| As a new kind of spring steel with excellent performance,60Si2CrA is used as material of the elastic rods in rail fasteners to supply higher fastening pressure and longer service life. However, in practical application, failure problems as loosening or fracture of fastener system happen during the life cycles of the elastic rods, due to the friction and wear that occurs between the elastic rod and base plate. The wear of the elastic rod results in the size change of the contact surfaces and the decrease of the actual fastening pressure, and stress concentration produces at the wear zone to promote the fretting fatigue damage to fracture. Therefore, it is important to improve the wear resistance of this kind of spring steel to increase the actual service life and to guarantee the safe operation of the railway.In this paper, the60Si2CrA steel was treated to obtain three kinds of samples by ion nitriding and laser quenching in single and combination processes, i.e. ion nitriding (IN), laser quenching (LQ), and combination treatment (CT) of first IN then LQ. On a PLINT fretting wear test machine, the tangential reciprocating fiction and wear tests for the substrate material and three kinds of modified layers under different displacement amplitudes and normal loads were carried out with the contact configuration of ball-on-flat. Combined with the analyses of micro-hardmeter, X-ray diffractomer (XRD), optical microscope (OM), scanning electron microscopy (SEM), electron energy dispersive X-ray spectrum (EDX) and3D profile-meter, the material performances and friction and wear properties of all the samples were analyzed in detail. The main results were as follows:1. The surface modification treatments of three ways could all enhance the hardness of the60Si2CrA steel. The IN samples presented high surface hardness but low hardened-layer depth, the LQ samples achieved both high surface hardness and hardened-layer depth, and the CT samples appeared the highest surface hardness and the hardened-layer depth did not reduce obviously compared with the LQ samples.2. The reciprocating sliding wear tests indicated that all the surface modification treatments presented the anti-friction action with decreasing of the friction coefficients. The friction coefficients of the substrate material were the highest, but decreased with the increase of the displacements and normal loads. The friction coefficients of the IN samples increased with the increase of the displacement, and they were the lowest under lower normal loads but ascended greatly under high normal loads. The friction coefficients of the LQ and CT samples were in the middle, they increased with the increase of the displacement amplitudes and were the lowest of all under the higher normal loads. The friction coefficients of the CT samples were always lower than that of the LQ samples.3. The wear mechanisms of the60Si2CrA steel substrate and three kinds of surface modified samples were abrasive wear and oxidation wear, and the oxidation wear debris played an important role during the wear processes. The wear scars of the substrate appeared higher plastic deformation. A debris anti-friction mechanism was formed well combined with the adhesion of the debris. For the IN samples, a severer abrasive wear was formed due to the brittleness of the hardened layer. And the LQ and CT samples of were worn slightly.4. All the three surface treatments improved the wear resistance of60Si2CrA steel in different degrees. The improvement of the IN layer was limited because of serious abrasive wear. However, for the LQ samples, the wear resistance improved greatly due to the higher hardness and thicker hardened-layer of the modified layer, and this superiority was more obvious with the increase of the normal loads. For the combination treatment of first ion nitrating then laser quenching, the advantages of the two sample surface treatment ways were carried forward to appear a well combination effect, and the best anti-wear property was displayed. |
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