Hot-rolled steel sheet
View Patent ↗A hot-rolled steel sheet includes a chemical composition represented by, in mass %, C: 0.010% to 0.100%, Si: 0.30% or less, Cr: 0.05% to 1.00%, Nb: 0.003% to 0.050%, Ti: 0.003% to 0.200% and others, wherein a proportion of grains having an intragranular misorientation of 5° to 14° in all grains is 20% or more by area ratio, the grain being defined as an area which is surrounded by a boundary having a misorientation of 15° or more and has a circle-equivalent diameter of 0.3 μm or more.
1. A hot-rolled steel sheet comprising
a chemical composition represented by, in mass %,
C: 0.010% to 0.100%,
Si: 0.30% or less,
Mn: 0.40% to 3,00%,
P: 0.100% or less,
S: 0.030% or less,
Al: 0,010% to 0.500%,
N: 0.0100% or less,
Cr: 0.05% to 1.00%,
Nb: 0.003% to 0.050%,
Ti: 0.003% to 0.200%,
Cu: 0.0% to 1.2%,
Ni: 0.0% to 0.6%,
Mo: 0.00% to 1.00%,
V: 0.00% to 0.20%,
Ca: 0.0000% to 0.0050%,
REM: 0.0000% to 0.0200%,
B: 0.0000% to 0.0020%, and
a balance: Fe and impurities,
wherein
relationships represented by Expression 1 and Expression 2 are satisfied,
Expression 1: 0.005 5≤[Si]/[Cr]≤2.000
Expression 2: 0.5≤[Mn]/[Cr]≤20.0
wherein [Si], [Cr], and [Mn] in the Expression 1 and Expression 2 each represent a content, in mass %, of each of the elements, respectively, and
wherein a proportion of grains having an intragranular misorientation of 5° to 14° in all grains is 20% or more by area ratio, wherein each grain is defined as an area which is surrounded by a boundary having a misorientation of 15° or more, and wherein each grain has a circle-equivalent diameter of 0.3 μm or more,
the hot-rolled steel sheet comprising a microstructure represented by
a volume ratio of cementite: 1.0% or less,
an average grain diameter of cementite; 2.00 μm or less,
a concentration of Cr contained in cementite; 0.5 mass % to 40.0 mass %,
a proportion of cementite having a grain diameter of 0.5 μm or less and an aspect ratio of 5 or less in all cementite: 60 vol % or more,
an average grain diameter of a composite carbide of Ti and Cr: 10.0 nm or less, and
a number density of the composite carbide of Ti and Cr: 1.0×10 13 /mm 3 or more.
2. The hot-rolled steel sheet according to claim 1 , wherein, in the chemical composition represented by, in mass %,
Cu: 0.2% to 1.2%,
Ni: 0.1% to 0.6%,
Mo: 0.05% to 1.00%, or
V: 0.02% to 0.20%, or
any combination thereof is satisfied.
3. The hot-rolled steel sheet according to claim 1 , wherein, in the chemical composition represented by, in mass %,
Ca: 0.0005% to 0.0050%, or
REM: 0.0005% to 0.0200%, or
a combination thereof is satisfied.
4. The hot-rolled steel sheet according to claim 1 , wherein, in the chemical composition represented by, in mass %, 13: 0.0002% to 0.0020% is satisfied.
5. The hot-rolled steel sheet according to claim 1 , comprising a galvanized film on a surface.