Effect of solutes on the formation of primary carbides during solidification of hypereutectic high chromium cast irons through thermodynamic modeling

The present work investigates the effect of different solutes on the formation of primary carbides in high chromium cast irons (HCCI) through thermodynamic modeling. Growth restriction factor, Q, for the growth of primary carbide in a multicomponent HCCI is evaluated with the assistance of the CALPHAD method. Thermodynamic modeling indicates that modification of the primary carbide by growth restriction through solute addition is ineffective because commonly used solutes in ferrous alloys such as Ti, Nb, and Mn, form carbides or other intermetallic compounds in the melt prior to the formation of primary carbide and non-reactive solutes, such as Cu, Ni, Si, and Co, cannot lead to the formation of sufficient constitutional undercooling zone at the front of the growing carbide to enable the new nucleation event. Hence, it is suggested that external addition or in-situ formation of inoculants to promote heterogeneous nucleation of primary carbides is a more effective approach to refine or modify the primary carbides in HCCIs.