Crystallographic Orientation and Microstructure Dependences of Surface Potential for Annealed S45C Steel Using Combined Scanning Kelvin Force Probe Microscopy and Electron Backscatter Diffraction Analyses

Abstract

Scanning Kelvin force probe microscopy (SKPFM) and subsequent electron backscatter diffraction (EBSD) measurements were performed across the same area of a ferrite/pearlite microstructure for annealed S45C steel. Larger potential differences were observed at the heterogeneous phase boundaries between cementite and ferrite. The EBSD measurements confirmed the dependence of potential on the crystallographic orientation of the ferrite phases. Specific orientation relationships between ferrite and cementite phases were observed when both phases nucleated in the same pearlite colony, however, such relationships were not valid when nucleation occurred in separate colonies. The heterogeneous phase boundaries exhibiting larger potential differences, in addition to having no specific orientation relationship, could be considered as a highly plausible candidate location for corrosion initiation. Thus, combined SKPFM and EBSD analyses are a powerful technique to improve the evaluation of the corrosion initiation process in ferrite/pearlite microstructures with respect to potential difference and crystallographic orientation relationships.