Effect of Phosphorus on the Magnetic Properties of Non-oriented Electrical Steel

Abstract

The addition of Si to electrical steel is used to reduce the core losses, whichare a consequence of induced eddy currents. As the electrical resistivityincreases by the addition of Si-the induced eddy current losses are reduced. P isalso very effectively increases the electrical resistivity of α-Fe. However theeffect of P on the magnetic properties of electrical steels has not been studied indetail. The effect of P as a alloying addition for a development of a new type ofnon-oriented electrical steel was therefore investigated in the presentdissertation research.P is known to segregate to grain boundaries in steel and this has beenreported cause brittle fracture during deformation. In order to utilize P-addedsteels, an in depth analysis was needed of the deformation behavior of P-addedsteels in production conditions. In the present study, the hot workability of theFe-2%Si steels with varying P contents was characterized by the hightemperature compression tests. The activation energies for plastic flow at hightemperature were found to increase with increasing P content. In additiondynamic recrystallization was suppressed in Fe-2% Si-0.15% P steel.The intrinsic magnetic properties of a P-added 2% Si steels wereinvestigated. The electrical resistivity values increased sharply with increasing P content up to 0.1% in both Fe-0.05% Si and Fe-2% Si steels. The magneticinduction values decreased and the coercivity values increased with increasing Pcontent.The effect of P on the grain boundary migration was also investigated. Theactivation energy for grain boundary migration increased due to 0.1% P additionin Fe-Si steels. The effect of P on an increase of the activation energy for grainboundary migration was however reduced by addition of 20 ppm B. Abnormalgrain growth by the solute drag effect of P was observed in Fe-3%Si-0.1%Psteel annealed at 800℃ for 150 min and at 900℃ for 10 min. The grain growthof grains having near {111}<112> orientation was suppressed whereas the graingrowth of the {112}<361> oriented grains was clearly accelerated. The additionof B was found to weaken the effect of P on both of the grain growth andcrystallographic texture evolution.A decrease of anomalous losses and an increase of hysteresis lossesoccurred in the Fe-2%Si-0.05%P steel. Both types of magnetic losses increasedin the Fe-2%Si-0.10%P steel. Small secondary domains, so-called spikes,formed near at precipitates were observed in Fe-2%Si-0.10% P steel. A complexmagnetic domain structure was created in Fe-2%Si-0.05%P steel due to theinteraction of the domain wall with the fine P precipitates.