Abstract

The aging of fully austenitic FeMnAlC alloys at temperatures ranging from 500°C to 750°C for a short period of time produces a fine structure of (Fe.Mn)3 AlC carbide (K-phase) precipitation within the austenitic matrix, but not on grain Ixiundaries. However, with increasing aging times an alpha+kappa, or alpha+kappa+beta-Mn transition has been detected on grain boundaries. In order to improve the strength, corrosion resistance and high-temperature oxidation, silicon has been added lo Fe-Mn-Al-C alloys. In the present work, the grain boundary precipitation in an austenitic Fe -28Mn-8Al-1C alloy with 1,25%Si was investigated by transmission electrón midróscopy (TEM) and atomic and magnetic force microscopy (AFM and MFM). Isothermal holding at temperatures above 800'C results, in the initial stages, in a mixture of alpha+kappa-phase in the grain boundaries, followed by a gradual alpha—>B2 transition. At 700°C, isothermal holding gives Origen to kappa-phase and B2, which gradually transforms to DO3 detected by magnetic force microscopy. Therefore, it is concluded that Si addition stabilizes the DO3 phase only at temperatures below 700"C.