Nippon Steel Sumitomo Metal Corporation

Honda Motor Co., Ltd.

Nippon Steel Corporation

Sumitomo Metal Industries, Inc.

Dowa Thermotech Co., Ltd.

Hideki Imataka

Masayuki Horimoto

Yuya Gyotoku

Kosuke Tanaka

Atsushi Kobayashi

Susumu Maeda

Masato Yuya

Akira Shiga

Hitoshi Matsumoto

Kiyotaka Akimoto

Yuichiro Shimizu

Yoshihiro Daitoh

Masao Kanayama

Akihito Ninomiya

Yoshinari Okada

Tetsuya Asai

Daisuke Suzuki

Masaomi Nakaoka

Yusuke Usui

Hayato Onda

Gen Kato

Mitsuru Fujimoto

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 case hardening steel material having a chemical composition consists of, by mass percent, C: 0.15 to 0.23%, Si: 0.01 to 0.15%, Mn: 0.65 to 0.90%, S: 0.010 to 0.030%, Cr: 1.65 to 1.80%, Al: 0.015 to 0.060%, and N: 0.0100 to 0.0250%, further containing, as necessary, one or more kinds selected from Cu and Ni of predetermined amounts, the balance being Fe and impurities; 25&#x2266;Mn/S&#x2266;85, 0.90&#x2266;Cr/(Si+2Mn)&#x2266;1.20, and 1.16Si+0.70Mn+Cr&#x2267;2.20; P, Ti and O in the impurities being P&#x2266;0.020%, Ti&#x2266;0.005%, and O&#x2266;0.0015%; and having a structure consisting of 20 to 70% in an area ratio being ferrite; and the portion other than the ferrite being one or more kinds of pearlite and bainite. The steel material is used suitably as a raw material of the carburized part such as a CVT pulley shaft.

Case hardening steel material

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].

A method for producing a steel component by performing the treatments of the following sequentially steps 1 and 2 to a steel material containing, by mass %, C: 0.15 to 0.25%, Si: 0.01 to 0.10%, Mn: 0.50 to 0.80%, S: 0.003 to 0.030%, Cr: 0.80 to 1.20%, Mo: 0.30 to 0.45%, Al: 0.015 to 0.050%, and N: 0.010 to 0.025%, wherein Cr/Mn is 1.3 to 2.4, the balance being Fe and impurities, and contents of P and O among the impurities are P: not more than 0.010%, and O: not more than 0.0020%:

Method for producing steel component

A rolled steel bar or a wire rod for hot forging capable of coping with both bending/surface fatigue strength of components and machinability at a high level includes: a composition containing, in mass %, C: 0.1 to 0.25%, Si: 0.01 to 0.10%, Mn: 0.4 to 1.0%, S: 0.003 to 0.05%, Cr: 1.60 to 2.00%, Mo: 0.10% or less (including 0%), Al: 0.025 to 0.05%, and N: 0.010 to 0.025%, where a value of fn1 represented in a following formula (1) satisfies 1.82&#x2266;fn1&#x2266;2.10: fn1=Cr+2&#xd7;Mo (1); impurities containing P: 0.025% or less, Ti: 0.003% or less, and O (oxygen): 0.002% or less; and a cross section in which a maximum value/a minimum value of an average ferrite grain diameter is 2.0 or less when measurement by observation is randomly carried out in 15 visual fields with an area per visual field set to be 62500 &#x3bc;m.

Rolled steel bar or wire for hot forging

A hot forged non-heat treated steel for induction hardening, comprising by mass percent, C: 0.35 to 0.45%, Si: 0.20 to 0.60%, Mn: 0.40 to 0.80%, S: 0.040 to 0.070%, Cr: 0.10 to 0.40%, Ti: 0.020 to 0.100%, Ca: 0.0005 to 0.0050%, B: 0.0005 to 0.0030%, O: 0.0015 to 0.0050%, Mo: 0 to 0.05%, P: 0.025% or less, V: 0.03% or less, Al: 0.009% or less and N: 0.0100% or less, and the balance being Fe and impurities, with Fn1=C+(Si/10)+(Mn/5)+(5Cr/22)+1.65V&#x2212;(5/7S)+1.51&#xd7;(Ti&#x2212;3.4N)&#x2266;0.63, Ca/O&#x2266;1.0, and 25.9&#xd7;Fn1+27.5&#xd7;(Ti&#x2212;3.4N)&#x2212;7.9&#x2267;5.7, has more excellence in the machinability than a conventional steel and also has fatigue strength equal to or more than that of a conventional steel, while using the steel product in a hot forged state as a starting material.

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Tokyo, Japan

Hideki Imataka