Microstructure evolution and mechanical properties of Fe–Cr–B alloys with varying Mo additions

Abstract

The continuously net-like morphology of borides accounts for the poor toughness of Fe–Cr–B wear-resistant alloys. To effectively modify the morphology of Fe2B, Mo element has been introduced in Fe–Cr–B alloys, and the microstructure evolution and mechanical properties have been systematically investigated. The results show Fe–Cr–B alloys are mainly composed of martensite, M2B, M23(B, C)6 and lamellar M3B2 after Mo addition. With the increase of Mo addition, the content of M3B2 increases gradually while that of M23(B, C)6 increases firstly and then decreases. Consequently, the net-like structure of M2B can be effectively broken to acquire the isolated bulk-like morphology, which is mainly attributed to the growth inhibition effect of lamellar structure M3B2. In addition, the hardness varies depending on the volume fraction of borides. However, the fracture toughness of Fe–Cr–B alloy can be dramatically improved by 34.3% with Mo addition increasing from 1 to 4%. Grain morphology modification of M2B plays the predominant role in the toughness improvement because the crack propagation path can be blocked. Furthermore, the lamellar M3B2 structure can effectively hinder the cracking propagation so as to improve the alloy's fracture toughness. Mo addition has been proved to be an effective way to modify the grain morphology of M2B hard phase.