Diffusion induced recrystallization in Fe(Zn) system characterized by EBSD

Abstract

Diffusion induced recrystallization (DIR) has been studied by zincification of pure iron as well as interstitial free steel with particular attention on the local misorientation in grains caused by DIR. A change in microstructure was investigated as a function of annealing temperature from 723 K up to 963 K. Misorientation was measured using Electron Back Scattering Diffraction (EBSD) technique. Fine grains of ferrite nucleate on the surface of substrates considerably in the couples annealed at a higher temperature such as 963 K and complete a fine-grained surface layer. Boundaries between the fine grains are regarded as high angle boundaries since they are micro-etched strongly with the eventual formation of grooves along them. In contrast to the fine grains formed at a higher temperature, sub-grains form at a lower temperature such as 723 K and boundaries between sub-grains are regarded as low angle boundaries. The sum of local misorientation along a particular scanning direction, however, depends on the direction. The largest variation of misorientation in the original grains in which sub-grains caused by DIR exist is often observed along the scanning direction which terminates with high angle boundaries of original grains at least on one of its ends, while a smaller variation in misorientation is obtained along the direction which terminates with Σ or low angle boundaries on both ends. A possible interpretation of DIR is developed that the largest variation of misorientation leads high angle boundaries to be formed with the eventual formation of fine grains with high angle boundaries.