These are flat steel in sheet having a width in the range of 1.000-3.800 mm and a thickness in the range of 5.00-200.00 mm and flat steel in the form of coils or sheets varying in thickness from 1.50 to 20.00 mm, obtained by hot rolling and in hot rolling mill, a semi-product of rectangular cross-sectional form, called slab, formed by the solidification of liquid steel by continuous casting.