According to the different content of free cutting elements, it can be divided into sulfur free cutting steel, lead free cutting steel, calcium free cutting steel, and composite free cutting steel. According to their different uses, free cutting steel can be divided into steel for automatic machines, structural free cutting steel, and special free cutting steel (heat-resistant steel, stainless steel, tool steel, etc.). According to the different properties of easy cutting, it can be divided into general easy cutting steel, super easy cutting steel, etc.

(1) Sulfur free cutting steel. Sulfur forms sulfide manganese inclusions with manganese and iron in steel, which can cut the continuity of the base metal and promote the formation of small and short curling radii during cutting, making it easy to remove, reducing tool wear, reducing machining surface roughness, and improving tool life. Usually, the machinability of steel increases with the increase of sulfur content in the steel. However, there is a significant difference in the longitudinal and transverse mechanical properties of steel, with poor plasticity and toughness in the transverse direction, as well as reduced fatigue and corrosion resistance. When the sulfur content in steel is too high, it can lead to thermal brittleness, making it difficult to heat work the steel and deteriorating its mechanical properties. The sulfur content is usually between 0.08% and 0.30%, and some can be increased to 0.4%. The sulfur content in both easy cutting tool steel and stainless steel should be between 0.06% and 0.10%. The combination of phosphorus and sulfur is added to steel, usually with a phosphorus content of 0.04% to 0.12%. Phosphorus solid solution in ferrite will increase hardness and strength, reduce toughness, make chips easy to break and remove, and thus obtain good machining surface roughness. However, excessive phosphorus content will significantly reduce plasticity, increase hardness, and actually have a harmful effect on the cutting performance of steel.

(2) Lead free cutting steel. Lead is in the form of small metal particles in steel, evenly distributed or attached to the surroundings of sulfides. Due to the low melting point of lead, it melts and seeps out during cutting to provide lubrication, reduce friction, and improve cutting performance, but it does not affect the mechanical properties at room temperature. The lead content in steel is generally between 0.10% and 0.35%. Due to the high proportion of lead, if the content is too high, it can easily cause serious segregation and form large particle inclusions, which can actually reduce the beneficial effect of lead on cutting processing. The composite addition of lead and sulfur to low-carbon structural steel can significantly improve the cutting effect of the steel.

(3) Calcium free cutting steel. Calcium in steel combines with aluminum and silicon to form low melting point composite oxides (mainly CaO. Al2O3. SiO2). During high-speed cutting, calcium based oxides attach to the surface of the cutting tool for lubrication and friction reduction, thereby improving the tool's service life. If elements such as sulfur and lead are present simultaneously, their combined effect will improve the cutting effect.

(4) Selenium, tellurium, bismuth free cutting steel. The content of tellurium and bismuth is about 0.03% to 0.10%, and the content of selenium can reach 0.15%. Selenium exists in the form of selenides such as FeSe and MnSe in steel, and its effect is similar to that of sulfur. For steel that requires both high cutting ability and good plasticity, adding selenium to the steel is better than sulfur. Tellurium can be added alone or together with lead or sulfur to form composite inclusions in steel, reducing cutting resistance and cutting heat, making it easy to remove chips, significantly improving the cutting performance of the steel, and achieving good machining surface roughness. However, adding tellurium can slightly reduce the plasticity and toughness of the steel. Selenium and tellurium are generally used in alloy steel. The role of bismuth in steel is similar to that of lead, with small metal particle inclusions that are uniformly distributed or attached to sulfides.