Solidified Microstructure of Wear-Resistant Fe-Cr-C-B Overlays

Iron-based alloy overlays are widely utilized in industry to extend the service life of components subjected to wear and corrosion attack. Welding is an overlay process commonly employed because of its low cost and high efficiency. The microstructure of an as-welded chromium carbide overlay and a new Fe-Cr-C-B overlay containing multiple alloying elements has been characterized by optical microscopy, scanning electron microscopy, X-ray diffraction, and electron backscatter diffraction (EBSD). The microstructure of the chromium carbide overlay consists of large M7X3 primary carbides and austenite and carbide eutectic phases. The microstructure of the new overlay consists of granular MX-type primary carbide (M = Nb, Ti, Mo; X = C and B), dendritic d-ferrite/austenite, eutectic phases of austenite and M2B boride (M = Fe and Cr). The austenite portion of the microstructure has been subsequently transformed into martensite and retained austenite. The fine MX-type hard particles and refined eutectic and matrix microstructure lead to the high hardness of the overlay. The non-equilibrium solidification process for the complex microstructure is discussed using ThermoCalc.