Deformation twinning feature and its effects on significant enhancement of tensile ductility in columnar-grained Fe-6.5wt.%Si alloy at intermediate temperatures

► Tensile ductility of the Fe-6.5wt.%Si alloy with columnar grains was enhanced. ► Elongation of columnar-grained specimens was 6.6%, 51.1%, 51.3% at 300, 400, 500 °C. ► Elongation of equiaxed-grained specimens was 2.9%, 25.3%, 28.1% at 300, 400, 500 °C. ► The enhancement was mainly ascribed to the formation of a large amount of twins.