304 Stainless Steel
Also: AISI 304, UNS S30400, 304L (UNS S30403), 18-8 stainless, 18/8, A2 stainless (fasteners), 1.4301, X5CrNi18-10, 1.4307 (304L), SUS304, CF8 (cast 304), CF3 (cast 304L)
304 is the workhorse 18-8 austenitic stainless: weldable, formable, corrosion-resistant and stocked in every form. Use 304L for welded work. Values annealed.
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At a glance
| Density | 8 g/cm³ (0.289 lb/in³) |
|---|---|
| Tensile strength | 515-620 MPa (75-90 ksi); ASTM A240 minimum 515 MPa (75 ksi), 485 MPa (70 ksi) for 304L |
| Yield strength | 205-290 MPa (30-42 ksi); minimum 205 MPa (30 ksi), 170 MPa (25 ksi) for 304L |
| Hardness | 70-90 HRB (about 150-200 HB); ASTM A240 maximum 201 HB (92 HRB) |
| Elongation | 40-60% (minimum 40%) |
| Modulus of elasticity | 193 GPa (28 Msi) |
| Thermal | Melts at 1400-1450 °C (2550-2650 °F); thermal conductivity ~16 W/m·K; expansion ~17 um/m·K; scaling resistance to about 925 °C (1700 °F) continuous, 870 °C (1600 °F) intermittent |
| Composition | Fe, 18-20% Cr, 8-10.5% Ni, up to 0.08% C (304L up to 0.03%), up to 2% Mn, up to 1% Si, up to 0.1% N |
Typical values, Annealed (solution treated at 1010-1120 °C / 1850-2050 °F and water quenched). Confirm against the mill certificate and the purchase spec.
- MachinabilityFair
- About 45% of B1112. It work-hardens under a rubbing tool, so use sharp positive-rake carbide, rigid setups and a steady feed; never dwell. Chips are long and stringy. Choose 303 for turned parts in volume.
- WeldabilityExcellent
- Welds by every arc process with 308L filler and no preheat. Use 304L base metal on sections over about 5 mm (3/16") so the heat-affected zone does not sensitize. Expect distortion: expansion is 50% higher than carbon steel with a third of the conductivity.
- FormabilityExcellent
- The deep-drawing stainless: sinks, cups and shells draw in one or two stages. Springback and work hardening are high, so bend at 1-2t inside radius, plan 50% more tonnage than mild steel, and anneal between severe draws.
- Corrosion resistanceGood
- Excellent in atmosphere, fresh water, food and most organics; pits and crevice-corrodes in chlorides, and stress-corrosion cracks in warm chloride solutions above about 60 °C (140 °F). Marine, pool and de-icing-salt service wants 316 or 2205.
304 is the most produced stainless steel in the world: 18% chromium, 8% nickel, fully austenitic, non-magnetic as annealed. It is stocked in sheet, plate, bar, tube, pipe, angle, wire and fasteners, in 2B, #4 brushed and bright-annealed finishes, and every laser shop, fabricator and machine shop in the U.S. runs it daily. 304L is the same alloy with carbon held to 0.03% so welds do not sensitize; most sheet and plate is dual-certified 304/304L.
Annealed, it gives 515-620 MPa (75-90 ksi) tensile with 40-60% elongation, which is why it deep-draws sinks and cups and takes tight bends. It cannot be hardened by heat treatment; cold-worked strip (ASTM A666 quarter-hard to full-hard) is how it reaches spring and structural strengths up to about 1275 MPa (185 ksi). It resists atmosphere, fresh water, food acids, most organics and oxidizing media, and holds useful strength to about 425 °C (800 °F) in continuous service.
Its limits are chlorides, heat in the wrong band and the machine tool. Chloride pitting starts around 200 ppm in warm water and stress-corrosion cracking appears in warm chloride solutions above about 60 °C (140 °F): that is when to move to 316 or 2205. Holding 304 (not 304L) at 425-870 °C (800-1600 °F) sensitizes the grain boundaries. And at roughly 45% of B1112 it machines slowly, work-hardens under a dull tool and galls on threads; turned parts in volume go to 303.
Heat treatment
Not hardenable by heat treatment; strength comes only from cold work. Solution anneal at 1010-1120 °C (1850-2050 °F) and water quench to dissolve carbides and restore ductility and corrosion resistance. Avoid holding 304 at 425-870 °C (800-1600 °F): chromium carbides precipitate at the grain boundaries and the steel sensitizes; 304L tolerates that range because it has too little carbon. Low-temperature stress relief at 350-400 °C (660-750 °F) is used on machined parts that must hold size.
Tempers and conditions
- Annealed (2B, 2D, BA, #4 and #8 finishes on sheet)
- 1/4 hard, 1/2 hard, 3/4 hard and full hard strip (ASTM A666)
- Cold-drawn bar
- Hot-rolled, annealed and pickled plate (HRAP)
Stock forms
- Sheet and coil (2B mill, #4 brushed, BA)
- Plate
- Round, square, hex and flat bar
- Pipe (ASTM A312) and tube (ASTM A269 seamless, A554 ornamental)
- Angle, channel and structural shapes
- Wire and fasteners
- Castings as CF8 (304) and CF3 (304L)
Relative cost
Tier 3 of 5. The baseline stainless: about 2-3x the price of mild steel per pound and 15-30% under 316. Price follows the nickel market. Cheapest in sheet and standard bar sizes.
