304 Stainless Steel Chemical Composition
Grade 304 / UNS S30400 is an austenitic stainless steel built around 18.0–20.0% chromium and 8.0–10.5% nickel. For ASTM A240 flat products, carbon is limited 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.
304 austenitic microstructure: Melancholia~itwiki, Wikimedia Commons, CC BY-SA 4.0.
Forms and repairs the chromium-rich passive film that makes the alloy corrosion resistant in suitable environments.
Supports the austenitic structure, ductility, formability and toughness associated with conventional 304.
The upper limit for standard 304. Low-carbon 304L reduces sensitization risk in many welded applications.
Iron is the base metal. Its percentage is calculated after the specified and residual alloying elements are accounted for.
The purchase standard controls—not the “18/8” nickname.
“18/8 stainless” is useful shorthand for the nominal chromium and nickel concept behind 304. It is not an acceptance document. A real order must identify the grade, product form and governing product specification. ASTM A240/A240M covers chromium and chromium-nickel stainless plate, sheet and strip for pressure-vessel and general applications; bar, pipe, tubing, forgings and fasteners use different product standards.
The table below presents the commonly specified ASTM A240 heat-analysis limits for UNS S30400. A mill can legally deliver chemistry anywhere inside the permitted window. A supplier datasheet often publishes typical chemistry—such as about 18.1% Cr and 8.1% Ni—but typical values are not guaranteed limits unless the purchase order makes them contractual.
That distinction matters for welding, deep drawing, corrosion exposure, magnetic response and material verification. Two heats can both meet 304 while behaving slightly differently in forming or becoming more or less magnetic after cold work. Chemistry also cannot substitute for surface condition, heat treatment, mechanical properties or corrosion testing.
304 stainless steel chemical composition by weight.
This chart is an engineering summary for UNS S30400 flat products ordered to ASTM A240/A240M. Always check the edition and product standard named on the purchase order.
| Element | Symbol | Minimum, wt.% | Maximum, wt.% | Why it is controlled |
|---|---|---|---|---|
| Carbon | C | — | 0.08 | Strength and processing response; excessive carbon increases susceptibility to chromium-carbide sensitization. |
| Manganese | Mn | — | 2.00 | Steelmaking deoxidation and austenite balance; not a substitute for verifying nickel and chromium. |
| Phosphorus | P | — | 0.045 | Residual element limited to protect ductility, hot workability and weld integrity. |
| Sulfur | S | — | 0.030 | Residual element restricted for weldability and corrosion performance; free-machining grades intentionally differ. |
| Silicon | Si | — | 0.75 | Deoxidizer and oxidation-response contributor. Note that some non-ASTM tables show a different limit. |
| Chromium | Cr | 18.0 | 20.0 | Creates the chromium-rich passive surface film and is the defining corrosion-resistance element. |
| Nickel | Ni | 8.0 | 10.5 | Stabilizes austenite and supports ductility, formability and toughness. |
| Nitrogen | N | — | 0.10 | Austenite former and strength contributor; also enters pitting-resistance calculations. |
| Iron | Fe | Balance | The base metal after specified and residual elements are accounted for. | |
“—” means no minimum is listed in this summary. It does not mean that the element is absent. Heat analysis and product analysis can also have different permitted variation rules.
What each alloying element changes—and what it does not prove.
Composition establishes the metallurgical starting point. Final behavior still depends on product form, solution annealing, cold work, welding, finish and service environment.
Chromium reacts with oxygen to produce a thin, self-repairing surface film. Damage can repassivate when oxygen and the environment allow it, but chlorides, deposits, heat tint and crevices can defeat local protection.
It supports room-temperature ductility, deep drawing and toughness. Nickel content also influences phase stability and how readily cold work creates strain-induced martensite.
Carbon affects strength and high-temperature behavior. During unfavorable thermal exposure it can combine with chromium at grain boundaries, leaving adjacent zones depleted in chromium.
It acts as a deoxidizer and austenite former. A maximum limit does not imply every mill heat runs near that maximum.
