Free-cutting structural steel is made by adding some elements to the steel that make the steel brittle so that the steel is easily broken into chips when cutting, which is beneficial to increasing the cutting speed and extending the tool life. The element that makes steel brittle is mainly sulfur. Elements such as lead, tellurium, and bismuth are used in ordinary low-alloy free-cutting structural steel.
The sulfur content of this steel is in the range of 0.08%-0.30%, and the manganese content is in the range of 0.60%-1.55%. Sulfur and manganese in steel exist in the form of manganese sulfide. Manganese sulfide is very brittle and has lubricating properties, making the chips easy to break and helping to improve the quality of the machined surface.
