A railroad spike is a large, specialized nail driven into the wooden cross ties of a railway to secure the rails and tie plates in place. This component maintains track gauge, the precise distance between the two rails, ensuring train safety and operational stability. The spike must withstand substantial lateral forces and constant vibration from passing trains. Therefore, the material composition must balance strength with a degree of flexibility. The steel used is carefully chosen and manufactured according to precise industry standards to perform this demanding function reliably.
The Standard Steel Classification
Railroad spikes are made from carbon steel, a common iron alloy with controlled amounts of carbon. Specifically, they are typically produced from medium-carbon steel, though the precise carbon content varies based on the intended use. The presence of carbon significantly increases the steel’s hardness and tensile strength compared to low-carbon steel. This allows the spike to resist bending under the track’s load.
The railway industry often uses the term “Higher Carbon” (HC) to denote a specific grade of spike. These HC spikes typically contain a minimum of 0.30% carbon, placing them at the lower end of medium-carbon steel (0.3% to 0.6% carbon). This level provides the necessary rigidity without making the steel overly brittle, ensuring the spike is tough enough to absorb impact without fracturing.
Industrial Specifications and Performance Requirements
The material must meet stringent performance criteria established by regulatory bodies to ensure safety. In the United States, the American Society for Testing and Materials (ASTM) sets requirements under standards like ASTM A65, which specifically covers steel track spikes. This specification categorizes spikes into different grades, such as a lower carbon Grade 1 and a higher carbon Grade 2, selected based on the stresses of the track section.
These specifications mandate specific mechanical properties that guarantee the spike’s structural integrity, not just chemical composition. Standard carbon steel spikes are required to meet a minimum tensile strength, often around 520 megapascals (MPa), to withstand the pulling and shear forces exerted by the rail. The steel must also possess adequate impact resistance to prevent brittle failure, especially in cold environments where metal becomes less ductile.
To achieve this balance of strength and toughness, the finished spike’s hardness is closely controlled, typically falling within 25 to 35 on the Rockwell C scale (HRC). Limiting elements like phosphorus and sulfur is necessary, as excessive amounts introduce weaknesses. Phosphorus can cause cold brittleness, while sulfur can lead to hot shortness during manufacturing. These controlled metrics ensure the spike handles the constant, cyclical loading of train traffic without prematurely failing.
How Railroad Spikes Are Manufactured
The desired mechanical properties are achieved through hot-forging, a specific high-temperature manufacturing process. This method begins with cutting steel bar stock into blanks, which are then heated to temperatures ranging from 900°C to 1100°C for shaping. The high heat makes the steel malleable enough to be formed without cracking and allows the internal grain structure to be refined.
The heated blanks are fed into specialized machinery that first points the tip and then uses a powerful heading machine to form the characteristic large, flat head. Forming the spike while hot is a deliberate action because this process refines the metal’s grain structure. This grain refinement contributes significantly to the spike’s final durability and its resistance to fatigue under repeated stress.
Following forging, the spikes often undergo a heat treatment, such as quenching and tempering or normalizing, to further enhance their strength and fatigue life. This final thermal treatment locks in the desired hardness and toughness. It ensures the manufactured spike meets the mandated performance requirements for long-term railway service.