A New Process for Imparting Fatigue Damage Resistance to Railway Axles

Since the beginning of the railway industry, one of the most serious mechanical failures of critical components has been the fatigue failure of axles. About half of these fatigue failures initiate in the axle’s main body between the wheel seats due to surface damage and about half initiate in the wheel seat and journal filet areas due to corrosion and fretting. Fatigue cracks in the axle body almost always initiate at surface damage such as scratches, dents, and gouges (e.g., due to ballast impact, improper handling, etc.) where bending stresses are greatest. Efforts to improve axle fatigue life have focused on developing new, more fatigue-resistant steel grades; increasing the body diameter to reduce operating stresses; and modifying the properties (most notably near the axle surface) of the steel through heat treatment. The new process described in this paper improves an axle’s resistance to fatigue failure by imparting a refined microstructure and beneficial compressive residual stress to just the body without additional alloy enhancements or design changes. A 35% increase in fatigue strength and 47% increase in near-surface yield strength over standard Grade F axles have been obtained while also achieving modest improvements in ductility.