Hot-rolled steel sheet

Abstract

This hot-rolled steel sheet has a desired chemical composition and microstructure, an average sphere equivalent radius of alloy carbides in the ferrite is 0.5 nm or more and less than 5.0 nm, an average number density of the alloy carbides in the ferrite is 3.5×1016/cm3 or more, an E value that indicates periodicity of the microstructure is 10.7 or more, and an I value that indicates uniformity of the microstructure is 1.020 or more, a standard deviation of a Mn concentration is 0.60 mass % or less, and a tensile strength is 980 MPa or more.

1 . A hot-rolled steel sheet comprising, in terms of mass %, as a chemical composition:
 C: 0.050% to 0.250%;   Si: 0.05% to 3.00%;   Mn: 1.00% to 4.00%;   one or more of Ti, Nb, and V: 0.060% to 0.500% in total;   sol. Al: 0.001% to 2.000%;   P: 0.100% or less;   S: 0.0300% or less;   N: 0.1000% or less;   O: 0.0100% or less;   Cu: 0% to 2.00%;   Cr: 0% to 2.00%;   Mo: 0% to 1.00%;   Ni: 0% to 2.00%;   B: 0% to 0.0100%;   Ca: 0% to 0.0200%;   Mg: 0% to 0.0200%;   REM: 0% to 0.1000%;   Bi: 0% to 0.020%;   one or more of Zr, Co, Zn, and W: 0% to 1.00% in total;   Sn: 0% to 0.05%; and   a remainder comprising Fe and impurities,   wherein, a microstructure having,
 in terms of area %, 
 residual austenite at less than 3.0%, 
 ferrite at 15.0% or more and less than 60.0%, and 
 pearlite at less than 5.0%, 
 an average sphere equivalent radius of alloy carbides in the ferrite of 0.5 nm or more and less than 5.0 nm, 
 an average number density of the alloy carbides in the ferrite of 3.5×10 16 /cm 3  or more, 
 an E value that indicates periodicity of the microstructure of 10.7 or more, 
 an I value that indicates uniformity of the microstructure of 1.020 or more, 
 a standard deviation of a Mn concentration of 0.60 mass % or less, and 
 a tensile strength of 980 MPa or more. 
   
     
     
         2 . The hot-rolled steel sheet according to  claim 1 , further comprising, in terms of mass %, one or more of, as the chemical composition:
 Cu: 0.01% to 2.00%;   Cr: 0.01% to 2.00%;   Mo: 0.01% to 1.00%;   Ni: 0.02% to 2.00%;   B: 0.0001% to 0.0100%;   Ca: 0.0005% to 0.0200%;   Mg: 0.0005% to 0.0200%;   REM: 0.0005% to 0.1000%; and   Bi: 0.0005% to 0.020%.