How railroad rail is made

Make very clean steel

A basic oxygen or electric arc furnace makes high-carbon steel, then vacuum degassing removes dissolved hydrogen and oxygen. Hydrogen left in the metal can crack a rail months or years after it is laid.

Cast the blooms

Degassed steel is continuously cast into large rectangular blooms, typically around 280×380 mm.

around 280×380 mm

Roll through shaped grooves

From a reheating furnace, the bloom passes through roughing, intermediate and finishing mills with grooved rolls. A universal mill usually does the last passes, setting head, web and foot at once to within about ±0.5 mm.

reheated to about 1250 °C

Harden the head

Spray quenching with the rail's own rolling heat, or later quenching and tempering in a separate facility, can harden the running surface to HB300 or more. The core stays tougher.

Control the cooling

On the cooling bed, mills control how the rail lies, since the thick head and thinner foot shrink at different rates. Rushed cooling locks in stress that shows up as warping weeks or months after installation.

Straighten with rollers

A roller straightener works the rail from the horizontal and vertical directions. One patent describes massive rollers exerting 100 to 180 tons.

Cut and mark

The rail is cut to ordered length, with 12m, 25m and 100m all common, and may be drilled for bolts. Grade, melt number and maker are rolled into the web or stamped on the end.

Inspect by ultrasound

Ultrasonic testing looks for inclusions, voids and cracks inside the head, web and foot. Eddy current testing catches surface flaws the eye would miss.

Weld into long strings

Lengths are joined by welding, in a depot or in the field, which removes joints, the weakest part of a line. Welded track began around the 1940s and was widespread by the 1960s.