Metallurgy and Magnetic Properties of an Fe-Co-V Alloy

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Abstract
A comprehensive study of the Fe-49% Co-2% V alloy has revealed many new aspects of the metallography of the alloy and led to a better understanding of its mechanical and magnetic properties. Results of the study necessitate revision of previous reports on the metallography by Greiner and Ellis and Köster and Schmidt. In addition to the well-known phase transformation of γ(fcc) to α(bcc) and the ordering of the αphase, a martensitic transformation has been established. The rapid kinetics of the γ→α transformation can be suppressed by drastic quenching in favor of a diffusionless transformation. Martensite is a metastable bcc structure which decomposes slowly into ordered α at intermediate temperatures. Ordering of the α phase is accompanied by pronounced grain refining. X-ray diffraction studies, elevated temperature measurements of saturation, and metallographic examination have not, however, confirmed the decomposition of the ordered α phase suggested by Greiner and Elli. The problem of brittleness has been broadly investigated. Cleavage fracture is a major cause of brittleness. Other causes include the gaseous (hydrogen and oxygen) embrittlement at grain boundaries and the cracking at the incoherent interface between the α phase and martensite. Unless specially treated, all bcc constituents, including disordered α, are inherently susceptible to cleavage fracture. The effect of order on the susceptibility to cleavage fracture and the multiple functions of quenching in the attainment of ductility have been elucidated in terms of current theories of cleavage fracture and lattice imperfections. The main purpose of quenching is to produce a martensitic structure. Only when a ductile matrix has been prepared, can ordering exert an adverse effect on the ductility of the alloy. Measurements of saturation magnetic moment at elevated temperatures disclose a 2% increase caused by ordering. Room-temperature magnetization curves are compared for different microstructures. The electronic configuration outside the argon core of vanadium atoms is discussed in relation to the composition variation of the average magnetic moment of Fe-Co-V alloys.

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