Failure Modes of Carbon Nitride Coated Steels During Rolling Contact

摘要

Carbon nitride thin films were deposited on the substrates of 0.55 wt percent C-1.68 wt percent Mn induction-hardened steels by ion beam assisted deposition. Rolling contact fatigue tests were conducted using Polymet RCF-1 machine under elastohydrodynamic lubricating condition at room temperature. Failure modes during rolling contact were investigated on the basis of surface and subsurface observations of the failed coated steels. Many micropits were formed on the creater surface of wear track of the coated steels in the wedge forming mode. Subsurface cracks were initiated at the relatively large oxide inclusions and propagated in the intergranular fracture mode. It was also found in the surface of wear track after the substrate deformation during repeated rolling contact that Carbon and Oxygen elements of the coating were retained. It was suggested on the basis of the experimental results that failures during rolling contact of the steels were delayed or protected by carbon nitride coating of the steels with smaller oxide inclusions and finer grains.