Denso Corporation

Nippon Steel Sumitomo Metal Corporation

Nippon Steel Corporation

Toshimasa Itou

Hitoshi Matsumoto

Yutaka Neishi

Naoki Matsui

Taizo Makino

Yoshihiro Tanimura

Kouji Morita

Masashi Higashida

Naoyuki Sashima

Rolled steel bar for hot forging consisting, by mass percent, of C: 0.25-0.50%, Si: 0.40-1.0%, Mn: 1.0-1.6%, S: 0.005-0.035%, Al: 0.005-0.050%, V: 0.10-0.30%, N: 0.005-0.030% with the balance being Fe and impurities, i.e., P: 0.035% or less and O: 0.0030% or less, wherein Fn1=C+Si/10+Mn/5+5Cr/22+1.65V&#x2212;5S/7 is 0.90 to 1.20. The predicted maximum width of nonmetallic inclusions at the time when a cumulative distribution function obtained by extreme value statistical processing by taking the width of nonmetallic inclusion in an R/2 part of a longitudinal cross section of the steel bar as W (mm) is 99.99% is 100 &#x3bc;m or narrower. The number density of sulfides each having a circle-equivalent diameter of 0.3 to 1.0 &#x3bc;m observed per unit area of the R/2 part of a transverse cross section of the steel bar is 500 pieces/mmor higher.

Rolled steel bar for hot forging, hot-forged section material, and common rail and method for producing the same

A rolled steel bar for hot forging consisting, by mass percent, of C: 0.25-0.50%, Si: 0.40-1.0%, Mn: 1.0-1.6%, S: 0.005-0.035%, Al: 0.005-0.050%, V: 0.10-0.30%, and N: 0.005-0.030%, and the balance of Fe and impurities, i.e., P: 0.035% or less and O: 0.0030% or less, wherein Fn1=C+Si/10+Mn/5+5Cr/22+1.65V&#x2212;5S/7 is 0.90 to 1.20. The predicted maximum width of nonmetallic inclusions at the time when a cumulative distribution function obtained by extreme value statistical processing by taking the width of nonmetallic inclusion in an R/2 part of a longitudinal cross section of the steel bar as W (&#x3bc;m) is 99.99% is 100 &#x3bc;m or narrower. The number density of sulfides each having a circle-equivalent diameter of 0.3 to 1.0 &#x3bc;m observed per unit area of the R/2 part of a transverse cross section of the steel bar is 500 pieces/mmor higher.

Hot-forged section material and common rail

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Aichi, Japan

Toshimasa Itou