Corrosion resistance and microstructural evaluation of the chromized coating process in a dual phase FeMnAlCr alloy

Chromizing is a suitable method for coating development for high temperature surface protection, corrosion and wear resistance. A homogenized dual phase Fe–24%Mn–8.3%Al–5%Cr–0.38%Si–0.34%Mo–0.45%C cast alloy was chromized with a pack cementation process at 1000 °C for 1–16 h. A chromized surface layer and an adjacent processing-related ferrite layer ranging from 80 to 100 μm in depth were formed. The thickness of the chromized layer X vs. the coating time t obeys the parabolic law: X=Kt, where K is evaluated to be 5.89 μm/h. The primary phase on the chromized surface is (Cr, Fe)2N1−x and the rest is Cr23C6, while the internal part of chromized layer is Cr7C3 phase. An appreciable increase of the surface hardness ranging from 2015 to 2458 HK is achieved due to the formation of chromium carbide layer. A significant improvement of the corrosion resistance in 3.5 wt.% NaCl aqueous solution is obtained. Chromized specimens exhibit only one-tenth weight loss compared to uncoated specimens when immersed in 90% Na2SO4 and 10% NaCl molten salt at 877 °C for 48 h.