Patent ID: 6231696
Filing Date: 2001-05-15
Classification: B21B,C21D,C22C

Abstract:
In a method of manufacturing microalloyed structural steels by rolling in a CSP plant, wherein a cast slab strand is divided into rolling lengths and is supplied through an equalizing furnace to a multiple-stand CSP rolling train and is continuously rolled in the CSP rolling train into hot-rolled wide strip, is cooled in a cooling stretch and is reeled into coils, wherein the improvement comprises, for achieving optimum mechanical properties in hot-rolled wide strip by thermomechanical rolling, carrying out a controlled structure development as the thin slabs travel through the CSP plant, the method comprising the steps of:(a) changing the cast structure by adjusting defined temperature and shape changing conditions during a first transformation, wherein the temperature is above the recrystallization stop temperature, so that a complete recrystallization of the cast structure takes place at least one of during and after the first deformation and prior to a beginning of a second deformation step;(b) carrying out a deformation in the last roll stands at temperatures below the recrystallization stop temperature, wherein the deformation is not to drop below a quantity of 30% and a final rolling temperature is near the austenite/ferrite transformation temperature;(c) carrying out a controlled cooling of the hot-rolled strips in the cooling stretch, wherein the polymorphous transformation of the austenite takes place at a temperature between the austenite/ferrite transformation temperature and the bainite start temperature; and further comprising, for achieving high-strength microalloyed structural steels with a yield point of .gtoreq.480 MPa and with optimum properties with respect to strength and toughness, the additional step of effecting an additional structure influence in the thin slab by changing the material composition thereof by one of(d) an increased silicon content for a targeted mixed crystal strengthening, and(e) an increased content of copper, chromium, nickel for a complex mixed crystal strengthening.