Correlation of the M 23C 6 precipitation morphology with grain boundary characteristics in austenitic stainless steel

Abstract

The relationship between grain boundary characteristics and the formation of grain boundary carbides in AISI 304 stainless steel have been investigated by using the electron backscattered diffraction (EBSD) technique. It was observed that an increase in the misorientation between two adjacent grains resulted in a change in the carbide morphology from a plate-like to an acute triangular form, where carbides preferentially maintained coherency with the grain for which the {111} planes made the smallest angle with the grain boundary plane. The carbides grew into the other grain at a later stage, having the lowest interfacial energy, which subsequently resulted in the triangular carbide morphology. After low cycle fatigue with a hold time at tensile peak strains, it was observed that cavity formation was more pronounced at random boundaries than at coincidence site lattice (CSL) boundaries. This result provides a good explanation that acute triangular carbides, which predominantly precipitate at random boundaries, are more likely to lead to cavity nucleation than the plate-like carbides precipitate at CSL boundaries.