Effect of Oxi-Nitrocarburizing on the Microstructure, Nanohardness and Corrosion Properties for Low Carbon Steel

摘要

Oxi-nitrocarburizing treatment was performed to improve the anti-corrosion and anti-wear properties of low carbon steels. The oxi-nitrocarburizing was carried out in 2 steps: a gas nitrocarburizing step at 560 degrees C and an oxidation step at 550 degrees C for 30 min with steamed water. The mechanical and chemical properties of the samples were then measured using nanoindentaion test with a load of 10 mN and salt spray test. Investigation on the surface hardening layer with scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis and electron prove microanalysis (EPMA) were also carried out. The thickness and nanohardness of the oxide layer were about 4 gm and 470 Hv, respectively. The oxi-nitrocarburized sample fabricated by gas nitrocarburizing for 50 min followed by oxidation for 30 min showed much better anti-corrosion property than the sample prepared by the conventional gas nitrocarburizing method for 100 min. The improved anti-corrosion property of the oxi-nitrocarburized samples was due to the formation of a dense magnetite (Fe3O4) layer during the oxidation process on the porous nitride layer. These results indicate that oxi-nitrocarburizing is effective for surface treatment of low carbon steels with high anti-corrosion and high wear resistance.