Materials · Stainless steel

Stainless Steel CNC Machining Service

Austenitic, martensitic and precipitation-hardening grades machined to your drawing — 9 grades published here, from 201 and 303 through 316L and 17-4 PH.

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9Grades published

±0.125mmAchievable · ISO 2768

0.80 mmMinimum wall

3–10 daysPublished lead time

Polished stainless steel tube stock in the Prolean material store

Specifications

Stainless steel specifications: ±0.125 mm tolerance, 0.80 mm wall, 3 to 10 days lead time

Six numbers a buyer asks for before sending a drawing — the process, the
tolerance we hold, the minimum wall, the largest envelope, the lead time and the price band.

Process

CNC mill · CNC lathe3-axis and 5-axis milling, turning

Achievable tolerance

Not lower than ±0.125mm (±0.005″)Based on the drawing, ISO 2768

Minimum wall

0.80 mmVaries with the grade and the part

Maximum part size

200 × 80 × 100 cmLargest envelope quoted online

Lead time

3–10 daysComplex parts sit at the far end

Price band

$$$$Where stainless steel sits against the other 22 materials

Read this first. Process, maximum part size and lead time are
identical on all 23 material pages — they describe the shop, not the material. Tolerance,
minimum wall and price band are the three that change from one material to the next.

Grade guide

The stainless grades we machine: 201 to 17-4 PH

Family and heat-treatment route for each published grade. Both follow from the AISI/UNS designation itself, so nothing here can drift out of date.

Grade matrix · sourced from the published stainless list on this page

Grade	AISI / UNS	Family	Heat treatment	Where it usually fits
201	AISI 201 · S20100	Austenitic · 200-series (Cr-Mn)	Solution anneal · work-hardening	Trim, brackets, dry-environment parts where cost drives the choice
301	AISI 301 · S30100	Austenitic	Solution anneal + cold work	Springs, clips, conveyor bands — wherever cold work does the strengthening
303	AISI 303 · S30300	Austenitic · free-machining (S-added)	Solution anneal	Screw-machine parts, shafts, fittings — the high-volume turned part
304L	AISI 304L · S30403	Austenitic · low carbon	Solution anneal	Food, dairy and architectural parts; welded assemblies that cannot be re-annealed
316L	AISI 316L · S31603	Austenitic · Mo-bearing	Solution anneal	Marine, chemical and medical parts — anywhere chlorides are present
410	AISI 410 · S41000	Martensitic	Through hardening (Q&T)	Pumps, valves, fasteners — hardness chosen over corrosion resistance
420	AISI 420 · S42000	Martensitic · higher carbon	Through hardening (Q&T)	Cutlery, surgical instruments, plastic moulds
440C	AISI 440C · S44004	Martensitic · high carbon	Through hardening (Q&T)	Bearings, races, valve seats — hardest of the 400 series
17-4 PH	UNS S17400	Precipitation hardening (martensitic)	Solution treat + age (H900–H1150)	Aerospace and medical shafts, fittings, fasteners

Deliberately missing: tensile strength, hardness and density. Those follow the condition, not the grade number — 304L annealed and 304L cold-worked are the same grade at very different strengths — so one figure per row would mislead. Ask for the datasheet in your condition, or put the condition on the drawing and we machine and confirm to it.

The family name is doing a lot of work here. Every row above is a stainless steel, yet 440C will rust in a marine atmosphere and 316L will not. Corrosion resistance follows the grade and the surface condition — passivation included — not the heading.

Which grade?

Stainless, alloy steel or aluminum: choosing by corrosion and strength

Each answer points at a page on this site that covers it in more depth — a
comparison, a grade guide or a process page.

Will the part see weather, salt or wash-down?

Then it is a 300-series job: 304L for everyday corrosion, 316L where chlorides are present. The 200 series is a cost decision, not a corrosion one.

304 vs 304L vs alloy steel

Read the grade comparison →

Does it need to be hard as well as corrosion resistant?

That is the martensitic trade: 410, 420 or 440C, quenched and tempered. Corrosion resistance falls as carbon rises, so it is a deliberate compromise rather than a free win.

Hardness chart Stainless properties

Read the properties guide →

High volume, turned from bar?

303 exists for exactly that — sulphur added on purpose to break the chip. It machines faster than 304L and gives up a little corrosion resistance for the privilege.

Machinability How machinability works

Read the machinability guide →

Not sure stainless is the right call at all?

