Influence of nanoprecipitates, solid solution and grain size on the magnetic and electrical properties of Fe-P-Si alloys

Abstract

Fe-P-Si alloys with two levels of phosphorous (0.11 and 0.33 wt%) were prepared through the wrought alloy route. The as-cast alloys were forged and rolled at high temperature (>1000 °C) followed by stack hot rolling up to ~0.5 mm thickness. The alloys were further solutionized at 1000 °C/1h followed by aging at 500 °C/30 min and characterized for microstructural, magnetic and electrical properties. X-ray diffraction studies revealed that the alloys are of single phase α-Fe. From electron backscattered diffraction (EBSD) analysis, it was inferred that the grains were equiaxed with no retained austenite phase in the alloys. Transmission electron microscopic (TEM) and Electron Energy Loss Spectroscopy (EELS) showed the presence of Fe3P/Fe3(P,Si) nanoprecipitates whose volume fraction increased from 1.17% to 2.08% as P content (wt.%) of the alloys increased from 0.11 to 0.33%, with a corresponding increase in precipitates size from 1.7 nm to 2.6 nm. To rationalize the influence of various microstructural parameters on the magnetic and electrical properties of the alloys, we have used the existing theoretical models. As a result, it is now possible to estimate the relative contributions of the microstructural features to the various electrical and magnetic properties. Low core loss (~186 W/kg) combined with low coercivity (47 A/m) and high saturation magnetization (2.1 T) obtained in high P content (0.33%) Fe-P-Si alloy makes it a promising material for automotive applications.