Abstract: A non-thermal refined nitrocarburized component with excellent bending straightening and fatigue strength, includes a base metal steel material having a composition consisting of: (mass %), C: 0.35 to 0.50%; Si: 0.10 to 0.35%; Mn: 2.3 to 2.8%; S: 0.01% or less; N: 0.0030 to 0.0250%; Cu: 0 to 1.0%; Mo: 0 to 0.3%; Ni: 0 to 0.5%; Ti: 0 to 0.020%, the balance: Fe, impurities, and 3.10 £ (0.316 C+0.122)·(0.7 Si+1)·(5.1 Mn?1.12)·(0.364 Ni+1)·(2.16 Cr+1)·(3 Mo+1) £ 6.00. Impurities include P: 0.08% or less, Al: 0.05% or less, and Cr: less than 0.20%. In a stress concentrated region, an HV hardness 0.05 mm from a surface is 410 to 480, an HV hardness 1.0 mm from the surface is 200 or more, a compound-layer depth is 5 mm or less, and a base metal micro-structure is bainite.

Abstract: An age-hardenable steel having a composition consisting of: C: 0.05 to 0.20%, Si: 0.01 to 0.50%, Mn: 1.5 to 2.5%, S: 0.005 to 0.08%, Cr: more than 0.50% and not more than 1.6%, Al: 0.005 to 0.05%, V: 0.25 to 0.50%, Mo: 0 to 1.0%, Cu: 0 to 0.3%, Ni: 0 to 0.3%, Ca: 0 to 0.005%, and Bi: 0 to 0.4%, the balance being Fe and impurities. Within the impurities, P?0.03%, Ti<0.005%, and N<0.0080%, and [C+0.3Mn+0.25Cr+0.6Mo?0.68], [C+0.1Si+0.2Mn+0.15Cr+0.35V+0.2Mo?1.05], and [?4.5C+Mn+Cr?3.5V?0.8Mo?0.12]. The steel has hardness before aging of not more than 310 HV. After aging, the fatigue strength is not less than 480 MPa and absorbed energy at 20° C. is not less than 12 J.

Abstract: An age-hardenable steel consists of: C: 0.05 to 0.20%, Si: 0.01 to 0.50%, Mn: 1.5 to 2.5%, S: 0.005 to 0.08%, Cr: 0.03 to 0.50%, Al: 0.005 to 0.05%, V: 0.25 to 0.50%, Mo: 0 to 1.0%, Cu: 0 to 0.3%, Ni: 0 to 0.3%, Ca: 0 to 0.005%, and Bi: 0 to 0.4%, the balance being Fe and impurities. Within impurities, P £ 0.03%, Ti<0.005%, and N<0.0080%, and [C+0.3Mn+0.25Cr+0.6Mo3 0.68], [C+0.1Si+0.2Mn+0.15Cr+0.35V+0.2Mo £ 0.85], and [?4.5C+Mn+Cr?3.5V?0.8Mo3 0.00]. The hardness before aging is not more than 290 HV, a quantity of hardening by aging being not less than 25 HV, fatigue strength is not less than 350 MPa, and absorbed energy at 20° C. after aging is not less than 16 J.

Abstract: Provided is a non-thermal refined soft-nitrided component including chemical composition of a steel material of a base metal containing: in mass %, C: 0.25 to 0.40%; Si: 0.10 to 0.35%; Mn: more than 2.0% to 2.8% or less; N: 0.0030 to 0.0250%; Cu: 0 to 1.0%; Mo: 0 to 0.3%; Ni: 0 to 0.5%; Ti: 0 to 0.020%; and a balance being Fe and impurities, the impurities including P: 0.08% or less; S: 0.10% or less; Al: 0.05% or less; and Cr: less than 0 20%, wherein a Vickers hardness at a position of 0.05 mm from the surface is 400 to 480, a Vickers hardness at a position of 1.0 mm from the surface is 200 or more, and a compound-layer depth at a stress concentrated region is 5 ?m or less. This non-thermal refined soft-nitrided component has an excellent bending straightening property and a high fatigue strength.

Abstract: 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 IFe4N (111) of a (111) crystal plane of Fe4N and X-ray diffraction peak intensity IFe3N (111) of a (111) crystal plane of Fe3N, which are measured on a surface of the nitrided steel member by X-ray diffraction, an intensity ratio expressed by IFe4N (111)/{IFe4N (111)+IFe3N (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 ?m.

Abstract: A steel for nitriding having 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: ?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: ?0.30% and Ni: ?0.25% [0.61Mn+1.11Cr+0.35Mo+0.47?2.30], and the balance of Fe and impurities. P, N, Ti and O among the impurities are P: ?0.030%, N: ?0.008%, Ti: ?0.005%, and O: ?0.0030%. The steel is easily subjected to cutting before nitriding and suitable for use as an automobile ring gear. The nitrided component having a surface hardness of 650-900 HV, core hardness being ?150 HV, and effective case depth of ?0.15 mm has excellent bending fatigue strength and surface fatigue strength although the content of Mo is as low as ?0.05% and has a small amount of expansion caused by nitriding.