Free Cutting Steel
Steel with sulphur, and sometimes lead, added deliberately so that chips break short at the tool tip and machining speeds can be raised.
How it works
Sulphur combines with manganese to form soft manganese sulphide inclusions strung out along the rolling direction. They act as internal crack starters in the chip, so it snaps into short pieces instead of curling into a continuous ribbon that wraps the tool and the part.
What you give up
Those same inclusions are the reason the steel will not weld — they cause hot cracking — and the reason transverse ductility and corrosion resistance drop. Free cutting grades also do not respond usefully to hardening. Machined parts, not stressed parts.
Related terms
Where this applies
Free Cutting Bright Bars
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