billet

A billet is a short, solid length of metal that has been roughly shaped but not yet finished. It occupies the middle ground in metal processing: too advanced to be raw stock, but not refined enough to be a final product. Billets typically measure a few inches to a few feet in length and are the direct output of primary shaping processes like casting or extrusion. They serve as feed material for secondary operations such as rolling, forging, or drawing.

The most common billets come from continuous casting, where molten metal is poured into a mold, cooled partially, and then withdrawn as a long strand. This strand is cut into lengths ranging from 500 mm to 2 m depending on the metal and intended end use. Steel billets for wire rod mills are often 100 to 150 mm in cross-section; aluminum billets for extrusion can be 200 to 250 mm in diameter and weigh several hundred kilograms. Copper and brass billets follow similar patterns. The cross-sectional shape is usually square, round, or rectangular, chosen to suit the downstream machinery.

Temperature control is critical at this stage. Billets destined for hot working must be kept within a narrow range, typically 1100 to 1200 degrees Celsius for steel, to maintain workability without excessive oxidation or grain growth. Cold billets intended for cold drawing or cold rolling are stored at ambient temperature. Surface quality matters more than it might appear: cracks, deep scale, or segregation in the billet will propagate into the finished product and create scrap or weak points.

Variants and uses across industries

In rod and wire mills, billets feed into roughing stands where they are elongated and reduced in section. In forging shops, billets are reheated and then hammered or pressed into shape. Extrusion presses accept billets as their raw material, pushing them through dies to create complex profiles. Tube mills use pierced billets. The billet stage is where defects are graded and rejected before expensive finishing work begins, making the quality of the billet a major cost driver in downstream production.

The term comes from French billette, meaning a short stick or log, reflecting the simple geometry. In trade conversation, "billet" is nearly always paired with its material: steel billet, aluminum billet, brass billet. Suppliers list billets by their cross-sectional dimensions and length, often with chemistry specification and surface finish grade. Knowing the billet specification is essential because it determines what tolerances and properties the finished part can achieve.