Effect of nitrocarburizing on corrosion resistance of carbon steel

ABSTRACT The effect of nitro carburizing on corrosion resistance of carbon steel (AISI / 1020) is investigated. Test specimen 20x10 mm were manufactured according to ASTM. An one hour liquid nitriding at 550 °C followed by liquid carburizing at 925 °C for one hour, at saline medium is done. The sight and microscopic hardness for the hardened layer after carburizing, nitration and nitrocarburizing are studied, as well a corrosion test by an electrochemical cell in sea water is done, where the test specimen represents the cell's positive pole. Tafel's equation was adopted to calculate the corrosion average. The microstructures of all specimen group (nitration, carburizing and nitrocarburizing) were photographed. The resulting phases after each heat treatment were tested by x-ray diffraction apparatus. The results shown that the hardness of specimens increasing directly after the nitration, carburizing and nitrocarburizing processes. The corrosion average of the specimen after surface heat treatment was found to be less than that of the original metal