Excellent enhancement of corrosion properties of Fe-9Al-30Mn-1.8C alloy in 3.5% NaCl and 10% HCl aqueous solutions using gas nitriding treatment

Abstract

The as-quenched Fe-9.0Al-30Mn-1.8C (in wt.%) alloy gas nitrided at 550 degrees C for 4 h show excellent corrosion resistance investigated in 3.5% NaCl and 10% HCl solutions. Owing to the high corrosion resistance components, the gas-nitrided layer consists mainly of AlN with a slight amount of Fe3N and Fe4N identified by grazing incidence X-ray diffraction technique. Therefore, the pitting potential and corrosion potential of the nitrided sample are + 1860 mV and + 30 mV, respectively. Surprisingly, it is worthy to be pointed out that the nitrided and then tensile-tested alloy reveals very shallow in fracture depth and the excellent lattice coherence is shown between the nitrided layer and the substrate. Moreover, due to the extremely high nitrogen concentration (about 17-18 wt.%) at stretched surface, the corrosion resistance of present gas-nitrided and then tensile-tested alloy is superior to those optimally gas-nitrided or plasma-nitrided high-strength alloy steels, as well as martensitic stainless steels. The nitrided and then stretched alloy still retains a satisfactory corrosion resistance (E-pit = + 890 mV; E-corr = + 10 mV). Furthermore, only nanoscale-size pits were observed on the corroded surface after being immersed in 10% HCl for 24 h. (C) 2015 Elsevier B.V. All rights reserved.