.005% to 0.500%,   B: 0.0001% to 0.0030%,   Ca: 0.0001% to 0.0500%,   Mg: 0.0001% to 0.0500%,   Zr: 0.0005% to 0.0500%,   REM: 0.0005% to 0.0500%,   Sb: 0.0050% to 0.0500%,   Sn: 0.0050% to 0.0500%,   As: 0.0050% to 0.0500%, and   Te: 0.0050% to 0.0500%.   
     
     
         4 . The steel sheet according to  claim 1 , comprising:
 a hot dip galvanized layer on a surface of the steel sheet.   
     
     
         5 . The steel sheet according to  claim 1 , comprising:
 a galvannealed layer on a surface of the steel sheet.   
     
     
         6 . The steel sheet according to  claim 2 , comprising, by unit mass %, one or more selected from the group consisting of
 Cr: 0.01% to 5.00%,   Mo: 0.01% to 5.00%,   Ni: 0.01% to 5.00%,   Cu: 0.01% to 5.00%,   Nb: 0.005% to 0.500%,   Ti: 0.005% to 0.500%,   V: 0.005% to 0.500%,   W: 0.005% to 0.500%,   B: 0.0001% to 0.0030%,   Ca: 0.0001% to 0.0500%,   Mg: 0.0001% to 0.0500%,   Zr: 0.0005% to 0.0500%,   REM: 0.0005% to 0.0500%,   Sb: 0.0050% to 0.0500%,   Sn: 0.0050% to 0.0500%,   As: 0.0050% to 0.0500%, and   Te: 0.0050% to 0.0500%.   
     
     
         7 . The steel sheet according to  claim 2 , comprising:
 a hot dip galvanized layer on a surface of the steel sheet.   
     
     
         8 . The steel sheet according to  claim 3 , comprising:
 a hot dip galvanized layer on a surface of the steel sheet.   
     
     
         9 . The steel sheet according to  claim 6 , comprising:
 a hot dip galvanized layer on a surface of the steel sheet.   
     
     
         10 . The steel sheet according to  claim 2 , comprising:
 a galvannealed layer on a surface of the steel sheet.   
     
     
         11 . The steel sheet according to  claim 3 , comprising:
 a galvannealed layer on a surface of the steel sheet.   
     
     
         12 . The steel sheet according to  claim 6 , comprising:
 a galvannealed layer on a surface of the steel sheet.