Rail Spike Materials: Q235, 45#, 40Mn2 and 20MnSi Compared

How Rail Spikes Are Classified by Material

Rail spikes hold the rail to the sleeper and resist longitudinal creep and lateral displacement of the track panel. Two families dominate modern supply: the dog spike, a tapered spike driven into a timber sleeper, and the screw spike, a threaded fastener turned into a pre-drilled hole in a timber or concrete sleeper. Material choice fixes the strength, wear resistance and service life of the spike, and the range splits into carbon structural steels for standard lines and manganese or manganese-silicon alloy steels for heavy-haul, high-speed and industrial track.

Materials Used for Dog Spikes

Dog spikes are produced in square or round section, cut or forged to length, with a head that bears on the rail foot and a tapered shank that grips the timber. Common sizes are 5/8 in x 6 in, 9/16 in x 5-1/2 in, 1/2 in x 3-1/2 in and 3/8 in x 3-1/2 in, and other sections and lengths are produced to drawing. The table below lists the materials and surface conditions normally quoted with these sizes.

Materials and Property Classes for Screw Spikes

Screw spikes combine a driven or turned thread with a head that clamps the rail foot or the baseplate, and they are specified by type, raw material, property class and surface finish. The main types are Ss5, Ss8, Ss25 and Ss36 together with the UIC 864-1 series, and the usual raw materials are Q235, 35 steel, 45 steel, 40Mn2 and 20MnSi. Property classes 4.6, 4.8, 5.6 and 8.8 follow the familiar metric fastener convention, in which the first digit gives one tenth of the nominal tensile strength and the second gives the ratio of yield strength to tensile strength.

Carbon Structural Steel versus Alloy Steel

The two groups serve different duty levels, and the difference is visible in the alloy content as much as in the price.

Carbon structural steel. Q235 to GB/T 700, and 35 steel and 45 steel to GB/T 699, are low to medium carbon grades with good strength and plasticity, low cost and easy machining. They suit general railway lines and light-duty track.

Manganese and manganese-silicon steel. 40Mn2 and 20MnSi are alloy grades with higher strength, higher toughness and better wear resistance. They are used where frequent heavy axle loads and impact loads must be tolerated over a long service life.

Special grades. A3 steel is a common carbon steel used for light-duty or temporary track, easy to process but lower in strength and wear resistance than the alloy grades. 55# steel is a medium carbon grade with higher strength and hardness than Q235, chosen where the spike must carry a defined load.

Choosing the Right Material for the Track

Selection follows the track category rather than a single preferred grade. Standard and light lines are normally served by Q235 or 45# steel, which cover rail fixation and load bearing at the lowest cost. Heavy-haul, high-speed and industrial tracks take 40Mn2 or 20MnSi so that wear resistance and impact capacity are raised at the same time. Where the line runs through a corrosive or persistently damp environment, material selection is combined with a surface treatment such as hot-dip galvanizing, zinc plating or a protective paint system, which extends the working life of the spike without changing the grade. Dimensions, thread form, head geometry and any required test certificates are confirmed against the drawing or sample before production, and spikes are supplied together with matched rail pads, tie plates, rail clips and fishplates so that the whole fastening assembly is compatible.

Frequently Asked Questions

Q: What material are rail spikes made of?
Most rail spikes are made from carbon structural steel such as Q235, 35 steel, 45 steel or A3, or from alloy grades such as 40Mn2 and 20MnSi for heavy-haul and high-speed track. Higher carbon grades including 55# are used where greater hardness and load capacity are needed.

Q: What is the difference between a dog spike and a screw spike?
A dog spike is driven into a timber sleeper and grips by friction and the taper of its shank. A screw spike is turned into a pre-drilled hole and holds by thread engagement, so it resists withdrawal far better and can be used in timber or, with a plastic dowel, in concrete sleepers.

Q: Which spikes are suitable for heavy-haul lines?
Heavy-haul and high-speed lines normally use screw spikes in 40Mn2 or 20MnSi, because these manganese-bearing steels provide the strength, toughness and wear resistance needed under repeated heavy axle loads.

Q: What do the property classes 4.6, 4.8, 5.6 and 8.8 mean?
They follow the metric fastener convention. The digit before the point is one tenth of the nominal tensile strength in MPa, and the digit after the point is ten times the ratio of yield strength to tensile strength, so class 8.8 is considerably stronger than class 4.6.

Q: How are rail spikes protected against corrosion?
Spikes are supplied plain and oiled, painted, zinc plated or hot-dip galvanized. In damp, coastal or chemically exposed locations a zinc-based coating or a paint system is normally specified to extend service life.

Q: Can rail spikes be made to a drawing?
Yes. Section, length, head shape, thread form and material grade are all produced to customer drawings or samples, and surface treatment is applied to the specified finish.