Functions of steel rail:
- Provide the wheels with continuous, smooth and the least resistance of the rolling surface, guide the rolling vehicle forward.
- The rail is subjected to great vertical pressure from the wheels and will be passed to the sleepers in a dispersed form.
- Provide conductor for track circuit.
Types and length of steel rail:
- Rail types are expressed as mass per 1m rail. Standard rails are 75kg/m, 60kg/m, 50kg/m, 45kg/m,43kg/m, etc.
- The standard rail length is 12.5m and 25m.The length of the fixed-length rail used for new passenger dedicated lines in China is 50m or 100m.
Rail section and size:
There are three parts in steel rails: rail head, rail waist and rail bottom.The rail head shall have sufficient surface area and thickness to delay the crushing and abrasion of the rail head.Rail waist mainly bears shear force, which can make the rail have greater vertical stiffness.Rail bottom is the pressure distribution and stable, and should have a certain width.Rail cross section is an I-shaped section.
Material and mechanical index of rail:
Material of the rail refers to the chemical composition and metallographic structure of the rail. The premise to make the rail have high reliability is that the rail material has high purity and reasonable chemical composition.The main form of rail quality problems is due to the rail’s internal inclusions and defects caused by fatigue damage.Therefore, improving the purity of rail material is one of the effective ways to reduce rail fatigue damage, improve rail reliability and prolong service life.
Carbon (C) is the main source of rail tensile strength, generally 0.65%, but generally less than 0.82%. If the carbon content is too large, the elongation, section shrinkage and impact toughness of the rail will be reduced.
Manganese (Mn) can improve rail strength and toughness, and remove harmful iron oxide and sulfur inclusions, such as steel containing manganese content more than 1.2%, it is called high manganese steel, steel hardness, impact resistance, abrasion resistance can be greatly improved, but manganese has a negative impact on rail welding.
Silicon (Si) is easy to combine with oxygen to remove bubbles in the steel and increase the density of the steel. If the silicon content in the steel is relatively high, the wear resistance of the steel can also be improved. If SiO2 exists in the steel with non-metallic inclusions, it is often the fatigue damage source of the steel.
Phosphorus (P) is a harmful component, such as too much phosphorus in the rail, it will appear cold brittleness, in the cold region, easy to cause rail fracture.
Sulfur (S) is also a harmful component. If too much sulfur is contained in steel, hot brittleness will occur when the rail temperature reaches 800~1200℃, resulting in rail fracture during rolling or hot processing and a large amount of waste products.General requirements of phosphorus and sulfur content are less than 0.04%, but some foreign rail phosphorus and sulfur content or less than 0.015%.
Mechanical properties of steel rail:
It includes strength limit, yield limit, fatigue limit, elongation, area shrinkage, impact toughness and Brinell hardness,etc.These indexes have great influence on the bearing capacity, abrasion, crushing, fracture and other damage of the rail.