Abstract: The workpiece was processed with salt bath nitriding(QPQ) for 1.5 hours at high temperature of 645 ℃, then treated through different temperature oxidation, at the temperature of seven selected temperatures between 225 ℃ and 420 ℃.The surface hardness data of the sample was obtained: the surface hardness improved at lower temperature oxidation.Through X-ray diffraction analysis, it is concluded that the surface hardness of ascension is due to nanoscale nitrogenous substance precipitation in the oxidation of nitrogen austenitic galleries.Nanoscale dispersion distribution in austenitic galleries plays the role of dispersion strengthening, hence, enhances the surface hardness of the sample.