Patent ID: 8475605
Filing Date: 2013-07-02
Classification: C21D,C22C,C23C,F16G

Abstract:
1. A surface layer-hardened steel part treated with a carburizing treatment or a carbonitriding treatment which includes a nitriding treatment at any given point in time during a total carburizing treatment time, a chemical composition of a steel of a non-carburized portion of the steel part comprising, by mass %: C: 0.10% to 0.60%; Si: 0.01% to 2.50%; Mn: 0.20% to 2.00%; S: 0.0001% to 0.100%; Cr: 2.00% to 5.00%; Al: 0.001% to 0.50%; N: 0.0020% to 0.0200%; P: 0.001% to 0.050%; O: 0.0001% to 0.0030%; and the balance consisting of iron and unavoidable impurities, wherein a total amount of Cr, Si, and Mn of the non-carburized portion of the steel satisfies, by mass %, 2.0≦Cr+Si+Mn≦8.0; in a surface layer portion from the topmost surface to 50 μm in depth of a carburized layer, an area ratio of a carbide in the surface layer portion is 15% or more; the surface layer portion contains at least one precipitate of (Cr,Fe) a reticular carbide of 10 μm or more along a prior γ austenite grain boundary is 2.5 pieces/mm