Rail rolling contact fatigue. The performance of naturally hard and head-hardened rails in track: Fid-Bau Portal

Rail rolling contact fatigue. The performance of naturally hard and head-hardened rails in track

Muster, H. / Schmedders, H. / Wick, K. / Pradier, H.

In the framework of the ERRI D 173 programme on fatigue caused by rail rolling contact, the influence of different rail steel grades on the occurence of cracks caused by rolling contact was studied on specially selected curves of four European railway networks. Two lines were operated with and two without lubrication by passing locomotives. The rails were made of continuously cast, vacuum-treated steel with no addition of aluminium for deoxidation. The three rail grades were 900 A in accordance with UIC 860-V (equivalent to 260 HB hardness in the as rolled state) and two head-hardened variants with 340 HB and 370 HB. The test sections are inspected at regular intervals in accordance with a given programme. The results obtained to date after total traffic loading of between 60 MGT and 170 MGT are as follows. Wear is reduced substantially by the use of harder rails and also by constant lubrication. Fatigue defects occured in the form of head-checks on the high rails of the curves; the phenomenon was much more pronounced and the crack distance greater in the case of grade 900 A rails than that of grade 340 HB and 370 HB. With rails of grade 900 A, spalling occured in the case of a lubricated test section with a 350 m (5 deg) curve, this damage was so great that the rails had to be removed after 64 MGT. On samples of grades 900 A (260 HB) and 370 HB taken from this test section it was found that the grade 900 A material exceeds its ductility limit earlier because of pronounced cold deformation so that plastic shear deformations and ultimately cracking and spalling occur. Because of their higher yield point, the head-hardened rails prove far more resistant to fatigue damage. Cold deformation is much lower and so also is crack formation. The service life can therefore be expected to be greater than for grade 900 A rails.