High cleanliness spring steel and high cleanliness spring excellent in fatigue properties

摘要

High cleanliness spring steel useful in manufacturing a spring with SiO 2 -based inclusions being extremely controlled and excellent in fatigue properties is provided.
High cleanliness spring steel which is steel containing;
C: 1.2% (means mass%, hereafter the same with respect to the component) or below (not inclusive of 0%),
Si: 1.2-4%,
Mn: 0.1-2.0%,
Al: 0.01% or below (not inclusive of 0%),
and the balance comprising iron with inevitable impurities,
wherein;
the total of oxide-based inclusions of 4 or above of L (the large diameter of an inclusion)/D (the short diameter of an inclusion) and 25 µm or above of D and oxide-based inclusions of less than 4 L/D and 25 µm or above of L, in the oxide-based inclusions of 25 mass% or above of oxygen concentration and 70% (means mass%,
hereafter the same with respect to inclusions) or above of SiO 2 content when Al 2 O 3 + MgO + CaO + SiO 2 + MnO = 100% is presumed, out of inclusions in the steel, is 20 nos./500 g or below.