Torsional fretting wear of sulfurized-nitrided layers prepared on axle steel

The sulfurized-nitrided layers were prepared on the surface of LZ50 steel by sulfurized-nitrided duplex processes. Base on the characterizations of the sulfurized-nitrided layers, the torsional fretting wear tests of the sulfurized-nitrided layers and LZ50 steel were carried out in dry condition under different torsional angular displacement amplitudes. The results indicated the sulfurized-nitrided layers were composed of ε-Fe2-3N, γ′-Fe4N, FeS and FeS2 phases. The fretting regimes of the sulfurized-nitrided layers were changed, i. e. the range of the mixed fretting regime was diminished, and the slip regime shifted to the direction of smaller angular displacement amplitude. The friction torques of the sulfurized-nitrided layers were lower than that of the substrate in the partial slip and slip regimes due to the support of the hard nitrided layer and the lubricating of the sulfide layer. Comparing with the substrate, the wear of material reduced greatly for the sulfurized-nitrided layers. The damage in the partial slip regime was slight, but in the mixed and slip regimes the damage mechanisms of the modified layer were mainly delamination, abrasive wear and oxidative wear.