4140 steel CNC machining is one of the most frequent jobs on our floor. This chromium molybdenum alloy steel gives designers high strength, good toughness and deep hardenability at a moderate price, and it is sold both annealed and prehardened. Wexmar turns and mills 4140 components in Canastota, New York for industrial, fluid power and government customers, with material certs and heat-lot traceability available on every order.
4140 machinability: annealed vs prehard
Annealed 4140 has an approximate machinability rating of 66 against AISI 1212 at 100. Prehardened 4140, commonly supplied at 28 to 32 HRC and often sold as 4140 HT or 4140 PH, drops to roughly 50. The choice matters. Annealed bar machines faster but has to be heat treated afterward, which brings distortion and scale. Prehard bar costs more tool life up front but lets the part go straight from the machine to inspection with no heat treat step and no size change.
Tolerances and surface finish
Typical tolerances on precision 4140 turned parts are plus or minus 0.001 in on diameters and plus or minus 0.0005 in on critical fits when the setup is dedicated to them. Horizontal milling holds typical true position within 0.002 in on bolt patterns and ports. Prehard 4140 takes a very good finish; 32 Ra is typical on turned surfaces and 63 Ra on milled faces. Where a print calls for ground diameters or flats, centerless and surface grinding are available in-house. All values are typical and depend on part geometry.
Tooling, chips and heat in 4140
- Prehard tool wear. At 28 to 32 HRC, we use tough coated carbide grades, lower surface speeds than annealed stock, and steady flood coolant to control heat at the tool tip.
- Chip control. 4140 forms tough, springy chips. Medium feed chip breakers on the lathes and high pressure coolant through the spindle on the horizontals keep chips short and out of deep bores.
- Drilling and tapping. Prehard material is less forgiving of dull drills. Carbide drills with through coolant and form taps or thread milling give consistent threads in blind holes.
- Distortion after heat treat. When 4140 is machined annealed and then hardened, we leave finish stock on critical features and finish after treatment, since the part will move and scale.
- Quench cracking. Sharp internal corners and abrupt section changes raise cracking risk during hardening. We flag these on review and suggest radii where the design allows.
Heat treat and finish options
Through qualified outside processors we arrange quench and temper to a specified hardness, stress relieving, gas or salt bath nitriding, and induction hardening. Finish options include black oxide, zinc plating, manganese phosphate, electroless nickel and hard chrome. High strength steel that is electroplated needs a hydrogen embrittlement relief bake, and we specify it with the processor when the drawing or hardness calls for it.
Common 4140 parts and matching processes
- Shafts, spindles, arbors and drive components, turned complete on live tool lathes
- Hydraulic piston rods, pistons, glands and clevises for fluid power equipment
- High pressure blocks, adapters and fixture bodies, milled on horizontal machining centers
- Tool holders, collars, bushings and spacers
- Small pins and threaded studs up to 32 mm diameter on the Swiss-type machines
Prismatic 4140 parts suit our horizontal mills because pallet changers and 4-axis indexing reach several faces in one clamping. See our horizontal CNC milling page for work envelope details.
4140 cost index compared with other steels
| Material | Approx. machinability (1212 = 100) | Cost index vs 6061 | Notes |
|---|---|---|---|
| 6061-T6 aluminum | ~180 | 1.0 | Baseline |
| 1018 cold drawn | ~78 | 1.1 | Low carbon, weldable |
| 1045 cold drawn | ~57 | 1.3 | Medium carbon |
| 4140 annealed / prehard | ~66 / ~50 | 1.6 | Prehard skips heat treat |
| 4340 annealed / prehard | ~57 / ~45 | 2.0 | Higher toughness in heavy sections |
| 17-4 PH stainless | ~40 | 2.8 | Corrosion resistant, age hardens |
Figures are typical and illustrative for a comparable part; actual quotes depend on geometry, quantity, tolerances and mill pricing.
Where 4140 parts are used
We machine 4140 for pump and fluid power builders, power transmission and bearing OEMs, oil and gas tooling suppliers, industrial automation, and defense build-to-print programs. If a design needs more toughness in thick sections, compare our 4340 steel machining page. FAI reports in AS9102 format and CMM inspection data are available through our inspection and quality program. For a 4140 prehard machine shop in New York that ships nationwide, our Central New York location keeps freight simple across the Northeast and beyond.
Getting a quote
For pricing on 4140 components, upload a drawing for an instant estimate or call (315) 400-2654. A human estimator confirms every quote, including material condition and any outside heat treat or finish.