Comparative Tribological Behavior of Nitrided and Non-Nitrided SAE XEV-F Valve Steel in Dry Sliding

The differences between tribological performance of nitrided and non-nitrided samples of SAE XEV-F valve steel were investigated in dry sliding conditions. Experimental tests were conducted using an SRV-4 tribometer in a ball-on-disc configuration (i.e. non-conformal contact) with reciprocating type of movement. Two kinds of samples (discs) were tested: valve steel and nitrided valve steel. The ball (i.e. the counter-body) was made of AISI 52100 bearing steel. Room temperature and fixed conditions of time, load, frequency and stroke were used. Wear was evaluated by means of mass loss, from both disc and ball, and post examination of the worn surfaces. Post examination was conducted using scanning electron microscopy (SEM), coherence correlation interferometry (CCI), and X-Ray diffraction (XRD). Wear debris resulting from tribological interaction were also investigated using SEM and XRD. Additionally, the friction coefficient response curve was recorded and discussed regarding possible transitions observed during tests. Results show good repeatability. The nitrided SAE XEV-F valve steel samples presented wear values lower by nearly two orders of magnitude when compared to the untreated samples.