Is 304 stainless hard to machine?

304 is moderately difficult — its machinability is roughly 45% relative to free-machining steel, and it work-hardens if the tool dwells or rubs. We machine it with sharp, rigid tooling, positive feeds that keep the cut under the work-hardened layer, and good coolant. The result is clean, accurate parts; it simply runs slower than aluminium or free-machining grades.

304 vs 316 — what is the difference?

Both are austenitic stainless steels with similar strength. 316 adds 2–3% molybdenum, which gives markedly better resistance to chlorides and pitting — so 316 is preferred for marine and aggressive chemical environments, while 304 is the cost-effective choice for general corrosion resistance, food and architectural use.

Is 304 stainless magnetic?

In the annealed condition 304 is essentially non-magnetic. Cold working and machining can induce slight magnetism at the surface. If non-magnetic behaviour is critical, tell us and we account for it in processing.

Do you passivate 304 parts?

Yes. Passivation removes free iron from the surface and restores the chromium-oxide layer that gives stainless its corrosion resistance. We recommend it after machining, especially for food, medical or wet-environment parts, and we can also electropolish.

304 Stainless Steel CNC Machining — Properties, Tolerances, Uses

The Default Stainless Steel

304 (and its low-carbon variant 304L) is the most widely used stainless steel in the world. The "18/8" composition — about 18% chromium, 8% nickel — gives excellent general corrosion resistance, good strength, full weldability and a clean, hygienic surface, which is why it dominates food, beverage, architectural, medical and general industrial parts. It costs less than 316 and covers the large majority of "I need it in stainless" jobs.

Batch of CNC-machined 304 stainless steel threaded couplings by EKINSUN — CNC-turned stainless couplings — 304 is the everyday corrosion-resistant choice.

304 Mechanical & Physical Properties

Property	Typical value (304, annealed)
Ultimate tensile strength	≥515 MPa (often ~580)
Yield strength (0.2%)	~215 MPa (min 205)
Elongation at break	~40–55%
Hardness	~70 HRB (~150 HB)
Density	8.0 g/cm³
Elastic modulus	193 GPa
Composition	~18% Cr, ~8% Ni
Magnetism	Essentially non-magnetic (annealed)
Machinability	~45% — work-hardens

304L lowers carbon for better weldability and intergranular-corrosion resistance with slightly lower strength. We machine to the certified mill spec and provide certs on request.

304 Chemical Composition

304 is an austenitic 18/8 stainless — chromium forms the passive oxide layer, nickel stabilises the austenitic structure. Nominal composition (balance iron):

Element	Content	Element	Content
Chromium (Cr)	18.0–20.0%	Manganese (Mn)	≤2.0%
Nickel (Ni)	8.0–10.5%	Silicon (Si)	≤0.75%
Carbon (C)	≤0.08% (304L ≤0.03%)	Phosphorus (P)	≤0.045%
Nitrogen (N)	≤0.10%	Sulphur (S)	≤0.030%

How We Machine 304

304 is tougher to cut than carbon steel or aluminium because it's gummy and work-hardens — if a tool rubs instead of cuts, the surface hardens and tool life collapses. Our approach:

Sharp, rigid tooling and positive feeds that stay under the work-hardened skin
Generous coolant to manage the heat 304 holds onto
Tolerances: ±0.025 mm (±0.001 in) on critical features; turned diameters tighter — see tolerance & inspection
For free-machining needs we may suggest 303 (adds sulphur) where its slightly lower corrosion resistance is acceptable

Tooling, Speeds & Feeds — Starting Points

The single rule that decides success with 304: never let the tool dwell or rub — 304 work-hardens at roughly twice the rate of plain steel, so the moment a tool stops cutting it glazes the surface and wrecks the next pass and the tool. Cut firmly, keep the feed on, and stay under the hardened skin. Typical starting points (tuned per part):

Parameter	Typical for 304
Tooling	Coated carbide — TiAlN or TiCN for heat resistance
Cutting speed	~60–75 m/min (200–250 SFM) carbide end mills; coated-carbide inserts can run higher
Feed / chip load	0.15–0.35 mm/rev — positive & consistent, never trailing off
Depth of cut	Stay below the previously work-hardened layer on each pass
Coolant	High-pressure flood — heat & lubrication are critical
Golden rule	Tool always engaged & cutting — no dwell, no rubbing

Most "304 machining" pages list properties but skip the part that actually matters on the floor — managing work-hardening with the right speed, feed and coolant. That's where parts succeed or scrap.

Finishing 304

Passivation — restores the chromium-oxide layer; recommended after machining
Electropolishing — bright, ultra-clean surface for medical/food
Bead blast — uniform matte
Brushed / polished — architectural finishes

304 vs 316 — Quick Comparison

	304	316
Key addition	—	2–3% molybdenum
Chloride / pitting resistance	Good	Excellent
Marine / chemical use	Limited	Preferred
Cost	Lower	Higher
Best for	General, food, architectural	Marine, medical, chemical

If the part sees salt water or aggressive chemicals, choose 316; otherwise 304 is the cost-effective default.

Typical 304 Parts

Fittings, couplings and fasteners — e.g. our stainless sensor fittings
Shafts and spindles — e.g. keyed stainless shaft
Food and beverage equipment parts
Architectural hardware and trim
General industrial brackets and enclosures

Frequently Asked Questions

Moderately — machinability ~45% and it work-hardens. We use sharp rigid tooling, positive feeds under the work-hardened layer, and good coolant for clean, accurate parts; it just runs slower than aluminium.

316 adds 2–3% molybdenum for much better chloride/pitting resistance, so it's preferred for marine and chemical use. 304 is the cost-effective choice for general, food and architectural parts.

Essentially non-magnetic when annealed; machining can induce slight surface magnetism. Tell us if non-magnetic behaviour is critical.

Yes — passivation restores the protective oxide layer and is recommended after machining, especially for food, medical or wet-environment parts. Electropolishing is also available.

304 Stainless Steel CNC Machining