The Effect of Chromium Addition on the Microstructure Evolution and Mechanical Properties of Fe-4.5 Wt% B-Mo Alloy

Abstract

The inherent brittleness of primary M2B and the continuous network morphology of eutectic borides are the key factors leading to the toughness deficiency of hypereutectic Fe-B wear-resistant alloys. To effectively enhance the ductility of M2B and the morphology of eutectic structures, Cr and Mo elements have been introduced in Fe-4.5 B alloys, and the microstructure and mechanical properties have been systematically investigated. The results indicate that the Fe-B-Mo alloy mainly comprises M2B, α-Fe, and irregular Mo2FeB2 after adding Cr, while the Mo element maintains the intermittent characteristics of its eutectic structure. The increase of the Mo2FeB2 phase and its irregular growth mode interrupted the continuous network growth of the M2B phase and promoted it to transform into an isolated block structure. These changes result in an increase in the fracture toughness of the alloy, in which the enhancement of M2B toughness and the transformation of the eutectic structure play the predominant role in the improvement of alloy toughness. Furthermore, the irregular Mo2FeB2 phase effectively impedes crack propagation, thereby further enhancing the alloy's fracture toughness. Consequently, incorporating Cr and Mo constitutes an effective strategy for improving the toughness of hypereutectic Fe-B alloys.

Keywords: Fe-B-Mo alloys, Surfacing, M2B borides, Microscopic structure, Fracture toughness.