Effects of Nb on the Microstructure and Properties of Ti-Added Hypereutectic High-Cr Cast Iron

Effects of Nb on the microstructure and properties of Ti-added hypereutectic high-Cr cast iron were studied. With the addition of Nb, a new phase (Nb,Ti)C was formed. The microstructure analysis revealed that the amount of primary carbides was decreased from 18.6 to 8.8% and the primary and eutectic carbides were greatly refined. The decrease in the amount of primary carbides was attributed with the shrinking of primary M₇C₃ phase zone in the phase diagram, while the refinement of primary carbides was attributed to the heterogeneous nucleus of (Nb,Ti)C phase for the primary M₇C₃ carbides. The macrohardness of the alloy increased from 60.8 to 63.5HRC, and the impact toughness increased from 3.8 to 5.2 J cm⁻². Furthermore, the wear resistance was enhanced with the addition of Nb due to the formation of hard (Nb,Ti)C carbides.