Thermal stability of primary carbides and carbonitrides in two cast Ni-base superalloys

Thermal stability of primary MC carbide and M(CN) carbonitride in K452 and K446 alloys is investigated. In K452 alloy, primary MC is very unstable relative to M(CN) for the former contains a higher content of the weakeners (W and Mo) than the latter. The ratios of element contents (at.%) (W + Mo)/Cr, (W + Mo)/(Ti + Nb) and Nb/Ti are three important parameters, which together determine the thermal stability of primary MC. Also, primary MC degeneration plays an important role in the microstructural instability of K452 and K446 alloys.