Nippon Steel Sumitomo Metal Corporation

Honda Motor Co., Ltd.

Nippon Steel Corporation

Dowa Thermotech Co., Ltd.

Yuya Gyotoku

Hideki Imataka

Masayuki Horimoto

Kosuke Tanaka

Atsushi Kobayashi

Susumu Maeda

Masato Yuya

Kiyotaka Akimoto

Yuichiro Shimizu

Masao Kanayama

Yusuke Usui

A nitrided component has a chemical composition consisting of, by mass percent, C: 0.07-0.14%, Si: 0.10-0.30%, Mn: 0.4-1.0%, S: 0.005-0.030%, Cr: 1.0-1.5%, Mo: &#x2264;0.05% (including 0%), Al: 0.010% or more to less than 0.10%, V: 0.10-0.25%, optionally at least one element selected from Cu: &#x2264;0.30% and Ni: &#x2264;0.25%, [0.61Mn+1.11Cr+0.35Mo+0.47V&#x2264;2.30], and the balance of Fe and impurities. P, N, Ti and O among the impurities are P: &#x2264;0.030%, N: &#x2264;0.008%, Ti: &#x2264;0.005%, and O: &#x2264;0.0030%. The nitrided composition is suitable for use as an automobile ring gear. The nitrided component has a surface hardness of 650-900 HV, core hardness being &#x2265;150 HV, effective case depth of &#x2265;0.15 mm, has excellent bending fatigue strength and surface fatigue strength although the content of Mo is as low as &#x2264;0.05% and has a small amount of expansion caused by nitriding.

Nitrided component

A steel for cold forging/nitriding has, by mass percent, C: 0.01 to 0.15%, Si&#x2264;0.35%, Mn: 0.10 to 0.90%, P&#x2264;0.030%, S&#x2264;0.030%, Cr: 0.50 to 2.0%, V: 0.10 to 0.50%, Al: 0.01 to 0.10%, N&#x2264;0.0080%, and O&#x2264;0.0030%, further according to need a specific amount of one or more elements selected from Mo, Cu, Ni, Ti, Nb, Zr, Pb, Ca, Bi, Te, Se and Sb, with the balance being Fe and impurities, and further satisfying the conditions of [399&#xd7;C+26&#xd7;Si+123&#xd7;Mn+30&#xd7;Cr+32&#xd7;Mo+19&#xd7;V&#x2264;160], [20&#x2264;(669.3&#xd7;logC&#x2212;1959.6&#xd7;logN&#x2212;6983.3)&#xd7;(0.067&#xd7;Mo+0.147&#xd7;V)&#x2264;80], [140&#xd7;Cr+125&#xd7;Al+235&#xd7;V&#x2265;160] and [90&#x2264;511&#xd7;C+33&#xd7;Mn+56&#xd7;Cu+15&#xd7;Ni+36&#xd7;Cr+5&#xd7;Mo+134&#xd7;V&#x2264;170] are excellent in cold forgeability and machinability after cold forging.

Steel for cold forging/nitriding, steel material for cold forging/nitriding, and cold-forged/nitrided component

A nitrided steel member including an iron nitride compound layer formed on a surface of a steel member having predetermined components, wherein: in X-ray diffraction peak intensity IFeN (111) of a (111) crystal plane of FeN and X-ray diffraction peak intensity IFeN (111) of a (111) crystal plane of FeN, which are measured on a surface of the nitrided steel member by X-ray diffraction, an intensity ratio expressed by IFeN (111)/{IFeN (111)+IFeN (111)} is 0.5 or more; Vickers hardness of the iron nitride compound layer is 900 or less, Vickers hardness of a base metal immediately under the iron nitride compound layer is 700 or more, and a difference between the Vickers hardness of the iron nitride compound layer and the Vickers hardness of the base metal is 150 or less; and a thickness of the iron nitride compound layer is 2 to 17 &#x3bc;m.

Nitrided steel member and manufacturing method thereof

A steel material for nitriding has a composition comprising, by mass percent, C: more than 0.15% and not more than 0.35%, Si&#x2266;0.20%, Mn: 0.10 to 2.0%, P&#x2266;0.030%, S&#x2266;0.050%, Cr: 0.80 to 2.0%, V: 0.10 to 0.50%, Al: 0.01 to 0.06%, N&#x2266;0.0080%, O&#x2266;0.0030%, and optionally one or more elements of Mo, Cu, Ni, Ti, Nb, Zr, Pb, Ca, Bi, Te, Se and Sb, the balance being Fe and impurities. The composition satisfies the conditions of [20&#x2266;(669.3&#xd7;logC&#x2212;1959.6&#xd7;logN&#x2212;6983.3)&#xd7;(0.067&#xd7;Mo+0.147&#xd7;V)&#x2266;80] and [140&#xd7;Cr+125&#xd7;Al+235&#xd7;V&#x2267;160]. The microstructure is a ferritic-pearlitic structure, a ferritic-bainitic structure, or a ferritic-pearlitic-bainitic structure. The area fraction of ferrite is 20% or more and the precipitate content of V is 0.10% or less.

Steel material for nitriding and nitrided component

A steel comprises, by mass percent, C: 0.10 to 0.15%, Si: not less than 0.02% and less than 0.10%, Mn: more than 0.90% and not more than 2.50%, P&#x2266;0.030%, S&#x2266;0.050%, Cr: 0.80 to 2.0%, V: 0.05 to 0.50%, Al: 0.01 to 0.07%, N&#x2266;0.0080%, O&#x2266;0.0030%, and one or more selected from Mo, Cu, Ni, Ti, Nb, Zr, Pb, Ca, Bi, Te, Se and Sb, the balance being Fe and impurities. The composition satisfies [35&#x2266;Mn/S&#x2266;200], [20&#x2266;(669.3&#xd7;logC&#x2212;1959.6&#xd7;logN&#x2212;6983.3)&#xd7;(0.067&#xd7;Mo+0.147&#xd7;V)&#x2266;80], [140&#xd7;Cr+125&#xd7;Al+235&#xd7;V&#x2267;160] and [150&#x2266;511&#xd7;C+33&#xd7;Mn+56&#xd7;Cu+15&#xd7;Ni+36&#xd7;Cr+5&#xd7;Mo+134&#xd7;V&#x2266;200].

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Tokyo, Japan

Yuya Gyotoku