The Structure Change and Corrosion Protectivity of the Oxide Scale on An SS400 Hot-rolled Steel Plate

Various oxide scales with different compositions and structures have been obtained by heat treatments of a SS400 hot-rolled steel plate with the mill oxide scale,including initial isothermal heating at 800 ℃ in high purity N2 for 90 min and the following processes of slow cooling in the furnace,quenching,slow cooling to 480 ℃ then quenching and slow cooling to 480 ℃ with staying at 480 ℃ for 8h then quenching in the protective atmosphere.The rusting behavior and electrochemical properties of the treated specimens in a 2% Na2SO4 solution were evaluated and compared by the constant temperature humidity test and electrochemical testing techniques including E-t curves,potentiodynamic polarization curves and EIS.The results show that the rusting behavior and electrochemical properties are significantly different for specimens with various oxide scales,indicating that the scale composition and structure affect the rusting behavior of hot-rolled steel plates greatly.The relationship between oxide scale structure and its protectivity is also discussed in the present paper.