EFFECT OF LASER QUENCHING ON MICROSTRUCTURE AND PROPERTIES OF THE SURFACE OF TRACK MATERIALS

With the rapid development of rail transit, the wear problem of track has become a serious challenge. Laser quenching is a new surface modification process, and it is expected to improve the service life of the track. Laser quenching was carried on the surface of rails by using 6 kW fiber laser. The microstructure, hardness, wear resistance, and contact fatigue resistance (CFR) of the phase transformation hardening layer were studied by optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness tester, and wear tester. The results show that the microstructure of the hardened layer is composed of fine martensite and a small fraction of retained austenite. The microstructure of substrate is pearlite and ferrite. The hardness of rails quenched by the laser increased nearly two times than that of the un-treated track materials. When the laser power is 1000 W, the depth of hardened layer reaches 0.8 mm, and the wear resistance of hardened layer increases 167% than that of the substrate. The number, length, and depth of fatigue cracks decreased on the cross-section of worn rails after laser quenching, which indicates that laser quenching can improve the CFR of rails.