Free-Machining Steel
Free-machining steels are low- or medium-carbon steels with sulfur (0.08–0.35 %) and often lead or bismuth added so the chip breaks short and the tool runs cool: 12L14 rates about 170 on the machinability index where 1212 is 100 and 1018 about 70, and leaves a bright finish straight off the tool. Yield is modest (12L14 and 1215 cold-drawn about 400 MPa) and the sulfide inclusions that help the cutting hurt toughness, ductility and weldability, so these grades are chosen for turned parts made in volume, not for structure.
Popular free-machining steel grades
Compare in the explorer| Grade | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Weldability | Best for |
|---|---|---|---|---|---|---|
| 12L14 | 230 | 395 | 7.87 | Excellent | Poor | Screw-machine standard; leaded, bright finish |
| 1215 | 250 | 415 | 7.87 | Excellent | Poor | Lead-free 12L14 for RoHS parts |
| 1117 | 235 | 425 | 7.87 | Very good | Fair | Carburizable free-machining pins and small gears |
| 1141 | 360 | 675 | 7.85 | Good | Poor | Medium-carbon, hardenable turned shafts |
| 1144 | 400 | 670 | 7.85 | Very good | Poor | Stress-relieved bar for strong turned shafts |
| 11SMn30 | 250 | 420 | 7.85 | Very good | Not recommended | EN lead-free free-cutting bar (matches 1215) |
| SUM24L | 235 | 395 | 7.87 | Excellent | Not recommended | JIS leaded free-cutting bar (matches 12L14) |
Choose free-machining steel for
Turned fittings, bushings, spacers, studs, hydraulic and pneumatic fittings, shafts and pins made by the hundred or thousand on a lathe or Swiss machine — where cycle time and surface finish set the price and the part is neither welded nor heavily loaded.
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Free-machining steel by application
- High-volume turned fittings
- 12L14 where lead is allowed, 1215 or 11SMn30 where it is not. Both run at high speed with short chips and hold ±0.02 mm on a Swiss lathe.
- Pins and small gears with a hard case
- 1117 or 1118 carburized 0.3–0.8 mm and quenched for 58–62 HRC on the surface; the lower sulfur keeps the case sound. SMn420 and SMnB420H are the JIS carburizing-grade equivalents.
Working with free-machining steel
- Machining
- The whole point: 12L14 runs about 170 on the machinability index (1212 = 100, 1018 about 70) with short chips, low tool pressure and a bright finish; 1215 about 135. Sharp positive tooling, high speed, moderate feed; taps and thread rolls cut cleanly. The medium-carbon 1141 / 1144 grades run at about 70–80 on the same scale.
- Welding
- Not recommended. Sulfur and lead cause hot cracking and porosity, and lead fume is a health hazard. If a free-machining part must be joined, braze or silver-solder it, or press-fit; where welding is unavoidable, 1117 with low-hydrogen filler is the least bad choice.
- Heat treatment
- 12L14, 1215 and 1212 do not harden (about 0.10 % C) — case-harden by carbonitriding for a thin 0.1–0.3 mm skin only. 1117 / 1118 carburize; 1137, 1141 and 1144 quench-and-temper like 1035–1045 to 25–45 HRC. Sulfide stringers make these grades weaker across the bar than along it, so keep loaded sections axial.
- Finishing
- Plate, black-oxide or phosphate-and-oil as for any carbon steel; the smooth as-turned surface often needs no polishing. Lead-bearing grades leave a gray smear on ground faces that must be cleaned before plating.
Other steel series
- Low-Carbon and Mild Steel
- Medium and High-Carbon Steel
- Alloy Steel
- Case-Hardening Steel
- Tool Steel
- Mold Steel
- Spring and Bearing Steel
- Structural and HSLA Steel
- Wear Plate and Advanced High-Strength Steel
- Pressure Vessel and Chromium-Molybdenum Steel
- Electrical Steel and Soft Magnetic Alloys
- Aerospace and Maraging Steel
- Cast Steel
- Cast Iron
- Steel Welding Consumables
Free-Machining Steel — frequently asked
What is free-machining steel?
Free-machining steels are low- or medium-carbon steels with sulfur (0.08–0.35 %) and often lead or bismuth added so the chip breaks short and the tool runs cool: 12L14 rates about 170 on the machinability index where 1212 is 100 and 1018 about 70, and leaves a bright finish straight off the tool. Yield is modest (12L14 and 1215 cold-drawn about 400 MPa) and the sulfide inclusions that help the cutting hurt toughness, ductility and weldability, so these grades are chosen for turned parts made in volume, not for structure.
Which grade of free-machining steel should I use?
12L14 is the screw-machine standard: the lead makes the finish and the tool life, and it plates well. 1215 is the lead-free equivalent (resulfurized and rephosphorized) for RoHS parts, a little rougher in finish; 1212 and 1213 are the older versions. 1117 and 1118 carry less sulfur and can be carburized to a hard case, so they suit pins and small gears. 1141 and 1144 are medium-carbon resulfurized grades that quench-harden or come stress-relieved (1144 at about 620–690 MPa yield) for shafts that need strength and machinability together. On EN and JIS drawings 11SMn30 / 11SMnPb30 match 1215 / 12L14 and SUM23 / SUM24L match 1213 / 12L14; 42CrMoS4 and C45Pb are the free-cutting versions of 4140 and 1045.
Which grade of free-machining steel is the strongest?
SMnB443H has the highest yield strength in the series at 780 MPa; 42CrMoS4 follows at 720 MPa. Values are for each grade's default condition.
Which grade of free-machining steel is easiest to machine?
Y15Pb (machinability excellent, 98/100), then 9SMnPb28 (95/100).
Is free-machining steel heat-treatable?
Some grades are. Check the conditions listed on each grade page.
12L14 or 1215?
12L14 machines faster (rating about 170 versus 135), leaves a brighter finish and gives longer tool life because the lead lubricates the cut; 1215 gets its machinability from sulfur and phosphorus alone, so the chips are slightly less clean and tolerances a touch harder to hold. 1215 is the choice when RoHS, drinking-water or food-contact rules bar lead — otherwise the two are interchangeable in strength (about 400 MPa yield) and plating behaviour.
Can free-machining steel be case-hardened?
The 0.10 % C grades (12L14, 1215, 1212) can be carbonitrided for a thin 0.1–0.3 mm skin at 55–60 HRC — enough for wear on a spacer, not for a gear tooth. For a real case use 1117 or 1118 (lower sulfur, 0.15–0.20 % C): carburize 0.5–1.0 mm and quench for 58–62 HRC. 8620 is the answer when the core must be strong too.