Classification by Mass per Meter
National standard rails are commonly classified by their approximate mass per meter: 43 kg/m, 50 kg/m, 60 kg/m and 75 kg/m. The mass reflects the load-bearing capacity of the rail: heavier rails have larger cross-sections and can carry larger axle loads and traffic volumes. The choice of rail class is one of the fundamental design decisions of a railway line, because it sets the limit of what the track can carry for decades.
Classification by Material
In terms of material, rails fall into carbon rails, micro-alloyed rails and low-alloy rails. Carbon rails such as U71Mn have lower cost and mature production processes, but their strength and wear resistance are relatively limited, which makes them suitable for ordinary lines. Micro-alloyed rails such as U75V add elements like vanadium and titanium, which refine the grain structure and improve strength, toughness and fatigue resistance, making them suitable for heavy-haul lines. Low-alloy rails add a small amount of alloy such as chromium, giving excellent wear and corrosion resistance for harsh environments or highly worn lines.
Application Scenarios by Class
The 43 kg/m rail is generally used on branch railways or lines with small traffic volume, because its bearing capacity is relatively low. The 50 kg/m and 60 kg/m rails are the workhorses of the network: 50 kg/m is often used on existing ordinary trunk railways, and 60 kg/m is the common choice for newly built ordinary trunk lines and some passenger dedicated lines. The 75 kg/m rail has high strength and is mainly used on heavy-haul railways, where it bears large axle loads and traffic volumes.
How to Select the Right Rail
Selection requires a comprehensive consideration of line purpose, traffic volume, axle load and driving speed. Passenger dedicated lines need good ride comfort and mostly select high-quality rails of 60 kg/m and above. Heavy-haul railways, with large axle loads and traffic volumes, should choose 75 kg/m rails with high strength or rails of special materials. Branch railways or lines with small traffic volumes can select 43 kg/m or 50 kg/m rails according to cost and demand. The selected rail must also match the fastening system, fishplates and other track components.
Standard Lengths and Laying
In terms of standard lengths, 43 kg/m rails are 12.5 m or 25 m long, while rails above 50 kg/m are available in 25 m, 50 m and 100 m lengths. Seamless lines often use 100 m rails produced by the steel mill, which are welded into 500 m long rails in a welding plant and then welded to the required length on site. Longer rails reduce the number of joints, reducing impact and vibration during train operation and improving line smoothness, but they require higher technical and equipment standards for laying, including professional welding equipment and processes.
Frequently Asked Questions
What are the common national standard rail classes? The common classes by mass are 43 kg/m, 50 kg/m, 60 kg/m and 75 kg/m.
What is the difference between carbon and micro-alloyed rails? Carbon rails are cheaper but limited in strength and wear; micro-alloyed rails add vanadium or titanium for higher strength and fatigue resistance.
Which rail is used on heavy-haul lines? The 75 kg/m rail, because its high strength carries large axle loads and traffic volumes.
What factors drive rail selection? Line purpose, traffic volume, axle load and driving speed.
Why are longer rails used on seamless lines? Fewer joints reduce impact and vibration, improving smoothness, but require professional welding equipment.