C - Chemistry – Metallurgy – 21 – D
Patent
C - Chemistry, Metallurgy
21
D
148/34.4
C21D 8/02 (2006.01) C21D 8/04 (2006.01) C21D 1/19 (2006.01)
Patent
CA 1139644
METHOD FOR PRODUCING A DUAL-PHASE STEEL SHEET HAVING EXCELLENT FORMABILITY, HIGH ARTIFICIAL- -AGING HARDENABILITY AFTER FORMING, HIGH STRENGTH, LOW YIELD RATIO, AND HIGH DUCTILITY ABSTRACT OF THE DISCLOSURE A high-strength cold-rolled steel sheet with dual- phase structure, recently developed by the Japanese steel producers have a low yield ratio of approximately 0.6 or lower, is free of the yield-point elongation and is of excellent press-formability. One of the production methods of this steel is a continuous annealing at a temperature range of two-phase structure of ferrite (.alpha.) + austenite (.gamma.). In order to improve the formability, the artificial-aging hardenability after forming, yeild ratio and ductility over those of the known dual-phase steel, the present invention provides a method for producing a dual-phase steel, which comprise a step of cooling from the annealing temperature to a temperature not higher than 200°C at an average cooling rate (R1) in the range of 1°C/second?R1?30°C/second over the primary cooling stage from the annealing temperature down to an intermediate temperature (T) in the range of 420°C?T?700°C, and at an average cooling rate (R2) in the range of 100°C/second?R2?300°C/second over the secondary cooling stage from the intermediate temperature (T) down to the temperature not higher than 200°C.
366495
Furukawa Takashi
Koyama Kazuo
Goudreau Gage & Associates
Nippon Steel Corporation
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