Compositional dependence of the Néel transition, structural stability, magnetic properties and electrical resistivity in Fe–Mn–Al–Cr–Si alloys

Compositional dependence of the Néel transition temperature, TN, structural stability, magnetic properties, and anomaly of resistivity, ρ, have been investigated in γ-Fe–Mn–Al–Cr–Si–C alloys. In the Fe–(20–32.5 at.%)Mn-based alloys, an increase in Mn, Al, Cr or C content will inhibit the γ→ε→α′ martensitic transformation and lower the ε martensitic transformation temperature Ms or deformation-induced martensitic transformation temperature Md, while an increase in Si content promotes the γ→ε martensitic transformation and increases the Ms and Md temperature. Manganese raises TN, decreases the susceptibility, χ, and slightly increases the anomaly of electrical resistivity, ρ. The temperature dependence of χ for Fe–Mn binary alloys shows a break at TN and χ becomes almost independent of temperature above TN. The effects of Cr on χ versus T and ρ versus T are similar to that of Mn but lowering TN. With increasing Al or Si content, TN decreases markedly; above TN, the magnetic state of the alloys changes from Pauli-paramagnetism to the Curie–Weiss behavior, and the anomalous ρ increases rapidly, leading to a negative temperature coefficient below TN. An empirical formula has been developed to express the compositional dependence of TN in γ-Fe–Mn–Al–Cr–Si alloys. The alloying elements that lower TN are in increasing order of severity, Cr, Al, Si and C. Manganese is the only element which both raises TN and decreases χ and Ms. Adding up to 10 at.% Al to Fe–Mn based alloys strongly stabilizes the γ phase and retains antiferromagnetism down to 4 K. Increasing the Ni content of Fe–Cr–Ni steels improves their stability relative to the α′ martensitic transformation but induces a transition from the paramagnetic γ-phase to the ferromagnetic one at very low temperatures. Alloying Fe–Mn based alloys with Al and Cr exhibits an excellent combination of FCC structural stability, corrosion resistance and antiferromagnetism down to liquid helium temperature. The present results are valuable for the design of cryogenic non-magnetic steels and certain functional Fe–Mn based alloys.