산질화처리가 저탄소강의 미세조직과 나노경도 및 부식특성에 미치는 영향

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 ℃ and an oxidation step at 550 ℃ 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 μm and 470 Hv, respectively. The oxi-nitrocarburized sample fabricated by gas nitrocarburizing for 50 min followed by oxidation for 30 min showed much better anticorrosion 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 (Fe 3 O 4 ) 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.