Nippon Steel Corporation

Nippon Steel Sumitomo Metal Corporation

Hiroaki Tahira

Kison Nishihara

Ken Yoshino

Yoko Sueyasu

Kisung Kim

Junichi Okubo

Masato Yuya

Satoru Okawa

Taketo Maejima

Yoshiyuki Kashiwara

Yuta Mizobe

The steel shaft component consists of C: 0.40 to 0.60%, Si: 0.05 to 1.00%, Mn: 1.00 to 2.00%, P: 0.030% or less, S: 0.005 to 0.100%, Cr: 0.10 to 0.50%, V: 0.10 to 0.30%, Al: 0.005 to 0.050%, N: 0.0050 to 0.0200%, Ti: 0 to 0.050%, and the balance: Fe and impurities. A Vickers hardness Hs of the surface of the shaft part is 620 HV or more. A Vickers hardness Hb at an R/2 position satisfies Formula (1). A depth of the hardened layer Hr (mm) having a Vickers hardness of 620 HV or more satisfies Formula (2). The microstructure at the R/2 position is composed of ferrite and pearlite. Within the hardened layer, the number of density of V-containing precipitates having an equivalent circular diameter of more than 100 nm is 10 particles/276 μmor less./2.3≤≤350  (1)0.05≤≤0.40  (2)

Steel shaft component

Provided are a roughly-shaped steel material for a nitrided part, and a nitrided part obtained by nitriding the roughly-shaped steel material for a nitrided part, having a determined chemical composition, in which the portion with a diameter or width ranging from 60 to 130 mm of the roughly-shaped steel material for a nitrided part has a microstructure at a depth of 14.5 mm from a surface including, in terms of area fraction: tempered martensite and tempered bainite in total: from 70 to 100%; remaining austenite: from 0 to 5%; and a balance: ferrite and perlite; and has a microstructure at a depth of 15 mm or more from the surface including, in terms of area fraction: tempered martensite and tempered bainite in total: from 0 to less than 50%; remaining austenite: from 0 to 5%; and a balance: ferrite and perlite.

Roughly-shaped steel material for nitrided part, and nitrided part

A hot forged steel material in the present embodiment includes a chemical composition that consists of, in mass %, C: 0.14 to 0.20%, Si: 0.20 to 1.00%, Mn: 1.00 to 1.90%, P: 0.030% or less, S: 0.030% or less, V: 0.16 to 0.30%, Al: 0.015 to 0.050%, N: 0.0050 to 0.0250%, Cr: 0.10 to 0.30%, Cu: 0 to 0.10%, and Nb: 0 to 0.10%, with the balance being Fe and impurities, and that satisfies Formula (1) and Formula (2), wherein a grain size number of ferrite in the steel is 9.0 or more, and an absorbed energy at &#x2212;30&#xb0; C. is 100 J or more in the Charpy impact test using a V notch specimen.0.36&#x2264;C+(Si+Mn)/6+(Cr+V)/5+Cu/15&#x3c;0.68&#x2003;&#x2003;(1)51/12&#xd7;C&#x2212;V&#x2264;0.52&#x2003;&#x2003;(2)

Hot forged steel material

There is provided a hot forged product having excellent wear resistance and fatigue strength even when the hot forged product is produced with a thermal refining treatment and a case hardening thermal treatment after hot forging omitted, and having a chemical composition consisting of, in mass %, C: 0.45 to 0.70%, Si: 0.01 to 0.70%, Mn: 1.0 to 1.7%, S: 0.01 to 0.1%, Cr: 0.05 to 0.25%, Al: 0.003 to 0.050%, N: 0.003 to 0.02% with the balance being Fe and impurities. The matrix at the depth of 500 &#x3bc;m to 5 mm from an unmachined surface of the forged product is a ferrite-pearlite structure, in which a pro-eutectoid ferrite area fraction is 3% or less or a pearlite structure, and the average diameter of pearlite colonies in the pearlite structure at the depth of 500 &#x3bc;m to 5 mm from the unmachined surface is 5.0 &#x3bc;m or less.

Hot forged product

A forged crankshaft () includes a carbon steel containing S, wherein in a portion corresponding to a machined outer circumferential surface of a shaft part such as journals (J), crank pins (P), a front part (Fr), and a flange (Fl), a ratio x/y of an area rate x of sulfide in a position (X) corresponding to a parting surface of a die for finish forging to an area rate y of sulfide in a position (Y) corresponding to a bottom of a die impression of the die for finish forging is equal to or lower than 1.5. The forged crankshaft () can avoid an occurrence of machined surface cracks on the journals (J) and the crank pins (P) after the outer circumferential surface is machined.

Forged crankshaft and method for manufacturing the forged crankshaft

To provide a forged crankshaft having an excellent wear resistance. The forged crankshaft according to the present embodiment includes a non-heat treated steel material. The non-heat treated steel material has a chemical composition which contains, by mass %, C: 0.45 to 0.70%, Si: 0.75 to 1.30%, Mn: 1.00 to 2.00%, S: 0.03 to 0.30%, Cr: 0.05 to 0.30%, Al: 0.005 to 0.050%, and N: 0.005 to 0.020%, the balance being Fe and impurities, and satisfies the following Formula (1):1.1C+Mn+0.2Cr&#x3e;2.0&#x2003;&#x2003;(1)where a symbol of each element in Formula (1) is substituted by the content (mass %) of the each element. A matrix of the non-heat treated steel material is a ferrite-pearlite microstructure in which an area ratio of pro-eutectoid ferrite is less than 10% or a pearlite microstructure.

Forged crankshaft

There is provided a steel for induction hardening in which cracks are less liable to occur and high hardness and seizure resistance are attained even if a tempering process after induction hardening is omitted. The steel for induction hardening according to the present invention contains, by mass percent, C: 0.20 to 0.34%, Si: at most 0.20%, Mn: 0.75 to 2.0%, P: at most 0.03%, S: at most 0.20%, Cr: 0.05 to 1.2%, Ti: at least 0.002% and less than 0.030%, Al: 0.005 to 0.04%, and N: 0.0040 to 0.020%, the balance being Fe and impurities, and satisfies Formula (1):1.20&#x2266;Mn+Cr&#x2266;2.10&#x2003;&#x2003;(1)where the content (mass %) of each element is substituted for each of the symbols of elements in Formula (1).

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Kizugawa, Japan

Hiroaki Tahira