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

Compositional dependence of the Neel transition temperature, T-N, structural stability, magnetic properties, and anomaly of resistivity, p, have been investigated in gamma-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 gamma --> epsilon --> alpha' martensitic transformation and lower the a martensitic transformation temperature M, or deformation-induced martensitic transformation temperature M-d, while an increase in Si content promotes the gamma --> epsilon martensitic transformation and increases the M-s and M-d temperature. Manganese raises T-N, decreases the susceptibility, x, and slightly increases the anomaly of electrical resistivity, rho. The temperature dependence of chi for Fe-Mn binary alloys shows a break at T-N and chi becomes almost independent of temperature above T-N. The effects of Cr on Z versus T and p versus T are similar to that of Mn but lowering T-N. With increasing Alor Si content, T-N decreases markedly; above T-N, the magnetic state of the alloys changes from Pauli-paramagnetism to the Curie-Weiss behavior, and the anomalous p increases rapidly, leading to a negative temperature coefficient below T-N. An empirical formula has been developed to express the compositional dependence of T-N in gamma-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 T-N and decreases chi and M-s. Adding up to 10 at.% Al to Fe-Mn based alloys strongly stabilizes the gamma phase and retains antiferromagnetism down to 4 K. Increasing the Ni content of Fe-Cr-Ni steels improves their stability relative to the alpha' martensitic transformation but induces a transition from the paramagnetic gamma-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. (C) 2002 Elsevier Science B. V. All rights reserved.