440C Stainless Steel (UNS S44004) is a very difficult-to-machine material that we run regularly for export customers. It has a density of 7.65 g/cm3, a tensile strength of 1970 MPa and a typical hardness of HRC 58. Those numbers make it the right choice for bearing races and valve seats, and a poor choice when cost or corrosion resistance matters more than mechanical performance.
On our machines we hold +/-0.03 mm on turned and milled features and reach Ra 1.6 um where the drawing calls for it. Standard lead time for 440C Stainless Steel parts is 5-10 working days, including material procurement, machining and any finishing operation you specify.
440C Stainless Steel: key properties
| Property | Value |
|---|---|
| UNS / designation | S44004 |
| Density | 7.65 g/cm3 |
| Tensile strength | 1970 MPa |
| Hardness | HRC 58 |
| Machinability | Very difficult |
| Suggested cutting speed (carbide) | 40-70 m/min |
| Relative material cost | 3 of 5 |
Machining 440C Stainless Steel: what to plan for
- Only machinable in annealed state
- Grinding after hardening
- Cracking risk on thin sections
Cutting speed for 440C Stainless Steel with carbide tooling sits around 40-70 m/min. Going faster burns the edge; going much slower causes rubbing and a poor surface. Flood coolant is not optional here. If your part has thin walls or a lot of stock to remove, say so in the RFQ — we plan roughing, stress relief and finishing as separate operations when the geometry demands it.
Parts we machine in 440C Stainless Steel
- Bearing races
- Valve seats
- Knife blades
- Wear plates
Most 440C Stainless Steel work arrives as 2D drawings with a mix of critical and non-critical features. Loosening tolerance on the non-critical ones is the fastest way to cut cost, and we will tell you which features those are before we quote.
Tolerances, finish and lead time
| Item | Capability |
|---|---|
| General tolerance | +/-0.03 mm |
| Achievable surface finish | Ra 1.6 um |
| Minimum wall thickness | 0.8 mm (aluminium) / 1.0 mm (steel and stainless) |
| Typical lead time | 5-10 working days |
| Prototype quantity | 1 piece |
| Production quantity | 10 to 50,000 pieces |
Frequently asked questions
What is the lead time for 440C Stainless Steel parts?
Standard is 5-10 working days from drawing release, assuming the material is in stock. Exotic grades and cast forms can add 5 to 10 days. Finishing such as anodizing or plating adds 3 to 5 days.
What tolerance can you hold in 440C Stainless Steel?
+/-0.03 mm is routine on turned and milled features. Tighter than that is possible on specific features by grinding or lapping, but it is quoted separately because it changes the process.
Do you keep 440C Stainless Steel in stock?
We hold common sizes of 440C Stainless Steel and buy mill-certified stock for everything else. Material certificates are supplied with the parts on request.
Can you supply 440C Stainless Steel parts with a certificate of conformity?
Yes. We issue a dimensional report, a material certificate and a certificate of conformity as standard for production orders, and full PPAP or AS9102 paperwork when the programme requires it.
Related pages
- Materials — the full index for this section.
- 420 Stainless Steel CNC Machining: Hardened Parts
- Titanium Grade 5 (Ti-6Al-4V) CNC Machining Guide
- 17-4 PH Stainless Steel CNC Machining After H900 Aging
- Titanium Grade 2 CNC Machining for Chemical Equipment
- Instant CNC quote
- Tolerance quick reference
- Frequently asked questions
Get a price for your part
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