Hot-rolled steel sheet
View Patent ↗A hot-rolled steel sheet according to the present invention has a chemical composition comprising, in mass %, C: 0.03 to 0.2%, Mn: 0.1 to 3.0%, P: 0.10% or less, S: 0.03% or less, Al+Si: 0.2 to 3.0%, N: more than 0% and equal to or less than 0.01%, O: more than 0% and equal to or less than 0.01%, and the balance: iron and impurities. A microstructure of the hot-rolled steel sheet contains bainite as the main constituent, and contains hard phases constituted by martensite and/or austenite in an amount of, in area fraction, equal to or more than 3% and less than 20% where 60% or more of the hard phase present in a sheet-thickness central portion have an aspect ratio of 3 or more, the hard phases present in the sheet-thickness central portion have a length in a rolling direction of less than 20 μm, and the sum of X-ray random intensity ratios of <011> orientation and <111> orientation as viewed from the rolling direction is 3.5 or more, and an X-ray random intensity ratio of <001> orientation as viewed from the rolling direction is 1.0 or less.
1. A hot-rolled steel sheet having a chemical composition consisting of, in mass %,
C: 0.03 to 0.2%,
Mn: 0.1 to 3.0%,
P: 0.10% or less,
S: 0.03% or less,
Al+Si: 0.2 to 3.0%,
N: more than 0% and equal to or less than 0.01%,
O: more than 0% and equal to or less than 0.01%,
Ti: 0 to 0.3%,
Nb: 0 to 0.3%,
Mg: 0 to 0.01%,
Ca: 0 to 0.01%,
REM: 0 to 0.1%,
B: 0 to 0.01%,
Cu: 0 to 2.0%,
Ni: 0 to 2.0%,
Mo: 0 to 1.0%,
V: 0 to 0.3%,
Cr: 0 to 2.0%, and
the balance: iron and impurities, and
a microstructure of the hot-rolled steel sheet which contains bainite as the main constituent, and contains hard phases constituted by martensite and/or austenite in an amount of, in area fraction, equal to or more than 3% and less than 20%,
wherein 60% or more of a number of the hard phases present in a sheet-thickness central portion have an aspect ratio of 3 or more,
the hard phases present in the sheet-thickness central portion have a length in a rolling direction of less than 20 μm, and
the sum of X-ray random intensity ratios of <011> orientation and <111> orientation as viewed from the rolling direction is 3.5 or more, and an X-ray random intensity ratio of <001> orientation as viewed from the rolling direction is 1.0 or less.
2. The hot-rolled steel sheet according to claim 1 , wherein Ti, Nb or a combination thereof are present and are in mass %,
Ti: (0.005+48/14[N]+48/32[S])% or more to 0.3% or less, and
Nb: 0.01 to 0.3%,
where [N] indicates an N content (mass %) and [S] indicates an S content (mass %).
3. The hot-rolled steel sheet according to claim 1 ,
wherein Mg, Ca, REM or a combination thereof are present and are in mass %,
Mg: 0.0005 to 0.01%,
Ca: 0.0005 to 0.01%, and
REM: 0.0005 to 0.1%.
4. The hot-rolled steel sheet according to claim 1 , wherein B is, in mass %,
B: 0.0002 to 0.01%.
5. The hot-rolled steel sheet according to claim 1 , wherein Cu, Ni, Mo, V, Cr or a combination thereof are present and are in mass %,
Cu: 0.01 to 2.0%,
Ni: 0.01 to 2.0%,
Mo: 0.01 to 1.0%,
V: 0.01 to 0.3%, and
Cr: 0.01 to 2.0%.
6. A hot-rolled steel sheet having a chemical composition consisting of, in mass %,
C: 0.03 to 0.2%,
Mn: 0.1 to 3.0%,
P: 0.10% or less,
S: 0.03% or less,
Al+Si: 0.2 to 3.0%,
N: more than 0% and equal to or less than 0.01%,
O: more than 0% and equal to or less than 0.01%,
Ti: 0 to 0.3%,
Nb: 0 to 0.3%,
Mg: 0 to 0.01%,
Ca: 0 to 0.01%,
REM: 0 to 0.1%,
B: 0 to 0.01%,
Cu: 0 to 2.0%,
Ni: 0 to 2.0%,
Mo: 0 to 1.0%,
V: 0 to 0.3%,
Cr: 0 to 2.0%, and
the balance: iron and impurities, and
a microstructure of the hot-rolled steel sheet which contains bainite as the main constituent, and contains hard phases constituted by martensite and/or austenite in an amount of, in area fraction, equal to or more than 3% and less than 20%,
wherein 60% or more of a number of the hard phases present in a sheet-thickness central portion have an aspect ratio of 3 or more,
the hard phases present in the sheet-thickness central portion have a length in a rolling direction of less than 20 μm, and
the sum of X-ray random intensity ratios of <011> orientation and <111> orientation as viewed from the rolling direction is 3.5 or more, and an X-ray random intensity ratio of <001> orientation as viewed from the rolling direction is 1.0 or less, and
the hot-rolled steel sheet has a hot-dip galvanized layer or a galvannealed layer on its surface.