Corrosion behavior and structure of oxide scales formed on hot rolled strips after coiling with different oxygen supplies

The structure of oxide scales and corrosion resistance of SS400 hot-rolled strips at different positions in plate width were studied by scanning electron microscopy (SEM), X-ray diffraction quantitative analysis, salt spray test and electrochemical methods. The results show that oxide scales at the plate edge are the thickest, relatively uniform and compact, and there is obvious magnetite/iron eutectoid in them. Oxide scales at the edge and one-fourth of plate width mainly consist of magnetite, hematite and magnetiteiron eutectoid, but oxide scales at the center are composed of magnetite and iron. It is shown by salt spray corrosion test that the corrosion rate is the minimum at the edge, the second at one-fourth of plate width, and the most serious at the center. By potentiodynamic polarization curve test, the corrosion potential at the edge is bigger than those at the two other parts, and the current is the minimum. After the hot rolled strips being coiled, the difference in oxygen supply in the width direction leads different structures of oxide scales, which influence the corrosion resistance of oxide scales.