Patent ID: 6475308
Filing Date: 2002-11-05
Classification: C21D,C22C

Abstract:
A process for the production of a hot rolled steel strip, wherein the steel has the following weight compositioncarbon: 0.12-0.25%, manganese: 1-2%, aluminum: 0.03-2.5%, silicon: 0.03-2%, chromium: 0.04-2%, phosphorus: 0.02-0.09%, sulfur optionally up to 0.01%, titanium up to 0.15%, niobium up to 0.15%, vanadium up to 0.15%, balance iron and residual impurities, wherein said steel is subjected to:rolling at a temperature below 880Â° C., a first cooling over a time less than 10 seconds, a second cooling with a cooling speed V ref1 between 20Â° C./sec. and 150Â° C./sec. as a function of the thickness of the rolled steel strip, the temperature at the end of said second cooling being below the Ar3 transformation point for austenite to ferrite, the temperature at the end of the second cooling being between 700Â° C. and 750Â° C., a third cooling between 3Â° C./sec. and 20Â° C./sec. to a temperature between 700Â° C. and 640Â° C., a fourth cooling between 20Â° C./sec. and 150Â° C./sec. as a function of the thickness of said rolled steel strip, the temperature at the end of said fourth cooling being between 350Â° C. and 550Â° C.