Effects of boron on microstructure and mechanical properties of Fe-6.5 wt.%Si alloy fabricated by directional solidification

摘要

Effects of boron additions on the microstructure, elemental distribution and tensile properties at an intermediate temperature of the Fe-6.5 wt%Si alloy fabricated by directional solidification were inves tigated. The results showed that the undercooling degree of the liquid phase at the frontier of solid-liquid interface was increased with boron additions, leading to significant refinement of the columnar grains of the alloy. When the boron content was increased from 0 to 0.058 wt.%, the width of the columnar grains was reduced from 2157 to 514 μm. Boron facilitated to homogenize silicon in the Fe-6.5 wt.%Si alloy because the solidification segregation level of silicon was decreased due to the inter action between boron and silicon. In the same range of boron content (0-0.058 wt%), the equilibrium partition coefficient of silicon was increased from 0.961 to 0.982. Meanwhile, both the strength and ductility of the Fe-6.5 wt.%Si alloy at 400 °C could be improved due to the boron addition. Compared with that of the alloy without boron, the ultimate tensile strength of the alloy containing 0.040 wt.% B was increased from 712 to 792 MPa and its elongation was further increased from 38.5 to 54.4%.