Simulation of Dilatation Curve Associated with Martensitic Transformation in a Dual-Phase Steel

The specific volume of alloys can be calculated using Thermo-Calc®for the problem of diffusion transformation in equilibrium or a single phase. The martensite transformation in a displacive manner can not be treated directly with Thermo-Calc®. A method to calculate the thermal dilatation curves for a dual-phase steel was established in this research associated with martensitic transformation from ferrite plus austenite after intercritical annealing. The equilibrium phase diagram, martensite starting temperature, as well as transformed martensite fraction have been involved in the calculations. The results showed that the calculated dilatation curves were in accordance with the measured curves by dilatometer, and indicated the reason for the ambiguous volume change in the dual-phase steel owing to its small fraction of austenite associating with martensite transformation.