Study On Mechano-chemical Behavior Of Various Hull Steel

The mechano-chemical effect refers to the stronger corrosion behavior produced by the metal under stress and corrosion media than in the pure corrosion media,because structural stress causes the electrochemical potential and electrochemical degree of the metal increased.The research on stress corrosion has been developed for a long time,but because the interaction between stress and corrosion media is complex and the materials are diverse,the research on this problem has been very challenging so far.In this paper,the theoretical and experimental studies on the mechano-chemical effects of Q235 low-carbon steel,316L stainless steel and 304 stainless steel which are commonly used in shipbuilding and marine engineering structures were made in 3.5%NaCl solution.The corrosion model of metals under the consideration of stress is deduced based on the thermodynamic,kinetic and mechano-chemical effects theory,which lays a theoretical foundation for the experimental measurement of mechano-chemical effects.According to the experimental requirements,the multi-sample PVC device which can provide constant stress loading,the multi-channel circuit board which can realize series/parallel and auto switching were designed independently,the devices mentioned above cooperate with the three-electrode system,electrochemical workstation and stress strain gauge to form a complete experiment system.Through EIS,LPR technology combined with roughness test,the effect of elastic and plastic stress on the corrosion behavior of Q235 low carbon steel in 3.5%NaCl solution was studied.Studies have shown that stress can reduce the charge transfer resistance of the interface between the metal and the corrosion medium of Q235 and|Z|_0.01,which characterizes the state of the metal surface,the roughness of the surface of Q235 increases with increasing stress.This is because the high stress makes the Q235 surface more active and the electrochemical activity increases.A corrosion model of the Q235 elastoplastic stage is proposed.The corrosion rate of the metal under plastic deformation is greater than that of the elastic stage.Through electrochemical methods such as PDY,CP,OCP,EIS and ZRA,the mechano-chemical behavior of 316L stainless steel and the effect of temperature,cathodic protection and the combined effect of both on the mechano-chemical behavior of 304 stainless steel were studied.The research shows that:the corrosion potential gradually decreases with the increase of the applied stress,while the corrosion current density gradually increases,which indicates that the stress causes declines of corrosion resistance of 316L.High-stress samples preferentially act as anodes during the test period,and other samples are protected as cathodes.Over time,the cathodes under lower stress gradually transfer to anodes from high stress to low.Without external stress,there is a mathematical relationship between the charge transfer resistance and the cathodic protection potential.The increase in temperature and stress will make the optimal cathodic protection potential of 304 stainless steel negatively shift,and the corrosion resistance of 304 will be weakened.This paper hopes to further study the mechano-chemical behavior of various hull steel materials through the above research.According to the proposed low carbon steel elastoplastic stress corrosion model and the mathematical relationship between the stainless steel charge transfer resistance and cathodic protection potential,I prefer to provide a reference for life prediction and cathodic protection during service of various hull steel materials.