| As the most commonly used structural material in concrete buildings,steel bars are frequently withdrawn from service due to chloride corrosion,resulting in a large amount of economic and resource waste.In this paper,the 600 MPa high-strength antiseismic and corrosion-resistant steel bar is taken as the research object,and its corrosion behavior in the chloride-salt environment and service environment is taken as the research content,and the corrosion resistance mechanism in the early and late stages of corrosion is clarified.Corrosion test and electrochemical test methods,with the help of optical microscope,XRD,SEM,EDS and other means,compare its electrochemical characteristics with ordinary steel bars,obtain its corrosion behavior and corrosion resistance mechanism in the corrosion initiation stage,and study its corrosion expansion in the later stage of corrosion Behavior and mechanism of rust growth.Through chemical composition design and rolling process formulation,a 600 MPa level low-alloy corrosion-resistant steel bar was developed,which ensured its chloride ion corrosion resistance while improving its strength.The corrosion resistance of the original corrosion-resistant steel bar is better than that of the original ordinary carbon steel bar.The open circuit voltage fluctuation is not obvious,but the AC impedance spectrum shows that the arc radius of the former is larger,the impedance modulus increases significantly with the frequency,and the anode area has a passivationbreaking passivation-secondary passivation reaction.After alkaline passivation,the corrosion resistance of the two kinds of steel bars is improved,but the corrosion resistance is not positively correlated with the prolongation of passivation time.The corrosion resistance characteristics of low-alloy corrosion-resistant steel bars are most significantly improved after short-term passivation,and the resistance arc radius gradually decreases with the prolongation of passivation time.And the long-term passivation does not significantly increase the impedance modulus value under each frequency response.And the secondary passivation after passivation only occurs after a medium passivation time.Too short passivation time or too long passivation time directly affects its electrochemical stability.For example,the self-corrosion current density Icorr decreases,and the self-corrosion Corrosion potential Ecorr shifts positively,pitting potential Epit shifts positively,etc.The effect of corrosion expansion on the corrosion resistance of steel bars under service conditions is mainly related to the chloride ion corrosion time and surface corrosion time,and the passivation time has little effect.Affected by corrosion after passivation,the change of open circuit potential of low-alloy corrosion-resistant steel bars is more stable than that of ordinary carbon steel bars in any state,and the longer the pre-corrosion time,the lower the corrosion rate,which is related to the oxidation(corrosion)reaction of the steel bar surface In the process of electrochemical detection,the former promoted the further reaction of the compound,and the electrochemical activity was significant,which caused the experimental results to be contrary to common sense.In the early and late stages of corrosion in the chloride salt environment,the corrosion-resistant steel bars and the carbon steel rebar substrate surface were corroded to varying degrees,and the former had less corrosion weight loss and a lower corrosion rate due to the control of Cr,Mo,Ni,Cu and V element alloys.Both corrosion initiation forms are pitting corrosion.From the surface corrosion morphology,element distribution ratio,corrosion expansion law and corrosion product phase composition,it can be seen that the control of alloy composition significantly reduces the lateral expansion speed of the outer rust layer surface in the early stage of steel corrosion.and the longitudinal growth rate of the inner rust layer.The corrosion weight loss and corrosion rate show that the corrosion weight loss and corrosion rate of low-alloy corrosion-resistant steel bars are lower than those of ordinary carbon steel bars at the initial stage of corrosion,and the corrosion resistance is better.In the corrosion stage from 72 hours to 576 hours,the corrosion rate of the former accounted for 33.43%,62.27%,57.81%,and 67.32% of the corrosion rate of the latter;The layer thickness distribution is 26.95%,69.1%,33.11%,75.1% of the latter rust layer thickness.It can be seen from the corrosion degree and macroscopic appearance that 576 small proves that the regulation of alloying elements inhibits the development of corrosion process in the late stage of corrosion,improves the stability and density of the rust layer,hinders the infiltration of corrosive media in the rust layer,and thus improves the corrosion resistance.Due to the low content of alloying elements,the inhibitory effect reflected by the corrosion rate is also gradually reduced.Under the chloride salt environment,the evolution process of the outer rust layer of the two steel bars is quite different in the late stage of corrosion.The low-alloy corrosion-resistant steel bar is different from the appearance and density of the rust layer,as well as the growth rate and growth law of the rust layer within the same corrosion time.The corrosion performance is better than that of ordinary carbon steel bars,which directly determines that the service time of the former is longer than that of the latter.Among them,in the corrosion stage of 72 hours to 288 hours,Cr element is enriched in the swelling part of the rust layer,which improves the density and stability of the oxide film layer at the deformation position,and has a certain hindering effect on Cl.When the surface of the rust layer has obvious swelling phenomenon,black crystals with extremely high content are produced on the surface of the flat and dense rust layer,and enriched with the expansion of corrosion,and play an anchoring role in the outer rust layer.After 576 hours,when the steel bar completely entered the expansion failure stage,the expansion of the rust layer of the corrosion-resistant steel bar was affected by the alloy elements,and the phenomenon of expansion and collapse occurred,and the center of the collapse did not appear cracks and broken features of the rust layer due to the enrichment of alloy elements,which proved that in the late stage of corrosion The structure of the surface rust layer is still very stable,and the corrosion volume expansion of steel bars is controlled,and the enrichment of alloying elements on the surface of the rust layer also hinders the infiltration of chloride ions. |
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