Effect of air flow-rate on plasma oxynitridation of 45-steel surfaces

The 45-steel surfaces were modified, for the first time, by plasma oxynitridation with a mixture of air, nitrogen and oxygen. The impact of the air flow-rate on the phase-structures and mechanical properties of the modified steel surfaces was investigated with X-ray diffraction, metallurgical microscope, and electrochemical workstation. The results show that depending on the air flow-rate, the newly-developed plasma oxynitridation significantly outperforms the conventional plasma nitridation. To be specific, modified at an optimized air flow-rate of 0.2 L/min and a temperature of 550 for 4 h, the plasma oxynitridation layer, consisting mainly of Fe3O4phase, was 60 μm thick, over two times thicker and with much higher corrosion resistance than the conventional plasma niridation layer. As the air flow-rate increased to over 0.4 L/min, both the thickness and corrosion resistance decreased, possibly due to formation of Fe2O3phase. © 2015, Science Press. All right reserved.