Hot rolled dual phase steel strip having features of a cold rolled strip

Abstract

A hot rolled dual phase steel strip with Thickness® 1.0 mm can be used for producing cold pressed and cut pieces, in particular for the car manufacturing industry, by replacing with the same mechanical performances the cold rolled dual phase steel strip usually employed for these purposes. Said hot rolled strip in peritectic steel has a carbon percentage between 0.06 and 0.15% with chemical analysis without any important addition of chromium and phosphorous, with a constant geometrical profile on the whole length and tolerances, particularly with respect to the thickness, which are typical of a cold rolled strip with parallelism <0.05 mm, crown between strips centre and side edges <0.07 mm, while showing a structure with a microcrystalline fineness better than grade 10 of the ASTM 112 standard in a percentage higher than 80% of the whole structure.

1 - 5 . (canceled) 
     
     
         6 . A hot rolled, low carbon dual phase steel strip, having:
 a structure composed of i) ferrite and martensite or ii) ferrite and bainite,   a thickness ≧1.0 mm,   a crown between a strip centre and a strip side edge lower than 0.07 mm,   a composition: C 0.06-0.15%, Mn 1.0-2.0%, Si ≦0.80%, P ≦0.010%, S ≦0.005%, Cr <0.30%, Ni ≦0.30%, Mo ≦0.03%, Al 0.030÷0.050%, balance Fe and impurities,   a constant geometrical profile on a length thereof,   thickness tolerances between ±0.06 and 0.12 mm for thickness values of up to 8.00 mm, and   a homogeneous microcrystalline structure with fineness better than grade 10 of the ASTM E112 standard for more than 80% of its whole structure.   
     
     
         7 . The dual phase steel strip according to  claim 6 , having a breaking strain coefficient >20%. 
     
     
         8 . The dual phase steel strip according to  claim 6 , made of peritectic steel in absence of a significant addition of chromium and phosphor. 
     
     
         9 . The dual phase steel strip according to  claim 6 , having a parallelism of less than 0.05 mm. 
     
     
         10 . A method to manufacture the dual phase steel strip of  claim 6 , the method comprising:
 performing a first liquid core reduction downstream of a continuous casting step;   performing a roughing step;   performing heating in an induction furnace;   subsequently keeping temperature in a furnace with an internal mandrel before finishing rolling;   performing a compact controlled cooling; and   performing a final coiling on a reel.