In the present investigation, samples treated by the electric are technique surface were used to assess the increase in surface hardness and resistance to oxidation of the AISI 304 stainless steel. In preparing these samples, disk plates, 50 mm in diameter and 10 mm thick, were obtained from AISI 304 (Fe-0.08 C-18 Cr-8.5 Ni-1.5 Mn-0.7 Si) rods. Special Fe-30 Cr-4 C and Fe-30 Cr-4 C-3 Si electrodes were used because of their ability to form a hyper-eutectic surface alloy which exhibits a greater hardness and resistance to oxidation than the eutectic or the hypo-eutectic ones. The manufacturing conditions were as follows : vertically oriented electrode, 250 A AC current (direct polarity), electrode sweeping speed of 8 mm/s, electrode overall diameter (including the coating) of 8 mm and wire (core of the electrode) diameter of 3 mm. The overlap of adjacent weeps required for adequate coating of the whole surface was 25 % approximately. Each sweep was 8 mm wide. Electric are depositions led to good quality, crack-free surface alloys with a thickness of I mm where the electrode composition is maintained after the coating solidification. The morphology and the structure of the surface alloys are similar. The SEM metallographics have shown that the surface alloys are essentially formed by a hypereutectic structure consisting of (Fe,Cr)(7)C-3 primary precipitates completely surrounded by the eutectic, iron solid solution plus (Fe,Cr)(7)C-3 carbides. The average hardness and mass loss measured on the surface alloys and substrate show that the electric are deposition of Fe-30 Cr-4 C or Fe-30 Cr-4 C-3 Si leads to a significant increase in the hardness and wear resistance in relation to the substrate. The surface alloys present a high hardness (850 HV), compared to the AISI 304 stainless steel (200 HV), permitting a decrease in mass loss by a factor of 100 after wear tests : the mass loss of the substrate was 10 mg and that of the surface alloys were 0.1 mg. Micrographic observations of the oxide layers formed on the materials after 100 h of oxidation showed that the thickness of oxide layers varies between 2 and 5 mum. On the substrate, a large part of the layer has been detached and we could only distinguish an oxide film rich in chromium; silicon X mapping showed the presence of interne oxides riches in silicon. X-ray diffraction analysis has detected the Cr2O3, Fe,O-2(3) and M3O4 (M = Fe, Cr, Mn) oxides on the substrate. On the surface alloys, the oxidation layer is constituted of (Fe,Cr)(2)O-3 (Fe-30 Cr-4 C surface alloy) or Cr2O3 oxide (Fe-30 Cr-4 C-3 Si surface alloy). In the Strauss test (intergranular corrosion test), observations from cross-sectional cuts of the alloys have been made in a optic microscope. These observations showed that some zones of the Fe-30 Cr-4 C surface alloy have been severely attacked, which confirm the important mass loss measured to this alloy. The Fe-30 Cr-4 C-3 Si surface alloy presents some points of corrosion to the proximity of the surface. Its mass loss is higher than that of the substrate, nevertheless remains low. On the other hand, the substrate did not show any trace of corrosion.
