BORIDES IN MICROCRYSTALLINE FE-CR-MO-B-SI ALLOYS

The formation and transformation of borides during melt-quenching and subsequent annealing in Fe-Cr-Mo-B-Si microcrystalline alloys was systematically investigated. Metastable M3B forms during melt-quenching and soon disappears when annealing is carried out. During annealing, M2B and M3B2 precipitate from the supersaturated alpha-Fe solid solution. As the annealing temperature is raised, M2B gradually transforms from an Fe2B-dominated state to a Cr2B-dominated state, the remaining Fe2B coexisting with Cr2B in the form of stacking faults; meanwhile, there is a gradual increase in the Mo concentration in M3B2, together with the continuous increase in the lattice parameters of M3B2. The pre-formed M2B and M3B2 further transform into M23B6 within a narrow temperature range around 925-degrees-C.