Hot-rolled steel sheet
View Patent ↗A hot-rolled steel sheet including predetermined components, in which the amounts of Cr and Al added satisfy Expression (1) below, a metallographic structure has, by % by volume, a ferrite fraction of more than 90% and 98% or less, a martensite fraction of 2% to less than 10%, and, a fraction of a residual structure made of one or more of pearlite, bainite, and residual austenite being less than 1%, the ferrite has an average circle-equivalent diameter of 4 μm or more and a maximum circle-equivalent diameter of 30 μm or less, and the martensite has an average circle-equivalent diameter of 10 μm or less and a maximum circle-equivalent diameter of 20 μm or less. [Cr]×5+[Al]≥0.50 Expression (1) Here, in Expression (1), [Cr] represents an amount of Cr (mass %), and [Al] represents an amount of Al (mass %).
1. A hot-rolled steel sheet comprising: by mass %,
C: 0.02% to 0.20%;
Si: more than 0% to 0.15%;
Mn: 0.5% to 2.0%;
P: more than 0% to 0.10%;
S: more than 0% to 0.05%;
Cr: 0.05% to 0.5%;
Al: 0.01% to 0.5%;
N: more than 0% to 0.01%;
Ti: 0% to 0.20%;
Nb: 0% to 0.10%;
Cu: 0% to 2.0%;
Ni: 0% to 2.0%;
Mo: 0% to 1.0%;
V: 0% to 0.3%;
Mg: 0% to 0.01%;
Ca: 0% to 0.01%;
REM: 0% to 0.1%; and
B: 0% to 0.01%,
with a remainder consisting of Fe and impurities, in which amounts of Cr and Al added satisfy Expression (1) below,
wherein a metallographic structure has, by % by volume, a ferrite fraction of more than 90% and 98% or less, a martensite fraction of 2% to less than 10%, and, furthermore, a fraction of a residual structure made of one or more of pearlite, bainite, and residual austenite being less than 1%,
the ferrite has an average circle-equivalent diameter of 4 μm or more and a maximum circle-equivalent diameter of 30 μm or less, and the martensite has an average circle-equivalent diameter of 6 μm or more and 10 μm or less and a maximum circle-equivalent diameter of 20 μm or less,
where a tensile strength is 590 MPa or more:
[Cr]×5+[Al]≥0.50 Expression (1)
here, in Expression (1), [Cr] represents an amount of Cr (mass %), and [Al] represents an amount of Al (mass %).
2. The hot-rolled steel sheet according to claim 1 , further comprising:
by mass %, one or two of
Ti: 0.02% to 0.20%; and
Nb: 0.005% to 0.10%.
3. The hot-rolled steel sheet according to claim 1 , further comprising:
by mass %, one or more of
Cu: 0.01% to 2.0%;
Ni: 0.01% to 2.0%;
Mo: 0.01% to 1.0%; and
V: 0.01% to 0.3%.
4. The hot-rolled steel sheet according to claim 1 , further comprising:
by mass %, one or more of
Mg: 0.0005% to 0.01%;
Ca: 0.0005% to 0.01%; and
REM: 0.0005% to 0.1%.
5. The hot-rolled steel sheet according to claim 1 , further comprising:
by mass %,
B: 0.0002% to 0.01%.
6. The hot-rolled steel sheet according to claim 1 , further comprising:
by mass %, one or more of
Ti: 0.02% to 0.20%;
Nb: 0.005% to 0.10%;
Cu: 0.01% to 2.0%;
Ni: 0.01% to 2.0%;
Mo: 0.01% to 1.0%;
V: 0.01% to 0.3%;
Mg: 0.0005% to 0.01%;
Ca: 0.0005% to 0.01%;
REM: 0.0005% to 0.1%; and
B: 0.0002% to 0.01%;
V: 0.01% to 0.3%;
Mg: 0.0005% to 0.01%;
Ca: 0.0005% to 0.01%;
REM: 0.0005% to 0.1%; and
B: 0.0002% to 0.01%.