Free Cutting Steel
Free cutting steel is known as free machining steel. In order to improve the turning resistance, Sulfur (S), tellurium (Te), or 0.15-0.35% of the chemical composition of lead (Pb; Plumbum) is added in general carbon steel or tool steel.
Free machining steel is steel that forms small chips when machined. This increases the machinability of the material by breaking the chips into small pieces, thus avoiding entanglement in the machinery. This enables automatic equipment to run without human interaction. Free machining steel with lead also allow for higher machining rates. Free machining steel costs 15 to 20% more than a standard steel, but this is made up by increased machining speeds, larger cuts, and longer tool life.