Nippon Steel Corporation

Nippon Steel & Sumitomo Metal Corporation

Aoyama Seisakusho Co., Ltd.

Tetsushi Chida

Yutaka Neishi

Naoki Matsui

Keisuke Chiba

Daisuke Hirakami

Toshimi Tarui

Akihisa Obata

Shoji Hori

Manabu Kubota

Masayuki Hashimura

Hideo Kanisawa

Makoto Kosaka

Kazuoki Shibuya

Kazutaka Aoyama

Ryoko Inagaki

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.

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

A steel which is excellent in delayed fracture resistance containing, by mass %, C: 0.10 to 0.55%, Si: 0.01 to 3%, and Mn: 0.1 to 2%, further containing one or more of Cr: 0.05 to 1.5%, V: 0.05 to 0.2%, Mo: 0.05 to 0.4%, Nb: 0.001 to 0.05%, Cu: 0.01 to 4%, Ni: 0.01 to 4%, and B: 0.0001 to 0.005%, and having a balance of Fe and unavoidable impurities, the structure being a mainly tempered martensite structure, the surface of the steel being formed with (a) a nitrided layer having a certain thickness range and a nitrogen concentration higher than the nitrogen concentration of the steel by 0.02 mass % or more and (b) a low carbon region having a certain depth range from the surface of the steel and having a carbon concentration of 0.9 time or less the carbon concentration of the steel.

High strength steel and high strength bolt excellent in delayed fracture resistance and methods of production of same

The present invention provides a steel for nitriding with a composition including, by mass %: C: 0.10% to 0.20%; Si: 0.01% to 0.7%; Mn: 0.2% to 2.0%; Cr: 0.2% to 2.5%; Al: 0.01% to less than 0.19%; V: over 0.2% to 1.0%; Mo: 0% to 0.54%; N: 0.001% to 0.01%; P limited to not more than 0.05%; S limited to not less than 0.2%; and a balance including Fe and inevitable impurities, the composition satisfying 2&#x2266;[V]/[C]&#x2266;10, where [V] is an amount of V by mass % and [C] is an amount of C by mass %, in which the steel for nitriding has a microstructure containing bainite of 50% or more in terms of an area percentage.

Steel for nitriding and nitrided part

Growing community of inventors

Nishinomiya, Japan

Tetsushi Chida