US Patent 7367208 Coil winding method for metal in bars

Coil winding method for steel bars providing, at the outlet of the rolling mill (2), cooling stages by means of WB (4′, 4″, 4′″) and equallsation in air so as to perform “soft” hardening on the bar which generates a microstructure consisting, on the surface, of martensite and bainite and, in the center, of ferrite and pearlite, and winding of the bar in the form of a compact coil by means of a coil winder (5). In the position wound on the coil, the bar cools slowly with tempering of the bainite and martensite formed on the surface. This is followed by a straightening stage, jo performed during the coil unwinding phase, and a natural ageing stage, maintaining the bar at ambient temperature.