Filament for high strength steel cord

1. A filament for a high strength steel cord, which has a wire diameter R of 0.1 mm to 0.4 mm, comprising, in a chemical composition, by mass %:

C: 0.70% to 1.20%;

Si: 0.15% to 0.60%;

Mn: 0.10% to 1.00%;

N: 0.0010% to 0.0050%;

Al: more than 0% and 0.0100% or less; and

a remainder of Fe and impurities,

wherein a surface part and a central part are included, the surface part covers the central part,

a thickness of the surface part is 0.01×R to 0.10×R,

the central part includes a pearlite structure in a proportion of 95% to 100% by area %,

a C content of the surface part is 40% to 95% of a C content of the central part, and

a ratio of a thickness of a lamellar cementite at a center of the thickness of the surface part to a thickness of a lamellar cementite in the central part is 95% or less.

2. The filament for a high strength steel cord according to claim 1 , further comprising, in the chemical composition, by mass %,

one or two or more of

Ti: more than 0% and 0.1000% or less,

Cr: more than 0% and 0.5000% or less,

Co: more than 0% and 0.5000% or less,

V: more than 0% and 0.5000% or less,

Cu: more than 0% and 0.2000% or less,

Nb: more than 0% and 0.1000% or less,

Mo: more than 0% and 0.2000% or less,

W: more than 0% and 0.200% or less,

B: more than 0% and 0.0030% or less,

REM: more than 0% and 0.0050% or less,

Ca: more than 0.0005% and 0.0050% or less,

Mg: more than 0.0005% and 0.0050% or less, and

Zr: more than 0.0005% and 0.0100% or less.