The Pitting And Repassivation Behavior Of SS430 Under Wet-dry Cycling Condition

The low cost advantages of 430 ferritic stainless steel make it widely used.However,in the marine atmosphere environment,the corrosive environment is rather harsh and 430 stainless steel can also be corroded.Due to factors such as the environment and the material itself,the occurrence of pitting corrosion is random and requires probabilistic statistical laws.Therefore,it is particularly important to select an appropriate method for evaluating atmospheric corrosion.Conventional salt spray corrosion,salt deposition corrosion,and other simulated atmospheric corrosion methods have a long experimental period.So in this paper,the effect of temperatures and surface states on the pitting of SS430 was investigated through multi-droplet electric potential monitoring under wet-dry cycling condition,and compared with bulk solution.We summarizes the pitting characteristics under atmosphere environment.The main contents are as follows:(1)The critical condition of pitting corrosion of SS430 at different temperatures was studied by means of multi-droplet electric potential monitoring.The results show that with the temperature increases from 10 °C to 50 °C,the probability of pitting corrosion of the specimen increases from 5/35 to 25/35.The average critical relative humidity of pitting corrosion increased from 55% to 63%,the corresponding chloride concentration decreased from 7.4 M to 6.4 M.The average critical repassivation relative humidity increased from 74% to 91%,the corresponding chloride concentration decreased from 5.0 M to 2.5 M.The temperature' increase made it more susceptible to pitting corrosion.(2)The effect of different surface roughness on pitting corrosion under droplet wet-dry cycles was studied.The results show that ground reduces the pitting probability from 33/35 to 15/35.There are residual defect on the surface of the as-received sample,processing residual defects reduces the corrosion resistance of the sample.(3)Potentiodynamic polarization curves were used to evaluate the electrochemical corrosion behavior of SS430 in magnesium chloride solution and compared with the droplet wet-dry cycle.The results show that the increase of temperature promotes the initiation of pitting corrosion.The pitting potential under the wet-dry cycling condition of the droplets is distributed in the vicinity of the fitting straight line of the solution pitting potential.(4)The initiation and growth process of pit were studied by observing the morphology of pits and combining color-change method.The results show that pitting corrosion preferentially grows in the horizontal direction.Color-change method can be used to evaluate the initiation of pitting corrosion,the volume of pit increases in a short period of time,and the degree of color development becomes deeper.