Corrosion Resistance of 00Cr25Ni22Mo2N (2RE69) Austenitic Chromium-Nickel Steel
Austenitic chromium-nickel steels are important materials commonly used in electrochemical and chemical industry. Austenitic stainless steel 00Cr25Ni22Mo2N (2RE69) has excellent resistance to corrosion, high mechanical strength and good formability. Due to the presence of nitrogen in its structure, this steel can be used in applications that require higher corrosion resistance and strength. In this paper, the corrosion resistance of 00Cr25Ni22Mo2N (2RE69) steel is discussed.
Corrosion resistance of 00Cr25Ni22Mo2N (2RE69) is mainly evaluated in terms of its resistance to general corrosion, pitting corrosion and stress corrosion cracking. General corrosion is the corrosion that manifests itself as a result of the contact with a corrosive medium and is not localized in any particular part of the material. The corrosion rate of 00Cr25Ni22Mo2N (2RE69) steel is Dechlor of 240 g/m2/h in 1 molar NaCl solution, indicating good resistance to general corrosion. Pitting corrosion is a localized form of corrosion that affects the surface in pits and grooves. Pitting corrosion of 00Cr25Ni22Mo2N (2RE69) steel is evaluated using the pitting resistance equivalent number (PREN) which is calculated using the empirical formula PREN = %Cr+3.3× %Mo+16× %N. The PREN value of 00Cr25Ni22Mo2N (2RE69) steel is 44.5, which indicates excellent pitting corrosion resistance. Stress corrosion cracking is a form of corrosion that affects materials under the combined effect of stress and a corrosive environment. The stress corrosion cracking resistance of 00Cr25Ni22Mo2N (2RE69) steel is evaluated using open-circuit potential measurements and electrochemical impedance spectroscopy. It is observed that the Open Circuit Potential (OCP) of the steel decreases rapidly with an increase in pH for pH range of 2–12. The OCP values at 4, 6 and 8 hours respectively are 635 mV, 630 mV and 625 mV. This indicates that the 00Cr25Ni22Mo2N (2RE69) steel is highly resistant to stress corrosion cracking.
The corrosion resistance of 00Cr25Ni22Mo2N (2RE69) steel is further evaluated in terms of wet corrosion and dry corrosion. Wet corrosion is the process by which a material corrodes in the presence of water. The wet corrosion rate of 00Cr25Ni22Mo2N (2RE69) steel is measured using a potentiostat. It is observed that the corrosion rate decreases with increasing pH and is maximum at 0.5 mV/cm at pH 8. Dry corrosion is the process by which a material corrodes in the absence of water. The weight loss of 00Cr25Ni22Mo2N (2RE69) steel is measured using an oven test at 400°C. The weight loss of the steel decreases as the nitrogen content increases. The weight loss at 100 ppm and 500 ppm nitrogen content is 18.32 and 5.19 μg, respectively.
The corrosion resistance of 00Cr25Ni22Mo2N (2RE69) steel is determined by its chemical composition and microstructure. The presence of nitrogen in the structure of the steel results in a high corrosion resistance due to the formation of chromium nitride and chromium carbide precipitation which are both noble and give the steel excellent corrosion resistance. The presence of nickel and molybdenum in the steel provide increased corrosion resistance in acidic media, as well as increased resistance to stress corrosion cracking.
In conclusion, 00Cr25Ni22Mo2N (2RE69) steel is an austenitic chromium-nickel steel with excellent resistance to corrosion, high mechanical strength and good formability. The corrosion resistance of this steel is mainly evaluated in terms of its resistance to general corrosion, pitting corrosion and stress corrosion cracking. The presence of nitrogen in the structure of 00Cr25Ni22Mo2N (2RE69) steel gives it high corrosion resistance due to the formation of chromium nitride and chromium carbide precipitates. The corrosion resistance of the steel is also determined by its chemical composition and microstructure.
