The Influence of Decarburized Layer on Rail Surface Fatigue Performance
What is rail decarburization layer and how is it formed?
The rail decarburization layer is a surface layer with lower carbon content formed during high-temperature rolling. It is caused by carbon atoms reacting with oxygen and losing from the steel surface. It is a microstructure change rather than an external mechanical damage. A thin decarburization layer is normal, but an excessive one becomes a defect. It reduces surface hardness and directly affects wear and fatigue resistance.
What risks does an excessive decarburization layer bring?
An excessive decarburization layer has low hardness and deforms easily under train load. It reduces fatigue life and makes the rail surface prone to micro-cracks. Cracks may develop into scabbing, shelling or even spalling. It also weakens welding quality and joint stability. It shortens service life and increases maintenance and replacement costs.
What are the differences between Chinese and international standards on decarburization?
Chinese standards set clear limits for ordinary rails for general-speed lines. International standards such as UIC, EN and AREMA have stricter limits for high-speed and heavy-haul rails. International rails usually adopt precise temperature control to reduce decarburization. Export rails must meet the stricter one of relevant standards. Decarburization control reflects the manufacturing level of rail steel.
How to judge possible excessive decarburization on site?
On-site staff cannot measure thickness directly but can observe abnormal surface conditions. Early excessive wear, uneven bright bands or rapid plastic deformation may indicate a problem. A short service life in a certain section also raises alerts. The most accurate method is metallographic sampling and testing. Regular crack observation also helps identify potential surface defects.
What is the difference between decarburization, scale and rust?
Decarburization is an internal structure defect with low carbon content, invisible to naked eyes. Scale is surface oxide formed at high temperature, mostly removed before installation. Rust is later corrosion product, unrelated to internal structure. Decarburization harms strength and fatigue; scale and rust mainly affect appearance. They have different causes, positions and hazards and should not be confused.