Influence of Mn content on the magnetic properties and microstructure in Fe–Mn–Mo alloys

The effects of the Mn content on the magnetic properties and microstructure of the Fe–Mn–Mo alloys have been investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction, and Mössbauer spectroscopy. Experiments reveal that two types of thermal-induced martensites, ɛ (h.c.p.) and α′ (b.c.c.) martensites, form in the as-quenched alloys and these transformations have athermal characters. ɛ and α′ martensites coexist in the Fe–Mn–Mo alloys with 13.4–17.2 wt%Mn content. However, the Mn content affects considerably the amount of martensites and the amount of α′ martensite decreases drastically while the amount of ɛ martensite increases with an increase in Mn content. Furthermore, only ɛ martensite appears in the case of 20.2 wt%Mn. Mössbauer spectra of the alloys reveal a paramagnetic character with a singlet for the γ (f.c.c.) austenite and ɛ martensite phases and a ferromagnetic character with a broad sextet for α′ martensite phase. With an increase in Mn content, the magnetic character of the Fe–Mn–Mo alloys changes and the ferromagnetic character disappears completely in the case of 20.2 wt%Mn.