Study On Corrosion And Wear Properties Of Stainless Steel In Marine Environment

With the rapid development of economy and technology,people rely more and more on the ocean,and invest more and more in the exploration and collection of marine resources.Advanced marine equipment can greatly improve the efficiency of exploitation and utilization of marine resources,but the corrosion and wear of marine equipment and its complex interaction often affect the reliability and efficiency of marine equipment.Therefore,it is of great practical significance to study the coupled tribological behavior of marine materials under load,fluid and corrosion conditions.The growth of passive film on stainless steel has been studied systematically in this paper starting from passivation film of stainless steel metals.On this basis the interaction between corrosion and wear of 316L and 304 stainless steel was discussed.Firstly,corrosion current and surface impedance of 316L stainless steel and 304stainless steel at different constant potential were measured by electrochemical method.The two materials show Very similar electrochemical properties.When the constant potential of loading is in the passivation zone of stainless steel,the polarization resistance increases and the corrosion current decreases with the increase of Voltage.When the constant potential of loading exceeds the breaking potential,the polarization resistance decreases and the corrosion current increases substantially.Then,the change of electrochemical parameters was confirmed at the micro level,that is,the surface morphology was observed by scanning electron microscopy?SEM?.The results show that there is a thin passivation film on 304 and 316L stainless steel,and the passivation film tends to grow with the increase of potential.The passivation film becomes dense gradually from sparse.When the potential exceeds the breaking passivation potential,pitting corrosion occurs on the material surface.Finally,the change of passive film is explained from the chemical mechanism,that is,EDS,XRD and other components of the test samples were measured.It is found that the passivation film on stainless steel is mainly composed of trivalent oxide of Cr and bivalent and trivalent oxide of Fe.In the passivation region,the content of Cr element on the surface of stainless steel increases with the increase of potential,and the content of Cr element in the dense area of passivation film is higher than that in the sparse area.On this basis,the electrochemical parameters such as open-circuit potential,polarization curve and potentiostatic current of two stainless steel metals during wear were measured by self-made corrosion and wear tester.According to ASTM G199-09standard,corrosion and wear were calculated in detail and at the end,the electrochemical and corrosion wear properties of 304 and 316L stainless steel materials were compared and analyzed.The open-circuit potential test results show that the open-circuit potential in dynamic state is 240 mV-360 mV lower than that in static state,indicating that wear can promote corrosion.The results of potentiostatic wear and corrosion test show that with the increase of potentiostatic potential,the total wear and corrosion loss of stainless steel increases,but it is much larger than the pure wear loss,indicating that corrosion promotes wear.Polarization curve test shows that the stainless steel material will have similar polarization curve with static state when wearing.There will be polarization zone,passivation zone and oxygen evolution zone in the anode,and the passivation zone in dynamic state is that the old passivation film is constantly destroyed and the new passivation film is continuously formed to achieve a dynamic balance.According to ASTM G199-09 standard,the total loss T,wear amount WC,corrosion amount C_W,pure wear amount W₀,pure corrosion amount C₀,corrosion promoting amount?W_C,wear promoting amount?C_W and interaction S of wear and corrosion were calculated.The results show that wear can greatly promote corrosion.Under wear conditions,the corrosion rate will increase by one or two orders of magnitude.At the same time,corrosion can also greatly promote wear,increasing the wear rate of stainless steel materials by 43.7%-57.1%.In the whole process of corrosion and wear,mechanical wear accounts for the main part,which is about 94.8%-97.7%.The corrosion resistance of 316L stainless steel is better than that of 304 stainless steel.The wear and corrosion resistance of 304 stainless steel is better than that of 316L stainless steel at loads of 0.25 MPa and 0.5 MPa,but at loads of 0.75 MPa,the wear and corrosion resistance of 304 stainless steel is worse than that of 316L stainless steel.