Steel sheet, coated steel sheet, method for producing hot-rolled steel sheet, method for producing full-hard cold-rolled steel sheet, method for producing heat-treated sheet, method for producing steel sheet, and method for producing coated steel sheet
US10920294B2 · kind B2 · utility
Assignee
Inventors
Key dates
| Filing date | Mar 17, 2017 |
| Grant date | Feb 16, 2021 |
| Priority date | — |
| Expiry date | Oct 5, 2037 |
Classification
- Technology area (CPC C)Chemistry; Metallurgy
- CPC primaryC22C38/38
- WIPO fieldMaterials, metallurgy
- WIPO sectorChemistry
Abstract
A steel sheet having low yield ratio, tensile strength of 780 MPa or more, and good bending fatigue properties. The steel sheet includes a specific chemical composition and a steel microstructure having an area percentage of a ferrite phase of 20% or more and 80% or less and an area percentage of a martensite phase of 20% or more and 80% or less, the area percentage being determined by microstructure observation, in which a surface layer portion of the steel sheet has an average ferrite grain size of 5.0 μm or less and an inclusion density of 200 particles/mm−2 or less, and in which the steel sheet has a surface hardness of 95% or more when the steel sheet has a hardness of 100% at a position ½t, where t represents the thickness of the steel sheet, away from a surface of the steel sheet in the thickness direction.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.