Steel sheet

1. A steel sheet comprising:

a chemical composition represented by, in mass %,

C: 0.15% to 0.45%,

Si: 1.0% to 2.5%,

Mn: 1.2% to 3.5%,

Al: 0.001% to 2.0%,

P: 0.02% or less,

S: 0.02% or less,

N: 0.007% or less,

O: 0.01% or less,

Mo: 0.0% to 1.0%,

Cr: 0.0% to 2.0%,

Ni: 0.0% to 2.0%,

Cu: 0.0% to 2.0%,

Nb: 0.0% to 0.3%,

Ti: 0.0% to 0.3%,

V: 0.0% to 0.3%,

B: 0.00% to 0.01%,

Ca: 0.00% to 0.01%,

Mg: 0.00% to 0.01%,

REM: 0.00% to 0.01%, and

the balance: Fe and impurities, and comprising

a steel structure represented by, in a volume fraction,

tempered martensite and bainite including lower bainite: 70% or more and less than 92% in total,

retained austenite: 8% or more and less than 30%,

ferrite: less than 10%,

fresh martensite: less than 10%, and

pearlite: less than 10%, in which

a number density of iron-base carbides in the tempered martensite and lower bainite is, in term of pieces/mm 2 , 1.0×10 6 or more, and

an effective crystal grain diameter of the tempered martensite and the bainite is 5 μm or less.

2. The steel sheet according to claim 1 ,

wherein the chemical composition further comprises, in mass %, one type or more selected from the group consisting of

Mo: 0.01% to 1.0%,

Cr: 0.05% to 2.0%,

Ni: 0.05% to 2.0%, and

Cu: 0.05% to 2.0%.

3. The steel sheet according to claim 1 ,

wherein the chemical composition further comprises, in mass %, one type or more selected from the group consisting of:

Nb: 0.005% to 0.3%,

Ti: 0.005% to 0.3%, and

V: 0.005% to 0.3%.

4. The steel sheet according to claim 1 ,

wherein the chemical composition further comprises, in mass %,

B: 0.0001% to 0.01%.

5. The steel sheet according to claim 1 ,

wherein the chemical composition further comprises, in mass %, one type or more selected from the group consisting of

Ca: 0.0005% to 0.01%,

Mg: 0.0005% to 0.01%, and

REM: 0.0005% to 0.01%.