Carbonitrided steel having excellent hydrogen flutter type surface fatigue strength and carbonitrided part using the same

摘要

PROBLEM TO BE SOLVED: To inexpensively provide a carbonitrided steel the surface fatigue strength of which can be sufficiently secured.SOLUTION: The carbonitrided steel is provided which contains, by mass%, C:0.10 to 0.40%, Si:0.35 to 0.50%, Mn:0.80 to 1.50%, P:0.030% or less, S:0.030% or less, Cr:1.50 to 2.50%, Al:0.050% or less, O:0.0015% or less, N:0.025% or less, Mn/Si:2.00 or more, Mn+Cr:2.50 to 4.00% and the balance Fe with inevitable impurities and which has been subjected to a carbonitriding, hardening and tempering treatments and in which after the tempering treatment, a surface layer C concentration is 0.80 to 1.50%, a surface layer N concentration is 0.10 to 1.00% and a surface hardness is HRC 58 or more and less than 64, and the number of Cr nitride and Si nitride having a particle diameter of less than 300 nm of nitride dispersion deposited on the surface is 10/mmor more.