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.
Lugged steel frame construction
Lugs used today on higher performance bicycles are investment cast (aka lost wax process). Copies of the lugs are made in wax, and they are attached together into a "tree". The tree is surrounded by ceramic and fired in a kiln, thereby melting the wax and setting the ceramic. Finally, molten steel is poured in to produce the lug. Cast lugs have many advantages over stamped lugs: they allow much finer detail, tighter tolerances (and correspondingly less manipulation and file work), and more accurate angles, and they can be made from superior materials (chromoly or stainless steel). The disadvantages of cast lugs are few: casting doesn't allow for long points or cutouts (done for aesthetic appeal), it is difficult to bend the lug to change the angle (requiring framebuilders to order lug sets that precisely match the desired frame geometry), and they are more expensive.