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What the Network Runs on SUS Stainless, and What It Holds
Every figure on this page is typical for the right shop on the right machine. The number that applies to your part is confirmed on your quote, against your drawing. We are a trading company: the shops are ours to choose and manage, the result is ours to answer for.
JIS grades we cover, with the AISI and EN equivalents
A grade change on the drawing is a cost change in the quote. SUS303 and SUS316L are the same shape and roughly double the cycle time apart. Where the certificate matters, say on the drawing which standard it has to name.
| JIS | AISI / ASTM | EN | Family | Machinability | What to expect |
|---|---|---|---|---|---|
| SUS303 | 303 | 1.4305 | Austenitic | 78 | Sulphur added for chip breaking. Cuts roughly twice as fast as SUS304 but is not for welding and pits sooner in chlorides.Turned parts in volume, shafts, fittings |
| SUS304 | 304 | 1.4301 | Austenitic | 45 | The default grade on most JIS drawings. Work hardens under a rubbing tool, so it needs sharp edges and a feed that never dwells.General machined parts, brackets, housings |
| SUS304L | 304L | 1.4307 | Austenitic | 45 | Low carbon version of SUS304. Specified when the part is welded and cannot be solution annealed afterwards.Welded assemblies that see corrosion |
| SUS316 | 316 | 1.4401 | Austenitic | 36 | About 2 % molybdenum for chloride resistance. Gummier than SUS304, expect longer cycles and more insert wear.Marine, chemical, food contact parts |
| SUS316L | 316L | 1.4404 | Austenitic | 36 | Low carbon SUS316. Usually comes with a surface finish and a passivation call-out attached.Pharma, semiconductor and vacuum wetted parts |
| SUS321 | 321 | 1.4541 | Austenitic | 36 | Titanium stabilised against carbide precipitation in the 400 to 800 degC range. Titanium carbides are abrasive on tooling.Exhaust, heat exchanger, hot gas parts |
| SUS410 | 410 | 1.4006 | Martensitic | 54 | Hardenable to roughly 40 to 45 HRC. Machine annealed, then harden, then finish grind the critical features.Shafts, fasteners, valve parts |
| SUS420J2 | 420 | 1.4028 | Martensitic | 45 | Higher carbon than SUS410 and takes a higher hardness. Plan the sequence around the heat treat distortion, not around the roughing.Blades, mould inserts, wear parts |
| SUS430 | 430 | 1.4016 | Ferritic | 54 | Magnetic and cheaper than the 300 series. Machines closer to carbon steel but cannot be hardened by heat treatment.Trim, panels, indoor hardware |
| SUS440C | 440C | 1.4125 | Martensitic | 40 | The hardest of the common grades, around 58 HRC after hardening. Finish features are ground or hard turned, not milled.Bearing races, cutting edges, nozzles |
| SUS630 | 630 / 17-4 PH | 1.4542 | Precipitation hardening | 48 | Precipitation hardening. Rough in condition A, age to the H condition the drawing calls out, then finish the tight features.Aerospace fittings, pump shafts, tooling |
Machinability is a typical handbook index for annealed bar, 100 being AISI B1112 free-machining steel. Equivalents are close matches, not identical chemistry. Twenty grades with PREN and UNS in the grade converter. Families, hardening and grade selection: materials.
Processes and what each one holds
Capacity is deepest in turning and 3-axis milling of SUS303, SUS304 and SUS316L. Grinding and EDM of hardened grades is a shorter list, here as everywhere.
| Process | What it suits | Typical tolerance | Send this with it |
|---|---|---|---|
| CNC turning | Shafts, pins, fittings, unions and adapters from SUS bar. Live tooling for cross holes and flats. | ±0.02 mm on diameters, h7 to roughly 30 mm | Thread class to JIS B 0209, the certificate standard, and whether a gauge result is required. |
| Sliding head turning | Small turned parts under 20 mm in SUS303 and SUS304, from a few hundred pieces up. | ±0.01 mm on diameters | Annual volume as well as this order. The second number moves the unit price. |
| CNC milling, 3-axis and 4-axis | Brackets, manifolds, plates and covers from SUS304 and SUS316L plate. | ±0.02 mm on called-out features, flatness 0.02 mm over 200 mm with a second operation | Datum scheme and the geometrical class from the title block. |
| Surface and cylindrical grinding | Hardened SUS420J2 and SUS440C, fine finishes on SUS304 and SUS316L. | ±0.005 mm, Ra 0.4 | Hardness after heat treatment and the finish called out on the drawing itself. |
| Wire and sinker EDM | Hardened details, sharp internal corners, slots that a cutter cannot reach. | ±0.01 mm | Material condition and the corner radius you can accept. |
| Passivation and electropolishing | Wetted, vacuum and food contact parts in SUS316L. Passivation to ASTM A967 or AMS 2700. | To the named standard; electropolish needs a target Ra | The standard, what to mask, and the Ra you need after polishing. |
Part families
Machined stainless parts to JIS grades, from a single prototype to a repeat annual volume.
