C - Chemistry – Metallurgy – 21 – D
Patent
C - Chemistry, Metallurgy
21
D
148/33
C21D 8/02 (2006.01) C21D 8/04 (2006.01) C21D 1/18 (2006.01)
Patent
CA 1128841
METHOD FOR MANUFACTURING HIGH-STRENGTH COLD-ROLLED STEEL STRIP EXCELLENT IN PRESS-FORMABILITY ABSTRACT OF THE DISCLOSURE A method for manufacturing a high-strength cold- rolled steel strip excellent in press-formability, which comprises the steps of: preparing a slab of an aluminum- killed steel consisting essentially of, in weight percentage: Carbon from 0.02 to 0.06 %, Manganese from 0.06 to 0.25 %, Phosphorus from 0.01 to 0.06 %, Soluble aluminum from 0.020 to 0.060 %, Nitrogen up to 0.005 %, and the balance iron and incidental impurities; hot-rolling said slab to prepare a hot-rolled steel strip; coiling said steel strip at a temperature within the range of from 650 to 770°C; cold-rolling said hot-rolled steel strip thus coiled to prepare a cold-rolled steel strip; subjecting said cold-rolled steel strip to a continuous annealing treatment for a prescribed period of time at a temperature within the range of from 750 to 880°C; cooling said cold-rolled steel strip continuously annealed at a cooling rate of at least: exp {- 5.6 (Cwt.% ? + Mn wt.%/6 + Si wt.%/24) + 7.8} °C/sec from a temperature region of from Ar1 to Ar1 + 60°C to convert the structure thereof into a dual-phase structure of ferrite and a low-tempera- ture transformation phase; and then, subjecting said cold-rolled steel strip having said dual-phase structure to an over-ageing treatment for a prescribed period of time at a temperature within the range of from 260 to 360°C.
365310
Hosoya Yoshihiro
Nakaoka Kazuhide
Nishimoto Akihiko
Macrae & Co.
Nippon Kokan Kabushiki Kaisha
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