Optimizing Annealing Parameters with Gleeble simulation for Cold Rolled Continuous Annealed Dual Phase Steel Sheet

Abstract

Cold rolled dual phase steel sheet with 590 MPa UTS level (DP590) were processed in continuous annealing line and results were compared with Gleeble simulated results. To achieve the typical characteristics like fatigue, hole expansion, phosphatability and good aesthetics; it requires design of compositions and suitable microstructures by controlling the processing parameters of rolling, heating and cooling processes. Thus, the effect of Different annealing parameters for DP590 steel was studied at Gleeble-3800 thermo mechanical simulator and continuous annealing line (CAL). Microstructure and mechanical properties are compared with different annealing cycles. Tensile strength has significant improvement with decrease in rapid cooling temperature were observed in simulated samples and in CAL inline coils, whereas decrease in tensile strength were observed due to decomposition of martensite at higher rapid cooling as well as overaging temperatures. It is also concluded that increasing annealing temperature beyond Ac3 does not increase the martensite fraction as well as tensile strength in continuous annealed steel. In addition, Influence of higher Mn weight% on phosphate chemical conversion coating treatment was investigated. Hole expansion results of DP590 steel for different C weight% were also compared.