Relation between Magnetic and Mechanical Properties of the Transformation-Type Magnet Alloys

On the workability of permanent magnet materials-I

Abstract

The materials for permanent magnets exhibit high coercive force and residual induction. The coercive force is called magnetic hardness and materials with high coercive force are in general mechanically hard. The study on the relation between magnetic and mechanical properties of materials for permanent magnets is important of commercial fabrication. The materials now in use are classified metallographically into some groups and these workability is studied. In this paper, quench-hardening magnet steels, γ-α transformation magnet alloys and order-disorder transformation magnet alloys are studied.
In quench-hardening magnet steels, coercive force is proportional to square root of the volume of retained austenite and the best valne of magnet is obtained, when fine particles of martensite needles are distributed in the retained austenite and the ratio of martensite to austenite is 2 to 1. The magnet steels are mechanically hard in the quenched state, but are machinable in the annealed state withont martensite structure.
In the γ-α transformation magnet alloys, γ phase transforms to α phase during cold-working and some α phase is converted to γ during aging. When γ is dispersed highly in α, the coercive force of materials increases. In the simple γ-α transformation alloys, mechanical hardness decreases lineally with the precipitation of γ. In the γ-α transformation alloys with meta-stable order structure, the mechanical hardness increases rapidly with transformation of disorder α to meta-stable order α', but depends hardly upon the precipitation of γ. These alloys are necessary to machine after cold working and ageing.
In order-disorder transformation magnet alloys, coercive force increases remarkably during aging, bnt mechanical hardness slightly. The workability of the disordered state is easier than ordered state.
The workable state of transformation type magnet alloys is a disordered γ phase- and when this disordered γ phase exists in room temperature, the coldworking is possible.