High tensile steel sheet having excellent stretch flanging formability
AssigneeKawasaki Steel Corporation
InventorsSusumu Okada, Kouichi Hirata, Susumu Sato, Masahiko Morita, Tsuguhiko Nakagawa
Life of this patent
Estimating the term…
Abstract
A high tensile steel sheet excelling in workability and stretch flanging formability, which is of a composite texture composed of a ferrite phase and a 2nd phase selected from the group consisting of martensite, bainite, pearlite, retained austenite and cold-transformed ferrite, wherein the volume fraction of the 2nd phase is not less than about 1.3 times higher at an outer region of the steel sheet than the volume fraction of the 2nd phase in a central region of the sheet thickness.
Claims4
A high tensile steel sheet having excellent stretch flanging formability which is of a composite texture composed of a ferrite phase and a second phase selected from the group consisting of at least one of martensite, bainite, pearlite, retained austenite and low-temperature transformed ferrite,
- wherein said second phase has a volume fraction not less than about 1.3 times higher at (A) an outer position extending from a location adjacent the surface of the steel sheet to a depth of about 1/4 of the sheet thickness, than in (B) an inner region extending from a depth corresponding to 1/4 of the sheet thickness to the center of the sheet.
Dependencies are inferred from the claim text.