A study on the cavitation resistance of ion-nitrided steel

Cavitation is a common deterioration process of a material resulting from high-speed fluid attack. Surface treatments are usually preferably considered to promote cavitation resistance because economic reason and longer durability consideration. The cavitation behaviors of ion-nitrided carbon steel, the response of nitriding layer to various cavitation environments, in particular, were studied. An ASTM G32-85 standard method was conducted to proceed cavitation test in fresh water, 3.5 wt.% NaCl and 3.5 wt.% HCl aqueous electrolytes, respectively. Experimental results show that nitriding of steel would reduce the cavitation rate of the S48C steel in fresh water due to the hard nitrided surface which could resist mechanical damage. Electrochemical corrosion plays a part in the case of 3.5 wt.% NaCl and 3.5 wt.% HCl electrolytes. Ion-nitrided specimens in the former electrolyte, therefore, become less protective than in fresh water with, however, lower cavitation rate than blank steel. Ion-nitrided specimen in the later electrolyte subjecting primarily to electrochemical attack to the nitriding layer, which has high corrosion current, shows inferior cavitation resistance than blank substrate. Therefore, the method of surface modification should be properly determined depending on what electrolyte would be used. Ion nitriding of carbon steel in our case is suitable for fresh water and 3.5 wt.% NaCl electrolyte, but not for 3.5 wt.% HCl electrolyte.