Refinement of Microstructure and Enhancement of Wear Resistance of Ni–Cr Cast Iron by NbC

Abstract

This article investigates the influence of niobium addition on the microstructure and properties of Ni–Cr cast iron. In situ observations and analysis of phase precipitation during solidification are conducted through a high‐temperature laser scanning confocal microscope and Thermo‐Calc software. The refining mechanism of the microstructure and the enhancement of wear resistance by NbC are explored. The results indicate that with an increase in Nb content, the precipitation temperature of NbC particles gradually rises. When the niobium content exceeds 0.2%, NbC becomes the first precipitated phase during the solidification of the liquid phase. NbC particles can serve as heterogeneous nucleus for austenite, refining the grain structure of Ni–Cr cast iron. The existence of NbC particles within the grain impedes the elongation of martensite and bainite bundles while providing additional nucleation sites to accelerate the phase transformation. The grain refinement and the obstructive influence of NbC particles collectively induce a more disordered bainitic structure. Moreover, the exceptional hardness of NbC particles effectively safeguards the matrix from abrasion, consequently enhancing the wear resistance of Ni–Cr cast iron.