Nanoprecipitation behavior and resultant mechanical and magnetic properties in Fe–Si–Ni–Al–Mn high strength non-oriented silicon steel

Abstract

Low mismatch and low energy interface between precipitates and ferrite matrix was adopted to promote the precipitation of high density of uniformly dispersed coherent NiAl phase in the silicon steel, aiming to improve strength to meet the requirement of drive motor. The precipitation mechanism of NiAl and its influence on magnetic and mechanical properties of silicon steel were studied. The theoretical lattice mismatch between precipitation and matrix was 0.72%, and a new high strength non-oriented silicon steel reinforced by B2 structure NiAl precipitation with a volume content of 1.73% and an average size of 15 nm was prepared. The uniformity of precipitation size and minimization of interface energy remarkably reduced the driving force for NiAl precipitation and hindered the Ostwald ripening. The texture of annealed silicon steel was characterized by strong α* fiber with a peak at {411}<148> and a moderate γ fiber texture with a peak at {111}<110>. With increase in aging time (from 0 h to 16 h), the strength of silicon steel increased to peak values then decreased and the magnetic properties decreased slightly. The nano-scale NiAl precipitation had little effect on coercivity and hysteresis loss of silicon steel while improving the strength of silicon steel, P10/400 and P10/1000, of silicon steel was as low as 21.7 W/kg and 93.3 W/kg, respectively in the peak-aged condition (at 550 °C for 4 h), and the yield strength was 802 MPa. Thus, it is underscored that using NiAl precipitation as strengthening phase improves the mechanical properties of silicon steel without excessively deteriorating the magnetic properties.