On the formation and growth of grain boundary κ-carbides in austenitic high-Mn lightweight steels
Mohamed Naguib Elkot, Binhan Sun, Xuyang Zhou, Dirk Ponge, Dierk Raabe
Abstract
The precipitation of grain boundary (GB) -carbides critically influences the damage-tolerance ability of high-Mn high-Al lightweight steels, particularly in harsh environments (cryogenic and H environments).The formation and growth behavior of these carbides thus need to be understood.In this work, we use atom probe tomography and four-dimensional scanning transmission electron microscopy to study the formation mechanisms of GB -carbides in a Fe-28Mn-8Al-1.3C (wt.%) steel that is aged at 550C, a temperature at which GB -carbide formation is often believed to be delayed or avoided.We observe that the formation of GB -carbides results from spinodal decomposition of grain interior (GI) -carbides and their further interaction with GB planes rather than from heterogeneous GB nucleation, as has been formerly proposed.However, the subsequent growth of GB -carbides shows different kinetics in comparison to GI -carbides.The underlying reason and its implications for future microstructure design of such steels are discussed.