Method for producing a dual-phase steel sheet having excellent f

Details Method for producing a dual-phase steel sheet having excellent f Method for producing a dual-phase steel sheet having excellent f

1980-12-04

1983-07-19

Skiff, Peter K.

Metal treatment

Compositions

Heat treating

148 124, C21D 802

Patent

active

043941869

ABSTRACT:
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, yield 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.degree. C. at an average cooling rate (R.sub.1) in the range of 1.degree. C./second.gtoreq.R.sub.1 .ltoreq.30.degree. C./second over the primary cooling stage from the annealing temperature down to an intermediate temperature (T) in the range of 420.degree. C..ltoreq.T.ltoreq.700.degree. C., and at an average cooling rate (R.sub.2) in the range of 100.degree. C./second.ltoreq.R.sub.2 .ltoreq.300.degree. C./second over the secondary cooling stage from the intermediate temperature (T) down to the temperature not higher than 200.degree. C.

REFERENCES:
patent: 3951696 (1976-04-01), Gondo et al.
patent: 4062700 (1977-12-01), Hayami et al.
patent: 4113517 (1978-09-01), Nakaoka et al.
patent: 4159218 (1979-06-01), Chatfield et al.
patent: 4285741 (1981-08-01), Furukawa et al.

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