Cast iron
Cast iron is made from pig iron, which is the product of smelting iron ore in a blast furnace. Cast iron can be made directly from the molten pig iron or by re-melting pig iron, often along with substantial quantities of iron, steel, limestone, carbon (coke) and taking various steps to remove undesirable contaminants. Phosphorus and sulfur may be burnt out of the molten iron, but this also burns out the carbon, which must be replaced. Depending on the application, carbon and silicon content are adjusted to the desired levels, which may be anywhere from 2–3.5% and 1–3%, respectively. If desired, other elements are then added to the melt before the final form is produced by casting.
Cannon
Field artillery cannon in Europe and the Americas were initially made most often of bronze, though later forms were constructed of cast iron and eventually steel. Bronze has several characteristics that made it preferable as a construction material: although it is relatively expensive, does not always alloy well, and can result in a final product that is "spongy about the bore", bronze is more flexible than iron and therefore less prone to bursting when exposed to high pressure; cast iron cannon are less expensive and more durable generally than bronze and withstand being fired more times without deteriorating. However, cast iron cannon have a tendency to burst without having shown any previous weakness or wear, and this makes them more dangerous to operate.