Kobe Steel, Ltd.

Kabushiki Kaisha Kobe Seiko Sho

Kabushiki Kaisha Kobe Seiko Sho (kobe Steel, Ltd.)

Fujifilm Corporation

Atsushi Inada

Masamichi Chiba

Yosuke Matsumoto

Nobuhiko Ibaraki

Nao Yoshihara

Mamoru Nagao

Koichi Makii

Takaaki Minamida

Hidetoshi Takayama

Kenji Ochiai

Yoshimasa Ureshino

Nobuhiko Katou

Reiko Kato

Sakae Wada

To provide a steel for high-strength bolts, which can exhibit the sufficient delayed fracture resistance under the severe environment, and also has excellent bolt formability. The steel for high-strength bolts of the present invention includes C: 0.10 to 0.30%; and Ni: 0.4 to 0.7%, with the chemical composition being appropriately adjust, and satisfies the following formulas (1) and (2):0.85&#x2264;[C]+[Si]/7+[Mn]/5+[Ni]/20+[Cr]/9+[Mo]/2&#x2264;1.3&#x2003;&#x2003;(1)[C]&#x2212;(0.07&#xd7;[Mo]+0.20&#xd7;[V])&#x2264;0.20&#x2003;&#x2003;(2).

Steel for high-strength bolts which has excellent delayed fracture resistance and bolt formability, and bolt

Provided are: a boron-added high strength steel for bolt excellent in delayed fracture resistance even having a tensile strength of 1100 MPa or more without addition of large amounts of expensive alloy elements such as Cr and Mo: and a high strength bolt made from the boron-added high strength steel for bolt. The high strength steel for bolt contains C of 0.23% to less than 0.40%, Si of 0.23% to 1.50%, Mn of 0.30% to 1.45%, P of 0.03% or less (excluding 0%), S of 0.03% or less (excluding 0%), Cr of 0.05% to 1.5%, V of 0.02% to 0.30%, Ti of 0.02% to 0.1%, B of 0.0003% to 0.0050%, Al of 0.01% to 0.10%, and N of 0.002% to 0.010%, with the remainder being iron and inevitable impurities. The steel has a ratio ([Si]/[C]) of the Si content [Si] to the C content [C] of 1.0 or more and has a ferrite-pearlite mixed microstructure.

Boron-added high strength steel for bolt and high strength bolt having excellent delayed fracture resistance

A steel is used for providing a bolt that has a high strength and still exhibits excellent hydrogen embrittlement resistance. The steel contains C of 0.30% to 0.50%, Si of 1.0% to 2.5%, Mn of 0.1% to 1.5%, P of greater than 0% to 0.015%, S of greater than 0% to 0.015%, Cr of 0.15% to 2.4%, Al of 0.010% to 0.10%, N of 0.001% to 0.10%, Cu of 0.1% to 0.50%, Ni of 0.1% to 1.0%, Ti of 0.05% to 0.2%, and V of 0% to 0.2%, with the remainder including iron and inevitable impurities, in which a ratio [Ni]/[Cu] is 0.5 or more, and a total content [Ti]+[V] is 0.085% to 0.30%.

Steel for bolt use, bolt, and method for manufacturing bolt

High-carbon steel wire superior in resistance to longitudinal cracking, steel product for the same, and process for production of the same

A non-heat treated wire or bar steel for springs which is characterized by having in its as-rolled state a tensile strength of 120-150 kgf/mm,and a bending breakage rate no higher than 15% when tested according to JIS Z-2248 under the condition of r/d&equals;2.8 where r (mm) denotes the inside radius of the bending curvature and d (mm) denotes the diameter of the as-rolled stock.

Non-heat treated wire or bar steel for springs

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Kobe, Japan

Atsushi Inada