High-ductility steel sheet excellent in press formability and strain age hardenability, and method for manufacturing the same

a high-ductility steel and press formability technology, applied in the field of automobile steel sheets, can solve the problems of poor press formability, ductility and a lower hole-expanding ratio, and weight reduction in automobile bodies has become a very important factor, and achieve excellent press formability, excellent strain age hardenability, and improved tensile strength.
US20050016644A1Inactive Publication Date: 2005-01-27JFE STEEL CORP
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Patent Information

Authority / Receiving Office
US · United States
Patent Type
Applications(United States)
Current Assignee / Owner
JFE STEEL CORP
Publication Date
2005-01-27
Estimated Expiration
Not applicable · inactive patent

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Abstract

A steel sheet composition contains appropriate amounts of C, Si, Mn, P, S, Al and N and 0.5 to 3.0% Cu. A composite structure of the steel sheet has a ferrite phase or a ferrite phase and a tempered martensite phase as a primary phase, and a secondary phase containing retained austenite in a volume ratio of not less than 1%. In place of the Cu, at least one of Mo, Cr, and W may be contained in a total amount of not more than 2.0%. This composition is useful in production of a high-ductility hot-rolled steel sheet, a high-ductility cold-rolled steel sheet and a high-ductility hot-dip galvanized steel sheet having excellent press formability and excellent stain age hardenability as represented by a ΔTS of not less than 80 MPa, in which the tensile strength increases remarkably through a heat treatment at a relatively low temperature after press forming.
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Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates mainly to steel sheets for automobiles, and more particularly, to high-ductility steel sheets having very high strain age hardenability and excellent press formability such as ductility, stretch-flanging formability, and drawability, in which the tensile strength increases remarkably through a heat treatment after press forming, and to methods for manufacturing the same. The term “steel sheets” as herein used shall include hot-rolled steel sheets, cold-rolled steel sheets, and hot-dip galvanized steel sheets. The term “steel sheets” as herein used shall also include steel sheets and steel strips. 2. Description of the Related Art In recent years, weight reduction in automobile bodies has become a very important issue in relation to emission gas control for the purpose of preserving global environments. More recently, efforts are made to achieve higher strength of automotive steel sheets and to re...

Claims

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