Failure causes and hardening techniques of railway axles – A review from the perspective of structural integrity

Abstract

Fatigue is a classic and longstanding issue, which challenges railway axles’ structural integrity. In spite of its almost 200 years of research history, it has always been a hot topic considering the increasing service speed and safety concern. Except for inclusions, defects from axle steel ingot, corrosion pit, fretting and flying ballast impact damage also bring potential failure risk. A broad overview on the four kinds of defects responsible for axle failures is given in present paper. Surface hardening techniques are utilized during axle manufacturing aiming to improve surface integrity of railway axles by means of both retarding crack initiation and decelerating crack growth rate due to introduction of residual compressive stress and formation of hardened layer. Mechanisms of surface hardening techniques, including shot peening, deep rolling and induction hardening, are briefly introduced and their applications to axles are reviewed. Based on state-of-the-art of axle manufacturing, induction hardening and anti-corrosion/impact coating is recommended as an efficient and prospective combination with regard to structural integrity of railway axles.