Localized Corrosion Behaviours Of Reinforcement Steel And Vanax Tooling Steel In Different Environments

1.Localized Corrosion Behaviour of Reinforcement Steel in Simulated Concrete Pore SolutionLocalized corrosion behavior and influence of microstructure of reinforcement steel were investigated in simulated concrete pore solutions by electrochemical measurements and local probing techniques.Optical microscopy examination and SEM/EDS analysis revealed that the reinforcement steel consists mainly of ferrite, with a certain amount of pearlite and some MnS inclusions.Scanning Kelvin probe force microscopy mapping of the polished surface,giving relative nobility of microstructural features,indicated a higher corrosion tendency of the ferrite grain boundaries,pearlite grains and MnS inclusions.Electrochemical impedance spectroscopy and potentiodynamic polarization measurements in simulated concrete pore solution demonstrated passivity and breakdown behavior of the steel,and the influence of pH value and chloride concentration of the solution.In-situ optical microscopy experiments visualized the development of localized corrosion along the ferrite grain boundaries and on the pearlite phase.In-situ AFM measurements in the solution revealed details of the localized corrosion on the steel surface,such as corrosion products related to the grain boundaries,and formation of pit cap and the growth of a pit.The experimental evidences indicate that the passivity and localized corrosion behavior of the reinforcement steel are influenced both by the pH and chloride concentration of the solution and by the microstructure features such as pearlite phase and MnS inclusions.2.A study of localized corrosion of tooling alloysThis research project aims at studying localized corrosion behavior of tooling alloys in NaCl solutions.Vanax 75 samples after a high temperature(HT) treatment and a low temperature(LT) treatment were investigated,by using electrochemical measurements including open-circuit potential(OCP) versus time,electrochemical impedance spectroscopy(EIS),and potentiodynamic polarization,as well as in-situ AFM measurements in the solution.Moreover,to evaluate corrosion tendency of the particles in the microstructure,Volta potential mapping by using scanning Kelvin probe force microscopy(SKPFM) was performed on the polished sample surface. Results suggest that the high temperature treatment leads to a more uniform material on a macroscopic.The low temperature treatment seems to result in a less uniform material on a macroscopic level,and less microscopic sites that are sensitive to localized corrosion.Apparently,the low temperature treated material exhibits a higher corrosion resistance.