Material Service

Stainless Steel CNC Machining in China

304, 316L, 303, 17-4 PH and 420 — milled and turned to ±0.01mm, passivated as standard, with the cutting parameters and work-hardening controls that stainless actually requires.

Send Drawing for Quote Cutting Parameters
Why stainless fights back

Three reasons stainless
costs more than aluminum

Stainless is not simply "harder aluminum". Three material properties change how it must be machined, and all three show up on the quote.

1. It work-hardens. The surface gets harder as it is cut. A tool that dwells — even for a second — hardens the surface and destroys the next pass. This is why stainless is machined with light, fast passes rather than heavy slow ones, which is the opposite of the instinct.

2. It conducts heat badly. Aluminum carries heat away into the chip and the workpiece; stainless leaves it at the cutting edge. The tool runs hotter, wears faster, and the insert has to be changed more often.

3. It galls. Austenitic stainless tends to pressure-weld to itself, which shows up first in threads, tapers and fine features. Sharp tooling and a lubricating cutting fluid matter more than parameter tweaks.

Precision CNC machined stainless steel components
Cutting parameters

How we cut each grade

Starting parameters for coated carbide tooling. These are shop working numbers, not brochure values — adjust for machine rigidity, holder and workholding.

Grade Surface speed Feed per tooth Tooling Shop note
303 80–150 m/min 0.05–0.15 mm/tooth Uncoated carbide, 3–4 flute Easiest stainless. Chips break cleanly.
304 / 304L 60–120 m/min 0.05–0.15 mm/tooth AlTiN coated carbide, 4–5 flute Work-hardens fast — never dwell.
316 / 316L 50–100 m/min 0.05–0.12 mm/tooth AlTiN coated, 4–5 flute More galling than 304, especially in threads.
17-4 PH (Cond. A) 60–100 m/min 0.05–0.12 mm/tooth AlTiN coated carbide Machine soft, then age. Avoid machining after H900.
420 (annealed) 50–90 m/min 0.05–0.12 mm/tooth AlTiN coated carbide Wear-resistant, abrasive. Hardened stock is slow.

For comparison, 6061 aluminum runs at 300–500 m/min — roughly four times faster. That difference alone explains most of the price gap between an aluminum and a stainless part of the same geometry. Details in CNC machining cost per hour.

Grades

Stainless grades
we machine daily

Stainless Steel 304 / 304L

The general-purpose austenitic grade. Good corrosion resistance, excellent weldability, food-safe, available everywhere. It work-hardens fast, so the tool must keep moving.

Typical applications: Food processing, kitchen hardware, architectural, chemical containers, general industrial.
Properties & parameters →

Stainless Steel 316 / 316L

Molybdenum-bearing, which is what makes it survive chlorides, salt water and many acids. Machines slightly worse than 304 — more galling and work hardening.

Typical applications: Marine hardware, pharmaceutical equipment, surgical instruments, chemical processing.
Properties & parameters →

Stainless Steel 303

Free-machining grade with sulfur added for chip breaking. The easiest stainless to machine and the cheapest per part for turned work — but it cannot be welded.

Typical applications: Fittings, fasteners, bushings, shafts, parts with extensive threading.
Properties & parameters →

Stainless Steel 17-4 PH

Precipitation hardening. Machined in Condition A (about 30 HRC), then aged to H900 (40 HRC, 1310 MPa) or H1025 for toughness. The part moves during aging — plan for it.

Typical applications: Aerospace fittings, high-pressure valves, pump shafts, medical instruments.
Properties & parameters →

Stainless Steel 420

Martensitic, hardenable to HRC 50+. Used where wear resistance matters more than corrosion resistance. Difficult to machine after hardening.

Typical applications: Cutlery, surgical instruments, valve components, wear-resistant tooling, moulds.
Properties & parameters →
Specifications

Capability overview

Milling 3-axis, 4-axis, 5-axis
Turning CNC turning + Swiss-type
Tolerance ±0.01mm achievable
Max part size 1200 × 600 × 500 mm
Surface finish Ra 0.4μm achievable
Finishing Passivation, electropolish, bead blast
Inspection CMM + dimensional report
Certificates Mill certs with every order
Finishing

Passivation, electropolish,
and when each applies

Machining leaves embedded free iron and disrupts the passive oxide layer — which is exactly where rust starts. Finishing is not cosmetic on stainless; it is what makes the corrosion resistance real.

