Cavitation Corrosion Behavior of Cast Duplex Stainless Steel in Seawater

摘要

The cavitation corrosion behavior of a commercial cast duplex stainless steel was studied in seawater using an ultrasonically induced cavitation facility at a frequency of 20 kHz and an amplitude of 25 μm. The work included measurements of the free corrosion potential and mass loss in addition to microscopic examinations. Cavitation caused an active shift in the free corrosion potential. The rate of mass loss was negligible in quiescent seawater, while, it significantly increased in the presence of cavitation. The application of cathodic protection reduced the rate of mass loss by 19%. Microsccpic examinations revealed that the first signs of cavitation damage were in the form of slip bands and small cavities in the austenite islands and at the ferrite/austenite boundaries. With the progress of cavitation, material loss became mainly at the austenite phase and spread to the ferrite phase at a later stage. Cathodic protection decreased slightly the number of cavities. Cross-sectional examinations revealed the presence of microcracks in the bulk of the material. The microcracks initiated at the surface in the ferrite matrix. Crack propagation was impeded by the austenite islands and branched along parallel slip systems.