Steel rail raw material and structure

Railtrack Part Material Introduction - Steel Rails

Steel Rails are the key parts of the rail track laid in two parallel lines to provide a continuous, steady and level surface for the runnings of trains. Heavier train and fast speed requires higher requirements to withstand stresses, so they are produced from high carbon steel (carbon -0.6 % to 0.8 %, manganese 0.8%-1.3 %, silicon 0.1 % -0.5 %, sulphur and phosphorus0.03 % maximum each, and aluminum 0.015 % maximum). Some grades of steel contain chromium (Cr- 0.8 % to 1.2 %). Steel Rails are also produced from special steels containing niobium (Nb- 0.04 % max.) or vanadium (V-0.2 % max.). In fierece conditions steel rails has to be made from corrosion resistant steels have also been developed.

Steel Rail Role in Railtrack System

Steel rail is the most important part in rail track system, it is a steel profile with shape of inverted T. Variety of steel rails are developed with different weight and dimensions. All types of Steel Rail has hardend head and flat bottom. This special shape is designed with a group of rail fastening parts that fix steel rail on rail sleepers: Rail Spike, Screw Spike, Elastic Rail Clip, Rail Clamp, etc.

Steel Rail Sections looks like similar to steel profiles used for steel structure in buildings, their main functions in rail track are as follows:

• Rails provide a continuous and level surface for the movement of trains.
• Rails provide a pathway which is smooth and has very little friction. The friction between the steel wheel and the steel rail is about one-fifth of the friction between the pneumatic tyre and a metalled road.
• Rails serve as a lateral guide for the wheels.
• Rails bear the stresses developed due to vertical loads transmitted to them through axles and wheels of rolling stock as well as due to braking and thermal forces.
• Rails carry out the function of transmitting the load to a large area of the formation through sleepers and the ballast.

Main Parts of Steel Rail

The main parts of a rail section are head, web, foot, fishing angle, and height of the rail. The requirements, as well as the main considerations, for the design of these rail parts are as follows.

• Head – The head of the rail needs to have adequate depth to allow for vertical wear. The rail head should also be sufficiently wide so that not only is a wider running surface available, but also the rail has the desired lateral stiffness.
• Web – The web is to be sufficiently thick so as to withstand the stresses arising due to the loads borne by it, after allowing for normal corrosion.
• Foot – The foot is to be of sufficient thickness in order to withstand vertical and horizontal forces after allowing for loss due to corrosion. The foot is to be wide enough for stability against overturning. The design of the foot is to be such that it can be economically and efficiently rolled.
• Fishing angles – Fishing angles must ensure proper transmission of loads from the rails to the fish plates. The fishing angles are to be such that the tightening of the plate does not produce any excessive stress on the web of the rail.
• Height of the rail – The height of the rail needs to be adequate so that the rail has sufficient vertical stiffness and strength as a beam.

The requirements for an High Quality Steel Rail are as follows.

• The rail should have the most economical section consistent with strength, stiffness, and durability.
• The centre of gravity of the rail section should preferably be very close to the mid-height of the rail so that the maximum tensile and compressive stresses are equal.
• There should be an economical and balanced distribution of metal in the different parts of the rail so that each of them can fulfill its requirements properly.

Steel Rail Structure and Length

Rail is produced from fully killed steel and each section of the rail is to be accurately rolled to its respective template within permissible tolerance or variations. It is to be free from all detrimental defects such as cracks of all kinds, flaws, piping, and lack of metal that have an unfavourable effect on the behaviour of rails in service.  It is also to be absolutely straight. Tolerances for end straightness are very stringent.