Wexmar performs CNC machining of 440C stainless steel, the high-carbon martensitic grade chosen when a part needs very high hardness and wear resistance along with moderate corrosion resistance. After hardening, 440C typically reaches 58 to 60 HRC, which is why it is used for bearing races and balls, valve seats, pump wear rings and precision pins. Getting good 440C parts is mostly about machining it in the right condition and leaving the right amount of stock for the steps after heat treatment.
440C machinability
Annealed 440C has an approximate machinability rating of 40 against AISI 1212 steel at 100. Its high carbon and chromium form hard primary carbides throughout the structure, and those carbides are what wear down cutting edges. It does not work harden like 316, but it is abrasive, so tool life is the main limit on speed. In practice, 440C machines most efficiently when bought fully annealed and cut before hardening.
Bar quality also matters. Carbide banding and segregation vary between mills, and coarse carbide stringers can pull out during finishing and leave pits on a polished or ground surface. For bearing and valve seat parts we source bar from mills that supply consistent structure and full mill test reports, and we can quote premium remelted 440C when a print calls for it. Round parts larger than stock bar can be cut from plate or forged blanks when the design requires it, and the quote will state which form was assumed.
Tolerances and finish
In the annealed state we typically hold plus or minus 0.001 in. on turned and milled features, leaving grind stock on functional diameters and faces. After hardening through qualified outside processors, those surfaces are finished by centerless and surface grinding in-house, or by hard turning where the geometry suits it. Typical finishes are 63 Ra as machined and 16 to 32 Ra after grinding. Actual results are typical, not guaranteed, and depend on part size and stability.
Tooling, sequence and gotchas
- Buy annealed. Hardened 440C bar can be turned with CBN, but drilling, tapping and milling hardened material is slow and costly. Annealed stock is the standard starting point.
- Abrasive wear. Use wear-resistant coated carbide grades and watch flank wear closely; a worn edge on 440C raises heat and hurts finish quickly.
- Grind allowance. Distortion and scale from hardening must be removed, so we plan stock of a few thousandths per side on precision surfaces.
- Threads and small holes. Cut all threads and cross holes before hardening. Tapping hardened 440C is not practical.
- Sharp corners. Internal sharp corners concentrate stress during quench. Radiused corners reduce cracking risk.
- Grinding care. Hardened 440C is sensitive to grinding burn, so light passes and plenty of coolant are used.
Heat treat and finishing
Hardening, sub-zero treatment for dimensional stability, and tempering are performed through qualified outside processors, with hardness test results provided. Passivation after grinding is also handled through qualified outside processors. Material certs and heat-lot traceability are available. Ground surfaces are checked for size and roundness before parts are released to finishing.
Common 440C parts
- Bearing races, balls and rollers for corrosive environments
- Valve balls, seats and needle valves
- Pump wear rings, shafts and plungers
- Precision pins, gauge components and knife edges
- Nozzles and wear inserts
Round parts run on our Mazak and Doosan lathes, small pins and plungers on Maier Swiss machines, and ground diameters are finished on the centerless grinder. Our capabilities page covers the full process list.
Cost index
| Material | Approx. machinability (1212 = 100) | Cost index vs 6061 | Notes |
|---|---|---|---|
| 6061-T6 aluminum | ~180 | 1.0 | Baseline |
| 410 stainless (annealed) | ~55 | 2.0 | Lower carbon, lower hardness |
| 440C stainless (annealed) | ~40 | 3.0 | Hardens to about 58 to 60 HRC |
| 17-4 PH (Cond A) | ~40 | 2.8 | Tougher, lower hardness |
| A2 / D2 / O1 tool steel | A2 ~42, D2 ~30, O1 ~45 | 2.5 | Not corrosion resistant |
| 4140 annealed | ~66 | 1.6 | Lower wear resistance |
These figures are typical and illustrative for a comparable part; actual quotes depend on geometry, quantity, tolerances and mill pricing.
Applications and industries
440C stainless machining services at Wexmar support bearing and power transmission manufacturers, pump and valve OEMs, instrumentation makers and food equipment builders. For less demanding wear service, compare with 410 stainless, or see the full materials list.
Getting a quote
Tell us the final hardness, which surfaces are ground and whether sub-zero treatment is required. You can upload a drawing for an instant estimate or call (315) 400-2654. A human estimator confirms every quote.