Effects of process variables in decarburization annealing of Fe-3%Si-0.3%C steel sheet on textures and magnetic properties

In Fe-3%Si-0.3%C steel sheet, a relatively strong //ND texture can evolve in the surface layer through the α→γ→α phase transformation in relatively low vacuum (4 Pa) for an annealing time of 10 min and at a cooling rate of 20 K/s. Oxidation of the steel sheet surface prevents the evolution of the //ND texture. However, vacuum-annealing under a vacuum pressure of 1.3×10 -3 Pa causes decarburization of the steel sheet, which suppresses oxidation of the steel sheet surface, and subsequent annealing in wet hydrogen of 363 K in dew points causes a columnar grain structure with the //ND texture. After the two-step-annealing (the vacuum annealing under a vacuum pressure of 1.3×10 -3 Pa and subsequent decarburizing annealing in wet hydrogen of 363 K in dew points), the decarburized steel sheet exhibits good soft magnetic properties in NO with 3%Si, W 15/50 (core loss at 1.5T and 50 Hz) = 2.47 W/kg and B 50 (magnetic flux density at 5000 A/m) = 1.71 T.