Nippon Steel Sumitomo Metal Corporation

Denso Corporation

Nippon Steel Corporation

Masashi Higashida

Hitoshi Matsumoto

Yutaka Neishi

Taizo Makino

Naoki Matsui

Tatsuya Hasegawa

Yoshihiro Tanimura

Kouji Morita

Takahiro Okada

Makoto Egashira

Toshimasa Itou

Sadanori Horikami

Naoyuki Sashima

Masato Yuya

Tadashi Nishiwaki

Motoki Takasuga

Toshimasa Ito

Tomomitsu Fukuoka

Yoshiro Tanimura

An age-hardenable steel having a composition consisting of: C: 0.05 to 0.20%, Si: 0.01 to 0.50%, Mn: 1.5 to 2.5%, S: 0.005 to 0.08%, Cr: more than 0.50% and not more than 1.6%, Al: 0.005 to 0.05%, V: 0.25 to 0.50%, Mo: 0 to 1.0%, Cu: 0 to 0.3%, Ni: 0 to 0.3%, Ca: 0 to 0.005%, and Bi: 0 to 0.4%, the balance being Fe and impurities. Within the impurities, P&#x2264;0.03%, Ti&#x3c;0.005%, and N&#x3c;0.0080%, and [C+0.3Mn+0.25Cr+0.6Mo&#x2265;0.68], [C+0.1Si+0.2Mn+0.15Cr+0.35V+0.2Mo&#x2264;1.05], and [&#x2212;4.5C+Mn+Cr&#x2212;3.5V&#x2212;0.8Mo&#x2265;0.12]. The steel has hardness before aging of not more than 310 HV. After aging, the fatigue strength is not less than 480 MPa and absorbed energy at 20&#xb0; C. is not less than 12 J.

Age-hardenable steel

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 round steel material contains C: 0.38 to 0.55%, Si: 1.0% or less, Mn: 0.20 to 2.0%, S: 0.005 to 0.10%, Cr: 0.01 to 2.0%, Al: 0.003 to 0.10%, B: 0.0005 to 0.0030%, Ti: 0.047% or less, Cu: 0 to 1.0%, Ni: 0 to 3.0%, Mo: 0 to 0.50%, Nb: 0 to 0.10%, V: 0 to 0.30%, Ca: 0 to 0.005%, and Pb: 0 to 0.30%, a remaining portion being constituted by Fe and an impurities, the impurities containing P in an amount of 0.030% or less and N in an amount of 0.008% or less, and has a chemical composition satisfying [3.4N&#x2264;Ti&#x2264;3.4N+0.02]. The microstructure is constituted by ferrite (F), lamellar pearlite (LP), and cementite (C) and microstructural features vary in terms of the lateral, longitudinal and central portions of the steel. This steel material has a high base material toughness and good machinability without performing thermal refining.

Rolled round steel material for steering rack bar, and steering rack bar

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

A rolled round steel material for a steering rack bar, having a chemical composition consisting of C: 0.38 to 0.55%, Si: not more than 1.0%, Mn: 0.20 to 2.0%, S: 0.005 to 0.10%, Cr: 0.01 to 2.0%, Al: 0.003 to 0.10%, and N: 0.003 to 0.03%, with the balance being Fe and impurities, and P being not more than 0.030% in the impurities, and a microstructure consisting of ferrite (F), lamellar pearlite (LP), and cementite (C). The average grain diameter of (F), an area fraction of (LP), and the number of particles of spheroidal cementite (SC) among C are controlled in a region from the surface to a position at &#xbd; radius and in a central part of the material. An average aspect ratio of F is controlled in a region from a surface to a position at &#xbd; radius.

Rolled round steel material for steering rack bar and steering rack bar

A rolled steel bar has a composition consisting, by mass percent, of C: 0.27 to 0.37%, Si: 0.30 to 0.75%, Mn: 1.00 to 1.45%, S: 0.008% or more and less than 0.030%, Cr: 0.05 to 0.30%, Al: 0.005 to 0.050%, V: 0.200 to 0.320%, and N: 0.0080 to 0.0200%, the balance being Fe and impurities. The contents of P, Ti and O in the impurities are, by mass percent, P: 0.030% or less, Ti: 0.0040% or less, and O: 0.0020% or less. Y1 expressed by the formula &#x3c;1&#x3e; is 1.05 to 1.18.Y1=C+(1/10)Si+(1/5)Mn+(5/22)Cr+1.65V&#x2212;(5/7)S&#x2003;&#x2003;&#x3c;1&#x3e;. C, Si, Mn, Cr, V, and S in the formula represent mass percent of the elements. A hot-forged part having a tensile strength of 900 MPa or higher and a transverse endurance ratio of 0.47 can be obtained by the rolled steel bar.

Rolled steel bar for hot forging

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Tokyo, Japan

Masashi Higashida