Effects of Mn, Al, and Cu on Austenite Stability and Corrosion Properties of High Cr-Equivalent Steels

Several Fe-based model alloys containing 15-28 wt.% Mn, 10-16 wt.% Cr, 0-5 wt.% Ni, 0-5 wt.% Al, and 0-3 wt.% Cu to obtain more economical corrosion-resistant steels were produced. The microstructural investigations showed that in the absence of Ni, even 28 wt.% of Mn failed to stabilize the austenite in the high Cr-equivalent alloys. An almost fully austenitic microstructure was developed in alloys comprising 5 wt.% Ni and 3 wt.% Cu. The potentiodynamic polarization and electrochemical impedance spectroscopy tests were performed in 3.5 wt.% NaCl solution. An alloy containing 28 wt.% Mn showed the lowest corrosion resistance (i(corr) approximate to 5.4 mu A/cm(2)), possibly because of the formation of less stable Mn oxides. In a 15 wt.% Mn steel, no satisfying corrosion resistance was obtained by 10 wt.% Cr and 5 wt.% Al (R-p approximate to 27 k Omega.cm(2)). Only 5 wt.% Ni enhanced the corrosion resistance, considerably. Alloys containing 16 wt.% Mn, 12 wt.% Cr, 3 wt.% Al, and 5 wt.% Ni with and without 3 wt. % Cu showed an R-p of similar to 525 and similar to 170 k Omega.cm(2), respectively. The Cr role was also crucial such that R-p for an alloy with a similar composition and 16 wt.% Cr reached similar to 700 k Omega.cm(2).