Method for producing a steel sheet with dual-phase structure composed of ferrite- and rapidly-cooled-transformed phases
AssigneeNippon Steel Corporation
InventorsSatohiro Hayami, Takashi Furukawa, Yoshihiko Takeoka
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Abstract
A method for producing a steel sheet of dual-phase structure composed of ferrite phase and transformed phase (or phases) produced by rapid cooling, which comprises isotropically dispersing a carbon concentrated phase by a pretreatment of the steel sheet and continuously annealing the steel sheet thus pretreated in the alpha-gamma range, followed by cooling at a rate not larger than about 10000.degree. C/min., as defined herein.
Claims8
A method for producing a steel sheet having a dual-phase structure composed of (b 1) a ferrite phase and (2) a transformed phase member selected from the group consisting of (a) a martensite phase, (b) a bainite phase and (c) both a martensite phase and a bainite phase, which method comprises
- pretreating a steel sheet, containing 0.03 to 0.15% carbon, 0.7 to 2.0% manganese and less than 0.7% silicon, by finish hot rolling the steel sheet with a finishing temperature only in the alpha-gamma temperature range, with a reduction not higher than 40% in the alpha-gamma temperature range, and coiling the finish hot rolled-steel sheet,
- continuously annealing the pretreated steel sheet in the alpha-gamma temperature range, and
- cooling the annealed steel sheet at a rate not higher than about 10,000.degree. C/min.
Dependencies are inferred from the claim text.