Why choose 316 over 304 stainless?

316 contains 2–3% molybdenum, which dramatically improves resistance to chlorides and pitting corrosion. Choose 316 for marine environments, salt exposure, chemical processing, and many medical and pharmaceutical parts. For general use without chloride exposure, 304 is more cost-effective.

What is the difference between 316 and 316L?

316L has lower carbon (≤0.03%), which prevents carbide precipitation at weld zones and so resists intergranular corrosion after welding. 316L is the better choice for welded assemblies; standard 316 has slightly higher strength for non-welded parts. We stock both.

Is 316 stainless harder to machine than 304?

Slightly — 316's machinability is around 36% versus about 45% for 304, and it work-hardens similarly. We use sharp rigid tooling, positive feeds and plenty of coolant. Parts come out clean and accurate; the cut simply runs slower, which is reflected in lead time and price.

Is 316 good for medical and food parts?

Yes. 316/316L is a standard for surgical, pharmaceutical and food-contact components because of its corrosion resistance and cleanability. We passivate and can electropolish parts to a bright, hygienic surface.

Passivation or electropolishing — which do I need for 316?

They do different jobs. Passivation is a chemical clean that removes free iron and machining residue so the chromium-oxide layer reforms; it does not change appearance or surface roughness. Electropolishing electrochemically removes a thin surface layer for a brighter, smoother (lower Ra) finish that resists biofilm and rouging. General marine and industrial parts usually need only passivation; medical, pharmaceutical and high-purity parts typically want both — electropolish then passivate.

316 / 316L Stainless Steel CNC Machining — Properties & Uses

When Corrosion Resistance Has to Be Serious

316 is 304's tougher sibling. The key difference is 2–3% molybdenum, which transforms resistance to chloride attack and pitting — the failure modes that destroy ordinary stainless in salt water and aggressive chemicals. That single addition makes 316/316L the standard for marine hardware, chemical processing, pharmaceutical and many surgical and food-contact parts. It costs more than 304 and machines a little slower, so it's the right choice specifically when the environment demands it.

Batch of CNC-machined 316 stainless steel fittings by EKINSUN — Stainless fittings — 316 is chosen where chlorides and chemicals would attack 304.

316 Mechanical & Physical Properties

Property	Typical value (316, annealed)
Ultimate tensile strength	≥515 MPa
Yield strength (0.2%)	~205 MPa (316L min ~170)
Elongation at break	~40%
Hardness	~79 HRB (~150–170 HB)
Density	8.0 g/cm³
Elastic modulus	193 GPa
Composition	~16–18% Cr, 10–14% Ni, 2–3% Mo
Magnetism	Essentially non-magnetic (annealed)
Machinability	~36% — work-hardens

316L's low carbon (≤0.03%) resists weld-zone (intergranular) corrosion, so it's preferred for welded assemblies. We machine to certified mill spec and supply certs on request.

316 Chemical Composition

316 is an austenitic stainless whose defining ingredient is molybdenum — it's what lifts chloride/pitting resistance above 304. Nominal composition (balance iron):

Element	Content	Element	Content
Chromium (Cr)	16.0–18.0%	Manganese (Mn)	≤2.0%
Nickel (Ni)	10.0–14.0%	Silicon (Si)	≤0.75%
Molybdenum (Mo)	2.0–3.0%	Phosphorus (P)	≤0.045%
Carbon (C)	≤0.08% (316L ≤0.03%)	Sulphur (S)	≤0.030%

How We Machine 316

316 behaves like 304 but cuts a little harder and holds heat, so discipline matters even more:

Sharp, rigid tooling with positive feeds to stay under the work-hardened layer
Strong coolant to carry heat away and protect tool life
Tolerances: ±0.025 mm (±0.001 in) on critical features — verified on inspection
We avoid cross-contamination with carbon steel so the corrosion resistance isn't compromised

Tooling, Speeds & Feeds — Starting Points

Same golden rule as 304 — never let the tool dwell or rub — but 316 is more demanding: lower machinability (~36%), more heat retained, faster tool wear. Cut firmly, flood it, and keep tool engagement constant. Typical starting points (tuned per part):

Parameter	Typical for 316 / 316L
Tooling	Coated carbide — TiAlN / TiCN for heat & wear
Cutting speed	~50–70 m/min (165–230 SFM) carbide end mills — a touch below 304
Feed / chip load	0.15–0.35 mm/rev — positive & consistent, never trailing off
Depth of cut	Stay below the previously work-hardened layer each pass
Coolant	High-pressure flood — non-negotiable on 316
Golden rule	Tool always cutting — no dwell, no rubbing

Finishing 316

Passivation — essential after machining to restore the protective oxide layer
Electropolishing — bright, ultra-clean, easy-to-sterilise surface for medical/pharma
Bead blast / brushed — uniform decorative or matte finishes

316 vs 304 — Quick Comparison

	316	304
Molybdenum	2–3%	None
Chloride / pitting resistance	Excellent	Good
Marine / chemical / medical	Preferred	Limited
Machinability	~36%	~45%
Cost	Higher	Lower

No chloride exposure? 304 is the cheaper default. See all options on our materials overview, or the full 304 vs 316 comparison with decision guide by application.

