SPRING STEEL WITH EXCELLENT FATIGUE RESISTANCE AND METHOD OF MANUFACTURING THE SAME

摘要

A spring steel includes a predetermined chemical composition and a composite inclusion having a maximum diameter of 2 μm or more that TiN is adhered to an inclusion containing REM, O and Al, in which the number of the composite inclusion is 0.004 pieces/mm2 to 10 pieces/mm2, the maximum diameter of the composite inclusion is 40 μm or less, the sum of the number density of an alumina cluster having the maximum diameter of 10 μm or more, MnS having the maximum diameter of 10 μm or more and TiN having the maximum diameter of 1 μm to 10 pieces/mm2.

主权项

1. A spring steel comprising as a chemical composition, by mass %:
C: 0.4% to less than 0.9%; Si: 1.0% to 3.0%; Mn: 0.1% to 2.0%; Al: 0.01% to 0.05%; REM: 0.0001% to 0.005%; T.O: 0.0001% to 0.003%; Ti: less than 0.005%; N: 0.015% or less; P: 0.03% or less; S: 0.03% or less; Cr: 0% to 2.0%; Cu: 0% to 0.5%; Ni: 0% to 3.5%; Mo: 0% to 1.0%; W: 0% to 1.0%; B: 0% to 0.005%; V: 0% to 0.7%; Nb: 0% to 0.05%; Ca: 0% to 0.0020%; and the balance consisting of Fe and impurities, wherein; the spring steel includes a composite inclusion having a maximum diameter of 2 μm or more that TiN is adhered to an inclusion containing REM, O and Al; a number of the composite inclusion is 0.004 pieces/mm2 to 10 pieces/mm2, and a maximum diameter of the composite inclusion is 40 μm or less; and a sum of the number density of an alumina cluster having the maximum diameter of 10 μm or more, MnS having the maximum diameter of 10 μm or more and TiN having the maximum diameter of 1 μm or more is 10 pieces/mm2 or less.