In-situ observation of growth characteristics of M7C3 carbides in hypoeutectic Fe-Cr-C alloys

Carbides with high hardness in the matrix have been shown to improve erosive wear characteristics in Fe-Cr-C alloys. In-situ experiments to observe the characteristics of nucleation and growth of carbides are important for an in-depth understanding of the formation mechanism of carbides. In this paper, the in-situ, real-time observation of phase transformation during melting-solidification of smelted hypoeutectic Fe-15wt%Cr-1.5.wt%C alloys was carried out using Confocal Laser Scanning Microscope (CLSM). The morphology and elements distribution of alloy specimens after in-situ observation were further characterized by Field Emission Scanning Electron Microscope (FE-SEM) and Energy Dispersive Spectrometer (EDS), respectively. The phase composition of the alloy specimens was verified by X-ray Diffractometry (XRD). Results show that phases in the alloy underwent different phase transformations and M7C3 carbides exhibited different states at different temperatures. Different holding times (1 s, 60 s, 300 s) at 1273 K also resulted in the formation of M7C3 carbides with different morphologies. The ejected of Cr and C elements from the austenite into the liquid phase provided the concentration requirement for the formation of M7C3 carbides. Lamellar eutectic carbides, as well as rosette-like carbides, required a larger growth space between austenite dendrites to form compared to rod-like and plate-like carbides. Finally, a comprehensive summary of the growth mechanisms of M7C3 carbides with different morphologies was presented based on in-situ experiments and SEM analysis, which provided a more comprehensive and vivid perspective on the formation and growth of M7C3 carbides.