Carbides Analysis Of The High Strength And Low Density Fe-Mn-Al-Si Steels

The work presents the results of investigations into the structure and phase composition of newly developed high manganese steels of the X98MnAlSiNbTi24-11 and X105MnAlSi24-11 type. The average density of such steels is 6.67 g/cm(3), which is 15% lower as compared to typical structural steels. An analysis of phase composition and structure allows to conclude that the investigated steels feature an austenitic gamma-Fe(Mn,Al,C) structure with uniformly distributed and elongated alpha-Fe(Mn,Al) ferrite grains on the boundaries of austenite grains and carbides. Examinations by diffraction of back scattered electrons (EBSD) allow to conclude that high-angle boundaries dominate in such steels, having significant influence on mechanical properties. Three types of carbides with differentiated chemical composition and size were identified in steel X98MnAlSiNbTi24-11 with scanning and transmission electron microscopy. kappa-(Fe,Mn)(3)AlC carbides, having a regular, face-centered cubic lattice (fcc), were identified in austenite. Transmission electron microscopy examinations have enabled to identify M7C3-type carbide in ferrite. Nb- and Ti-based complex carbides were identified in steel X98MnAlSiNbTi24-11, both, in ferrite and austenite. (NbTi)C-2 carbide precipitates were confirmed in an X-ray qualitative phase analysis. The size of the above-mentioned carbides is within several to several dozens of um. An X-ray qualitative phase analysis has confirmed the precipitates of M7C3 carbides in both steels.