Novel Effect of Post-Oxidation on the Comprehensive Performance of Plasma Nitriding Layer

In order to enhance the comprehensive performance of plasma nitrided heavy load components used in corrosive environments, post-oxidation was conducted under different conditions after plasma nitriding 42CrMo4 steel at 500 degrees C for 5 h. The results show that an oxide film composed of Fe3O4 and Fe2O3 was formed above the compound layer, resulting in a significant increase in corrosion resistance; the self-corrosion potential was greatly increased from -658.72 mV to -429.23 mV. Meanwhile, it needs to be emphasized that the characteristics of the plasma nitriding layer could be effectively adjusted as expected by post-oxidation. The compound layer thickness decreased from 9.41 mu m to 3.62 mu m by post-oxidation at 400 degrees C for 2 h, while the thickness of the effective hardening layer increased from 300 mu m to 378 mu m. Due to the expected change in the characteristics of the plasma nitriding layer, post-oxidation could simultaneously improve the toughness, hardness, and wear resistance of the samples; the brittleness level decreased from Grade 4 to Grade 1; the surface hardness increased from 765 HV0.05 to 825 HV0.05; and the wear rate decreased from 3 x 10-5 g center dot m-1 center dot N-1 to 1.19 x 10-5 g center dot m-1 center dot N-1, illustrating that the wear resistance was greatly improved.