Metal treatment – Stock – Ferrous
Reexamination Certificate
2006-03-16
2011-10-25
Yee, Deborah (Department: 1733)
Metal treatment
Stock
Ferrous
C148S334000, C148S335000, C148S908000, C148S568000, C148S595000, C148S598000, C148S599000, C148S580000
Reexamination Certificate
active
08043444
ABSTRACT:
A steel wire for a cold-formed spring according to the present invention contains a prescribed chemical component composition, wherein: a martensitic transformation start temperature MS1shown by the following expression (1) is in the range from 280° C. to 380° C.; the austenite grain size number N of austenite grains is No. 12 or more; the grain boundary share of carbide precipitated along the austenite grain boundaries is 50% or less; the amount of retained austenite after austenitized and tempered is 20 vol. % or less; and the tensile strength is 2,000 MPa or more;in-line-formulae description="In-line Formulae" end="lead"?MS1=550−361[C]−39[Mn]−20[Cr] (1),in-line-formulae description="In-line Formulae" end="tail"?where [C], [Mn] and [Cr] represent the contents (mass %) of C, Mn and Cr, respectively. Such a steel wire can: secure hot-rolling formability and subsequent drawability while aiming at higher strength and higher stress; moreover exhibit excellent corrosion resistance; and obtain a spring (mainly a suspension spring for an automobile) excellent also in fatigue strength which is a basic required characteristic.
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(Kobe Steel, Ltd.)
Oblon, Spivak McClelland, Maier & Neustadt, L.L.P.
Yee Deborah
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