High strength steel and high strength bolt excellent in delayed fracture resistance and methods of production of same
US8951365B2 · kind B2 · utility
Assignee
Inventors
Key dates
| Filing date | Mar 11, 2011 |
| Grant date | Feb 10, 2015 |
| Priority date | — |
| Expiry date | Mar 11, 2031 |
Classification
- Technology area (CPC C)Chemistry; Metallurgy
- CPC primaryC21D2221/10
- WIPO fieldMaterials, metallurgy
- WIPO sectorChemistry
Abstract
A steel which is excellent in delayed fracture resistance containing, by mass %, C: 0.10 to 0.55%, Si: 0.01 to 3%, and Mn: 0.1 to 2%, further containing one or more of Cr: 0.05 to 1.5%, V: 0.05 to 0.2%, Mo: 0.05 to 0.4%, Nb: 0.001 to 0.05%, Cu: 0.01 to 4%, Ni: 0.01 to 4%, and B: 0.0001 to 0.005%, and having a balance of Fe and unavoidable impurities, the structure being a mainly tempered martensite structure, the surface of the steel being formed with (a) a nitrided layer having a certain thickness range and a nitrogen concentration higher than the nitrogen concentration of the steel by 0.02 mass % or more and (b) a low carbon region having a certain depth range from the surface of the steel and having a carbon concentration of 0.9 time or less the carbon concentration of the steel.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.