UIC Leaflet 820: Technical Specification for the Supply of Axles

What is UIC Leaflet 820?

UIC Leaflet 820 is a fundamental technical document titled “Technical specification for the supply of axles for tractive and trailing stock.” The axle is perhaps the most critical component of Rolling Stock; it supports the entire weight of the vehicle and must withstand rotating bending stresses throughout its service life.

This leaflet provides the Technical Delivery Conditions that manufacturers must meet to supply axles for international rail traffic. It covers the entire production chain, from the melting of the Axle Steel to the final machining and inspection phases, focusing on preventing fatigue-related failures.

Metallurgical and Manufacturing Standards

UIC 820 dictates rigorous standards for the material used in axles. Unlike standard construction steel, axle steel must be exceptionally clean and homogenous.

• Manufacturing Process: Axles must be produced through Forging or rolling from vacuum-degassed steel ingots. This ensures the removal of impurities that could act as crack initiation points.
• Heat Treatment: Mandatory normalization or quenching and tempering processes are required to achieve a fine-grained structure, which is essential for high Fatigue Strength.
• Chemical Composition: Strict limits on elements like Sulfur and Phosphorus to prevent brittleness, especially in cold operating environments.

Testing and Quality Assurance

To ensure safety, every axle batch must undergo comprehensive testing as defined by UIC 820:

• Mechanical Testing: Tensile and impact tests (Charpy V-notch) are conducted on samples taken directly from the axle ends to verify strength and toughness.
• Non-Destructive Testing (NDT): Every single axle must undergo 100% Ultrasonic Testing (UT) to detect internal inclusions and Magnetic Particle Inspection (MPI) to find surface-breaking cracks.
• Dimensional Accuracy: Verification of the wheel seats, journal diameters, and transition radii, where even a slight error in machining can lead to stress concentration.

Relationship with EN 13261

In contemporary European rail operations, the technical content of UIC 820 has been largely mirrored and formalized in EN 13261. While the European Standard is now the primary regulatory document for the EU, UIC 820 remains a vital reference for global railway networks and the historical basis for current wheelset safety engineering.

Comparison: Typical Axle Steel Grades (UIC 820)