Patent ID: 8435363
Filing Date: 2013-05-07
Classification: B32B,C21D,C22C,C23C,Y10T

Abstract:
1. A method of making a complex metallographic structured steel sheet comprising: a) assembling a continuous metal slab caster having a casting mold, b) introducing molten steel into the casting mold and continuously casting the molten steel into a slab having a composition comprising the following elements by weight: c) hot rolling the steel slab having an exit temperature in a range between about (A d) cooling the hot rolled steel at a mean cooling rate of at least about 3° C./s (about 5.4° F./s); e) optionally, coiling the steel at a temperature between about 400° C. (about 752° F.) and about 800° C. (about 1472° F.); f) cold rolling the steel to a desired sheet thickness, with the cold rolling reduction being at least about 25%; g) heating the steel sheet to a temperature in the range between about 625° C. (about 1157° F.) and about 925° C. (about 1697° F.) for between about 10 seconds and 10 minutes; and h) cooling the steel sheet to a temperature in the range between about 400° C. (about 752° F.) and about 550° C. (about 1022° F.) for between about 1 second to below 10 seconds to obtain a multi-phase microstructure having in combination ferrite, martensite between 3% and about 65% by volume, and at least one microstructure selected from the group consisting of bainite and retained austenite, and having fine precipitates selected from the group of TiC, NbC, TiN, NbN, (Ti.Nb)C, (Ti.Nb)N, and (Ti.Nb)(C.N) particles having at least 50% smaller than 20 nm in size, and physical properties comprising tensile strength greater than about 780 megapascals and at least one of the properties of elongation greater than about 10%, yield ratio greater than about 70%, and hole expansion ratio greater than about 50%.