Research On Corrosion Resistance Of Marine Steel With Different Carbon Contents

The microscopic morphology and phase composition of the steel have a great influence on the corrosion resistance of the steel material in the marine service environment,such as the precipitation amount,distribution state,size of the carbide and the level of the internal free energy of the material.To a certain extent,it affects the corrosion type of steel and the oxide phase composition of the rust layer,resulting in materials with the same chemical composition having different corrosion performance in the same marine environment.In this paper,different heat treatments are carried out on low-carbon marine steel to change the internal phase composition and micro-morphology of the steel.The corrosion resistance of steels with the same chemical composition but different micro-compositions is studied.The field heating scanning electron microscope(SEM)was used to observe the micro-morphology of the material and the thickness and de nsity of the corrosion rust layer in each cycle.The salt spray box carried out the salt spray accelerated corrosion test to simulate marine corrosion to obtain the weightless corrosion curve.XRD carried out the rust layer product phase For analysis,the electrochemical workstation measured the electrochemical polarization curve and electrochemical impedance spectrum of the bare steel,and comprehensively evaluated the corrosion performance of the low and medium carbon marine steels with different heat treatments.The experimental results show that martensite has an electrochemical self-corrosion potential of-0.510V and a charge transfer resistance of 2067?·cm2,which has the lowest self-corrosion potential and the highest polarization resistance.Among the low-carbon marine steels,martensitic steel has the best corrosion resistance and bainite steel has the worst corrosion resistance.In the rust laye r morphology,the rust layer of martensitic steel is the thinnest and densest.The metal matrix is well protected,and the amount of carbide precipitation is the decisive factor for corrosion resistance.In the ocean steel with medium carbon content,the corrosion resistance decreases in the order of bainite steel,pearlite steel,martensitic steel,and tempered martensitic steel.Analysis of the electrochemical self-corrosion potential revealed that the lowest bainite potential was-0.5822V,and the highest tempered martensitic steel potential was-0.625V.The content of?-FeOOH and?-FeOOH in the rust layer is the highest,and the protective effect on the formation of the metal matrix is insufficient,Bainite steel has a high content of Fe3O4,which can better protect the metal matrix.The hot-rolled martensitic steels with different deformation variables have reduced corrosion resistance as the deformation variable increases.The self-corrosion potential and charge transfer resistance of the steel with 50%deformation are the lowest among the three steels,for-0.622V and 1810?·cm ~2 and the composition of the rust layer is trioxide The content of Fe3O4 and?-FeOOH is low,and it is not easy to form oxides that can protect the metal matrix.