Patent ID: 7343961

Claim:
Process for the continuous production of an ultrathin hot rolled steel strip from a thin slab obtained by continuous casting in a mould, comprising: a continuous casting step ( 1 ); a pre-transformation ( 5 ) subsequent to the continuous casting step ( 1 ); an induction heating ( 8 ); and a final transformation ( 18 ) with previous plastic stretching ( 17 ), descaling ( 17 a ) and subsequent cooling and coiling, characterized by: the slab leaving the mould with a central crown at each side; a reduction of a slab thickness in continuous casting during solidification ( 3 . 1 ) by 60% at maximum, from 100 to 70 mm, until a reduction from 80 to 40 mm; a secondary cooling during a liquid steel core reduction step ( 3 B) of the continuous casting step ( 1 ), performed by spray nozzles ( 3 a ), with the following characteristics: specific water delivery between 0.6 and 3.0 liters per kg of cast steel, decreasing cooling density in the direction of the slab advancement due to liquid core reduction, and selective control of cooling fluid flow rates between a front side and a back side of the slab; said pre-transformation being a roughing step of the thin slab upon solidification at a surface temperature of the slab >1100° C. with not more than four passes to obtain an intermediate strip ( 5 . 3 ) having different thicknesses chosen in the range from 30 to 8 mm with a central crown of up to 0.4 mm at each side; said induction heating ( 8 ) being adapted to fix various temperatures of the intermediate strip chosen between 1000 and 1400° C. and overheating function of a head and tail; said plastic stretching ( 17 ) combined with descaling ( 17 a ) to eliminate scale from the surface of the intermediate strip; said final transformation ( 18 ) being a rolling step down to a thickness of a finished strip of 0.4 mm as a minimum with not more than six passes and a controlled temperature of a hot rolled strip at an exit therefrom >750° C. (AC 1 ); and a controlled cooling ( 14 ) of a strip ( 13 ) in the time between the end of a final rolling ( 18 ) and the coiling until a minimum temperature of 200° C., according to a corresponding T.T.T. diagram ( 14 . 1 ) specific for a steel quality of the strip thickness.