reedy

In metallurgy, reedy describes cast or worked metal that has fractured into a bundle of thin rod-like pieces held together only weakly, if at all. The fracture typically runs lengthwise through the material rather than across it, leaving what looks like a sheaf of parallel fibres or reeds. This condition usually appears in ingots or blooms after solidification, especially in steel that has cooled too quickly or under poor casting conditions.

A reedy ingot will show these distinct longitudinal splits when struck or bent, with the pieces still mechanically interlocked but lacking true metallurgical continuity. The defect becomes obvious during the first stages of rolling or forging, when the pieces separate completely under stress. Historical iron and steel production saw this fault regularly in poorly controlled casting practices, where uneven cooling or residual tension in the ingot mould created the conditions for reedy failure.

Reedy conditions arise from rapid surface cooling combined with slower interior cooling, which sets up stresses that pull the nearly-solid metal apart before it has fully fused. Segregation of impurities along grain boundaries can worsen the effect. Prevention depends on controlled cooling rates, proper ingot mould design, and sometimes hot-top casting or exothermic coverings to maintain a more uniform temperature gradient. Reedy material cannot be salvaged once it has formed, so detection early in the ingot stage is critical to avoid wasting time on rolling or forging.

The term itself, borrowed from the appearance of reeds in a bundle, entered metallurgical vocabulary to describe this particular fracture pattern. It remains in use today despite advances in casting technology, mainly because foundries still encounter it in edge cases: unusual steel grades, oversized ingots, or plant conditions where temperature control has been compromised. Modern continuous casting has largely eliminated the problem for conventional production, but ingot casting for large forgings or specialty alloys still carries the risk.