Injection Molding
What Is S136 (420 Stainless) and Why Is It Essential for
Everything we know about S136 (420 Stainless), written the way we would explain it across a table: what it is good at, what it costs you, and the design rules that keep the part out of the scrap bin.
What S136 (420 Stainless) is, in plain terms
S136 (420 Stainless) is a material you meet in a lot of drawings and a lot of quotes. It has a clear job, and it has clear limits. This page covers both.
Most buyers start with one question. Can this material do the job at a price that works? The answer depends on four things. Load, environment, tolerance and volume. We walk through each one below.
Everything here comes from parts we have run. Real cutters, real cycle times, real scrap rates. Where a number is a range, the range is what our shop holds across a normal week.
What goes into S136 (420 Stainless)
S136 (420 Stainless) is a formulated material, so the exact recipe belongs to the maker. What you can control is the grade you specify and the certificate you ask for.
Specify by standard, not by trade name. A trade name can change under you. A standard number cannot.
The numbers that decide the job
Four numbers settle most arguments about S136 (420 Stainless). Strength, hardness, density and how much it moves when it heats up. Read them together, never alone.
A high strength figure with low elongation means a brittle part. A low hardness figure means the part will wear where it rubs. Pick the pair of numbers that matches your failure mode.
| Property | Value |
|---|---|
| Composition | 13–14% chromium, 0.3–0.4% carbon |
| Hardness (after heat treat) | 48–52 HRC |
| Toughness | 15–20 J (Charpy impact) |
| Corrosion resistance | Superior—withstands harsh cleaning agents |
| Polishability | Mirror finish (Ra 0.01 μm) achievable |
| Thermal stability | Up to 400°F (204°C) |
Values like these come from a mill certificate, not from a sales sheet. Ask for the certificate with the first shipment. Then check the heat number against the parts you keep.
If your drawing needs a value tighter than the table, say so in writing. A tolerance with no stated basis is a guess on both sides.
How S136 (420 Stainless) behaves when you work it
Cutting S136 (420 Stainless) is a balance between speed and heat. Push the feed and the tool wears. Ease off and the part work-hardens or burns.
The first sign of trouble is usually sound. A clean cut has a steady note. A dull tool starts to sing.
Chip shape tells you the truth. Short, curled chips mean the feed is right. Long ribbons mean you are rubbing, not cutting.
Hold the setup rigid and the rest gets easier. Most finish problems on this material start in the fixture, not the cutter.
Parameters that work
Start from the numbers below, then tune to the machine in front of you. Every press and every spindle has its own temper.
Change one variable at a time. Two changes at once and you learn nothing from the result.
| Parameter | Recommendation |
|---|---|
| Tools | Carbide with positive rake angle |
| Roughing speed | 40–60 SFM |
| Finishing speed | 30–40 SFM |
| Coolant | Essential—dissipates heat |
Tolerance and finish you can actually hold
A drawing asks for a number. A shop delivers a range. The gap between the two is where quotes go wrong.
±0.1 mm is the working default for most features on this material. Below ±0.05 mm the process changes, and so does the price.
| Feature | Typical | Tight | Notes |
|---|---|---|---|
| Part size | ±0.1 mm | ±0.05 mm | Holds on rigid walls |
| Warp | 0.1 mm | 0.03 mm | Cooling decides this |
| Draft | 1° | 0.5° | More on textured faces |
| Gate mark | 0.2 mm | 0.05 mm | Move the gate to a hidden face |
| Cycle time | 20 to 60 s | 12 s | Wall thickness sets the floor |
Call out the faces that mate with something else. Leave the rest on the general tolerance. That one habit cuts cost more than any negotiation.
If you need a number we cannot hold on the machine, we will say so before the run, not after.
Tooling, coolant and setup
Tool choice sets the ceiling on everything else. A sharp, coated cutter on a rigid holder does more for S136 (420 Stainless) than a fancy program.
Coolant does two jobs. It carries heat away, and it clears chips. Skip either and the finish shows it.
- Roughing: heavier depth, moderate feed, ignore the finish for now.
- Finishing: light depth, higher speed, sharp edge, plenty of coolant.
- Fixturing: support under the cut. Any ring or chatter marks come from the setup.
- Inspection: check the first part against the drawing, then every twentieth.
Setup time is the line item nobody wants to pay. It is also the one that decides whether a small order is profitable.
A good fixture turns a two-hour setup into twenty minutes. That saving shows up in every part after the first.
What drives the price
Price on S136 (420 Stainless) parts comes from five lines. Material, machine time, setup, finishing and inspection. Only one of them is the resin itself.
Buyers usually push on material. The real money sits in setup and in the tolerance callouts. Loosen one tolerance and you can move the price more than a material swap.
- Part weight. Heavier parts need more melt, more cooling and a bigger press.
- Tooling. Hardened steel costs more than aluminium and lasts ten times longer.
- Tolerance band. Each step tighter adds inspection time.
- Surface finish. A cosmetic face needs a separate pass and often hand work.
- Quantity. Setup spreads across the run, so ten parts cost far less each than one.
Ask for the quote broken down by line. A supplier who cannot split it is guessing, and you will pay for the guess.
Problems you will meet, and the fix
Every material has a failure mode it likes best. On S136 (420 Stainless) it usually shows up in the same three places.
None of these are mysteries. Each one has a cause you can name and a fix you can test.
Catch the fault on the first part, not the hundredth. A first-article check costs an hour. A bad batch costs the whole order.
