Magnetic ageing characteristics of low silicon electrical steels

Abstract

Increase is core-loss during the service life of soft magnetic materials is known as ‘magnetic ageing’. This is essentially due to the enhancement of coercive force owing to interaction of domain walls with precipitated carbide particles. Although the effect of silicon at 3 wt% is known, magnetic ageing studies in low-silicon electrical steels are few. This investigation studies through coercive force changes during isothermal ageing the magnetic ageing behaviour of three grades of steel with 0.3, 1.1 and 1.5 wt% silicon, respectively. For steels with 1.1 and 1.5 wt% silicon coercive force increase was slight even after prolonged ageing at low temperatures and initially at higher temperatures. Appreciable magnetic ageing was detected in these two grades at higher temperatures and in the steel with 0.3% silicon at all ageing temperatures. In all three steels the peak increase was larger at lower temperatures and the time required for the peak was longer. While the 0.3% Si-steel indicated sharp coercive force peaks at all ageing temperatures, the behaviour was considerably different for the other two grades. The observations are rationalized on the basis of the type, density and growth rate of precipitated carbides.