High-strength steel sheet

Abstract

A high-strength steel sheet has a chemical composition consisting of, in mass percent, C: 0.10 to 0.24%, Mn: 3.50 to 12.00%, Si: 0.005 to 5.00%, Al: 0.005 to 5.00%, P: 0.15% or less, S: 0.030% or less, N: 0.020% or less, O: 0.010% 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 0.50%, Ti: 0 to 0.50%, W: 0 to 0.50%, B: 0 to 0.010%, Ca: 0 to 0.05%, Mg: 0 to 0.05%, Zr: 0 to 0.05%, REM: 0 to 0.05%, Sb: 0 to 0.50%, Sn: 0 to 0.50%, As: 0 to 0.05%, and V: 0 to 2.0%, with the balance: Fe and impurities, and a steel micro-structure at a ¼ sheet-thickness position includes, in area percent, retained austenite: 10.0 to 55.0%, high temperature tempered martensite: 30.0 to 75.0%, and low temperature tempered martensite: 15.0 to 60.0%, with the balance including fresh martensite: 0 to 10.0%, pearlite: 0 to 5.0%, and bainite: 0 to 5.0%.

1 . A high-strength steel sheet having a chemical composition consisting of, in mass percent:
 C: 0.10 to 0.24%;   Mn: 3.50 to 12.00%;   Si: 0.005 to 5.00%;   Al: 0.005 to 5.00%;   P: 0.15% or less;   S: 0.030% or less;   N: 0.020% or less;   O: 0.010% 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 0.50%;   Ti: 0 to 0.50%;   W: 0 to 0.50%;   B: 0 to 0.010%;   Ca: 0 to 0.05%;   Mg: 0 to 0.05%;   Zr: 0 to 0.05%;   REM: 0 to 0.05%;   Sb: 0 to 0.50%;   Sn: 0 to 0.50%;   As: 0 to 0.05%; and   V: 0 to 2.0%;   with the balance: Fe and impurities, wherein   a steel micro-structure at a ¼ sheet-thickness position includes, in area percent:   retained austenite: 10.0 to 55.0%;   high temperature tempered martensite: 30.0 to 75.0%; and   low temperature tempered martensite: 15.0 to 60.0%;   with the balance including:   fresh martensite: 0 to 10.0%;   pearlite: 0 to 5.0%; and   bainite: 0 to 5.0%.   
     
     
         2 . The high-strength steel sheet according to  claim 1 , wherein, in the steel micro-structure, a total of area fractions of the fresh martensite, the pearlite, and the bainite is, in area percent, 0 to 5.0%. 
     
     
         3 . The high-strength steel sheet according to  claim 1 , wherein, in the steel micro-structure, area fractions of the pearlite and the bainite are 0%. 
     
     
         4 . The high-strength steel sheet according to  claim 1 , wherein the steel sheet has a tensile strength of 1180 MPa or more and a sheet thickness of 0.8 to 3.2 mm. 
     
     
         5 . The high-strength steel sheet according to  claim 1 , wherein the chemical composition contains, in mass percent, C: 0.13 to 0.21%. 
     
     
         6 . The high-strength steel sheet according to  claim 1 , wherein the chemical composition contains, in mass percent, Mn: 4.0 to 7.0%. 
     
     
         7 . The high-strength steel sheet according to  claim 1 , wherein the chemical composition contains, in mass percent, Cr: 0 to 1.50%. 
     
     
         8 . The high-strength steel sheet according to  claim 1 , wherein the chemical composition contains, in mass percent, Mo: 0 to 1.00%. 
     
     
         9 . The high-strength steel sheet according to  claim 1 , wherein the chemical composition contains, in mass percent, Ni: 0 to 1.50%. 
     
     
         10 . The high-strength steel sheet according to  claim 1 , wherein the chemical composition contains, in mass percent, Cu: 0 to 1.50%. 
     
     
         11 . The high-strength steel sheet according to  claim 1 , wherein the chemical composition contains, in mass percent, B: 0 to 0.003%. 
     
     
         12 . The high-strength steel sheet according to  claim 1 , wherein a surface of the steel sheet includes a galvanized layer, a galvannealed layer, or a Zn—Ni alloy plating layer. 
     
     
         13 . The high-strength steel sheet according to  claim 4 , wherein a surface of the steel sheet includes a galvanized layer, a galvannealed layer, or a Zn—Ni alloy plating layer. 
     
     
         14 . The high-strength steel sheet according to  claim 5 , wherein a surface of the steel sheet includes a galvanized layer, a galvannealed layer, or a Zn—Ni alloy plating layer. 
     
     
         15 . The high-strength steel sheet according to  claim 6 , wherein a surface of the steel sheet includes a galvanized layer, a galvannealed layer, or a Zn—Ni alloy plating layer. 
     
     
         16 . The high-strength steel sheet according to  claim 7 , wherein a surface of the steel sheet includes a galvanized layer, a galvannealed layer, or a Zn—Ni alloy plating layer. 
     
     
         17 . The high-strength steel sheet according to  claim 8 , wherein a surface of the steel sheet includes a galvanized layer, a galvannealed layer, or a Zn—Ni alloy plating layer. 
     
     
         18 . The high-strength steel sheet according to  claim 9 , wherein a surface of the steel sheet includes a galvanized layer, a galvannealed layer, or a Zn—Ni alloy plating layer. 
     
     
         19 . The high-strength steel sheet according to  claim 10 , wherein a surface of the steel sheet includes a galvanized layer, a galvannealed layer, or a Zn—Ni alloy plating layer. 
     
     
         20 . The high-strength steel sheet according to  claim 11 , wherein a surface of the steel sheet includes a galvanized layer, a galvannealed layer, or a Zn—Ni alloy plating layer.