Correlating the Microstructural Heterogeneity with Local Formability of Cold-Rolled Dual-Phase and Complex-Phase Steels Through Hardness Gradients

Development of the descriptors of the multiphase microstructure, which will allow comparing material's local fracture resistance, is the objective of the article. A hypothesis is made that local gradients of properties can realistically represent the tendency to the local fracture and can be an effective indicator for the stretch-flangeability properties. A novel gradient evaluation algorithm was developed within the study. The algorithm calculates the distribution of gradients for the data given in the form of a cloud of points, independently of the source of these data. Two industrial grade dual-phase (DP) and complex-phase (CP) steels are produced from the same cast chemical composition and with the same processing route; however, different parameter setups are studied using a correlative microstructure characterization approach to supply data for gradients evaluation. Obtained electron backscattered diffraction maps are used to generate the representative volume elements and statistically similar representative volume elements, which are subjected to deformation and used to calculate the properties gradients theoretically. The high-resolution hardness maps are used to directly obtain the hardness gradients. Both methods of gradients calculations are applied to the DP and CP microstructures and prove to be an effective and reliable method for the comparison of materials' stretch-flangeability.