Turned parts
Shafts, pins, fittings, adapters and unions, usually SUS303 or SUS304 bar on a lathe or a sliding head.
Milled housings
Brackets, manifolds, plates and covers from SUS304 or SUS316L plate, with a flatness or position call-out.
Vacuum and fluid parts
SUS316L wetted parts with a surface finish target, passivation and sometimes a permeability limit.
Hardened parts
SUS420J2 and SUS440C components where the sequence runs rough, harden, then grind or hard turn.
Thin wall parts
Tubes, rings and shells where work hardening and fixturing decide whether the part holds round.
Small precision parts
Sub 20 mm parts with tight diameters and fine threads, where the cost sits in gauging rather than cutting.
Finishing and treatment
Finishing runs in series with machining, not in parallel, so it adds days to the lead time rather than hours. It is quoted as its own line, with the processor queue named.
- As machinedRa 1.6 is a normal turned or milled finish on stainless. Ra 0.8 is held with attention to tooling. Below that an operation is added.
- PassivationCitric or nitric to ASTM A967, or AMS 2700 where the drawing calls for it. A treatment, not a coating. Specified on most wetted parts.
- ElectropolishingFor SUS304 and SUS316L. Not for SUS303, where sulphide inclusions pit. Give the target Ra after polishing, otherwise every shop assumes a different one.
- Bead blastingGlass bead for a uniform matte finish. State the grit and whether the part is passivated afterwards.
- Heat treatmentHardening of SUS420J2 and SUS440C, ageing of SUS630. Always in the sequence rough, treat, finish.
- MarkingLaser marking of part numbers, heat lot numbers and data matrix codes on a surface you nominate.
What each Ra level costs and how the legacy triangle marks map:surface finish converter.
Part size and quantity
- Turned partsBar work from 3 mm to roughly 100 mm diameter. Chucked parts to roughly 300 mm.
- Milled partsUp to roughly 800 x 500 x 400 mm. Larger is possible and the shop list gets short, so ask before you design around it.
- QuantityFrom a handful of prototypes to a few thousand pieces per release, and repeat orders on a blanket schedule.
- Thin walls and deep holesWall height to thickness above 10:1 and hole depth above 5D are quoted with the fixture and the through coolant they need, not as an ordinary feature.
Work we will not take
Saying this here saves you a week.
- Grades outside the SUS rangeTitanium, Inconel, aluminium and plain steel belong with a supplier that runs them every week. We will say so rather than quote them.
- Implantable medical devicesA different regulatory world with a different supply chain. We do not take them.
- Work that needs AS9100 or ITARWe do not hold those approvals, and a shop holding one does not transfer it to an order placed through us.
- Casting, forging, sheet metal and MIMDifferent tooling and a different industry. We take machining and the finishing around it.
- A prototype needed in three daysFreight alone eats that. A shop near you will be cheaper once you count the air waybill.
- A part without a drawingA photograph is not enough to price a toleranced part. Send a dimensioned drawing and we quote it.
Questions about capabilities
What tolerances can you hold on SUS parts?
Typically ±0.02 mm on turned diameters and milled features, h7 to roughly 30 mm without grinding, ±0.005 mm ground, Ra 0.4 with grinding or an added finishing operation. Tighter is possible and narrows the network to the shops with the right inspection room. The figure that applies to your part is confirmed on the quote, not promised here.
Do you machine grades outside the SUS range?
No. Titanium, Inconel, aluminium and plain carbon steel belong with a supplier that runs them every week. We take the JIS stainless range and the finishing around it, and we say so rather than quoting a grade we do not manage well.
Can you supply a JIS mill sheet or an EN 10204 3.1 certificate?
Yes, where you state it on the drawing or the quote request. A 3.1 certificate narrows which bar we can buy and can move the lead time, so it is quoted as its own line and ordered with the material rather than requested afterwards.
Who actually machines the parts?
A shop in the network we manage, chosen for the grade, the process, the part size and the measuring equipment your tolerance needs. We are a trading company and we do not own the machines. We audit the shop, place the order, follow it with an engineer, inspect the parts and ship them.