Comparison of corrosion modes of oxidation and sulphidation of weld metal with rare earth oxides

Through addition of rare earth oxides into the coating of electrodes, the high temperature oxidation and sulphidation resistance of weld metal were studied. The weight loss test results showed that the addition of rare earth oxides could improve the high temperature resistance of weld metal, especially in sulphidation environment. The reasons for the difference of corrosion rate between oxidation and suphidation were studied with the application of SEM. It was believed that different corrosion modes were the main reasons for that: oxidation rate was mainly decided by the Cr content of the weld metal and sulphidation rate was mainly decided by the inner corrosion occurring in the grain boundary. The marked effect of rare earth oxides in sulphur environment was related to the corrosion mechanism.