Patent ID: 9593404
Date: 2017-03-14
CPC Classifications: C21D,C23C,F16C

Claim:
1. A nitrocarburized crankshaft obtained by subjecting a bainitic microalloyed steel to a forging and a machining and further subjecting the bainitic microalloyed steel to at least a strain releasing heat treatment and a subsequent nitrocarburizing treatment, the bainitic microalloyed steel containing, as essentially added elements, in terms of mass %: 0.16% to 0.40% of C; 0.13% to 1.0% of Si; 1.0% to 2.0% of Mn; 0.05% to 0.40% of Mo; and 0.05% to 0.30% of V, and the bainitic microalloyed steel optionally further containing, as arbitrarily added elements, in terms of mass %: 0.01% to 0.1% of S; 0.005% to 0.2% of Ti; 0.001% to 0.03% of Al; 0.50% or less of Cr; 0.5% or less of Cu; and 0.5% or less of Ni, with the balance being Fe and unavoidable impurities, wherein at least a content of P as one of the unavoidable impurities is suppressed to be 0.025% or less, wherein the microalloyed steel satisfies the following expressions: in which [M] represents a content of element M in terms of % by mass, and wherein an amount of residual γ is controlled to be less than 5.0%, and a core part has a hardness of 270 HV or greater.