Strong and ductile Fe-24Mn-3Cr alloy resistant against erosion-corrosion

Abstract

The ternary-based Fe-24Mn-3Cr alloy has superior mechanical properties based on an attractive combination of high strength and ductility, with long-term environmental stability in highly corrosive environments compared to conventional ferritic steel alloys. This study reports that the environmental instability caused by the rapid electrochemical corrosion kinetics on the surface of conventional high Mn-bearing ferrous alloys could be overcome by a combination of high Mn–low Cr-balanced Fe and their synergistic interactions. In contrast to Cr-free Mn-bearing alloys, the high Mn–low Cr-bearing alloy showed comparatively lower corrosion kinetic parameters, without a continuously increasing trend, and higher polarization resistance according to electrochemical polarization and impedance spectroscopy measurements. Moreover, the rate of degradation caused by erosion–corrosion synergistic interaction under erosion–corrosion dynamic flow conditions was the lowest in the high Mn–low Cr-bearing alloy. These surface-inhibiting characteristics of the alloy were attributed primarily to the formation of a bilayer scale structure consisting of inner α-Fe2−xCrxO3/outer FexMn3−xO4 on the surface.

Long-Term Corrosion Behavior of Strong and Ductile High Mn-Low Cr Steel in Acidic Aqueous Environments

“…This is clearly different from the results obtained under a neutral environment, which showed rapid formation kinetics of the corrosion scale [1]. At the early immersion stages, the much higher icorr, and lower Rct and Rscale of the 24Mn3Cr sample, presented in the previous section, can be understood by the slower formation kinetics of α-Fe2−xCrxO3, known as an effective barrier against further corrosion [1,26]. With a prolonged immersion (28 days, Figure 6 and Table 5), however, the sample surface was fully covered with the inner layer of the (Fe,Cr)-enriched scale.…”

“…ple surface was not covered uniformly with the (Fe,Cr)-enriched oxide (Table 4), which was characterized previously as α-Fe2−xCrxO3, [1]. This is clearly different from the results obtained under a neutral environment, which showed rapid formation kinetics of the corrosion scale [1].…”

“…Recently, the development of ternary-based austenitic steel alloys (Fe 1−x−y Mn x Cr y with y << x << 1 and lower C concentrations) with attractive mechanical properties, an inhibiting nature in relation to hydrogen penetration, and erosion–corrosion resistance, were reported [ 1 , 2 , 3 ]. Despite the intrinsic weakness arising from their higher Mn concentrations (i.e., the standard reduction potential of Mn (−1.18 V) is much lower than that of Fe (−0.447 V) [ 4 , 5 ]), their long-term corrosion resistance is much higher than conventional API (American petroleum institute)-grade low-C steel and is even comparable to 9% Ni steel in a neutral aqueous environment.…”

“…Despite the intrinsic weakness arising from their higher Mn concentrations (i.e., the standard reduction potential of Mn (−1.18 V) is much lower than that of Fe (−0.447 V) [ 4 , 5 ]), their long-term corrosion resistance is much higher than conventional API (American petroleum institute)-grade low-C steel and is even comparable to 9% Ni steel in a neutral aqueous environment. A previous study [ 1 ] revealed that their superior resistance to the dynamic flowing erosion–corrosion as well as static corrosion was attributed primarily to the formation of an (Fe,Cr)-enriched oxide scale (i.e., α-Fe 2 -xCr x O 3 ) with an inhibiting nature on the surface. In 9% Ni steel, the higher corrosion resistance is caused mainly by the formation of an oxide scale composed of Ni x Fe 3 -xO 4 and NiO/Ni 2 O 3 on the surface [ 1 , 6 , 7 ].…”

“…A previous study [ 1 ] revealed that their superior resistance to the dynamic flowing erosion–corrosion as well as static corrosion was attributed primarily to the formation of an (Fe,Cr)-enriched oxide scale (i.e., α-Fe 2 -xCr x O 3 ) with an inhibiting nature on the surface. In 9% Ni steel, the higher corrosion resistance is caused mainly by the formation of an oxide scale composed of Ni x Fe 3 -xO 4 and NiO/Ni 2 O 3 on the surface [ 1 , 6 , 7 ]. However, these surface characteristics can only be manifested under a neutral aqueous environment.…”