For dry cyaniding, the non-thermal purified steel of the parts NITROCARBURIZED and NITROCARBURIZED part producing methods

摘要

Provided is a non-thermal refined steel for nitrocarburizing that provides nitrocarburized parts having excellent bending fatigue strength and straightenability after nitrocarburizing treatment. This non-thermal refined steel for nitrocarburizing has a chemical composition that contains, on a mass basis, 0.20 to 0.40% of C, 0.10 to 0.80% of Si, more than 1.20% to 1.60% of Mn, 0.100% or less of S, 0.005 to 0.030% of Al, 0.001 to 0.020% of Ti and 0.008 to 0.025% of N, with the remainder Fe and impurities, and satisfies the following formulae (1) and (2). The microstructure of the steel has a total area ratio of proeutectoid ferrite and pearlite of 95% or more, a proeutectoid ferrite fraction of 55% or more and an average crystalline grain size of proeutectoid ferrite of 10 to 90 µm. (1): 0.94 ≤ C + 0.43Mn + 2.19Cr ≤ 1.02 (2): C - 0.006Si + 0.076Mn + 0.46Cr ≤ 0.50 The contents (% by mass) of corresponding elements are substituted in the chemical symbols in the formulae (1) and (2).