High strength hot rolled steel sheet

Abstract

Provided is a high strength hot rolled steel sheet having a predetermined chemical composition, wherein when a total width in a direction perpendicular to a rolling direction and sheet thickness direction is W, a microstructure at a ¼ position in sheet thickness at all positions of a 1/10W position, 3/10W position, 5/10W position, 7/10W position, and 9/10W position from an end in a width direction comprises, by area %, tempered martensite: 95% or more, fresh martensite: 5% or less, and at least one of ferrite, upper bainite, and pearlite: 5% or less in total, and a difference between a maximum value and minimum value in tensile strength at all the positions in the width direction is 30 MPa or less.

1 . A high strength hot rolled steel sheet comprising a chemical composition comprising, by mass %,
 C: 0.050 to 0.100%,   Si: 0.010 to 0.200%,   Mn: 1.00 to 2.50%,   Ti: 0.001 to 0.120%,   Al: 0.001 to 0.050%,   B: 0.0005 to 0.0050%,   P: 0.100% or less,   S: 0.050% or less,   N: 0.0050% or less,   O: 0 to 0.0050%,   Cu: 0 to 0.20%,   Ni: 0 to 0.20%,   Sn: 0 to 0.10%,   Cr: 0 to 0.40%,   Mo: 0 to 0.20%,   Nb: 0 to 0.05%,   V: 0 to 0.10%,   As: 0 to 0.100%,   Zr: 0 to 0.100%,   Ca: 0 to 0.0050%,   Mg: 0 to 0.100%,   Bi: 0 to 0.020%,   Co: 0 to 0.20%,   W: 0 to 0.20%,   Zn: 0 to 0.20%,   REM: 0 to 0.1000%, and   balance: Fe and impurities, wherein   when a total width in a direction perpendicular to a rolling direction and sheet thickness direction is W, a microstructure at a ¼ position in sheet thickness at all positions of a 1/10W position, 3/10W position, 5/10W position, 7/10W position, and 9/10W position from an end in a width direction comprises, by area %,   tempered martensite: 95% or more,   fresh martensite: 5% or less, and   at least one of ferrite, upper bainite, and pearlite: 5% or less in total, and   a difference between a maximum value and minimum value in tensile strength at all the positions in the width direction is 30 MPa or less.   
     
     
         2 . The high strength hot rolled steel sheet according to  claim 1 , wherein the chemical composition contains, by mass %, at least one of
 O: 0.0001 to 0.0050%,   Cu: 0.001 to 0.20%,   Ni: 0.001 to 0.20%,   Sn: 0.001 to 0.10%,   Cr: 0.001 to 0.40%,   Mo: 0.001 to 0.20%,   Nb: 0.001 to 0.05%,   V: 0.001 to 0.10%,   As: 0.001 to 0.100%,   Zr: 0.0001 to 0.100%,   Ca: 0.0001 to 0.0050%,   Mg: 0.0001 to 0.100%,   Bi: 0.0001 to 0.020%,   Co: 0.001 to 0.20%,   W: 0.001 to 0.20%,   Zn: 0.001 to 0.20%, and   REM: 0.0001 to 0.1000%.   
     
     
         3 . The high strength hot rolled steel sheet according to  claim 1 , wherein a prior austenite grain size in the microstructure is 40 μm or less. 
     
     
         4 . The high strength hot rolled steel sheet according to  claim 2 , wherein a prior austenite grain size in the microstructure is 40 μm or less.