Honda Motor Co., Ltd.

Daido Steel Co., Ltd.

Diado Steel Co., Ltd.

Makoto Hobo

Takashi Kano

Shinichiro Kato

Takahiro Miyazaki

Masamichi Kawano

Keiichiro Kamiya

Isamu Saito

Yoshihiro Takitani

Yutaka Kurebayashi

Kazuhisa Ishida

Masakazu Hayaishi

Motohiro Ibuki

A nitrocarburized crankshaft member made of a steel that includes C in an amount by weight of 0.25 to 0.32% as a required element and an optional element that may be included, and Fe and inevitable impurities in a remaining portion. The steel-made crankshaft member mainly includes ferrite and perlite, wherein at least a portion of the steel surface thereof having a ferrite surface area of 50% or greater is imparted with a nitrocarburized hard layer. The nitrocarburized hard layer includes a surface compound layer suppressed to a thickness of 10 to 35 &#x3bc;m, and a nitrogen diffusion zone below the surface compound layer having a diffusion depth of 700 &#x3bc;m or greater. The steel includes C, Si, Mn, Cu, Ni, and Cr as the required elements and Mo, N, s-Al, and Ti as the optional elements.

Nitrocarburized crankshaft member and steel for nitrocarburized crankshafts

The invention relates to a crankshaft member having high fatigue strength and good bending correctability, and its method of manufacture. The steel made crankshaft member mainly consists of a two-phase structure of ferrite and perlite. The steel includes C, Ni, Mn, and Cr as required elements and Si, Cu, Mo, Ti, V, Nb, Ca, and S as optional elements that may be included, in the amounts of C within the range of 0.20 to 0.50 wt %, Si within the range of 0 to 0.6 wt %, Mn within the range of 0.5 to 1.5 wt %, Cu within the range of 0 to 0.7 wt %, Ni within the range of 0.05 to 1.5 wt %, Cr within the range of 0.05 to 0.45 wt %, and Mo within the range of 0 to 0.5 wt % to satisfy the condition 115&#x2267;70C+8Si+23Mn+11Cu+128Cr+83Mo&#x2267;50. A portion of the member surface is provided at least with a hard nitride layer having an average hardness within the range of 300 to 450 HV. Lamellar spacing of the perlite is 0.3 &#x3bc;m or less.

Manufacturing method for a crankshaft member

Disclosed is a steel for machine structural use having good machinability and chip-breakability as well as a method of producing the steel. The steel consists essentially of, by wt. %, C: 0.05-0.8%, Si: 0.01-2.0%, Mn: 0.1-3.5%, S: 0.01-0.2%, Al: 0.001-0.020%, Ca: 0.0005-0.02%, O: 0.0005-0.01% and N: 0.001-0.04%, and further, one or both of Ti: 0.002-0.010% and Zr: 0.002-0.025%, the balance being Fe and inevitable impurities. At production of the steel controlled deoxidization is conducted by operation meeting certain conditions so that at least a certain amount of &ldquo;duplex inclusion&rdquo; having a specific chemical composition may be formed, and Ti and/or Zr is added to precipitate finely dispersed MnS inclusion particles with nuclei of Ti-oxide and/or Zr-oxide. The finely dispersed MnS inclusions must share a determined part of the total sulfide inclusions.

Steel for machine structural use having good machinability and chip-breakability

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Nagoya, Japan

Makoto Hobo