Research On Corrosion Behavior Of Weathering Steel In Marine Atmosphere Of The South China Sea

The South China Sea is a typical high-humidity and temperature marine atmospheric environment,i.e.high temperature,high humidity,high salt spray,strong radiation,harsh natural environment.The material corrosion problems are very prominent.According to the ISO 9223 standard classification,the corrosiveness of the South China Sea exceeds the highest C5 level.In view of the high-humidity and temperature marine atmospheric environment in the South China Sea,traditional weathering steels cannot meet actual needs.At present,there are no finished products used in the coastal areas of the South China Sea.Therefore,it is particularly urgent to carry out researching and developing the corresponding types of weathering steels.Accelerated corrosion test,as an important method for evaluating the corrosion resistance of materials.The current standard method lacks relevant accelerated corrosion test methods in the marine atmosphere of the South China Sea,while the atmospheric exposure tests have the characteristics of long test cycles.Therefore,the establishment of an accelerated corrosion test method in the marine atmosphere of the South China Sea is the primary problem for material development.In this paper,through the study of the coupling relationship between multiple marine atmospheric environmental factors and corrosion resistance of materials,accelerated corrosion simulation tests are carried out in lab,and experimental steels are optimized for alloying elements.The acceleration and simulation of the simulation test method are compared and verified based on actual exposure test results.Finally,an accelerated corrosion test method was established to simulate the marine atmospheric environment of the South China Sea.The 3NiSnSb weathering steel suitable for service in the marine atmosphere of the South China Sea was optimized.And the corrosion mechanism model and corrosion life prediction of the Ni weathering steel in the marine environment of the South China Sea was preliminarily raised.The paper systematically discusses the influence mechanism of environmental factors such as chloridion concentration,light,temperature,relative humidity and ratio time of dry/wet on corrosion behavior,and a test method for simulating high-humidity and temperature atmospheric environment corrosion was established.The specific parameters are set as follows:the solution is 2.0 wt%NaCl solution;and the solution temperature is 45±2°C;relative humidity is 70±10%RH in test chamber;the cycle is 60 min,in which infiltration time is 12±1.5 min;and the light shines all day,and the maximum surface temperature of the sample after baking can reach 70±5°C;the testing time is about 72 h to 96 h.In order to obtain weathering steel materials for the marine atmosphere of the South China Sea and study the corrosion behavior and corrosion resistance mechanism,the results showed that when the Ni content exceeded 3 wt%,the corrosion resistance of the test steel had been improved very little,according to the theoretical derivation of Pourbaix potential-pH diagram and literature,combined with the laboratory simulation test and actual exposure test.So,considering the balance of good corrosion resistance and suitable economic cost of the test steel,test steel that contains 3 wt%Ni contents was suitable.The alloying elements Sn and Sb are beneficial to improve the corrosion resistance of the material.Sn,Sb can form SnO₂,Sb₂O₅ corrosion-resistant oxide film on the surface of steel and can also form Sn/Sb oxychloride precipitates by hydrolysis to attach and fill the corrode cracks or voids,which can improve the ability to block the permeation of aggressive chloride and the proportion of protective?-FeOOH and inhibits the poor protective?-FeOOH.In addition,Sn and Sb act as corrosion inhibitors on the eroded cathode and anode processes,resulting in good corrosion resistance of the material.Through the study of laboratory accelerated corrosion tests and actual atmospheric exposure tests,the alloy composition design of 3NiSnSb weathering steel was clarified.Corrosion loss,SEM,XRD,Raman spectroscopy,FTIR,and XPS,EPMA and electrochemical tests were used to study the corrosion behaviors and mechanisms of3NiSnSb weathering steel during actual exposure in typical marine atmosphere of the South China Sea--XiSha and WenChang,and clarify the corrosion mechanism of Ni-based weathering steel in high-humidity,temperature and marine atmospheric environment.Experiment of exposure in XiSha for 1 year showed that with the increase of Ni content,the ability of the rust layer to block the corrosion of Cl^-is stronger,the characteristic distribution of Cl element in the outer rust layer is more obvious,and the corrosion resistance is better.The exposure test in Hainan Wenchang showed that the corrosion weight loss tendency of the 3NiSnSb was significantly less than that of the Q235B carbon steel.The corrosion rate of 3NiSnSb weathering steel at atmospheric exposure of 1.5 years is 37%of Q235B.The results of the 72h corrosive depth of the 3NiSnSb and Q235B steels in the laboratory accelerated corrosion correlate quite well with the actual atmospheric exposure at Wenchang,Hainan for 0.5 years.This concludes that the laboratory acceleration ratio is 144.Through the calculation of the corrosion life prediction function equation,which verifies that the laboratory accelerated corrosion test method has good simulation and appropriate acceleration.