Steel wire

1. A steel wire having a chemical composition consisting of, in mass %,

C: 0.53 to 0.59%,

Si: 2.51 to 2.90%,

Mn: 0.70 to 0.85%,

P: 0.020% or less,

S: 0.020% or less,

Cr: 1.40 to 1.70%,

Mo: 0.17 to 0.53%,

V: 0.23 to 0.33%,

Cu: 0.050% or less,

Ni: 0.050% or less,

Al: 0.0050% or less,

Ti: 0.050% or less,

N: 0.0070% or less,

Ca: 0 to 0.0050%, and

Nb: 0 to 0.020%,

with the balance being Fe and impurities,

wherein a number density of V-based precipitates having a maximum diameter ranging from 2 to 10 nm is 500 to 8000 per μm 2 .

2. The steel wire according to claim 1 , wherein:

in the chemical composition, a Ca content is from 0.0001 to 0.0050%; and

when, among inclusions,

inclusions in which, in mass %, an O content is 10.0% or more are defined as oxide-based inclusions,

inclusions in which, in mass %, an S content is 10.0% or more and the O content is less than 10.0% are defined as sulfide-based inclusions, and

among the sulfide-based inclusions, inclusions in which, in mass %, a Ca content is 10.0% or more, the S content is 10.0% or more, and the O content is less than 10.0% are defined as Ca sulfides,

a numerical proportion of the Ca sulfides with respect to a total number of the oxide-based inclusions and the sulfide-based inclusions is 0.20% or less.

3. The steel wire according to claim 1 , wherein,

in the chemical composition:

an Nb content is 0.005 to 0.020%.

4. The steel wire according to claim 2 , wherein,

in the chemical composition:

an Nb content is 0.005 to 0.020%.