Growth characteristics of primary M(7)C(3) carbide in hypereutectic Fe-Cr-C alloy

The microstructure of the hypereutectic Fe-Cr-C alloy is observed by optical microscopy (OM). The initial growth morphology, the crystallographic structure, the semi-molten morphology and the stacking faults of the primary M(7)C(3) carbide are observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The in-suit growth process of the primary M(7)C(3) carbide was observed by confocal laser microscope (CLM). It is found that the primary M(7)C(3) carbide in hypereutectic Fe-Cr-C alloy is irregular polygonal shape with several hollows in the center and gaps on the edge. Some primary M(7)C(3) carbides are formed by layers of shell or/and consist of multiple parts. In the initial growth period, the primary M(7)C(3) carbide forms protrusion parallel to {[Image: see text]} crystal planes. The extending and revolving protrusion forms the carbide shell. The electron backscattered diffraction (EBSD) maps show that the primary M(7)C(3) carbide consists of multiple parts. The semi-molten M(7)C(3) carbide contains unmelted shell and several small-scale carbides inside, which further proves that the primary M(7)C(3) carbide is not an overall block. It is believed that the coalescence of the primary M(7)C(3) carbides is ascribed to the growing condition of the protrusion and the gap filling process.