Stainless for EDC: 304, 316L, 416 and 440C compared

Stainless in EDC is rarely the headline material, but it is in almost every product: pivots, detent balls, screws, liners, pocket clips, bezels, tail springs. Picking the wrong grade produces parts that either cost too much to machine or rust in a customer’s pocket.

304 — the general-purpose default

Austenitic, non-hardenable by heat treatment, good corrosion resistance, cheap and available everywhere.

Use it for: general hardware, non-critical brackets, spacers, anything where you want stainless without paying for a specialist grade.

The catch: it work-hardens aggressively. A shop that machines it like mild steel will glaze the surface and destroy tooling. It is also gummy, so surface finish on a small feature can disappoint. Expect longer cycle times than the price of the bar suggests.

316L — the corrosion grade

304 plus molybdenum. Meaningfully better against salt and sweat, which is the actual corrosion environment for EDC.

Use it for: anything carried against the body, coastal or marine-marketed products, parts that will live in a pocket with keys and sweat.

The catch: slightly harder to machine than 304 and modestly more expensive. The L means low carbon, which improves corrosion resistance after welding — relevant only if you are welding.

416 — the machinable one

Martensitic and free-machining, with added sulphur. It cuts fast, holds a good surface finish, and it can be heat treated to useful hardness.

Use it for: pivots, detent parts, threaded components, anything turned in quantity. When a shop is happy about a stainless job, it is usually 416.

The catch: the sulphur that makes it machinable also makes it the worst corrosion performer here. It will show surface rust in a sweaty pocket if it is not passivated, and sometimes even then. Do not use 416 for an exposed surface on a product sold as rust-proof — see passivation and why your stainless is rusting.

440C — the hardenable one

High carbon martensitic, hardens to around 58 to 60 HRC.

Use it for: parts that must resist wear and deform under load without galling. Detent balls, lock faces, wear inserts, and blade stock — though blades are a different supply chain from the hardware we are discussing.

The catch: difficult and slow to machine in the annealed state, then it needs heat treatment, then it usually needs grinding or EDM to reach final dimension because it moves during hardening. Budget one to two extra weeks. See heat treatment for EDC parts.

Choosing quickly

• Needs to look good and never rust: 316L
• Needs to be cheap and is not critical: 304
• Needs to be turned in quantity, hidden or coated: 416
• Needs to be hard: 440C

Finish and corrosion

All four benefit from passivation after machining, and 416 requires it. Bead-blasting increases surface area and can make corrosion slightly worse on marginal grades, so a blasted 416 part is the worst combination in this article. Stonewash on 316L is the safest.

PVD coating over stainless is common in EDC for black and bronze hardware. It is an outsourced step with its own minimums and adds one to two weeks — plan it into the schedule rather than adding it after the first article.

What to write in the RFQ

Grade and condition: “316L, annealed”, “440C, harden to 58-60 HRC after machining, grind to final on the marked dimensions”. If any face is exposed on the finished product, say which one, because that changes the grade advice. Send the part and we will tell you if the grade fights the job.

Magnetic behaviour, and why customers ask

304 and 316L are austenitic and nominally non-magnetic, though cold work from machining can make them slightly magnetic at the surface. 416 and 440C are martensitic and clearly magnetic.

This matters in two places. Magnetic detent systems in folders rely on a magnetic component, so specify 416 or 440C there rather than 316L. And customers who carry near magnetic-sensitive equipment sometimes ask — it is worth knowing the answer for your own product copy.

Work hardening, and the cost it hides

304 and 316L work-harden aggressively. If a tool rubs rather than cuts — because it is dull, or the feed is too light — the surface hardens and the next pass is cutting a harder material, which dulls the tool further.

The practical consequence is that austenitic stainless punishes timid machining. It wants sharp tooling, positive rake, a firm feed and rigid workholding. Shops that run it regularly know this; shops that do not will produce a poor finish and a long cycle time.

When you see a quote where 316L costs notably more than the material price justifies, this is usually why, and it is legitimate.

Sulphur, inclusions and cosmetic surfaces

416’s free-machining behaviour comes from manganese sulphide inclusions, which act as internal chip breakers. Those same inclusions are visible on a polished surface as fine streaks, and they are corrosion initiation sites.

So 416 is the wrong grade for a highly polished, exposed cosmetic face even before the corrosion question. Use it where it is hidden, coated, or where a bead-blast or stonewash finish disguises the surface — and always passivate it. See passivation.

Screws and small fasteners

Most EDC screws are bought, not made, and that is the right decision — a machined M2 torx screw is expensive and a purchased one is not.

When you do specify: A2 is broadly equivalent to 304, A4 to 316. For a knife pivot screw taking real torque, a hardened alloy steel screw with a coating usually outperforms any stainless, at the cost of corrosion resistance. Decide which failure you care about more.

Cost ordering

At EDC quantities, roughly cheapest first: 304, 416, 316L, 440C. Note that 416 sits second despite being a more specialised grade, because machining time dominates and 416 machines fast. That inversion surprises people and it is a genuine reason to use 416 where it is appropriate.

Welding

Rarely relevant for EDC, but if it is: 304 and 316L weld well, L grades specifically to avoid carbide precipitation at the weld. 416 and 440C do not weld acceptably for a structural joint. Design for fasteners or press fits instead.

For items carried against the skin and sold in the EU, see nickel release rules for EDC items.

FAQ

What grade are most production folder liners? Usually 410 or 420J2 in volume production, or titanium at the premium end. 304 appears in budget knives. The liner is a structural and spring component, so hardness and temper matter more than the grade name alone.

Can I get 316L hardened? No, not by heat treatment. Austenitic stainless does not harden that way. You can work-harden it or specify a cold-worked condition, but if you need hardness, you need a martensitic grade.

Is 440C the same as the 440C in knife blades? Same designation, but blade stock is bought in specific conditions and heat treated to a blade-specific recipe. For hardware — detent balls, wear inserts — a general 440C supply is fine. Blade production is a different supply chain.

What about Nitronic or 17-4PH? 17-4PH is genuinely useful for EDC: precipitation hardening, good strength, decent corrosion resistance, and it hardens with much less distortion than 440C. It is more expensive and less commonly stocked in Vietnam, so expect a material lead time. Worth asking about for a highly loaded small part.

Do I need to passivate if the part is PVD coated? Yes. The coater needs a clean, passive substrate, and any coating will eventually be breached. See passivation.

How do I stop my stainless parts arriving with rust spots? Passivate, pack dry, and use VCI paper. Most delivery rust is free iron from machining rather than the grade failing. Put it in the RFQ.