LAUSR

The effect of Nb on the corrosion resistance of steels in simulating an oil-corrosion environment was investigated by means of microstructure observation, electrochemical test, dissolved Nb content measurement and Nb segregation observation. The results show that the microstructure of the experimental steels is mainly ferrite with a little pearlite. The dissolved Nb contents of the experimental steels are 0.0235 and 0.0458 wt.%, respectively, while the undissolved Nb content is nearly the same. In addition to enhancing mechanical properties of the steel, dissolved Nb improves the corrosion resistance by enriching Nb in the rust layer. Nb oxides in the rust layer cause a decrease in the corrosion rate due to a decrease in the anodic reaction kinetics. The segregation of Nb at the grain boundaries suppresses the corrosion. Moreover, Nb is enriched at the bottom of the corrosion pit and prevents any further corrosion.