Structure and Corrosion Influence of Scale on Q235 Steel Surface in Production Liquid

The surface morphology of corrosion product films on surface of Q235 steel was observed by OM and SEM. The composition of films was analyzed by XRD and SEM. The corrosion rate of Q235 steel was measured by gravimetric method. The influence of surface scale growth on corrosion was studied by the corrosion rate. The results showed that there were three-layer structures of corrosion product films of Q235 steel in the solution at 50 ℃, the outer layer of FeCO3 crystals accumulated loosely, the inner layer of FeCO3 crystals accumulated closely and the size of crystals in the middle layer was between them. The main composition of surface film was FeCO3. The gravimetric method showed that the maximum value of corrosion rate was 0.1531 mm/a in the first three days, and then the corrosion rate began to decrease with the formation of the first-layer film. The minimum value of corrosion rate was 0.0259 mm/a because of deposition film on the 24 th day. The corrosion rate started to rise foom the 34 th day because the third-layer film was loose, and had no significantly change after 34 days.