Surface layer-hardened steel part and method of manufacturing the same
AssigneeNippon Steel & Sumitomo Metal Corporation
InventorsManabu Kubota, Tatsuro Ochi
Life of this patent
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Abstract
In the steel for a surface layer hardening which is treated with carburizing in a temperature range of 800° C. to 900° C., chemical composition thereof contains, by mass %, C: 0.10% to 0.60%, Si: 0.01% to 2.50%, Mn: 0.20% to 2.00%, S: 0.0001% to 0.10%, Cr: 2.00% to 5.00%, Al: 0.001% to 0.50%, N: 0.0020% to 0.020%, P: 0.001% to 0.050%, and O: 0.0001% to 0.0030%; the remaining portion thereof includes Fe and unavoidable impurities; and the total amount of Cr, Si, and Mn satisfies, by mass %, 2.0≦Cr+Si+Mn≦8.0.
Claims14
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)23C6 and (Cr,Fe)3C of 100 pieces or more per 100 μm2;
- and
- a reticular carbide of 10 μm or more along a prior γ austenite grain boundary is 2.5 pieces/mm2 or less in the surface layer portion.
A method for producing a surface layer-hardened steel part, the method comprising:
- a shape forming process of forming the steel part out of a steel for a surface layer hardening treatment, wherein a chemical composition of the steel comprises, by mass %,
- C:
- 0.10% to 0.60%,
- Si:
- 0.01% to 2.50%,
- Mn:
- 0.20% to 2.00%,
- S:
- 0.0001% to 0.10%,
- Cr:
- 2.00% to 5.00%,
- Al:
- 0.001% to 0.50%,
- N:
- 0.0020% to 0.020%,
- P:
- 0.001% to 0.050%,
- O:
- 0.0001% to 0.0030%,
- the balance consisting of iron and unavoidable impurities, and
- a total amount of Cr, Si, and Mn satisfies, by mass %, 2.0≦Cr+Si+Mn≦8.0;
- a carburizing process of precipitating at least one precipitate of (Cr,Fe)23C6 and (Cr,Fe)3C of 100 pieces or more per 100 μm2 in a carburized layer of the steel part in a temperature range of 800° C. to 850° C. by a gas carburizing treatment in which a carbon potential of a carburizing atmosphere keeps 0.90% or more through 50% or more of a total carburizing time or by a gas carbonitriding treatment in which a process to penetrate a nitrogen actively into the surface layer is added at any given point in time during the gas carburizing treatment in which the carbon potential keeps 0.90% or more through 50% or more of the total carburizing treatment time;
- and
- a quenching process of quenching from a temperature at which the gas carburizing treatment or the gas carbonitriding treatment are conducted or quenching just after holding at a temperature which is below the carburizing temperature, following the carburizing process.
Dependencies are inferred from the claim text.