| 英文摘要 |
Laser surface cladding was used to introduce super stainless steel layers on carbon steel to improve its corrosion resistance. The chemical composition, the resulting microstructure and the corrosion behavior in connection with the oxide films of the alloyed layers were analyzed in this investigation. Laser surface cladded nitrogen-containing super stainless steel layers on carbon steel could be produced successfully with preplaced mixed Fe-Cr--(Ni-Mn-Mo)-Si3N4 powders. Nitrogen alloying as a result of Si3N4 decomposition occurs during laser irradiation: The laser cladded super stainless steel layers, evaluated by poten-tiodynamic polarization tests in 3.5% NaCl solution (pH4) or 0.1M H2SO4, exhibited high resistance to pitting corrosion and the passive current densities decreased with increasing the Cr-N content in the surface alloys. Molybdenum additions to nitrogen-containing alloys are beneficial to the development of passivity and repassivation. Passive film resistance, as determined from EIS measurements in 3.5wt% NaCl solution (pH4) at open circuit potentials, increased with increasing the Cr+N content in the alloys. Nickel additions to nitrogen-containing alloys cause an increase in the passive film resistance. Nitrogen and molybdenum co-exist in the alloys show a combined benefit to the passive film resistance. The surfaces of the nitrogen-containing alloys, after EIS measurements, were analyzed by AES and XPS. The results show that nitrogen additions to the laser cladded alloys are responsible for enriching the passive film with Cr and Mo as a result of the tendency of selective dissolution of Fee Nitrogen in the passive film might exist either in nitride or ammonia, and the presence of SiO2 in the passive film could possibly modify the surface film and improved the resistance of the alloy to dissolution. |
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