Passivation

Acid bath (nitric or citric) that removes embedded free iron and restores the chromium oxide layer.

When: Standard on all machined stainless. Mandatory for food, medical and marine.

Cost: Included by default

Electropolishing

Electrochemical process that removes a thin surface layer, leaving a bright, smooth finish around Ra 0.2–0.4μm.

When: Pharmaceutical, semiconductor, food contact, and any part that must be easy to clean.

Cost: +15–30% on the part

Bead blasting

Uniform matte surface produced by media blasting.

When: Cosmetic parts, hiding tool marks, preparing a surface for coating.

Cost: Low cost, quick

Pickling

Acid treatment that removes scale and heat-tint after welding.

When: Welded assemblies before passivation.

Cost: Line item per batch

Send your stainless drawing — quote in 24 hours

Free DFM review. We will tell you which grade makes sense, which features are driving the price, and whether 303 would do the job for less.

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Resources

Stainless steel knowledge base

304 Stainless Steel: Properties, Parameters & Cost 316L Stainless Steel: Marine & Chemical Grade 17-4 PH: Machine Soft, Then Age Harden Stainless Steel CNC Machining: Complete Guide Surface Finishes: Passivation & Electropolishing CNC Machining Cost Per Hour: 2026 Rates CNC Machining Tolerances: What to Specify How to Choose a CNC Machining Shop View all resources →
FAQ

Stainless steel machining
common questions

304 vs 316L — which do I need?

304 covers most applications: food equipment, architectural, general industrial. Choose 316L if the part faces salt water, chlorides or acids — the molybdenum is what resists them. 316L costs roughly 20–40% more in material and machines slightly slower. If you are genuinely unsure, 316L does everything 304 does and more.

Why is stainless harder to machine than aluminum?

It work-hardens, conducts heat poorly, and galls. Cutting speeds are roughly a quarter of aluminum (60–120 m/min versus 300–500), tool wear is faster, and a dwell with a dull tool hardens the surface and ruins the next pass. That is why stainless parts cost more: not the material alone, but machine time and tooling.

Do my stainless parts need passivation?

Yes, on virtually all machined stainless. Machining embeds free iron from the tool into the surface, and that iron is where rust starts. Passivation removes it and restores the chromium oxide layer. It is normally included on our stainless quotes; for medical, food and marine parts it is mandatory.

Which grade is easiest to machine?

303 — the sulfur addition breaks chips and reduces tool wear, so it machines roughly twice as fast as 304. The catch is that 303 cannot be welded, and its corrosion resistance is slightly lower. Use it for turned fittings, fasteners and bushings where welding is not required.

Can you machine hardened stainless?

17-4 PH is machined in Condition A (about 30 HRC), then aged to H900 (40 HRC) or H1025. Machining after hardening is possible with carbide but slow and hard on tooling. Already-hardened 420 at 50+ HRC is feasible but expensive — usually it is cheaper to machine soft and harden afterwards, then grind the critical diameters.

What is the cost difference versus aluminum?

Expect 1.8–2.5× the price of the same part in 6061. Three factors: speeds are about a quarter of aluminum so cycle time is longer, tool wear is higher because stainless is abrasive and work-hardens, and the material itself costs roughly twice as much per kilogram. A $28 aluminum part typically lands at $52–60 in stainless.

Can stainless parts be welded after machining?

304 and 316L weld excellently (TIG or MIG). 303 must not be welded — the sulfur that makes it free-machining causes hot cracking. If the part needs both machining and welding, specify 304 or 316L, and expect a post-weld machining pass on critical faces to correct distortion.

What lead time should I expect?

Prototypes typically 5–12 days, production runs 15–25 days including passivation. Stainless takes longer than aluminum at every step — machining, deburring, finishing. Rush scheduling is available for most quantities and is quoted separately.

Get a stainless steel machining quote — free DFM review

Send your drawing for 304, 316L, 303, 17-4 PH or 420 parts. Line-item quote within 24 hours, with DFM notes on the features driving your price.

✓ Mill certificates ✓ Free DFM review ✓ Passivation included ✓ CMM inspection
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