Orientation gradients in grain boundary proximity studied by EBSD

ABSTRACT The goal of this study is the evaluation of local misorientation, its distribution and orientation gradient in the microstructural development of a deep drawing quality steel sheet (AKDQ). The microstructure is characterized at sub-grain level spatial resolution using Electron Backscatter Diffraction (EBSD) in samples submitted to interrupted uniaxial tension in a notched sample and to typical solicitations in forming process through Nakajima tests with different sample geometries. The use of a notched sample allows performing a local study of the microstructural evolution in a set of identifiable grains as the material deforms, while the samples corresponding to Nakajima tests are used to study the behavior of the orientation gradient with the distance to the grain boundary under a statistical approach. From the latter analysis, two new EBSD-based parameters are introduced, named Gradient Average Severity (GAS) and Boundary Effective Thickness (BET). In 0.67 mm thick AKDQ steel sheets, the BET value as an indicator of GB influence zone is, in an average sense, independent on the grain size and the loading condition, below 3 μm. The gradient severity shows a good correlation with the mesoscopic plastic deformation. It is also observed that local misorientation accumulates in the grain boundary proximity, showing differences for each loading condition.