GlossaryKind of term: Manufacturing termFree-cutting steel (11SMnPb30)
What is free-cutting steel?
Free-cutting steel is steel with added sulphur, and sometimes lead, so that the chip breaks short; it is made for turning small parts in large numbers.
Free-cutting steel is steel with added sulphur and, in the best-known grade, lead as well. Manganese sulphide inclusions and lead make the chip break short and reduce tool wear. 11SMnPb30 (1.0718) is the common leaded grade and 11SMn30 (1.0715) its lead-free counterpart. They are mostly supplied as bright drawn round, hexagon and square bar for bushes, pins, bolts, nipples and other small turned parts. 11SMnPb30 and 11SMn30 are not intended for heat treatment; separate free-cutting grades exist for case hardening or for quenching and tempering, such as 10SPb20 and 44SMn28.
What does the standard say about free-cutting steel?
Free-cutting steels are covered by EN ISO 683-4, which replaced EN 10087; bright bar also falls under EN 10277. Older drawings use DIN names such as 9SMnPb28 and 9SMn28, succeeded by 11SMnPb30 and 11SMn30 with slightly different composition limits. Lead has been on the REACH Candidate List of substances of very high concern since 2018. An article containing more than 0.1 % by mass, as leaded free-cutting steel does, carries a duty to inform along the supply chain. RoHS and the end-of-life vehicles directive grant exemptions for lead in steel, with their own limits and expiry dates; check the current position for your customer's product.
How does free-cutting steel behave in the shop?
On an automatic or sliding-head lathe free-cutting steel allows high cutting data and long tool life, and the short chips keep chip evacuation and unattended running manageable. The lead-free grade usually machines a little less well; by how much depends on tooling, cutting data and operation. The sulphide inclusions lower toughness and fatigue strength, especially across the rolling direction; for heavily or cyclically loaded parts the designer usually chooses another steel. Welding is not recommended, because the sulphur raises the risk of hot cracking. Free-cutting steel rusts; if the drawing calls for corrosion protection such as zinc or nickel plating, a finishing step is added, often subcontracted. If the customer excludes lead, settle that before you order material.
What is free-cutting steel often confused with?
Free-cutting steel is not free-machining stainless: 1.4305 is an austenitic stainless steel with sulphur added for machinability, while 11SMnPb30 rusts. It also differs from a structural steel such as S235, which is made for welding and forming rather than machining.
Frequently asked questions
Is 11SMnPb30 the same as 9SMnPb28?
Not exactly. 9SMnPb28 is the old DIN name; the European standard calls its successor 11SMnPb30, with the same material number 1.0718 but slightly different composition limits. Order by the name on the drawing, or agree the substitution with the customer.
When should I use lead-free free-cutting steel?
When the customer or the application excludes lead, for example through a restricted-substances list or the rules of its market. Expect it to machine a little less well than the leaded grade, which can mean lower cutting data or shorter tool life.
Can free-cutting steel be hardened?
11SMnPb30 and 11SMn30 are not intended for it. If the part must be hard, choose a free-cutting grade for case hardening such as 10SPb20, one for quenching and tempering such as 44SMn28, or a different steel.