Rail (Railway)

Rail is a steel component in railway systems that guides wheeled vehicles, serving both as a carrier and a director. Rails transfer loads to sleepers, which then distribute them to the ballast, ensuring that wheels move safely, quietly, and with minimal friction.

Structural Composition of Rails

Modern railway rails are manufactured from homogeneous steel materials shaped into a standard I-shaped (inverted T) cross-section. Their fundamental structural components are:

• Rail Head: The part that comes into direct contact with the wheels. It is specially hardened to resist wear.
• Rail Web: The central portion that provides mechanical strength. It resists impact, buckling, and bending.
• Rail Base (Foot): The wide surface on which the rail rests on the sleeper. It distributes the load and serves as the mounting point for fastening components.

These three components work together to determine the rail’s performance criteria, including strength, elasticity, and longevity.

Rail Material and Manufacturing Technology

Rails are typically produced from high-strength carbon steels containing 0.6–0.8% carbon, alloyed with elements such as manganese, silicon, and vanadium. The most common production standards in Türkiye and worldwide are the UIC 60 and S49 rail profiles.

Rails are shaped using hot rolling and subsequently undergo heat treatment or specialized cooling techniques to enhance mechanical properties such as surface hardness and toughness.

Rail Profiles and Types

The main types of rails used in railway lines are:

• UIC 60: Weighing 60.21 kg/m, this is a durable rail type used on high-speed train lines.
• S49: Weighing 49.43 kg/m, it is suitable for medium traffic loads.
• R220, R260, R350 HT: Rail steel quality classes defined according to the European EN 13674 standard.
• Maintenance Rail: Lighter-profile rails used in maintenance and service tracks.

When selecting rail profiles, factors such as line type (load, speed, gradient), ground conditions, and maintenance capabilities are taken into account.

Mechanical Properties of Rails

The key mechanical properties that determine rail performance are:

• Tensile Strength: Rail steel must exhibit a minimum tensile strength of 880–1180 N/mm².
• Hardness: The rail head has a Brinell hardness range of 260–350 HB.
• Wear Resistance: Especially the rail head must resist high traffic density.
• Toughness: The structure must resist fracture under dynamic loading.
• Impact Resistance: It must maintain its shape under high-speed and heavy-load conditions.

These properties are directly related to the alloy composition and heat treatment used during rail production.

Physical Properties of Rails

• Length: According to TCDD standards in Türkiye, rails are typically 36 meters long. On high-speed lines, they can be welded together to achieve lengths of 180 meters or more.
• Weight: The UIC 60 rail profile weighs 60.21 kg/m; a 36-meter rail weighs approximately 2.17 tons.
• Thermal Expansion: Rails are affected by seasonal temperature variations; therefore, expansion joints or welded systems are used during installation.

Compatibility of Rails with Fastening Systems

Rails are installed together with sleepers using various fastening components such as spikes, clips, anchors, and clamps. In concrete sleeper systems, modern elastic clip fastening systems (e.g., Nabla, E-clip) are employed. These fastening systems ensure that rails:

• Maintain lateral stability.
• Accommodate thermal movement.
• Absorb vibrations to protect the underlying structure.

Rail Wear and Maintenance Requirements

Rails, particularly the rail head, gradually wear due to wheel contact. Additionally, problems such as:

• Wavy wear
• Lateral plastic flow
• Rail head cracking
• Rail fractures

may also occur. Therefore, rails are periodically inspected using methods such as:

• Grinding
• Ultrasonic testing
• Surface hardness measurement
• Thermal imaging

TCDD carries out these inspections using its own maintenance teams and specialized measurement trains.

Rail Standards and Implementation in Türkiye

Rails used in Türkiye are manufactured in accordance with the TS EN 13674-1 standard. TCDD procures both imported and domestically produced rails. The conformity of rails is documented through quality control processes including:

• Chemical analysis
• Mechanical testing
• Microstructure evaluation