METHOD FOR MAKING A HIGH RESISTANCE AND HIGH FORMABILITY COLE ROLLED STEEL STRIP

摘要

The invention concerns a method which consists in: heating the strip at a speed of at least 150 DEG C/s (preferably 150 DEG C/s to 350 DEG C/s) up to a temperature ranging in the intercritical domain, that is Ac1 and Ac 3; and maintaining it at said temperature for at least 1 second (preferably up to a maximum of 20 seconds). The maintenance temperature ranging between 725 DEG C and 825 DEG C, and preferably between 470 DEG C and 800 DEG C; then cooling the strip to a temperature lower than the Ms point of the intercritical austenite at a speed of at least 300 DEG C/s (preferably 300 DEG C/s to 1000 DEG C/s). After quenching and back winding, the strip can be maintained at a temperature ranging between 120 DEG C and 340 DEG C for a time interval between 3 minutes and 15 minutes to enhance ageing resistance. The rapid heating is preferably carried out by electromagnetic induction, advantageously using a longitudinal flux inductor.