Exploring the effective way to improve Fe2B's toughness has always been the hot topic in the researches of Fe-B wear resistant alloys.In the present work,the effects of Cr on the microstructure,mechanical properties and lattice structure of directional Fe2B have been investigated.The affecting mechanism of Cr addition has been discussed according to the experimental and first-principle calculation analysis.The results show Cr addition can improve the toughness of directional Fe2B on the longitudinal sections perpendicular to (002) crystal plane,without sacrificing the hardness distinctly.The toughening mecha-nism by Cr substitution has been revealed:Cr addition enriches the electron density between the B atoms along[002]direction,contributing to the shrinkage of the bond length and the enhancement of the bond strength of B—B bonds.The obtained results provide insight into the intrinsic reason for toughening Fe2B by Cr doping.