What do you understand by a free-cutting steel? What elements are usually added to make a steel free cutting, and how they make the steel free. cutting?
A free-cutting steel is one in which an element like lead or sulphur is deliberately added to promote rapid machining
When sulphur is added to steel, it forms a brittle constituent with manganese, known as manganese sulphide, which being brittle, allows chip cracks to propagate and breaks chips into easily handled lengths.
The lead does not chemically combine with the other elements. It gets distributed throughout the mass as minute droplets, and thus chip cracks are propagated easily and the chips come out in easily handled lengths.