Sources and scope for this page: Industry convention — no single governing standard (conventional usage, definitions vary between sources), covering the definition of free-machining. No independent source check is recorded for this page: the content rests on the sources listed and on the working shown on the page. How sources, methods and updates are recorded.
Definition
Free-machining additives form microscopic stress raisers in the chip, so it fractures into short pieces instead of forming a long tangle. The result is dramatically better chip control, finish and tool life — AISI 12L14 rates 170% on the machinability scale against 78% for 1018.
The cost is real: the same additives reduce corrosion resistance and toughness and are usually detrimental to welding. Free-machining grades are for parts that are machined and then used as machined, not for welded or highly stressed ones.
Common misuse
Specifying a free-machining grade for a welded assembly. The sulphur that improves chip control causes weld porosity and cracking.