Mitigation of subsurface crack propagation in railroad rails by laser surface modification

SURFACE & COATINGS TECHNOLOGY

卷:106

Article; Proceedings Paper

DiMelfi, RJ ; Sanders, PG ; Hunter, B ; Eastman, JA ; Sawley, KJ ; Leong, KH ; Kramer, JM

关键词: amorphous metals;    friction;    laser glazing;    railroad rails;    rail steels;    wear;   

DOI  :  10.1016/S0257-8972(98)00487-3

来源: Elsevier

【 摘 要 】

We, address the mitigation of subsurface crack propagation in railroad rails via laser surface modification. Microhardness scans and tensile tests, performed on samples of unused and heavily used rail heads, indicate that the severe cyclic plastic deformation that occurs at rail gage corners, during service, leads to cracking. Reducing rail-wheel friction reduces shear forces that contribute to this problem. Laser glazing, the rapid melting and rapid re-solidification of a thin surface layer, is shown here to reduce the friction coefficient of rail steel. These treatments produce a thin (< 100 mu m) glazed surface layer, intimately bonded to a martensitic heat-affected-zone that is, itself, well bonded to the pearlitic rail steel substrate. The microhardness (Vickers) of the glazed layer ranges from H(v)655 to H(v)800, while that of the heat-affected-zone ranges from H(v)470 to H(v)1072. The pearlitic steel substrate typically has a hardness of H(v)300. Static block-on-ring friction experiments on standard specimens extracted from laser-treated samples show reductions in the friction coefficient by about 25% relative to untreated surfaces at loads corresponding to prototypic rail service loads. X-ray scans of treated surfaces were inconclusive regarding the nature of the glazed layer. The top surface of a six-foot length of rail was laser glazed on two areas, each similar to 10 cm long and similar to 2 cm wide. Friction measurements were made on these surfaces on the Association of American Railroad's Cyclic Rolling-Sliding Wear Machine after they were subjected to 20,000 run-in cycles at loads prototypic of service. The laser treatments remained intact after these cycles. Reductions of friction coefficient of similar to 40%, relative to untreated surfaces, were observed, which corresponds to a calculated reduction in the crack propagation rate by similar to 79%. (C) 1998 Elsevier Science S.A.

【 授权许可】

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