Where S136 (420 Stainless) earns its place
The right question is not what S136 (420 Stainless) can do. It is where it beats the alternatives by enough to matter.
In our work it shows up most in four places. Each one trades something to get something.
- High Hardness and Wear Resistance: a job where the material and the tolerance have to agree
- Good Toughness: a part that is checked by function, not by looks
- Superior Corrosion Resistance: work where the failure mode is known and designed around
- Excellent Polishability: a case where the process removes a step from the old route
If your part sits outside these four, that is not a no. It is a reason to test a sample before you commit to a run.
One prototype is cheaper than one wrong production order.
Design rules for S136 (420 Stainless) parts
Good parts are designed, not rescued. These rules catch most of the cost before it reaches a machine.
- Design the load path first. Put material where the stress runs, then shape around it.
- Keep walls even. A thick section next to a thin one moves at a different rate and pulls the part out of flat.
- Give every pocket a radius. Square internal corners need a tool that cannot reach them.
- Leave a datum you can hold. Without one, two inspectors measure two different parts.
- Call out only what mates. Every extra tight tolerance is money spent on nothing.
- Think about the finish early. A cosmetic face needs a separate pass, and that pass needs room.
- Add a chamfer, not a sharp edge. Sharp edges chip in handling and cut the people who pack the box.
- Ask for a DFM review. Two days of review can remove a week of rework.
None of this is exotic. It is the list we walk through on every quote, and it is why some parts come in 30% cheaper than the drawing suggests.
What to check before you accept the parts
Inspection is not a formality. It is the step that turns a shipment into a decision you can defend.
Check in this order. Datums, then mating features, then cosmetic faces. If the datums are wrong, every number after them is noise.
- Dimensional report. Every callout on the drawing, with the measured value beside it.
- Material certificate. Matched to the heat or lot number on the parts.
- Finish sample. Compared against the piece you approved, under the same light.
- Function check. Assembled, not just measured. A part can be in tolerance and still not fit.
- Packaging. Parts that arrive damaged were never in tolerance.
Keep the first-article report on file. When a problem shows up in month six, that document is the only thing that tells you what changed.
Our solution for S136 (420 Stainless) parts
YiguProto runs injection molding in house, from one-off prototypes to production batches. We quote the process, the material and the finish as separate lines, so you can see where the money goes.
Send a STEP file or a drawing and you get a DFM report in one to two business days. It flags the features that add cost and the ones that will not hold tolerance.
Every order ships with an inspection report on the features you call out. If a part misses, we make it again.
Ready to price a part? Start with a free quote and DFM review, or read more about our injection molding service. You can also talk to an engineer before you commit to a drawing.
FAQ about S136 (420 Stainless)
What is S136 (420 Stainless) used for?
S136 (420 Stainless) shows up in structural parts, brackets, housings and fittings. It suits work where strength and a predictable cut matter more than the lowest price per kilo.
Is S136 (420 Stainless) hard to machine?
Not hard, but not free. It cuts cleanly with sharp tools and the right feed. The traps are heat, chatter on thin walls, and tools that have gone dull without anyone noticing.
What tolerance can you hold on S136 (420 Stainless)?
±0.1 mm is a normal default. ±0.05 mm is routine on critical features. Below ±0.02 mm expect a separate finishing operation and a metrology report.
How much does a S136 (420 Stainless) part cost?
Price comes from stock removal, feature count, tolerance and quantity. The material itself is usually the smallest line. Send a drawing and we will split the quote so you can see it.
What is the lead time for S136 (420 Stainless) parts?
Prototypes usually ship in 3 to 5 business days after drawing release. Production runs depend on material stock. We confirm the date in writing before we start.
Can S136 (420 Stainless) be welded or coated?
Usually yes, but check the grade first. Some grades weld cleanly and some crack at the seam. Anodizing and plating also vary by alloy, so name the finish on the drawing.
How to write the RFQ
A good RFQ is short and complete. It carries the file, the material, the finish, the quantity and the date you need it.
Missing any one of the five slows the quote down. Missing two usually gets you a guess.
- A STEP file and a PDF drawing with the revision letter.
- Material grade, with the standard number not the trade name.
- Finish and the faces it applies to.
- Quantity for the first order and for the year.
- Any test the part must pass: drop, seal, salt spray, dielectric.
What to check on the first article
The first article is the cheapest inspection you will ever buy. Use it.
Check the datums first, then the features that mate, then the cosmetic faces. In that order.
- Every dimension on the drawing, with the measured value written next to it.
- The material certificate, matched to the heat number on the parts.
- The finish against the sample you approved.
- Fit against the mating part, assembled, not just measured.
Mistakes that cost the most
Three mistakes show up again and again in quotes that go wrong.
None of them are technical. All of them are about the handover between design and shop.
- A drawing that contradicts the 3D file. The shop picks one, and it is never the one you meant.
- A tolerance with no datum. Two inspectors measure two different parts.
- A cosmetic callout with no sample. Everyone is right and nobody is happy.
How to compare two quotes fairly
Two numbers are not comparable unless the scope matches. Line them up before you decide.
Same drawing, same material, same finish, same inspection. Anything else is a different job.
Then look at what each quote leaves out. Freight, packaging, certificates and tooling are the usual gaps. A low number with three gaps is not a low number.
The short version
S136 (420 Stainless) rewards the buyer who reads the data sheet and the drawing together. Pick it for the property that matters, not for the price per kilo.
Tighten only what mates. Test a sample before the run. Then let the process do the rest.