Nippon Steel Corporation

Jtekt Corporation

Aoyama Seisakusho Co., Ltd.

Neturen Co., Ltd.

Keisuke Chiba

Yutaka Neishi

Naoki Matsui

Manabu Kubota

Takahisa Suzuki

Tetsushi Chida

Akihisa Obata

Shoji Hori

Hideo Kanisawa

Takashi Sada

Kohei Kanetani

Makoto Kosaka

Kengo Iwanaga

Koichi Banno

Kazuoki Shibuya

Ryoko Inagaki

Ryuuichi Seki

Hirotsugu Miyamoto

Kazutaka Aoyama

Tsukasa Okamura

Fumiaki Fujiwara

Yukio Ebana

A steel consists of, in mass %, C: 0.25 to 0.45%, Si: 0.10 to 0.50%, Mn: 0.40 to 0.70%, P: 0.015% or less, S: 0.005% or less, Cr: 0.80 to 1.50%, Mo: 0.17 to 0.30%, V: 0.24 to 0.40%, Al: 0.005 to 0.100%, N: 0.0300% or less, O: 0.0015% or less, and the balance being Fe and impurities, and satisfies Formula (1) to Formula (4) described in the present specification, wherein: its microstructure is composed of ferrite and pearlite having a total area fraction of 5.0 to 100.0%, and a hard phase having a total area fraction of 0 to 95.0%; a proportion of a total area of CaO—CaS—MgO—AlOcomposite oxides with respect to a total area of oxides in the steel is 30.0% or more; and a number density of oxides having an equivalent circle diameter of 20.0 μm or more is 15.0 pieces/mmor less.

Steel

In a rolled steel bar or rolled wire rod for a cold-forged component having a predetermined chemical composition, Y1 represented by Y1=[Mn]&#xd7;[Cr] and Y2 represented by Y2=0.134&#xd7;(D/25.4&#x2212;(0.50&#xd7;&#x221a;[C]))/(0.50&#xd7;&#x221a;[C]) satisfy Y1&#x3e;Y2, the tensile strength is 750 MPa or less, an internal structure is a ferrite-pearlite structure, and the ferrite fraction in the internal structure is 40% or greater. AMOUNT IS 0.30%

Rolled steel bar or rolled wire rod for cold-forged component

In a rolled steel bar or rolled wire rod for a cold-forged component having a predetermined chemical composition, Y1 represented by Y1=[Mn]&#xd7;[Cr] and Y2 represented by Y2=0.134&#xd7;(D/25.4&#x2212;(0.50&#xd7;&#x221a;[C])/(0.50&#xd7;&#x221a;[C]) satisfy Y1&#x3e;Y2, the tensile strength is 750 MPa or less, an internal structure is a ferrite-pearlite structure, and the ferrite fraction in the internal structure is 40% or greater.

Steel for a suspension spring including, as a chemical composition, by % by mass: C: more than 0.40% and 0.65% or less; Si: 1.00% to 3.50%; Mn: more than 2.00% and 3.00% or less; Cr: 0.01% to 2.00%; V: 0.02% to 0.50%; P: 0.020% or less; S: 0.020% or less: N: 0.0100% or less; and a remainder of Fe and impurities, in which Kf is 280 or more, in which a structure contains a tempered martensite of which an area ratio is 90% or more, in which a Fe-based carbide precipitated in the tempered martensite is a cementite, and in which an average of an area ratios of prior austenite grains which stretch in a longitudinal direction of the steel and of which an aspect ratio exceeds 3.0, is 80% or more in a case of depths of 0.1 mm, 0.2 mm, and 0.3 mm in a sheet thickness direction from a surface of the steel.

Steel for suspension spring and method of manufacturing same

A bolt is provided that has high strength and excellent hydrogen embrittlement resistance characteristics. A bolt according to an embodiment of the present invention consists of, in mass %, C: 0.32 to 0.39%, Si: 0.15% or less, Mn: 0.40 to 0.65%, P: 0.020% or less, S: 0.020% or less, Cr: 0.85 to 1.25%, Al: 0.005 to 0.060%, Ti: 0.010 to 0.050%, B: 0.0010 to 0.0030%, N: 0.0015 to 0.0080%, O: 0.0015% or less, Mo: 0 to 0.05%, V: 0 to 0.05%, Cu: 0 to 0.50%, Ni: 0 to 0.30%, and Nb: 0 to 0.05%, with the balance being Fe and impurities. The bolt satisfies Formula (1) and Formula (2), and has a tensile strength of 1000 to 1300 MPa and satisfies Formula (3).4.9&#x2264;10C+Si+2Mn+Cr+4Mo+5V&#x2264;6.1&#x2003;&#x2003;(1)Mn/Cr&#x2264;0.55&#x2003;&#x2003;(2)[dissolved Cr]/Cr&#x2265;0.70&#x2003;&#x2003;(3)

Bolt

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Toyota, Japan

Keisuke Chiba