Morphology and distribution of martensite in dual phase (DP980) steel and its relation to the multiscale mechanical behavior.

Among generations of advanced high-strength steel alloys, dual-phase steels exhibit a unique combination of strength and formability making them excellent candidates for use in the automotive industry. In this study, we seek to establish a relation between mechanical properties and microstructure of DP980. Electron backscatter diffraction (EBSD)and nanoindentation are used to identify and characterize martensite and ferrite phases. Spatial distributions of martensite and ferrite phases of subjected to various annealing treatments are found using a 2-point correlation function. Micro- and macro-mechanical properties are measured with nanoindentation, Vickers hardness and tensile tests and the results are used to determine the relation between martensite and ferrite phases and the strength of the metal. During the annealing/recovery process, the strength of the martensite phase decreases, the dislocation structure relaxes in the phase boundary region of the ferrite, and the martensite alignment along the rolling direction decreases resulting in the observed metal strength reduction. It is also shown that the higher the annealing temperature, the more homogeneous and equiaxed the distribution of martensite. [ABSTRACT FROM AUTHOR]