Effect Mechanism Of Chloride Ions On Mechanical Property Of Stainless Steel Surface Layer Under Cavitation

Developping marine economy, enhancing the ability of exploiting marine resource is an important strategic goal of our country in this century. Corrosion research of metal in Chlorine ion flow system, is of great significance to the inventing of new corrosion-resistant materials and also the practical application of anti-corrosion measures.In this paper, Ultrasonic cavitation testing machine was used for corrosion experiment of stainless steel in Chlorine ion flow under cavitation.We quantitatively measured the nano-mechanical properties of the corroded surface layers by nano-indentation technology, meanwhile analyzed the surface profile and chemical change by SEM,XRD and XPS, finally revealed the effect mechanism of mechanical property of corroded surface layer of duplex stainless steel.The results showed that, with the improvement of the chloride ion concentration, the mechanical properties of the stainless steel surface constantly degraded; surface corrosion pores gradually expanded into corrosion pit; the composition ratio of the surface passive film decreased; the anode current density of passive film increased, and the surface resistance decreased. Thus, chloride ion destroyed the passive film, which is in a balance of disappearing and repairing, and formed some holes on the surface. The stainless steel substrate materials exposed to the cavitation impact, and the continuously formed cracks eventually led to the degradation of surface mechanical properties.The degradation of mechanical properties of the stainless steel surface layer intensified the synergistic effect, led to increasing damage of cavitation erosion. By reducing cathode protection measures can effectively reduce the degradation of the mechanical properties of the stainless steel surface under cavitation.Under cavitation of stainless steel, there was a comprehensive mechanical parameter threshold, which caused intensify corrosion. When H/E is greater than the threshold, the cavitation erosion rate is small; once H/E is less than the threshold, the cavitation erosion rate increased suddenly. This threshold can be used as a reference of mechanical properties for inventing a new corrosion-resistant stainless steel, also a judgment criteria of the failure cavitation erosion resistance of the stainless steel material.