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.
Garter spring
Carbon steel wire is typically used for garter springs due to its affordable price and usability, in comparison to stainless steel. Carbon steel springs tend to have very high yield strengths, and are able to return to their original shape when temporarily deformed. The carbon content in carbon steel wires range from 0.50 to 0.95 percent. This relatively small amount of carbon is enough to improve the toughness of the spring. The close proximity to oil and high-pressure engines mean heat treated garter springs are essential for enduring temperatures over 100 °C (212 °F). However, carbon steel is not suitable for highly corrosive environments; stainless steel would be a more viable option. Stainless steel differs from carbon steel in the amount of chromium present; stainless steel has between 10.5% to 11% chromium by mass, while carbon steel has about 1%.