Materials Glossary
Steel is iron plus a short list of added elements, each doing a specific job — hardening it, toughening it, protecting it from corrosion, or making it easier to cut. This page is a quick-reference map of the major players. For the full depth on any one element, follow the link through to its own page.
Plain iron on its own is soft and doesn't harden well. Alloying elements are added in controlled percentages to change that — raising strength, hardness, toughness, or corrosion resistance to suit an engineering job. From a machining standpoint, those same elements are also the reason two steels that look identical on a print can cut completely differently: one grade's chromium and molybdenum content can demand a tougher grade and slower speed than a plain carbon steel of similar hardness. Knowing what each element contributes helps explain why a material behaves the way it does under the tool, not just how strong it is on a spec sheet.
Carbon (C) is the primary hardening element in steel — more carbon means more strength and hardness, at the cost of ductility. It's also the reason carbide cutting tools exist in the first place.
Chromium (Cr) drives hardenability and, above roughly 11%, forms a protective oxide layer that makes stainless steel stainless. It also forms hard chromium carbides that improve wear resistance.
Molybdenum (Mo) boosts hardenability and adds red hardness — the ability to hold strength and a cutting edge at elevated temperature — which is why it shows up heavily in tool steels and high-temperature alloys.
Nickel (Ni) is an austenite stabilizer and the backbone of austenitic stainless steel, adding toughness, impact strength (even at low temperature), and corrosion resistance.
Vanadium (V) refines grain structure by forming fine, hard vanadium carbides that block grain growth, improving wear resistance while keeping the structure fine and tough.
Manganese (Mn) doesn't have its own page yet, but it earns a mention here: it's used as a deoxidizer during steelmaking and improves hardenability by allowing strength and hardness gains at a slower, more controlled quench rate. Manganese also combines with sulfur to form manganese sulfide inclusions — soft particles that act as internal chip-breakers and a dry lubricant at the cutting edge, which is one of the mechanisms behind free-machining steel.
Sulfur and lead are added specifically to improve machinability, not strength. In free-machining grades (the 11XX series is the classic example), sulfur reacts with manganese to form those chip-breaking sulfide inclusions, and lead can be added as fine, soft particles that act as a built-in lubricant during the cut. Both produce shorter, better-breaking chips and lower cutting forces — at a real cost to strength, ductility, and weldability, which is why free-machining grades are chosen for high-volume screw-machine parts rather than structural applications.