NITROCARBURIZED CRANKSHAFT AND METHOD OF MANUFACTURING THE SAME

摘要

Provided is a method of manufacturing a nitrocarburized crankshaft which is 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 %: 0.10% to 0.40% of C; 0.10% to 1.0% of Si; 1.0% to 2.0% of Mn; 0.05% to 0.40% of Mo; and 0.05% to 0.40% 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.

主权项

1. A method of manufacturing a nitrocarburized crankshaft which is 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 %:
0.10% to 0.40% of C; 0.10% to 1.0% of Si; 1.0% to 2.0% of Mn; 0.05% to 0.40% of Mo; and 0.05% to 0.40% 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 is selected so as to satisfy:
[C]+0.27[Mn]+0.32[Cr]+0.27[Mo]+0.38[V]≧0.72,[C]+0.01[Si]+0.09[Mn]+0.13[0]+0.12[Mo]+0.28[V]<0.65,and[C]+0.11[Si]+0.11[Mn]+0.09[Cr]+0.21[Mo]+0.60[V]≧0.54, in which [M] represents a content of element M in terms of % by mass, and wherein the strain releasing heat treatment is performed to satisfy the following expressions regarding a holding temperature T (° C.) and a holding time t (hr):
21.6+14.2[C]+1.5[Si]+2.6[Mn]+6.5[Cr]+2.7[Mo]+1.6[V]+10−7×γh12−3.7×10−3×γh1<0.70,andγh1=(T+273)×(20+Log(t)).