Typical 316 Parts

Marine fittings, fasteners and deck hardware
Chemical and pharmaceutical process parts
Surgical and medical-device components
Food and beverage contact parts
Sensor and instrumentation fittings — e.g. our stainless fittings batch

316 is our go-to grade for corrosion-critical custom fasteners and adapters & fittings, and for marine replacement parts.

Custom 316 Stainless Parts — Who Orders and Why

The buyers who specify 316 over 304 are usually fighting salt water, chlorides or a wash-down chemical — and they need the molybdenum grade machined and finished correctly, not substituted for cheaper steel.

// Marine / Refit Engineer

"A 316 deck fitting corroded/sheared — no drawing, need it remade from the old one"

Send us the broken or worn part. We reverse-engineer 316/316L through-hulls, stanchion bases, cleats, ferrules and nipples from the sample, passivate to maximise pitting resistance, and finish brushed or electropolished. MOQ 1 for one-off replacements; batches for build series.

// Chemical / Process Engineer

"Valve and pump parts exposed to chlorides — 304 keeps failing"

We machine custom valve bodies, spindles, nozzles and pump components in 316L for chloride and acid service, supply mill certs to the 316 spec, and electropolish where surface cleanliness matters. Material traceability documented per part.

// Medical / Surgical Device Engineer

"Instrument components in 316L — electropolished, biocompatible surface"

We machine custom 316L instrument and implant-adjacent components to tight tolerance, electropolish to a clean passive surface, and hold the process repeatable across batches. Low MOQ for development; scale-up on approval.

// Offshore / Energy Procurement

"316 fittings and brackets for an offshore install — certs and repeat supply"

We quote tiered pricing, machine a first sample for approval, supply 316 mill certs and traceability, then set up repeat supply. Naval brass or super-duplex available where 316 isn't enough — tell us the chloride exposure.

What 316 Stainless Buyers Search For

custom 316 stainless parts manufacturer China 316L CNC machining supplier marine grade stainless fitting custom 316 through-hull fitting machined electropolished 316L medical parts 316 stainless valve body custom 316 vs 304 seawater pitting 316 1.4401 / 316L 1.4404 equivalent custom 316 ferrule nipple machined passivated vs electropolished 316L 316L pharmaceutical part electropolished 316L stainless made to drawing low MOQ 316 stainless parts 316 stainless bushing stud custom replacement marine fitting from sample 316 stainless coupling machined China surgical grade 316L component custom 316 fittings with mill certs

Frequently Asked Questions

316's 2–3% molybdenum gives far better resistance to chlorides and pitting — essential for marine, salt, chemical and many medical parts. Without chloride exposure, 304 is more cost-effective.

316L has lower carbon (≤0.03%) to resist intergranular corrosion at welds — better for welded assemblies. Standard 316 has slightly higher strength for non-welded parts. We stock both.

Slightly — ~36% machinability vs ~45% for 304, and it work-hardens similarly. Sharp rigid tooling, positive feeds and good coolant give clean parts; it just runs slower.

Yes — it's a standard for surgical, pharma and food-contact parts. We passivate and can electropolish to a bright, hygienic surface.

They do different jobs. Passivation is a chemical clean that removes free iron and machining residue so the natural chromium-oxide layer reforms — it doesn't change appearance or surface roughness. Electropolishing electrochemically removes a thin surface layer, leaving a brighter, smoother (lower Ra) finish that resists biofilm and rouging. General marine/industrial parts usually need only passivation; medical, pharmaceutical and high-purity parts typically want both — electropolish then passivate. Tell us the application and we'll advise.

Yes — it's one of our most common marine and chemical jobs. Send the worn, seized or sheared fitting and we reverse-engineer it from the sample (no drawing needed): measure threads, bores and flange faces, rebuild the geometry, machine a new one in 316/316L and passivate. MOQ 1. If the original was specified in EN designations (1.4401 = 316, 1.4404 = 316L) or another standard, tell us and we match it.

316 / 316L Stainless Steel CNC Machining