Effect of QPQ nitriding time on wear and corrosion behavior of 45 carbon steel

Abstract

QPQ salt bath treatment of 45 steel was conducted by nitriding at 565°C for various time (60min, 90min, 120min, 150min and 180min), followed by the same post-oxidation process with heating temperature of 430°C and holding duration of 40min. Characterization of modified surface layers was made by means of optical microscopy, microhardness test, X-ray diffraction analysis, corrosion and wear resistance test. The results showed the formation of a very thin Fe3O4 oxide layer during post-oxidation on the top of the bright nitrides compound layer formed during nitriding. The maximum microhardness value of 630HV0.01 was obtained after nitriding at 565°C for 120min, which was two times higher than that of the untreated sample. The corrosion and wear resistance of 45 steel could be significantly improved by QPQ complex salt bath treatment, and the optimum nitriding duration for improving the wear and corrosion resistance was 120min and 90min, respectively.