Patent ID: 7591917

Claim:
A method of producing low carbon steel strip comprising the steps of: (a) continuously casting molten low carbon steel strip less than 5 mm thickness in a twin roll caster into austenite grains, said molten steel comprising a concentration of residuals of equal to or less than about 2.0 wt % selected with regard to the microstructure of the finished strip to provide a desired yield strength, said residuals selected from the group consisting of copper, nickel, chromium, molybdenum and tin where the residuals are selected from the group in the amounts of more than 0.15 wt % copper, more than 0.08 wt % nickel, more than 0.08 wt % chromium, more than 0.03 wt % molybdenum, more than 0.015 wt % tin, where if copper and tin are selected then an amount equal or more than 1.15 wt % copper plus tin is selected; and (b) cooling to form the cast strip as cast, without reheating, to transform austenite grains in the strip to ferrite in a temperature range between 850° C. and 400° C. at a selected cooling rate of at least 0.01° C./sec to produce a microstructure that provides a required yield strength of the cast strip, the microstructure being selected from the group consisting of: (i) predominantly polygonal ferrite; and/or (ii) a mixture of polygonal ferrite and low temperature transformation products.