Microstructure evolution, tensile properties and deformation mechanism of Fe-6.5 wt.% Si steel doped with yttrium

Abstract

Fe-6.5 wt.% Si steels doped with different contents of yttrium were fabricated by vacuum induction melting (VIM), forging, hot rolling and annealing. The microstructure evolution, ordered degree, tensile properties and deformation mechanism were investigated. The results showed that the amount of high-melting precipitates enriched in yttrium increased with the content of yttrium increasing. The solidification, hot rolling and annealing microstructures were refined due to the elevated nucleation rate and the effect of microstructure heredity. The steel containing the highest content of yttrium exhibited the highest tensile ductility and the most developed dimple patterns. Deformation bands appeared in the tensile microstructures at 400 °C. Most of the deformation bands in the steels without yttrium and doped with the intermediate content of yttrium possessed the special {112}<111> twinning mis-orientation with the matrix, implying the cooperation of the deformation twinning mechanism. Nevertheless, the smooth stress-strain curves and the absence of the deformation bands indicate the predominance of the dislocation sliding mechanism during the tensile test at 500 °C. The present work manifested that the doping of yttrium in Fe-6.5 wt.% Si steel could be utilized to raise the intermediate-temperature tensile ductility through purifying the matrix, refining the microstructure and reducing the ordered degree.