Abstract: The present invention relates to a mechanical part, which is obtained by: processing a steel into a shape of a part, the steel having an alloy composition containing, by weight percent, C: 0.10 to 0.30%, Si: 0.50 to 3.00%, Mn: 0.30 to 3.00%, P: 0.030% or less, S: 0.030% or less, Cu: 0.01 to 1.00%, Ni: 0.01 to 3.00%, Cr: 0.20 to 1.00%, Al: 0.20% or less, N: 0.05% or less, and the remainder of Fe and inevitable impurities, and the alloy composition satisfying the following condition: [Si %]+[Ni %]+[Cu %]?[Cr %]>0.50, in which [Si %], [Ni %], [Cu %] and [Cr %] represent the concentration of Si, the concentration of Ni, the concentration of Cu and the concentration of Cr in the alloy composition, respectively; subjecting the steel to a carburizing treatment in a vacuum, followed by gradually cooling the steel; and subsequently subjecting the steel to a high-frequency hardening to thereby harden a surface of the steel.

Abstract: The present invention provides a method of production of a steel soft nitrided machine part comprising: preparing a steel material containing, by mass %, C: 0.15-0.30%, Si: 0.03-1.00%, Mn: 0.20-1.5%, S: 0.04-0.06%, Cr: 0.01-0.5%, Mo: 0.40-1.5%, Nb: 0.005-0.05%, Ti: 0.005-0.03%, V: 0.2-0.4%, Ni: 0.05-1.5%, N: 0.002-0.0048%, a balance of Fe and unavoidable impurities, limiting P to 0.02% or less, limiting Ceq. (equation (1)) to 0.65-0.85, controlling DI (equation (2)) to 80-155, log Kp (equation (3)) to 2.5-8, and Si and Mn contents according to equation (4), heating the steel material to 1150-1280° C., hot forging the steel material to the shape of the part, cooling the steel material at a 0.5-1.5° C/sec cooling rate to obtain a hot forged part having a micrometallic structure with more than 50% of bainite, machining the hot forged part, and soft nitriding the machined hot forged part at 550-650° C. for 30 minutes or more.

Abstract: The present invention relates to a mechanical part, which is obtained by: processing a steel into a shape of a part, the steel having an alloy composition containing, by weight percent, C: 0.10 to 0.30%, Si: 0.50 to 3.00%, Mn: 0.30 to 3.00%, P: 0.030% or less, S: 0.030% or less, Cu: 0.01 to 1.00%, Ni: 0.01 to 3.00%, Cr: 0.20 to 1.00%, Al: 0.20% or less, N: 0.05% or less, and the remainder of Fe and inevitable impurities, and the alloy composition satisfying the following condition: [Si %]+[Ni %]+[Cu %]?[Cr %]>0.50, in which [Si %], [Ni %], [Cu %] and [Cr %] represent the concentration of Si, the concentration of Ni, the concentration of Cu and the concentration of Cr in the alloy composition, respectively; subjecting the steel to a carburizing treatment in a vacuum, followed by gradually cooling the steel; and subsequently subjecting the steel to a high-frequency hardening to thereby harden a surface of the steel.

Abstract: A method of production of a steel soft nitrided machine part with a high fatigue strength by hot forging the part, machining it while omitting heat treatment, then soft nitriding it, that is, a method of production comprising preparing a steel material of a composition containing Si, Mn, S, Cr, Mo, Nb, Ti, V, Ni, and N in predetermined amounts and a balance of Fe and unavoidable impurities, limiting the content of P in said unavoidable impurities to a predetermined amount of less, having a Ce. defined by the following equation (1) of 0.65 to 0.85, having a DI defined by the following equation (2) of 80 to 1355, having a log Kp defined by the following equation (3) of 2.5 to 8, and satisfying the following equation (4), heating it to 1150 to 1280° C., then hot forging it, then cooling it at 0.5 to 1.5° C./sec to obtain a hot forged part having a micrometallic structure in which a ratio of a bainite structure is 5% or more, then machining it, then soft nitriding it at 550 to 650° . for 30 minutes or more.