Steel sheet

Abstract

Provided is a steel sheet having a chemical composition comprising C: 0.020 to 0.100%, Mn: 1.00 to 2.50%, P: 0.100% or less, S: 0.0200% or less, Al: 0.005 to 0.700%, N: 0.0150% or less, O: 0.0100% or less, etc., and a balance of Fe and impurities, and a microstructure comprising, by area %, ferrite: 70 to 97% and a hard phase: 3 to 30%, wherein an Str of the surface is 0.35 to 0.75, and a difference ΔStr of the Str and the Str after imparting 5% tensile strain is 0.15 or less.

1 . A steel sheet having a chemical composition comprising, by mass %,
 C: 0.020 to 0.100%,   Mn: 1.00 to 2.50%,   P: 0.100% or less,   S: 0.0200% or less,   Al: 0.005 to 0.700%,   N: 0.0150% or less,   O: 0.0100% or less,   Si: 0 to 1.500%,   Cr: 0 to 0.80%,   Mo: 0 to 0.50%,   B: 0 to 0.0100%,   Ti: 0 to 0.100%,   Nb: 0 to 0.060%,   V: 0 to 0.50%,   Ni: 0 to 1.00%,   Cu: 0 to 1.00%,   W: 0 to 1.00%,   Sn: 0 to 1.00%,   Sb: 0 to 0.200%,   Ca: 0 to 0.0100%,   Mg: 0 to 0.0100%,   Zr: 0 to 0.0100%,   REM: 0 to 0.0100%, and   balance: Fe and impurities, and   a microstructure comprising, by area %,   ferrite: 70 to 97%, and   a hard phase: 3 to 30%, wherein   an Str of the surface is 0.35 to 0.75, and   a difference ΔStr of the Str and the Str after imparting a 5% tensile strain is 0.15 or less.   
     
     
         2 . The steel sheet according to  claim 1 , wherein the chemical composition contains, by mass %, one or more of
 Si: 0.005 to 1.500%,   Cr: 0.001 to 0.80%,   Mo: 0.001 to 0.50%,   B: 0.0001 to 0.0100%,   Ti: 0.001 to 0.100%,   Nb: 0.001 to 0.060%,   V: 0.001 to 0.50%,   Ni: 0.001 to 1.00%,   Cu: 0.001 to 1.00%,   W: 0.001 to 1.00%,   Sn: 0.001 to 1.00%,   Sb: 0.001 to 0.200%,   Ca: 0.0001 to 0.0100%,   Mg: 0.0001 to 0.0100%,   Zr: 0.0001 to 0.0100%, and   REM: 0.0001 to 0.0100%.   
     
     
         3 . The steel sheet according to  claim 1 , wherein the hard phase is comprised of one or more of martensite, bainite, tempered martensite, and pearlite. 
     
     
         4 . The steel sheet according to  claim 2 , wherein the hard phase is comprised of one or more of martensite, bainite, tempered martensite, and pearlite.