Typical applications
- Food, dairy and beverage equipment
- Kitchen sinks, counters and appliances
- Architectural panels, railings and trim
- Chemical and pharmaceutical tanks and piping
- Sheet-metal enclosures, hoods and brackets
- Fasteners (A2) and springs
- Heat exchangers and cryogenic vessels (304L)
- Automotive trim and exhaust components
Process compatibility
How 304 takes each process, and what to specify. Each process links to its own guide and to the shops that do it.
| Process | Rating | Notes |
|---|---|---|
| CNC Machining | FairFair | Slow and work-hardening; sharp carbide, steady feed, flood coolant. Fine for brackets and manifolds; use 303 for volume turning. |
| Laser Cutting | ExcellentExcellent | The most laser-cut stainless: nitrogen assist for a bright, weldable edge; fiber lasers cut to about 25 mm (1") in job shops. Can 304 stainless be laser cut? |
| Waterjet Cutting | ExcellentExcellent | No heat-affected zone at any thickness; the choice for thick plate and parts that must not be sensitized or heat-tinted. |
| Press Brake Forming | ExcellentExcellent | Bend at 1-2t inside radius; over-bend 2-4 degrees for springback and plan 50% more tonnage than mild steel. Can 304 stainless be bent? |
| Deep Drawing | ExcellentExcellent | Cups, sinks and shells draw deep in one or two stages; anneal between severe draws to reset work hardening. |
| Sheet Metal Fabrication | ExcellentExcellent | Enclosures, hoods and tanks: the standard fabricated stainless; call the #4 grain direction on cosmetic panels. |
| Welding | ExcellentExcellent | 308L filler by TIG or MIG; 304L base for heavy sections; argon back-purge tube and pipe so the root does not sugar. Can 304 stainless steel be welded? |
| TIG Welding | ExcellentExcellent | Thin sheet and tube, 308L or autogenous on light gauge; low heat input limits distortion and heat tint. |
| Passivation | ExcellentExcellent | ASTM A967 or AMS 2700 citric or nitric after machining removes free iron; standard on food and medical parts. Does 304 stainless need passivation? |
| Electropolishing | ExcellentExcellent | A bright, smooth, passive surface with Ra roughly halved; the finish for sanitary and semiconductor parts. |
| Investment Casting | GoodGood | Cast as CF8 (304) or CF3 (304L) for valve bodies, pump parts and fittings; castings carry a little ferrite and machine like the wrought grade. |
| Black Oxide | FairFair | MIL-DTL-13924 Class 4 gives a thin cosmetic black; no corrosion benefit, and it dulls the passive surface. Can 304 stainless steel be black oxide coated? |
| Heat Treating | Not recommendedNot recommended | Cannot be hardened. Use 17-4 PH, 410 or 440C for a hard part, or cold-worked strip for a strong austenitic one. |
| Hot-Dip Galvanizing | Not recommendedNot recommended | Zinc will not bond to the passive oxide and adds nothing; zinc in contact with hot stainless can cause liquid-metal cracking. |
Compare 304
Design and sourcing tips
- Write "304/304L dual certified per ASTM A240" when the part is welded; most sheet and plate in stock already meets both and it costs nothing extra.
- Call the surface finish on sheet parts: 2B (mill), #4 (brushed, with grain direction) or BA. Unspecified means whatever the shop has on the rack.
- Design for springback and work hardening: bend radii of 1t or more, and no bend line across a zone that was already cold worked.
- Specify passivation (ASTM A967) after machining and welding, and heat-tint removal (pickling or electropolishing) on welds that see chlorides or food.
- Stainless-on-stainless threads gall: use a dissimilar pair (304 nut on 316 bolt), a plated fastener or anti-seize.
- If the part sees chlorides warm, or salt spray, move to 316; if it sees chlorides hot and under tensile stress, move to 2205.
Frequently asked questions
- Is 304 stainless steel magnetic?
- Not as annealed: it is austenitic and a magnet will not stick. Cold work transforms some austenite to martensite, so bent flanges, drawn cups, cold-drawn bar and the edges of laser-cut parts can be faintly magnetic. That is normal and does not mean the material is wrong. 316 stays closer to non-magnetic after cold work.
- What is the difference between 304 and 304L?
- Carbon. 304 allows up to 0.08%, 304L up to 0.03%. The low carbon stops chromium carbides from forming in the heat-affected zone of a weld, so 304L welded assemblies keep their corrosion resistance without a post-weld anneal. 304L is about 15 MPa (2 ksi) weaker on paper. Most sheet and plate is dual-certified and meets both.
- Does 304 stainless rust?
- It can, in three situations: chlorides (salt spray, pool chemicals, de-icing salt, chloride cleaners), free iron picked up from steel tooling or blast media, and crevices where oxygen cannot reach. Passivation after fabrication removes free iron; design and drainage handle crevices; chlorides call for 316 or 2205.
- Can 304 stainless be hardened?
- Not by heat treatment: there is no quench-and-temper cycle for austenitic stainless. It hardens only by cold work, which is how spring-temper strip reaches about 1275 MPa (185 ksi). For a hard machined part, use 17-4 PH, 410, 420 or 440C.
- Is 304 or 316 better?
- For corrosion in chlorides, 316: its 2-3% molybdenum roughly doubles the pitting resistance and it stays non-magnetic after forming. For everything else, 304 is as good and 15-30% cheaper: same strength, same weldability, slightly better formability. Choose by exposure, not by reputation.
Processes that commonly use it
Related materials
Where to verify these values
- ASTM A240 and ASTM A276 (property minimums by product form)
- AMS 5513 and AMS 5639 (304); AMS 5511 and AMS 5647 (304L)
- ASM Handbook, Volume 1: Properties and Selection: Irons, Steels, and High-Performance Alloys
- Nickel Institute design guides and producer data sheets (Outokumpu, NAS, ATI)
