Fatigue failure of a flash butt welded rail.

Abstract

Medium carbon steel rails are commonly jointed by means of a flash butt welding procedure. To ensure an adequate service life for the structural component commonly subjected to fatigue loading, a rigorous quality control should be performed, both in welding parameters and in the surface quality of the welded joint. This work investigated the cause of a recurrent failure in a railway, with cracking always initiated in the rail in the region of the welded joint. All standard procedures of failure analysis were applied, with a careful assessment of the material characteristics and the fractured surface. It was concluded that fatigue cracks initiated near the weld bead and spread in a brittle mode, leading to premature fracture of the material. An in-depth analysis of the early cracks showed that the surface finishing of the weld bead was not appropriate, generating undesirable stress concentration. A recommendation to change the procedure of surface finishing of welded joint was held, aiming to decrease the number of accidents on the railway line.