Why 316 is the default for corrosion-critical parts
316 stainless is an austenitic chromium-nickel-molybdenum steel with 16–18% Cr, 10–14% Ni, and 2–3% Mo. The molybdenum addition — absent from 304 — gives 316 dramatically better resistance to chloride-induced pitting and crevice corrosion. This single property makes it the default for any application that sees saltwater, chlorinated sanitizers, body fluids, brine, or dilute acids: marine hardware, food processing equipment with chemical CIP cycles, medical devices, swimming pool fittings, chemical plant instrumentation, and pharmaceutical processing components.
Our typical 316 customer is building medical device components (orthopedic fixtures, surgical instrument parts), food-contact equipment (nozzles, valve bodies, heat exchanger tubes, processing chamber fittings), marine hardware (bolts, cleats, fittings for boats and offshore equipment), or chemical/pharmaceutical processing parts (reactor internals, ferrules, sight glass frames, sanitary clamp fittings). Orders range from 5-piece prototypes to 2,000-piece production lots, with the occasional high-volume Swiss-turn run into the tens of thousands.
316 vs 316L — and when to pay for the difference
316L is low-carbon 316 (maximum 0.03% C versus 0.08% for standard 316). The difference matters exactly when the part will be welded after machining, or when it will see extended time at temperatures between 425 °C and 815 °C. In both cases, standard 316 risks sensitization: chromium combines with carbon at grain boundaries to form chromium carbide, locally depleting the boundary of chromium and opening the door to intergranular corrosion. 316L prevents this by having so little carbon that carbides can't form.
Practical guidance: if the part will be welded (by you or downstream), specify 316L. If it will see high-temperature service, specify 316L or 316Ti. For everything else (machined-only parts at ambient or near-ambient temperature), standard 316 is mechanically equivalent and costs ~10% less. When in doubt, specify 316L — the cost premium is small and it's always safe. We stock both in common bar and plate sizes.
Machining parameters — slower than 304, longer tool life
316 work-hardens more aggressively than 304 and runs at roughly 80% of the cutting speeds. Our roughing parameters: 60–80 m/min surface speed, 0.10–0.15 mm feed per tooth, 1.5–3 mm axial depth of cut, generous flood coolant or high-pressure through-spindle. Finishing runs 90–110 m/min with sharp-edge uncoated or AlCrN-coated carbide. We climb-cut exclusively on 316, never dwell (a stopped cutter work-hardens the surface instantly and eats the next pass's tooling), and maintain coolant flow aggressively — 316 chips can weld to the tool face within seconds of coolant drop-out.
Swiss-turn features (medical fittings, sanitary connector bodies, food-grade pins) benefit from dedicated sharp-edge insert geometry and slower surface speeds (70–90 m/min) with consistent feed. In production we often achieve ±0.008 mm diameter tolerance on Swiss-turned 316L — tight enough for interference-fit medical assemblies.
Passivation and electropolish — when each matters
Machined 316 parts carry surface iron particles transferred from tooling, chip welds, and contact with non-stainless fixtures. These particles rust and seed pitting even on corrosion-grade stainless. Passivation — immersion in nitric acid (ASTM A967 Nitric 2) or citric acid (Citric 2) — dissolves free iron and restores the chromium-rich passive layer. Standard for any 316 part destined for corrosion-critical service. Lead time +2–3 days, cost 5–10% of finished-part price.
Electropolish is the next step up: anodic electrochemical polishing that preferentially dissolves surface peaks, reducing roughness from (e.g.) Ra 0.8 µm to Ra 0.4 µm or better and producing a visibly brighter finish. It also removes embedded iron more thoroughly than passivation alone, making it the standard for biopharmaceutical, semiconductor ultra-high-purity, and high-end medical applications. Lead time +5 days, cost 15–35% of finished-part price. For ultra-high-purity bio/pharma, specify electropolish to Ra ≤ 0.25 µm with ASME BPE SF1/SF4 documentation; tell us on the RFQ and we route to a qualified partner that handles the paperwork.
Certification documentation
Every 316 lot ships with: ASTM A276 or A479 mill certificate linking heat number to your PO, chemistry report (Cr, Ni, Mo, Mn, C, Si, P, S, N — critical elements for both specification compliance and corrosion performance), mechanical property report, passivation certificate per ASTM A967 if applicable, electropolish process record if applicable, first-article inspection, and Certificate of Conformance. For medical device customers we add process travelers, tool validation records, supplier chain of custody back to the original mill, and cleanliness documentation per ISO 19227 if the drawing calls for it. Food-contact parts get 3-A Sanitary Standards compliance documentation. Specify the certification scope during the RFQ so pricing and lead time reflect it correctly.
What to send for a 316 quote
Required: STEP file, PDF drawing with tolerances and surface-finish callouts (Ra values matter more on 316 than on aluminum), material callout (316, 316L, or 316Ti), target quantity, target delivery. Helpful: application context (medical, food-contact, marine, chemical — changes our fixture protocol), passivation / electropolish specification, required certification documentation scope, and any AVL constraints. For repeat medical-device customers we keep dedicated tooling sets to prevent cross-contamination and cycle time stays consistent across repeat runs. See the quality process page for full inspection scope.