Hot-rolled steel sheet

Abstract

In this hot-rolled steel sheet, a microstructure at a ¼ position from a surface includes, by area %, ferrite: 2.0% to 30.0%, bainite: 60.0% to 93.0%, and martensite: 5.0% to 20.0%, an area ratio of martensite, which is in contact with a 30° grain boundary, when a maximum value of a GAIQ value of the ferrite is indicated as Iα, which has a relative GAIQ value of Iα/3 or less, and which has a grain size of 2.0 μm or more, is 5.0% or more, and a tensile strength is 980 MPa or more.

1 . A hot-rolled steel sheet comprising, as a chemical composition, by mass %:
 C: 0.045% to 0.150%;   Si: 0.10% to 2.50%;   Mn: 1.50% to 3.50%;   sol. Al: 0.010% to 1.000%;   Ti: 0.050% to 0.200%;   P: 0.100% or less;   S: 0.0300% or less;   N: 0.1000% or less;   O: 0.0100% or less;   Nb: 0% to 0.050%;   V: 0% to 0.050%;   B: 0% to 0.0100%;   Cu: 0% to 2.00%;   Cr: 0% to 2.00%;   Mo: 0% to 1.000%;   Ni: 0% to 2.00%;   Ca: 0% to 0.0200%;   Mg: 0% to 0.0200%;   REM: 0% to 0.1000%;   Bi: 0% to 0.0200%;   one or two or more of Zr, Co, Zn, and W: 0% to 1.0000% in total;   Sn: 0% to 0.050%; and   a remainder comprising Fe and impurities,   wherein a microstructure at a ¼ position from a surface includes, by area %,
 ferrite: 2.0% to 30.0%, 
 bainite: 60.0% to 93.0%, and 
 martensite: 5.0% to 20.0%, 
   an area ratio of martensite,
 which is in contact with a 30° grain boundary, 
 which has a relative GAIQ value of Iα/3 or less, where Iα is a maximum value of a GAIQ value of the ferrite, and 
 which has a grain size of 2.0 μm or more, 
   is 5.0% or more, and   a tensile strength of the hot-rolled steel sheet is 980 MPa or more.   
     
     
         2 . The hot-rolled steel sheet according to  claim 1 , wherein the chemical composition contains, by mass %, one or two or more of the group consisting of
 Nb: 0.001% to 0.050%,   V: 0.001% to 0.050%,   B: 0.0001% to 0.0100%,   Cu: 0.01% to 2.00%,   Cr: 0.01% to 2.00%,   Mo: 0.001% to 1.000%,   Ni: 0.01% to 2.00%,   Ca: 0.0005% to 0.0200%,   Mg: 0.0005% to 0.0200%,   REM: 0.0005% to 0.1000%, and   Bi: 0.0005% to 0.0200%.