The Effect of N Content on the Microstructure and Wear Resistance of Improved High-Carbon Chromium Bearing Steel

The impact of varying nitrogen (N) contents (65 ppm, 90 ppm, 115 ppm, 140 ppm) on the microstructure and wear resistance of high-carbon chromium bearing steel enriched with niobium was explored through optical microscopy (OM), scanning electron microscopy (SEM), electrolytic extraction, X-ray diffraction (XRD), and room temperature dry sliding friction and wear tests. The findings indicate that an optimal nitrogen addition can effectively refine grains and precipitates. Increasing nitrogen content led to a rise in NbCrN formation, with nitrogen increasingly substituting for carbon in NbC, resulting in the creation of Nb(C,N). The niobium-containing precipitates progressively assumed elongated shapes. At a nitrogen level of 115 ppm, the experimental steel demonstrated superior wear resistance, primarily due to the Mechanical Mixture Layer (MML) mitigating metal-to-metal friction and the hard precipitates of niobium and nitrogen in the matrix obstructing abrasive grain displacement. Consequently, the wear mechanism evolved from abrasive to oxidized adhesive wear.