The Effect of Cr Addition on the Microstructure Evolution and Mechanical Properties of Fe–B–Mo Alloy

The limited fracture toughness of hypereutectic Fe–B alloy is due to the inherent brittleness of the primary Fe 2 B phase and its continuous eutectic network. To regulate the toughness and morphology of Fe 2 B, this study adopts a Cr/Mo synergistic alloying strategy to control the phase characteristics and microstructure, and systematically investigates the influence of elements on the microstructure evolution and mechanical properties. The surfacing alloy is mainly composed of Fe 2 B, α‐Fe, and dispersed Mo 2 FeB 2 phases. When the Mo content is 4 wt%, the eutectic structure is reconstructed because the irregular growth of Mo 2 FeB 2 disrupts the continuity of the eutectic network, forming isolated blocks that hinder crack propagation. Although 5 wt% Cr slightly improves the fracture toughness, 20 wt% Cr significantly enhances the fracture toughness due to the orthogonal Cr 2 B phase transition of tetragonal Fe 2 B, with a fracture toughness of ≈21.7 Mpa m 1/2 . At the same time, the alloy reaches a maximum hardness of 65.6 HRC, and the fracture surface exhibits ductility characteristics. This Cr/Mo synergistic effect provides a new toughening method for hypereutectic Fe–B alloys.