([ti mass%] - 3.43 × [n mass%]) / [s mass%] > 4.0 및 [ni mass%] + [cu mass%] < 0.75를 만족하며 mns의 외관 빈도는 1/4m 이상의 동등한 원 직경을 갖는 포함물 중 20% 미만이다. 표면으로부터의 지름
There is provided a spring steel including predetermined chemical composition, in which ([ti mass%] - 3.43 × [n mass%]) / [s mass%] > 4.0, and [ni mass%] + [cu mass%] < 0.75 are satisfied, and an appearance frequency of mns is less than 20% among inclusions having an equivalent circle diameter of 1 µm or more which are observed at a 1/4 position of a diameter from a surface.