Aluminium, alloy steel, titanium and the engineering plastics each have a page here. Stainless is often selected by habit rather than by requirement.

vs alloy steel Titanium vs steel Alloy steel Aluminum Titanium

See all 23 materials →

Machining & tolerance

Tolerancing and inspecting stainless steel parts to ISO 2768

The published tolerance on this page is Not lower than ±0.125mm (±0.005″)
on the drawing, to ISO 2768. Where a feature needs better than that, say so on the
drawing — that conversation belongs before the tool goes in, not after.

ISO 2768 general tolerancesWhat we hold when the drawing stays silent Tolerance & fits standardThe shop standard behind the number above DFM guidelinesWall thickness, fillets, thread depth — read before you draw Machinability of materialWhy some grades cut slower, and what that costs

Finishes

Finishing a stainless part: passivation, heat treatment and blasting

Passivation leads here rather than heat treatment — the point of stainless is the passive oxide layer, and free iron left on the surface defeats it.

Heat treatmentStainless Steel follow-on step Black oxideDimensional change ≈ 0 Zinc platingCorrosion protection Electroless nickelUniform on complex geometry PassivationFree iron removed Bead blastingMatte, pre-coat key Fine machiningTighter Ra band All 20 finishesWith Ra bands and process notes

Applications

Where stainless earns its cost: construction, automotive and aerospace

Construction & architectureFixings, cladding supports, handrail components
AutomotiveTrim, brackets and fasteners that must not corrode in service
Aerospace & defenceBrackets and fittings where 17-4 PH carries the load
Hardware & tool sectorsScrew-machine parts, shafts and fittings

All of it cut on the same floor —
see CNC machining and
how we hold tolerance.

303 stainless steel turned sleeves and shafts, as machined — 303 stainless steel sleeves and shafts, as machined.

Stainless steel in context: 304 vs 316, machinability and grades

Deeper reading from around this site — the comparisons, the standards and the
process notes behind this material.

Grade choice304 vs 304L stainless steel gradesThe low-carbon question, and when it actually mattersRead →

MachinabilityStainless steel machinability: benefits, techniques and tipsWhy 303 cuts and 316L fights backRead →

PropertiesStainless steel: hardness & alloy propertiesHB · HRC · HV and what drives themRead →

Material choiceAlloy steel vs stainless steel: a complete breakdownWhen corrosion decides it for youRead →

ProcessMachinability of material and its relation with CNC machiningWhat the cutting data is really telling youRead →

FinishingPassivation serviceFree iron removed — the stainless-specific finishRead →

FAQ

Stainless machining: grades, corrosion, tolerance and lead time

Straight answers to the questions that come up most often on a CNC quote —
with the figures published for this material, and a link for each point.

Which stainless steel grades can you machine?

The 9 published on this page: 201, 301, 303, 304L, 316L, 410, 420, 440C and 17-4 PH. The austenitic, martensitic and precipitation-hardening families are all covered, and the choice between them is usually a corrosion-versus-hardness decision rather than a price one.

What tolerance can you hold?

±0.125 mm, on the drawing, to ISO 2768 — the figure published on this page. Stainless work-hardens, so thin walls and interrupted cuts are where that number is most likely to need a conversation first.

What is the smallest wall and the largest part?

Minimum wall is 0.80 mm and it varies with the grade and the part. Maximum envelope is 200 × 80 × 100 cm. Both are shop-wide constants, identical on all 23 material pages.

How fast is a stainless steel part?

3 to 10 days, with complex parts at the far end. Austenitic grades work-harden as they cut, so they sit nearer the far end than a free-machining grade such as 303.

Can you heat treat as well as machine?

Yes — heat treatment is one of the finishes we run: Heat Treatment Service. Only the martensitic and precipitation-hardening grades respond to it; 304L and 316L are supplied annealed and are not hardened by heat treatment.

What files should I send?

STEP, STP, IGES, IGS, SLDPRT, STL, DXF, DWG, PDF, DOCX, JPG, JPEG, PNG or ZIP. The 2D PDF matters more than usual here — the surface condition and any passivation requirement belong on it.

Is my drawing kept confidential?

Uploads stay with the people quoting and making the part. If you need a mutual NDA in place first, say so on the contact form and it is arranged before files change hands.

Next step

Send the drawing — we come back with a grade and a price

Upload the model and the 2D PDF. You get a manufacturability note, a grade recommendation if the drawing leaves it open, and a price.

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Quoted in 1 business day on a clean drawing
Grade and heat-treat condition confirmed in writing
First article inspected before the run