Honda Motor Co., Ltd.

Daido Steel Co., Ltd.

Saga Tekkohsho Co., Ltd.

Nippon Steel Corporation

Yoshihiro Takitani

Shinichiro Kato

Tatsuya Hasegawa

Takahiro Miyazaki

Takashi Kano

Masato Yuya

Masaki Amano

Motoki Takasuga

Makoto Hobo

Keiichiro Kamiya

Isamu Saito

Shigefumi Nishitani

Tetsuya Asai

Katsuhiro Tsukiyama

Takehiko Egawa

Katsunori Daido Steel Co Ltd Takada

Makoto Daido Steel Co Ltd Hobo

Kazuyoshi Daido Steel Co Ltd Kimura

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

There is provided a screw treated by a chemical conversion coating of trivalent chromium having a torque characteristic approximately equivalent to a screw of a hexavalent chromate treatment. For the purpose, on a surface of a bolt, a zinc plating layer is formed by a zinc plating treatment. On the layer, a chemical conversion coating of trivalent chromium is also formed by a treatment of chemical conversion coatings of trivalent chromium. The coating is formed to be thin and soft so that the zinc-based plating layer can be exposed on the surface due to rubbing off of the chemical conversion coating of trivalent chromium at a contact portion to a fastened member of the bolt by tightening the bolt.

Screw and screw fastening structure

Growing community of inventors

Saitama-ken, Japan

Yoshihiro Takitani