NEMARCO project: Chemical Composition Effects on the Microstructure and Hot Hardness of NiCrSiFeB Self-Fluxing Alloys Manufactured via Gravity Casting

Ni-Cr-Si-Fe-B self-fluxing alloys are commonly used in hardfacing applications; in addition,

they are subjected to conditions of wear, corrosion, and high temperatures, but are not used in

casting applications. In this work, gravity casting is presented as a potential manufacturing route

for these alloys. Three alloys with different chemical compositions were investigated with a focus

on microstructure characterization, solidification path, and strengthening mechanisms. Phases and

precipitates were characterized using a field emission scanning electron microscope employing

energy-dispersive X-ray spectroscopy, wavelength dispersive spectroscopy, and electron backscatter

diffraction. Nano- and microhardness indentations were performed at different phases to understand

their contribution to the overall hardness of the studied alloys. Hardness measurements were

performed at room temperature and high temperature (650 C). The borides and carbides were

the hardest phases in the microstructure, thus contributing significantly to the overall hardness of

the alloys. Additional hardening was provided by the presence of hard Ni3B eutectics; however,

there was also a small contribution from the solid solution hardening of the  -Ni dendrites in the

high-alloy-grade sample. The amount and size of the different phases and precipitates depended

mainly on the contents of the Cr, C, and B of the alloy.