Optimization of material properties of high strength multiphase steels via microstructure and phase transformation adjustment

Abstract

For high strength multiphase steels for structural components in automotive applications many different material properties are required. Consequently, a diverse range of tests are performed to characterize the material properties during development as well as optimization of multiphase steels. These tests include classical tensile tests as well as formability tests which characterize bendability, edge crack sensitivity and deep drawability. All these properties are greatly dependent on the microstructure of the material. In the case of high strength multiphase steels, microstructure characterization involves evaluation of the volume fraction, stability, grain size as well as the distribution of the different phases present. Microstructural modifications - with the aim of obtaining the required material properties - may be achieved by variation of annealing parameters. In this paper it is shown how microstructural modification for high strength TRIP and Dual Phase steels resulted in better formability properties and different strength levels.