Magnetic Properties of Fe-Cr-C and Fe-Cr-C-Ni Alloys

Structures and magnetic properties of Fe-17.5mass%Cr-0.5mass%C and Fe-17.5mass%Cr-0.5mass%C-zmass%Ni(z=l-2.4) alloys were studied. The Fe-17.5mass%Cr-0.5mass%C alloy consisted of ferromagnetic α and M23C6 phases when annealed at temperatures below the A3 temperature, and showed good soft magnetic properties with a high relative permeability. On the other hand, the solution treatment of the alloy resulted in the formation of paramagnetic γ phase with a low relative permeability. However, the relative permeability of the alloy increased as the temperature decreased. This was due to the transformation from the γ phase to the ferromagnetic α' phase. The addition of Ni to the Fe-17.5mass%Cr-0.5mass%C alloy lowered the transformation temperature, Ms, and stabilized the paramagnetic γ phase. The annealing of the Fe-17.5mass%Cr-0.5mass%C-zmass%Ni alloys also resulted in theformation of ferromagnetic α and M23C6 phases, and showed soft magnetic properties. However, the soft magnetic properties of the Fe-17.5mass%Cr-0.5mass%C-zmass%Ni alloys were slightly inferior to those of the Fe-17.5mass%Cr-0.5mass%C alloy, mainly due to the smaller grain size of the Fe-17.5mass%Cr-0.5mass%C-zmass%Ni alloys. It was found that the soft magnetic properties of the Fe-17.5mass%Cr-0.5mass%C-zmass%Ni alloys were significantly dependent on the residual stress. The soft magnetic properties of the optimally annealed Fe-17.5mass%Cr-0.5mass%C-zmass%Ni alloys were superior to those of the commercial Fe-18mass%Cr-8mass%Ni alloy.