The marine and medical stainless — molybdenum-hardened against chlorides, machined in 316 and 316L for parts that stay wet.
316 is 304's chemistry with one decisive edit: two to three percent molybdenum. That addition targets the specific failure mode that takes 304 out of wet service — localized pitting and crevice corrosion driven by chloride ions. Salt spray, seawater, brines, chlorinated cleaners, road de-icing splash, and many sterilization chemistries all concentrate chlorides exactly where a passive film is weakest: under gaskets, inside crevices, at machining marks. Molybdenum stiffens the passive layer against that attack, which is why 316 is the default for marine hardware, why pharmaceutical and food-processing plants specify it for wetted process surfaces, and why the low-carbon 316L variant is the workhorse of surgical instruments and body-contact device hardware. Mechanically it sits close to 304 — similar strength, the same austenitic toughness and non-magnetic annealed structure — so the choice between them is almost purely environmental. Our rule at quote time: if the part will be wet more often than dry, or will ever meet salt or sterilants, price it in 316 from the start. Our stainless machining network runs 316/316L across milling, turning, and Swiss platforms every week.
Everything true of machining 304 is true of 316 with the volume turned up a notch: the alloy work-hardens under a rubbing edge, the chip is stringy and gummy, and heat stays at the tool. Molybdenum adds toughness, so cutting loads run a little heavier and surface speeds a little lower. The countermeasures are identical — sharp positive-rake tools, polished flutes, constant chip load, no dwell — applied on rigid iron: the network's VMCs (travels to 32.5" × 20.5" × 20.1"), the 5-axis trunnion platform, and turning centers with 1.625" to 3.05" bar capacity.
A large share of real-world 316L work is small turned geometry — instrument shafts, luer and sanitary fittings, probe bodies, fastener specials. The network's 5-, 7-, and 9-axis Swiss-type machines (.812" to 1.50" bar) run these complete in one cycle. 316's chip control is less forgiving than free-machining 303, so Swiss work in 316 leans on tuned chip-breaking geometries and high-pressure coolant rather than metallurgical shortcuts — the corrosion spec usually rules 303 out on exactly the parts that need 316.
The L grade caps carbon low enough that welding does not sensitize the heat-affected zone, and medical and pharma specifications typically name 316L outright. Strength differences are modest and rarely decide a machined-part design. In practice, dual-certified 316/316L bar satisfies either callout, which is how most of our stock is purchased — the drawing's requirement, not shop convenience, dictates what the certs must say, and the certs ship with the parts.
316L electropolishes exceptionally well, producing the smooth, chromium-enriched, crevice-free surfaces that sanitary and surgical drawings demand; passivation per ASTM A967 / AMS 2700 is the baseline treatment after machining. Bead blast and tumble give uniform satin finishes for handled hardware. All finishing runs through qualified processors in the ISO 9001:2015 certified production network, sequenced so marked, toleranced features are protected.
The 316 work crossing our network maps cleanly onto wet environments: deck and rigging hardware that lives in salt spray, wetted valve trim and pump internals for chemical and pharmaceutical processing, sanitary tri-clamp fittings, housings and probe bodies for water-quality and pressure instrumentation, and 316L components for medical devices from surgical handles to sterilizable trays. Defense and naval programs specify it wherever hardware meets seawater. When the load path, not the environment, is the hard requirement — shafts, high-pressure bodies, structural fittings — the conversation moves to 17-4 PH, which trades some chloride resistance for triple the strength.
Routine tolerances on 316 ship at ±.0002", with repeatability on precision turned features to ±.0001". As-machined finishes run 32 Ra or better on finish passes, and where sanitary or surgical drawings carry explicit Ra limits on wetted surfaces, those callouts are inspected and documented like dimensions. Electropolish, passivation, and bead-blast finishes are coordinated with qualified finishers on the program's schedule, and material certifications with full lot traceability — including the 316L pedigree medical work requires — accompany every shipment.
Molybdenum. 316 adds roughly two to three percent molybdenum to the 304 chemistry, which strengthens the passive film specifically against chloride attack — the pitting and crevice corrosion that salt water and brines inflict on 304. If the part lives near salt, in brackish or treated water, or sees chloride-bearing sterilants, 316 is the baseline, not the upgrade.
Somewhat. The molybdenum-bearing chemistry is tougher and slightly more abrasive, so tool loads run higher and surface speeds a bit lower, with the same work-hardening rules in force: sharp positive tools, constant chip load, no dwelling. On rigid machines with tracked tool life it is entirely routine — it simply prices slightly above an equivalent 304 part.
Whenever the part is welded, and on most medical and pharmaceutical drawings — the low-carbon grade resists weld-zone sensitization, and surgical specifications generally name 316L outright. Dual-certified 316/316L bar meets both requirements, so machined parts are usually cut from dual-certified stock that satisfies either callout.
The full stainless family — grades, finishes, and capabilities.
The economical general-purpose grade for milder environments.
Precipitation-hardening strength when the load path governs.
316L fittings, shafts, and probe bodies complete in one cycle.
Sterilizable 316L hardware with documented traceability.
Wet-service part? Send the print for 316 pricing.
