1. With increasing carbon concentrations in Alnico alloys the effective number of conduction electrons increases, which increases the thermal stability of γ phase. A single-phase structure cannot be obtained with over 0.05% C. 2. The precipitation of strongly magnetic phase from the supercooled solid solution occurs at 620–880°. The presence of γ phase in the original structure, the amount of which increases with the carbon content of the alloy, inhibits the formation of high-coercivity structure, and impairs the magnetic properties. 3. With increasing amounts of carbon the temperature of the αγ→γ polymorphous transformation shifts to higher temperatures — from 480° with 0.005% C to 520° with 0.2% C.