Microstructures and wear resistance of chromium coatings on P110 steel fabricated by pack cementation

In order to obtain a high-performance surface on P110 steel that can meet the requirements in oil/gas field environment, the chromium coatings were fabricated by pack cementation. The chromium coatings differed in with/without the addition of La ₂O ₃. Scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), X-ray diffractometer (XRD) and microhardness tester were employed to investigate the surface morphologies, surface element distributions, microstructures, phase constitutions and microhardness of the coatings. Friction-wear tests of the P110 steel substrate and the coatings were conducted in air at ambient temperature and humidity. The results show that uniform and continuous coatings are formed on P110 steel regardless of adding La ₂O ₃ or not. The chromium coatings consist of Cr ₂₃C ₆, Cr ₇C ₃, and (Cr, Fe) ₇C ₃. The La ₂O ₃-added chromium coating is more beneficial in terms of surface morphology, microstructure, thickness and microhardness as compared with the coating without adding La ₂O ₃. Chromizing treatment significantly improves the surface hardness and wear resistance of the P110 steel. The wear resistance of the tested samples can be sorted in the following sequence: La ₂O ₃-coating>no RE-coating>bare P110 steel.