Metal treatment – Stock – Ferrous
Reexamination Certificate
2007-04-18
2008-12-23
Yee, Deborah (Department: 1793)
Metal treatment
Stock
Ferrous
C148S663000, C148S653000
Reexamination Certificate
active
07468109
ABSTRACT:
Disclosed is a steel sheet including 0.10 to 0.20 mass % of C, 0.8 to 2.5 mass % of Si, 1.5 to 2.5 mass % of Mn, and 0.01 to 0.10 mass % of Al, wherein P is limited to less than 0.1 mass %, and S is limited to less than 0.002 mass % and more than 0 mass %, and the structure includes bainitic ferrite and residual austenite such that area percentage of the bainitic ferrite in relation to the entire structure is at least 70%, area percentage of the residual austenite is 2 to 20%, and total area percentage of polygonal ferrite and quasi-polygonal ferrite is up to 15%, and proportion of the residual austenite having an average particle size of up to 5 μm in the residual austenite is at least 60%. The steel sheet is a TRIP steel sheet which has bainitic ferrite as its matrix, and it has a tensile strength (TS) of at least 980 MPa as well as an excellent stretch flangeability.
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(Kobe Steel, Ltd.)
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Yee Deborah
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