Relationship Between The Surface Layer Mechanical Properties Of Austenitic Stainless Steel With Corrosion Failure

Cavitation corrosion, which is a type of flow-induced corrosion,occurs in various industries, resulting in heavy economic loss. Therefore,it is of great significance to study the cavitation corrosion mechanism ofmaterials for the choice of materials and development of new materials inthe flow system.The changes of surface layer mechanical properties andelectrochemical behavior of austenitic stainless steel were studied bynano indentation in combination of electrochemical method. Meanwhile,the corroded surface morphologies were analyzed by SEM and AFMtechnologies, and the relationship between the surface layer mechanicalproperties with corrosion failure was further researched to revealinteraction of mechanical properties and electrochemical corrosion.The results showed that the surface layer mechanical properties ofaustenitic stainless steel in3.5%NaCl solution under cavitation weredegraded, and depth of degradation was increased with the cavitaion times. When the conductivity of corrosive medium was reduced, or theinfluence of chloride ions was removed, the electrochemical corrosionwas retarded by using cathodic protection. The surface layer mechanicalproperties were strengthened instead of degradation, due to the formationof hardened layer. Besides, the microstructures of the stainless steel had asignificant impact on its surface layer mechanical properties.With increasing degradation, the cumulative weight loss of austeniticstainless steel was increased, and there was a threshold, once belowwhich the cumulative weight loss increased rapidly, and the corrodedmorphologies changed significantly. Under cavitation, the corrosionpotential of austenitic stainless steel decreased with the cavitaion times,and its anodic process changed from self passivation to activationpassivation, then the electrochemical impedance reduced, resulting inincreasing the electrochemical corrosion loss. There was a peak in thelow frequency region of BODE diagram, which could be used as thecharacteristic parameter to express the degradation of surface layermechanical properties and increase of cavitation corrosion loss.When the electrode made of austenitic stainless steel was polarizedby electrochemical polarization in3.5%NaCl solution, the cumulativeweight loss was accelerated by anodic polarization, and the corrosionweight loss increased. However, the condition of cathodic polarizationwas on the contrary. The surface of austenitic stainless steel was in the different passive states under anodic polarization. Although the surfacelayer mechanical properties were improved, the electrochemicalimpedance decreased with the increase of anodic potentials, and thecumulative weight loss increased by the synergism between fluidmechanics and corrosion. The mechanism was that electrochemicalcorrosion caused mainly non-electrochemical weight loss.