Corrosion Behavior And Mechanism Of Q235 Carbon Steel And Q420 Weathering Wteel In Two Typical Environments

Based on the principle of galvanic corrosion,this paper designs and develops a galvanic atmospheric corrosion online monitoring(ACM)sensor,which is compared with the traditional outdoor exposure test to study the impact of different environmental factors on the corrosion behavior of Q235 carbon steel and Q420 weathering steel,discussed the corrosion resistance mechanism of Q420 weathering steel in different environments.And on this basis,the research and development direction of weathering steel is proposed to provide technical support for the research and development of new weathering steel in China.By fitting the relationship between the current data monitored by the ACM sensor and the corrosion rate data of the hanging piece,the corresponding relationship between the two follows:v_corr=60.28275+15.686I_ACM^1.2746,the goodness of fit is R²=0.998,reflecting the outdoor corrosion rate of standard coupons has a good correlation with corresponding sensor data.Convert the induced current of the sensor to the corrosion rate of the carbon steel electrode on the sensor due to the galvanic effect,and compare it with the corrosion rate of the standard coupon.It is found that the galvanic corrosion rate of the carbon steel in the sensor is not greater than the self-corrosion rate of the carbon steel 6.82%,it is speculated that the galvanic acceleration effect will not greatly accelerate the corrosion process of the carbon steel electrode on the sensor.Based on the above analysis,it is believed that the data monitored by the sensor can reflect the real-time corrosion of the coupon in the atmospheric environment.The Q235 carbon steel in Qingdao has a corrosion loss weight 4 times that of Wuhan in one year,while the Q235 carbon steel/Cu type ACM sensor in Qingdao has 3.5 times the integrated power of Wuhan sensors,the data of the two are close and consistent.Comparing the rust layer cross section of Q235 carbon steel at two locations,the thickness of the rust layer of Qingdao's pendant is 3.2 times that of Wuhan,which is consistent with the weightlessness data and sensor data.By observing the change of the sensor current value in the previous month during the exposure period in Qingdao or Wuhan,it was found that the metal corrosion process generally occurs at night.After one year of outdoor exposure,the corrosion weight loss of Q235 carbon steel in Qingdao area is 1.42 times that of Q420weathering steel,while the weight loss of the two steels in Wuhan is the same,indicating that the exposure period is one year,and the areas with more serious corrosion show weather resistance.The development trend of the corrosion resistance of steel,but the corrosion resistance has not yet been fully reflected.This is different from the weathering steel studied by previous scholars.It needs to be exposed to the atmosphere for more than 3 to 10 years to form a stable protective rust layer,its corrosion resistance can reflect the same conclusion.By observing the microscopic morphology of the cross-section of the rust layer,it is found that the rust layer of the weathering steel after 1 year of corrosion has more obvious delamination,and some dense and continuous inner rust layers are gradually formed,but the protective rust layer is not yet fully formed.The micro-Raman technique was used to analyze the phase composition and distribution of corrosion products in the rust layer of two types of steel in Qingdao.It was found that the exposure period of 1 year,due to the action of chloride ions,the initiation and growth of?-Fe OOH in the rust layer of Q235 steel is promoted,and the initiation and growth of?-Fe OOH will lead to the reduction of the atmospheric corrosion resistance of the steel,causing the corrosion rate inside the rust layer and the steel matrix faster and faster,and the content of?-Fe OOH in the rust layer of weathering steel gradually increases,and the content of?-Fe OOH increases,which helps accelerate the formation of a protective rust layer.Comparison of the composition and distribution in the rust layer shows that the corrosion resistance of weathering steel is directly proportional to the exposure time.