Influence of QPQ treatment on the Corrosion Behavior for Carbon Steel

45 steel was selected as the testing material, QPQ salt bath treatment was conducted by nitriding at the same teperature of 565 degrees C for various time, followed by the same post-oxidation process. Characterization of modified surface layers was made by optical microscopy, X-ray diffraction and corrosion test. The results showed that the cross sectional microstructure was consisted of a thin oxide layer of Fe3O4 at the external surface formed during post-oxidation, a bright zone of E nitrides at the subsurface formed during nitriding and a diffusion zone related to the core. The corrosion resistance of 45 steel in hot water can be significantly improved by QPQ complex salt bath treatment, and the suitable duration of nitriding and post-oxidation to improve the corrosion resistance was 90min and 100min, respectively.