Crystallographic characterizations of eutectic and secondary carbides in a Fe-12Cr-2.5Mo-1.5W-3V-1.25C alloy

In this work, the morphology and structures of the eutectic and secondary carbides in a new high chromium Fe-1 2 Cr-2.5Mo-1.5W-3V-1.25C designed for cold-rolling work roll were systematically studied. The precipitated carbides inside the grains and along the grain boundaries were investigated with optical microscope, scanning electron microscopy with energy dispersive spectroscopy, transmission electron microscopy and X-Ray diffraction. Selected area diffraction patterns have been successfully used to identify the crystal formation and lattice constants of the carbides with different alloying elements. The results show that the eutectic carbides precipitated contain MC and M 2 C distributed along the grain boundaries with dendrite feature. The composition and crystal structure analysis shows that the eutectic MC carbides contain VC and WC with a cubic and hexagonal crystal lattice structures respectively, while the eutectic M 2 C carbides predominantly contain V 2 C and Mo 2 C with orthorhombic and hexagonal crystal lattices respectively. The secondary carbides contain MC, M 2 C, M 7 C 3 formed along the grain boundaries and their sizes are much larger than the eutectic carbides ones. The secondary M 23 C 6 is much small (0.3-0.5μm) and is distributed dispersively inside the grain. Similar to the eutectic carbides, the secondary carbides also contain VC, WC, V 2 C, and Mo 2 C. M 7 C 3 is hexagonal (Fe,Cr) 7 C 3 , while M 23 C 6 is indexed to be in a cubic crystal form.