Free-Cutting Steels

Free-cutting steels are steels with a carbon content ranging between 0.07% and 0.60%, a sulfur content between 0.15% and 0.40%, and a phosphorus content between 0.07% and 0.10%. Although the sulfur and phosphorus content is aimed to be reduced in all other grades, it is specifically added to free-cutting steels because it increases their machinability. These added elements provide metallic brittleness in the material, ensuring the formation of short, brittle chips. Furthermore, the addition of sulfur and phosphorus acts as a lubricant, enabling increased part durability and the attainment of clean surfaces. Free-cutting steels can also be found alloyed with lead. The added lead does not change the mechanical properties of the steel but increases its lubricating property. Free-cutting steels also have tempering and cementation (case hardening) properties.