Patent ID: 8911566
Filing Date: 2014-12-16
Classification: B21K,C23C,F16C,Y10T

Abstract:
1. A nitrocarburized crankshaft member made of a steel comprising ferrite and perlite and at least a portion of a steel surface thereof having a ferrite surface area of 50% or greater is imparted with a nitrocarburized hard layer, wherein the steel consists of C, Si, Mn, Cu, Ni, and Cr as required elements, Mo, N, s-Al, and Ti as optional elements that may be included, and Fe and inevitable impurities, wherein the required elements and the optional elements are in amounts by weight of: C within a range of 0.25 to 0.32%, Si within the range of 0.01 to 0.15%, Mn within the range of 0.55 to 0.90%, Cu within the range of 0.10 to 0.60%, Ni within the range of 0.05 to 0.30%, Cr within the range of 0.10 to 0.20%, Mo within the range of 0.05% or less, N within the range of 0.020% or less, s-Al within the range of 0.020% or less, Ti within the range of 0.020% or less, and Fe and the inevitable impurities in a remaining portion, and satisfies the conditions that 0.430≦C 0.380≦C a Ni to Cu weight ratio is 0.50≦Ni/Cu≦1.00; and amounts by weight of P and S, which are inevitable impurities, are suppressed to 0.03% or less and 0.15% or less, respectively, wherein the nitrocarburized crankshaft member includes a thickness of a surface compound layer of the nitrocarburized hard layer of 10 to 35 μm formed during establishment of a diffusion depth of a nitrogen diffusion zone below said surface compound layer of 700 μm or greater.