Effect of Mg Addition on the Ferrite Grain Boundaries Misorientation in HAZ of Low Carbon Steels

The relation between the Mg treatment and ferrite grain boundaries misorientation was investigated. The orientation imaging microscopy technique based on electron backscattered diffraction technique (EBSD) was used in this work. It was found that the addition of 0.005 wt% Mg to the steel could evidently increase the ratio of acicular ferrite crystals appearing at large angles boundaries to each other, which was attributed to the nucleation of the second-phase particles by the Mg treatment. The EBSD techniques provide a powerful method to characterize and quantify the ferrite grain boundaries misorientation, in order to relate it to toughness.