Ferritic Fe-Ni alloys for potential substitution of 2V-Permendur in telephone receivers

Magnetic and mechanical properties of ferretic Fe-Ni alloys containing 6-12 wt pct Ni have been investigated for potential substitution of high-cobalt 2V-Permendur currently used as a ring armature of a U-type telephone receiver. The soft magnetic properties of these alloys are significantly improved by heat treatment within the low temperature (α + γ) two-phase region, (Hc ∼ 1.2-2.7 Oe and \mu\max \sim 2000- 6000), even though the alloys decompose into a two-phase microstructure. The cause of the improvement is attributed to the relief of internal stress and annealing out of dislocations previously induced by the martensitic transformation that occurs during cooling. Magnetic, mechanlcal, and electrical properties of these alloys, as well as the acoustic performance of receivers using them, have been found to be comparable to those of 2V-Permendur.