Iron-Manganese (Fe-Mn) Phase Diagram
In pure iron, the A4 (1394 °C) and A3 (912 °C) transformations take place at constant temperatures. If an element enters into solid solution in iron — forming in that way a binary alloy — each of these transformations are required by the Phase Rule to occur over a range of temperature.
Some elements, such as manganese, raise the A4 and lower the A3 transformation temperatures (Figure 1), increasing, in effect, the extent of the gamma (γ) field in the iron-carbon phase diagram.
Figure 1. Fe-Mn phase diagram shows which phases are to be expected at equilibrium for different combinations of manganese content and temperature. The Fe-Mn phase diagram was calculated with Thermo-Calc, coupled with PBIN thermodynamic database. The melting point of iron and manganese at the pressure of 101325 Pa is 1538 °C and 1246 °C, respectively.
The iron-manganese binary system has recently become a basis for a new class of metallic degradable biomaterials manufactured by powder metallurgy. An example is Fe-35Mn alloy (wt. %) which is aimed to be used for stent applications. A cast Fe-35Mn alloy can achieve a yield strength as high as 200 MPa and elongation at rupture up to 50 % (T. F. Volynova: Metal Sci. Heat Treat., 1984, 26, 476-482).
Alloying with more than 29 wt. % manganese provides a completely austenitic structure which exhibits antiferromagnetic behavior (A. Rabinkin: Calphad, 1979, 3, 77-84).
• The phase diagram of Iron-Manganese binary system
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