Evaluation of misindexing of EBSD patterns in a ferritic steel

The systematic misindexing caused by pseudo-symmetry Kikuchi diffraction patterns in automated Electron Backscatter Diffraction analysis has been studied in a 9Cr-1 Mo ferritic steel. Grains with its [1 1 1] directed towards detector centre were found to be prone to misindexing, and the solutions exhibit a relative orientation of +/-30 degrees and 60 degrees about the common [1 1 1] axis (as compared to the true orientation). Fictitious boundaries were detected within such grains, which satisfy the Sigma 3 or Sigma 13b type coincidence site lattice boundary criteria. Misindexing rate was reduced with more than six detected bands, but 30 degrees rotated solution was comparatively more persistent, as the additional bands of (3 1 0)-type exhibited a nearly good pattern match. Increase in detector collection angle to 0.96 sr or number of detected bands to nine were found to be beneficial in preventing the misindexing problem.