Nitrided part and method of production of same

Abstract

A nitrided part excellent in contact fatigue strength plus rotating bending fatigue strength, the nitrided part having a steel material having a predetermined chemical composition as a material, wherein the nitrided part comprises a compound layer formed on the surface of the steel material, the compound layer containing iron, nitrogen, and carbon, a thickness of the compound layer being 3 μm to less than 20 μm; a phase structure in the compound layer in a range from the surface down to a depth of 5 μm contains γ′ phases in an area ratio of 50% or more; a pore area ratio in a range from the surface down to a depth of 3 μm is less than 10%; and a compressive residual stress of the compound layer surface is 500 MPa or more.

1 . A nitrided part having a steel material as a material, the steel material comprising, by mass %,
 C: 0.05% to 0.30%,   Si: 0.05% to 1.5%,   Mn: 0.2% to 2.5%,   P: 0.025% or less,   S: 0.003% to 0.05%,   Cr: over 0.5% to 2.0%,   Al: 0.01% to 0.05%,   N: 0.003% to 0.025%,   Nb: 0% to 0.1%,   B: 0% to 0.01%,   Mo: 0% to less than 0.50%,   V: 0% to less than 0.50%,   Cu: 0% to less than 0.50%,   Ni: 0% to less than 0.50%,   Ti: 0% to less than 0.05% and   a balance of Fe and impurities,   wherein   the nitrided part comprises a compound layer formed on a surface of the steel material, the compound layer containing iron, nitrogen, and carbon, a thickness of the compound layer being 3 μm to less than 15 μm;   a phase structure in the compound layer in a range from the surface down to a depth of 5 μm contains γ′ phases in an area ratio of 50% or more;   a pore area ratio in a range from the surface down to a depth of 3 μm is less than 10%; and   a compressive residual stress of the compound layer is 500 MPa or more.