Effect of Intercritical Annealing on the Properties of Dual Phase Steel via Finite Element Method

Dual phase (DP) steels are rapidly becoming more and more popular for automotive applications. They offer a weight reduction with a combination of energy absorption for crash zones. Rails, reinforcements, back panels, cross members, and pillars can be given as application examples. DP steels microstructure consists of a soft ferrite matrix with hard martensite islands. The hard martensite islands provide strength while the ductile ferrite provides formability. The strength level of DP steel is related to the amount of martensite in the microstructure, and the martensite amount can be arranged via intercritical annealing. In this work, thermodynamic analysis of St52 steel was carried out with Thermo-Calc software. A1 and A3 temperatures were determined by calculating the temperature-dependent phase fractions. Intercritical annealing temperatures were determined according to the calculated critical temperatures (A1 and A3). The intercritical annealing process was modelled by using Simheat NxT software. In this modelling and simulation work, the effect of intercritical annealing temperature on the final microstructure and hardness of DP steel was investigated.