Soft magnetism in nitrided Fe93Ni4Cr3 and Fe94Ni4Ti2 cold-rolled alloys

The magnetic properties in relation with the structure of nitrided cold-rolled Fe93Ni4Cr3 and Fe94Ni4Ti2 were studied. Various low-temperature nitriding treatments were applied in order to obtain soft magnetic materials. We show that the magnetic anisotropy depends sensitively on the nitrogen content. The lowest value of the coercive force, HC=40 A/m was obtained for samples containing TiN precipitates. For the Cr contained samples, a concentration of 14% (Fe-Ni)4N (γ')-phase decreases HC below values corresponding to the samples containing only CrN precipitates. We discuss the influence of the texture on the magnetic properties of samples containing only BCC α'-phase, a mixture of α'+γ'-phase, or samples which have been cycled through the ε-phase. Although grain refinement is observed after cycling and an almost random orientation of the grains is obtained, the magnetic properties do not improve. This is due to the fact the grain size is still too large to lead to averaging out of the magnetic anisotropy. Moreover, the stress/strain distribution developed during the treatments hampers domain wall motion and leads to an increased coercivity