Influence of adding various rare earths on microstructures and corrosion resistance of chromizing coatings prepared via pack cementation on P110 steel

Abstract

In order to improve the corrosion resistance and increase the service lifetime of P110 steel during operation, four chromizing coatings were formed onto its surface with/without addition of rare earths via pack cementation process. The surface morphologies and microstructures of the chromizing coatings were observed using scanning electron microscopy (SEM), and the phase constitutions were investigated by X-ray diffraction (XRD). Electrochemical corrosion behavior of the chromizing coatings in simulated oilfield brine at 30 °C was studied by means of open-circuit potential measurements and cyclic potential dynamic polarization tests. The results showed that the coatings were mainly composed of Cr 23C 6, Cr 7C 3, and (Cr, Fe) 7C 3. There were obvious differences in surface morphologies and microstructures of the coatings. The thickness values of the coatings were arranged as follows: CeO 2>-coating>Y 2O 3-coating>La 2O 3-coating>no RE-coating. The corrosion resistance of the coatings was sorted in the following sequence: CeO 2<-coating<no RE-coating<La 2O 3-coating<Y 2<O 3-coating. Adding various rare earths could influence the microstructures and corrosion resistance of the chromizing coatings indeed.