Corrosion and Cavitation Resistance of High-Strength Austenitic Nitrogen Stainless Steels in Seawater

Abstract—The corrosion and cavitation resistance of high-strength economically alloyed nitrogen-bearing chromium–nickel–manganese austenitic C10Cr19Mn10Ni6Mo2N and C09Cr19Mn10Ni6Mo2Cu2N stainless steels in seawater is compared experimentally with the properties of chromium–nickel C04Cr18Ni9 and C04Cr18Ni9N steels. The resistance to pitting corrosion is tested by a chemical method in a 100-g/L FeCl₃ · 6H₂O solution. The overall corrosion resistance is assessed by tests in synthetic seawater (3% NaCl). The cavitation resistance in seawater is tested by means of a high-intensity cavitation system based on a Hielscher Ultrasonic UIP 1000hd ultrasound unit in 3% aqueous NaCl solution (vibration frequency 20 kHz, power 1000 W, amplitude 25 μm) for 8–36 h. After cavitation treatment, the damage and change in microhardness at the sample surface is estimated, as well as the change in phase composition and mass of the samples in the tests. According to the tests, C10Cr19Mn10Ni6Mo2N and C09Cr19Mn10Ni6Mo2Cu2N steels are free of pits after exposure to seawater and iron-chloride solution. The overall corrosion rate is lower than for chromonickel Cr18Ni9 steel. Ultrasonic cavitation may lead not only to surface damage by erosion and intensification of local corrosion but also to change in the physical and mechanical properties on account of cold working and phase transformations. The resistance to ultrasonic cavitation in seawater is greater for C10Cr19Mn10Ni6Mo2N and C09Cr19Mn10Ni6Mo2Cu2N steels, containing thermally and mechanically stable austenite, than for chromonickel steels, especially C04Cr18Ni9, which is weaker and less stable. For example, after 36-h cavitational treatment in seawater, significant changes in state are seen in C04Cr18Ni9 and C04Cr18Ni9N steels: considerable damage (etching) and hardening of the surface and also the formation of a small quantity of martensite in C04Cr18Ni9 steel. For C10Cr19Mn10Ni6Mo2N and C09Cr19Mn10Ni6Mo2Cu2N steels, the tests indicate only slight change in state of the surface and hardening.