Effect of Ti-V-Nb-Mo addition on microstructure of high chromium cast iron

The effects of trace additions of multi-alloying elements (Ti, Nb, V, Mo) on carbides precipitation and as-cast microstructure of eutectic high chromium cast iron containing 2.85wt.% C and 31.0wt.% Cr were investigated from thermodynamic and kinetic considerations. The thermodynamic calculations show that Ti and Nb exist in the multi-alloying system in the forms of TiC and NbC. The formation of VC during the solidification is not feasible from the thermodynamic consideration. XRD analysis shows that the V exists in alloy compounds (VCr2C2, VCrFe8). The first precipitated high melting point particles (TiC, NbC) can act as the heterogeneous substrate of M7C3 carbides, which results in significant refinement of the M7C3 carbides. After the addition of alloying elements, C atom diffusion is hindered due to the strong affinities of the strong carbide forming elements for carbon, which decreases the growth rate of carbides. The combined roles of the increase of nucleation rate and the decrease of carbides growth rate lead to the finer microstructure.