Abstract: The static and dynamic corrosion rates of Cr7 steel after different tempering treatment in CO2 environment were gained by high temperature autoclaving to accelerate corrosion tests. The microstructure and corrosion products of the samples were analyzed by SEM and XRD. The results show that the microstructure of Cr7 steel after tempering at different temperatures was tempered martensite, and the corrosion resistance decreased with the increase of tempering temperature. The static corrosion products were Cr(OH)3 and FeCO3, and the dynamic corrosion film surface was also attached with particles composed of FeCO3 and CaCO3. The results of scanning Kelvin probe and electron backscatter diffraction analysis showed that the potential difference of the sample after tempering at 200 ℃ and 500 ℃ was about 80 mV, and the potential difference of the sample after tempering at 600 ℃ increased to 118 mV. The merging of martensite laths during the tempering process leads to an increase in the proportion of high-angle grain boundaries, which leads to increased micro-region potential fluctuations, which is the main reason for the decline of the corrosion resistance of Cr7 steel.
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