Microstructural Evolution During Normal/Abnormal Grain Growth in Austenitic Stainless Steel

The grain growth behavior of 304L stainless steel was studied in a wide range of annealing temperatures and times with emphasis on the distinction between normal and abnormal grain growth (AGG) modes. The dependence of AGG (secondary recrystallization) at homologous temperatures of around 0.7 upon microstructural features such as dispersed carbides, which were rich in Ti but were almost free of V, was investigated by optical micrographs, X-ray diffraction patterns, scanning electron microscopy images, and energy dispersive X-ray analysis spectra. The bimodality in grain-size distribution histograms signified that a transition in grain growth mode from normal to abnormal was occurred at homologous temperatures of around 0.7 due to the dissolution/coarsening of carbides. Continued annealing to a long time led to completion of secondary recrystallization and the subsequent reappearance of normal growth mode. Another noticeable abnormality in grain growth was observed at very high annealing temperatures, which may be related to grain boundary faceting/defaceting. Finally, a versatile grain growth map was proposed, which can be used as a practical guide for estimation of the resulting grain size after exposure to high temperatures.