Microstructure and crystallography of borides and mechanical properties of Fe-B-C-Cr-Al alloys

The solidification microstructure, crystallography of eutectic precipitations and mechanical properties of high boron steel with various aluminium and chromium concentrations have been investigated extensively in the present study, as the foundation of the further analysis about the corrosion and abrasion properties at elevated temperature. The experiment results indicate that the as-cast microstructures of test alloys mainly consist of a dendritic matrix with many interdendritic precipitations. The Fe-B binary alloy is mainly composed of ferrite, Fe₂B and pearlite and the Fe-B-Al ternary alloy consists of α-(Fe, Al) solid solution, Fe₂B and Fe₃AlC_0.5. When aluminium and chromium elements are added synchronously, the as-cast microstructure changes to α-(Fe, Al, Cr) solid solution, (Fe, Cr)₂B boride, M₇(C, B)₃ and M₂₃(C, B)₆ borocarbides. Moreover, the nucleation and growth of M₇(C, B)₃ borocarbide is adhere to (Fe, Cr)₂B boride because of an interphase match between crystal plane (101(-) 0) of M₇(C, B)₃ and (010) of Cr-rich (Fe, Cr)₂B. Alloy Fe-1.46 wt. % B-0.22 wt. % C-11.92wt. % Cr-8.73 wt. % Al shows the highest impact toughness value. The main fracture mode is brittle fracture of boride and tough fracture of matrix.