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Abstract

Provided is a method that enables manufacture, with good productivity, of a high-strength cold-rolled steel with improved elongation (EL), stretch-flangeability (λ), bendability (R), and balance of these properties (TS×EL×λ/1000), outstanding composite workability as evaluated by Erichsen test, and a tensile strength of at least 980 MPa. A steel material satisfying a prescribed constituent composition is held and soaked for at least fifty seconds at a temperature at or above the Ac₃ point, after which the steel material is cooled at an average cooling rate of at least 15° C./sec to a discretionary temperature (T) that satisfies expression (1) below, held for 5-180 seconds in a temperature range that satisfies expression (1) below, then heated to a temperature region that satisfies expression (2) below, held for at least 50 seconds in this temperature region, and then cooled.

description='In-line Formulae' end='lead'300° C.≦T1(° C.)<400° C.  (1)description='In-line Formulae' end='tail'

description='In-line Formulae' end='lead'400° C.≦T2(° C.)<540° C.  (2)description='In-line Formulae' end='tail'

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First Claim