Free cutting steel refers to alloy steel that adds a certain amount of one or more free cutting elements such as sulfur, phosphorus, lead, calcium, selenium, tellurium, etc. to improve its machinability. With the automation, high speed, and precision of cutting, it is very important to require steel to have good machinability. This type of steel is mainly used for processing on automatic cutting machines, so it is also a specialized steel.

The grade of free cutting steel (referred to as free cutting steel) usually consists of three parts:

Part 1: The symbol Y for easy to cut steel.

Part 2: The number after Y represents the carbon content, for example, for a free cutting steel with an average carbon content of 0.3%, its steel grade is "Y30".

Part 3: Symbols for easy to cut elements, such as easy to cut steel containing calcium, lead, tin, and other easy to cut elements represented by Ca, Pb, Sn, respectively. For sulfur and phosphorus added easy to cut steel, the symbols S and P are usually not added. High manganese content sulfurized and sulfurized phosphorus easy to cut steel, this section represents the manganese element symbol Mn; To distinguish between grades, for high sulfur content easy to cut steel, the sulfur element symbol S is added at the end of the grade. The sulfur content of free cutting steel ranges from 0.08% to 0.30%, and the manganese content ranges from 0.60% to 1.55%. Sulfur and manganese in steel exist in the form of manganese sulfide, which is brittle and has lubricating properties, making it easy for chips to break and improving the quality of the processed surface.