Dislocation Pipe Diffusion of Mn during Annealing of 5Mn Steel

The dislocation pipe diffusion of Mn during annealing of 5Mn steel was experimentally investigated using transmission electron microscopy (TEM). Many dislocations existed inside the ferrite and terminated at the alpha/gamma interface of the sample after intercritical annealing at 650 degrees C for 1 min. Line scans of Mn distribution demonstrated a high Mn concentration in austenite and Mn enrichment at dislocations, indicating that the dislocation pipe diffusion of Mn during intercritical annealing occurred in addition to the gamma/alpha interface diffusion. In-situ TEM observations at 500 degrees C revealed that due to Ostwald ripening, large cementite precipitates grew while small cementite precipitates dissolved via Mn diffusion along the dislocations between them.