Patent ID: 9593399
Date: 2017-03-14
CPC Classifications: C21D,C22C

Claim:
1. A process for manufacturing a cold rolled dual phase steel comprising: providing a steel slab having a chemical composition in weight percent within a range of 0.12-0.16 C, 1.6-2.0 Mn, 0.4 max Si, 0.2-0.5 Cr, 0.010 max Nb, 0.030-0.080 Ti, 0.02 max V, 0.04-0.10 Mo, 0.1 max Ni, 0.0040 max S, 0.015 max P, 0.0060 max N, 0.0004-0.0030 B, 0.02-0.05 Al, 0.004 max Ca, balance Fe and melting impurities; soaking the steel slab within a temperature range of 1200-1300° C.; hot rolling the soaked steel slab in a roughing treatment and producing a transfer bar; hot rolling the transfer bar in a finishing treatment and producing hot rolled strip, the finishing treatment having an entry temperature between 1040-1120° C. and an exit temperature between 900-970° C.; and cooling the hot rolled strip to a temperature between 540-620° C.; coiling the cooled hot rolled strip; cold rolling the coiled hot rolled strip with at least a 55% reduction in thickness and producing cold rolled sheet; intercritical annealing the cold rolled sheet at a temperature between 790-840° C.; and rapidly cooling using gas jet cooling and/or ultra rapid cooling using the URC, the intercritically annealed cold rolled sheet to a temperature between 450-500° C., the rapidly cooled sheet having a ferrite plus martensite microstructure.