Abstract Plasma nitriding is a surface treatment process which is increasingly used to improve wear, fatigue and corrosion resistance of industrial parts. Nevertheless, corrosion resistance can be further enhanced by oxidizing of nitrided components. This paper considers the duplex treatment of plasma nitriding and post-oxidation of AISI 1045 plain carbon steel which is used in manufacture of shock absorber rods in automotive industry. Plasma nitriding was carried out at 550 °C for 5 h in atmosphere having nitrogen and hydrogen with volume ratio of 3 to 1. The nitrided samples were post-oxidized at 500 °C for 1 h under O 2/H 2 volume ratios 1/2.5, 1/9, 1/12 and 1/20. The treated samples were characterized using metallographic techniques, XRD, SEM, micro-hardness and potentiodynamic methods. X-ray diffraction confirmed the development of gamma prime and epsilon iron nitride phases during nitriding and hematite (Fe 2O 3) and magnetite (Fe 3O 4) phases under oxidation process. Increasing the oxygen volume of the oxidizing gas led to an increase in the thickness of the oxide layer so that the thickest oxide layer (1.2 μm), consisting of mainly magnetite as well as hematite, was formed on the sample oxidized with gas composition of O 2/H 2: 1/2.5. This sample also displayed the highest corrosion resistance, 6 times of the nitrided sample and 15 times of the untreated one, which is believed primarily to be due to the magnetite phase formation. Microhardness measurements indicated a decrease in the surface hardness of the duplex-treated samples in comparison with the plasma nitrided one owing to the lower hardness of iron oxides than iron nitrides.