304 Stainless Steel Chemical Composition Chart
For ASTM A240/A240M-26 plate, sheet and strip, Type 304 (UNS S30400) contains 18.0–20.0% chromium and 8.0–11.0% nickel. The standard also limits carbon to 0.08%, manganese to 2.00%, silicon to 0.75%, phosphorus to 0.045%, sulfur to 0.030% and nitrogen to 0.10%, with iron as the balance. These are heat-analysis limits for a named product standard, not the recipe of every item sold as “18/8 stainless.”
Read the chart against the ordered product standard
Grade names do not stand alone. ASTM A240/A240M-26 currently covers stainless plate, sheet and strip for pressure-vessel and general applications. Bar, tube, pipe, forgings, fasteners and cast products use other specifications, and their chemistry limits can differ.
The values below are the A240/A240M-26 heat-analysis limits for S30400. A heat can comply anywhere within a stated range. A producer’s “typical composition” describes its usual melt practice; it does not narrow the contractual range unless the order says so.
| Element | Symbol | S30400 limit, wt.% | How to read the limit |
|---|---|---|---|
| Carbon | C | 0.08 max | An upper limit, not a target. Carbon becomes important when welding or heat exposure can create sensitization. |
| Manganese | Mn | 2.00 max | A maximum used with the rest of the chemistry; it does not mean a compliant heat contains 2.00%. |
| Phosphorus | P | 0.045 max | A controlled residual element. |
| Sulfur | S | 0.030 max | A controlled residual element. A free-machining stainless grade has a different chemistry and designation. |
| Silicon | Si | 0.75 max | A controlled deoxidizer. Do not import a 1.00% limit from another product specification. |
| Chromium | Cr | 18.0–20.0 | A required range. Chromium supports the passive surface film. |
| Nickel | Ni | 8.0–11.0 | A required range. Nickel helps stabilize the austenitic structure. |
| Nitrogen | N | 0.10 max | An upper limit for S30400; nitrogen-bearing 304N and 304LN are separate designations. |
| Iron | Fe | Balance | The remainder after alloying and residual elements are accounted for. |
Swipe horizontally on a narrow screen. “Max” means the element may be present below that ceiling; it does not mean zero and does not set a minimum. If acceptance uses product analysis, apply the sampling and permitted-variation rules named by the contract.
Why “18/8” is useful shorthand but weak acceptance evidence
“18/8 stainless” communicates the nominal chromium-nickel idea behind many austenitic products. It does not identify a UNS grade, product form, standard edition, finish, condition or inspection certificate. It also cannot distinguish a compliant S30400 heat from another alloy with a similar nominal description.
Defines allowed chemistry for a particular grade and product standard. It is the basis for contractual acceptance when the purchase order invokes it.
Shows what one producer commonly makes or what one certificate reports. It may sit well inside the standard range, but it does not redefine that range.
What the alloying elements change in practical use
Chemistry establishes the alloy’s metallurgical starting point. Final corrosion behavior, strength, formability and weld quality still depend on product condition, cold work, thermal history, surface finish, fabrication and service environment.
Chromium allows stainless steel to form a thin, protective oxide film. Chlorides, crevices, deposits, heat tint and contamination can still defeat local protection.
Nickel supports ductility, formability and toughness. The exact chemistry also affects how readily cold work can create magnetic martensite.
During a susceptible thermal cycle, carbon can participate in chromium-carbide precipitation. This is why 304, 304L and 304H are separate choices.
Its maximum does not show the actual amount in a heat. Read the certified value with chromium, nickel and the other controlled elements.
The permitted maximum depends on the product specification. A web chart that omits its standard can make a correct number look universal.
Phosphorus and sulfur are limited residuals. Nitrogen contributes to austenite stability and strength; intentional nitrogen variants have their own UNS numbers.
Composition and austenitic-grade context: worldstainless. Current A240/A240M scope and edition: ASTM International.
