The world's most-used stainless — 304 and 304L machined with the process discipline that work-hardening austenitics demand.
304 is the 18-8 austenitic that most of the world means when it says "stainless": roughly 18 percent chromium and 8 percent nickel, excellent general corrosion resistance, full weldability, and a service record spanning food plants, breweries, pharmaceutical lines, architecture, and general industry. It is non-magnetic in the annealed state, tough down to cryogenic temperatures, and takes everything from a mirror electropolish to a bead-blasted matte. What the datasheets undersell is how it behaves under a cutting tool. Austenitic stainless work-hardens ferociously: the very act of deforming the metal raises its hardness, so an edge that rubs instead of shearing — because it dulled, because the feed dropped, because the tool dwelled at the bottom of a hole — creates a hardened skin that accelerates wear on the next pass in a self-reinforcing spiral. Add gummy, stringy chips, built-up edge, and poor thermal conductivity that dumps heat into the tool rather than the chip, and 304 becomes the grade that most visibly separates disciplined shops from struggling ones. Our stainless machining network runs it on rigid platforms with the tooling and process control the alloy requires — and prices it honestly, at roughly a third of aluminum's feed rates.
The rules are simple and unforgiving: sharp, positive-rake tools with polished flutes; a constant, confident chip load that keeps the edge cutting beneath the previously hardened layer; no dwell, no rubbing, no interrupted pecking where a full-retract cycle will do. Climb milling keeps the edge entering thick and exiting thin. Drills and taps are where 304 punishes hesitation most — a tap seizing in a work-hardened hole is the classic 304 failure — so holemaking gets rigid setups, correct point geometries, and high-pressure coolant.
304's chip is stringy and its thermal conductivity is poor, so heat concentrates at the cutting edge instead of leaving with the chip. Rigid machines matter more than exotic tooling: the network's VMCs (travels to 32.5" × 20.5" × 20.1"), the 5-axis trunnion platform, and turning centers with bar capacity from 1.625" to 3.05" carry the stiffness to push 304 at steady production feeds without chatter — and chatter in 304 doesn't just sound bad, it work-hardens the surface it touches.
304L trades a little strength for low carbon so welded joints resist sensitization — specify it (or dual-certified stock) whenever a weld symbol appears. 303 goes the other direction: sulfur additions buy dramatically better machinability at the cost of weldability and chloride resistance. For a turned production part that will never be welded and lives in a mild environment, letting us re-quote a 304 drawing in 303 often cuts real money; for anything welded or wet, 304L or 316L is the correct answer.
Machined 304 cleans up beautifully: 32 Ra or better on finish passes, uniform satin from bead blasting, and electropolish where the drawing demands a drag-free, crevice-free surface. Passivation per ASTM A967 / AMS 2700 after machining removes embedded free iron from tooling contact and restores the passive layer — standard practice on food, medical, and pharma hardware, coordinated through qualified finishers in the network.
304 parts cross our network from every direction: sanitary fittings and pump components for food and beverage lines, sterilizable housings and handles for medical equipment, process hardware for pharmaceutical and chemical service, shafts and brackets for washdown-duty instrumentation, and general industrial components where "make it stainless" is the whole corrosion spec. It also serves cryogenic and vacuum applications where austenitic toughness at low temperature matters. When chlorides enter the picture — marine air, brines, aggressive sterilants — the same geometry moves to 316; when strength drives the design, 17-4 PH takes over.
Routine tolerances on 304 ship at ±.0002", with repeatability on precision turned features to ±.0001". Holding those numbers in a work-hardening alloy is a process-control story: tool life is tracked so finish passes always run on a sharp edge, and dimensional checks bracket the run rather than sampling its start. Surface finish runs 32 Ra or better on finish passes, with bead blast, tumble, electropolish, and passivation coordinated through the network's qualified finishers. Material certifications and full lot traceability accompany every shipment.
Work hardening. 304's austenitic structure hardens dramatically wherever it is deformed — including by a cutting edge that rubs instead of cuts. A dulled tool or a dwell leaves a hardened skin the next pass has to fight, escalating wear until something breaks. The cure is discipline: sharp positive-rake tools, constant chip load, no dwelling, feeds that keep the edge cutting under the hardened layer.
When the part will be welded. Standard 304 can sensitize in the weld heat-affected zone — chromium carbides precipitate at grain boundaries and invite intergranular corrosion. 304L's lower carbon avoids that. For purely machined parts standard 304 is fine, and dual-certified 304/304L bar covers both cases with minor strength differences.
Yes — 304 is the standard for food, dairy, and brewery contact surfaces and tolerates repeated washdown and autoclave cycles. Passivation after machining removes embedded free iron and restores the passive surface, and electropolishing is available where the drawing calls for it. For chloride-heavy service, step up to 316.
The full stainless family — grades, finishes, and capabilities.
The free-machining alternative for never-welded turned parts.
Molybdenum-bearing upgrade for chloride and marine service.
Rigid VMCs and 5-axis platforms that hold feeds in stainless.
Locked processes and tracked tool life across repeat runs.
Send the 304 print — we will quote it, and flag 303 or 316 if they fit better.
