Sumitomo Metal Industries, Inc.

Other

Yoshihiko Kamada

Masato Kurita

Mitsuo Uno

Seiichi Koike

Hitoshi Matsumoto

Koji Watari

Toru Kato

Naoyuki Sano

Mitsuo Takashima

Harunori Kakimi

Masanori Sakamoto

Takayuki Nakatani

Non-heat treated steel for soft-nitriding to form parts having high fatigue strength and excellent bend leveling property even in a case of applying soft-nitriding without thermal refining, comprising, by mass %, C: 0.30 to 0.45%, Si: 0.1 to 0.5%, Mn: 0.6 to 1.0%, Ti: 0.005-0.1% and N: 0.015 to 0.030%, and the balance Fe and impurities, having a mixed microstructure of bainite and ferrite whose bainite fraction is 5 to 90% or having a mixed microstructure of bainite, ferrite and pearlite whose bainite fraction is 5 to 90%, the steel could contain one or more of elements of Nb: 0.003 to 0.1% Mo: 0.01 to 1.0%, Cu: 0.01-1.0%, Ni: 0.01 to 1.0%, B: 0.001 to 0.005%, S: 0.01 to 0.1%, and Ca: 0.0001 to 0.005.

Non-heat treated steel for soft-nitriding

Non-heat treated, soft-nitrided steel parts

The present invention relates to manufacturing methods of nitrided steel parts, having high tensile strength, high fatigue strength, and excellent bending roughness, through nitriding without thermal refining, to thus-manufactured steel parts, and to steel products for nitriding, and steels for nitriding having a specific chemical composition, serving as steel stock for the manufacture of such steel parts. The chemical composition is as follows: C: over 0.20 to 0.60%, Si: 0.05 to 1.0%, Mn: 0.20 to 1.50%, P: 0.08% or less, S: 0.005 to 0.10%, Cu: 0.30% or less, Ni: 0.30% or less, Cr: 0.30% or less, Mo: 0.30% or less, V: 0.20% or less, Nb: 0.05% or less, Ti: 0.003 to 0.03%, Al: 0.08% or less, Ca: 0.005% or less, Pb: 0.30% or less, N: 0.008 to 0.030%, and the balance of Fe and unavoidable impurities. Steel products preferably have the ferrite-pearlite microstructure having a ferrite percentage of not less than 10%. Nitrided steel parts are formed from the steel products serving as steel stock therefor, and have a nitrided case formed in the surface portion thereof.

Steels, steel products for nitriding, nitrided steel parts

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Kitakyushu, Japan

Yoshihiko Kamada