304, 304L and 304H are separate carbon decisions
All three share the chromium-nickel base, but their carbon limits and intended thermal roles differ. State the full UNS designation when the suffix affects welding, corrosion service or elevated-temperature design.
| Grade | Carbon, wt.% | Nickel, wt.% | Selection meaning |
|---|---|---|---|
| 304 / S30400 | 0.08 max | 8.0–11.0 | The standard grade for general flat-product use when the design does not require the L or H variant. |
| 304L / S30403 | 0.030 max | 8.0–12.0 | Lower carbon reduces susceptibility to sensitization during many welding and thermal cycles. |
| 304H / S30409 | 0.04–0.10 | 8.0–10.5 | Controlled higher carbon supports specified elevated-temperature strength; product and code requirements still govern its use. |
Selected A240/A240M-26 limits for plate, sheet and strip. Other elements and product requirements also apply. Do not use this short comparison as a complete purchase specification.
Welding turns carbon and surface condition into practical requirements
A susceptible combination of time and temperature can precipitate chromium carbides at grain boundaries. The adjacent material may then have less chromium available for passivity and can become vulnerable to intergranular attack in a matching corrosive environment.
304L lowers this risk because less carbon is available, but the suffix does not guarantee a finished weld. Joint design, heat input, shielding, contamination, heat tint, filler selection and the required post-weld surface treatment still need a qualified procedure and acceptance criteria. The Nickel Institute fabrication guide explains the corrosion-service context.
For the grade decision, continue with Welding 304 vs 304L. For thin-sheet process planning, use the 304 stainless thin-sheet welding guide. Neither page replaces a procedure qualification for the actual joint.
Verify delivered 304 with traceability and the right analyzer
A magnet, appearance or one alloy reading cannot replace a heat-specific record. Build the inspection plan around the elements and product requirements that separate the accepted grade from plausible substitutions.
Write the grade, UNS number, product standard and edition, form, dimensions, condition and finish.
Match heat number, chemistry, mechanical results and product identity to the purchase order.
Handheld XRF can screen chromium, nickel, molybdenum and many other heavier elements. It cannot measure carbon.
Where L or H suffix verification matters, use qualified LIBS, OES or laboratory analysis with suitable calibration, preparation and sampling.
Specify more than “304 stainless”
A chemistry-only order leaves product condition, dimensions, finish and evidence unresolved. Write the fields that determine whether the delivered material can be fabricated and accepted.
For plate and sheet requirements beyond chemistry, see ASTM A240 vs A480 for 304 plate. For field identification limits, see the 304 vs 316 identification guide.
- Grade and UNSState 304/S30400, 304L/S30403 or 304H/S30409 as required.
- Product standard and editionDo not assume A240 applies to every product form.
- Dimensions and tolerancesName thickness, width, length, flatness and the applicable acceptance basis.
- Condition and finishDefine annealed or cold-worked condition, surface finish, critical face and protective film.
- Certification and traceabilitySpecify the required certificate, heat identity and transfer of identification to cut parts.
- Inspection planState sampling, PMI elements, carbon verification where needed and disposition of nonconforming material.
- Fabrication routeConnect forming and welding to the required procedure, inspection and post-weld cleaning.
- Service conditionsDocument chlorides, temperature, cleaning chemicals, pressure/design rules and corrosion acceptance.
What the composition chart cannot prove
304 has no required molybdenum addition. Type 316 includes molybdenum, but grade selection still depends on chloride level, temperature, deposits, cleaning chemistry and geometry.
Food-equipment suitability also depends on hygienic design, finish, fabrication, weld quality, cleaning, contamination control and the regulations for the actual market and use.
Annealed 304 is normally non-ferromagnetic, while cold work can create magnetic martensite. Magnet response is a screening clue, not grade certification.
Composition is one input. Penetration, defects, mechanical performance, corrosion condition and surface restoration need the inspection required by the part.
Grade families and austenitic structure: worldstainless. Cold-work magnetism in 304: Nickel Institute. ISO composition cross-references: ISO 15510:2014, confirmed current in 2025.
Send Oceanplayer Laser the full grade, thickness, joint drawing, surface condition, production target and weld acceptance criteria so the sample plan starts from the actual material.