It contributes to oxidation response and melt practice. Use the value from the correct standard—online charts frequently mix the 0.75% ASTM limit with limits from other specifications.
Keeping them low generally supports fabrication and corrosion reliability. Grade 303 deliberately uses more sulfur for machinability, which is one reason it is not simply interchangeable with 304.
It is limited in standard 304. Nitrogen-bearing variants such as 304N or 304LN are separate designations and must be ordered deliberately.
304 stainless pipe: Libowei111, Wikimedia Commons, CC BY-SA 4.0.
Surface finish, dimensional tolerance, heat treatment, cleanliness and traceability remain separate acceptance items.
304, 304L and 304H share a chromium-nickel base but solve different thermal problems.
The suffix is not cosmetic. Carbon level—and for 304H, additional product requirements—changes the correct welding and elevated-temperature decision.
304
The general-purpose grade, with carbon limited to 0.08%. It suits broad fabrication where the design, welding procedure and corrosion exposure do not require the low-carbon or high-carbon variant.
C: 0.08% maximum304L
Low carbon reduces the amount available for chromium-carbide precipitation. It is widely selected for welded corrosion-resistant equipment, especially when post-weld solution annealing is impractical.
C: 0.030% maximum304H
The controlled higher-carbon grade is intended for specified elevated-temperature applications where creep strength and code rules matter. Grade selection must follow the design code and product specification.
C: 0.04–0.10%304 vs 316: molybdenum changes the chloride conversation.
304 is not a lower-quality version of 316. They occupy different corrosion windows, and the correct choice depends on chlorides, temperature, deposits, cleaning chemistry and geometry.
| Composition factor | 304 / S30400 | 316 / S31600 | Engineering meaning |
|---|---|---|---|
| Chromium | 18.0–20.0% | 16.0–18.0% | Both rely on chromium passivity; chromium percentage alone does not rank real-world corrosion performance. |
| Nickel | 8.0–10.5% | 10.0–14.0% | The higher nickel range helps maintain the austenitic matrix but is not the principal reason 316 resists chloride pitting better. |
| Molybdenum | No required Mo addition | 2.0–3.0% | Molybdenum improves resistance to localized pitting and crevice corrosion, especially in chloride-bearing service. |
| Default use decision | General indoor, food, architectural and industrial service when the environment is compatible | Marine, coastal, salt, chemical or washdown duties where verified conditions justify added resistance | Service data and corrosion testing should decide—not a generic “316 is always better” rule. |
Do not use a magnet as the grade certificate.
Annealed 304 is normally weakly magnetic or effectively non-magnetic, but cold forming, machining and welding can create magnetic response. Conversely, a weak response does not prove that material is 304. Use traceability and chemistry-based PMI.
Do not call every chromium-nickel sheet “304.”
Grades 201, 301, 304, 304L, 321 and others can look similar. Composition, product certification and service requirements distinguish them. Surface appearance and spark tests are screening clues, not acceptance evidence.
Similar grade names are cross-references—not automatic legal equivalents.
ISO 15510 compiles stainless compositions across major systems, but an international designation does not replace the product standard, delivery condition or certification required by the project.
| System / region | Common designation | Typical chemistry distinction | What to verify before substitution |
|---|---|---|---|
| UNS / ASTM | S30400 / Type 304 | C ≤0.08; Cr 18.0–20.0; Ni 8.0–10.5 | The exact ASTM product standard, edition, dimensions, finish and mechanical requirements. |
| European EN | 1.4301 / X5CrNi18-10 | Often listed with C ≤0.07 and Cr 17.5–19.5 under the applicable EN composition table | Do not claim that the lower carbon ceiling makes 1.4301 equivalent to 304L / 1.4307. |
| Japanese JIS | SUS304 | A broadly comparable 18Cr-8Ni austenitic grade | Product form, JIS specification, dimensional tolerances and inspection certificate. |
| Chinese GB | 06Cr19Ni10 | A comparable chromium-nickel composition designation | The exact GB/T product standard, heat analysis, surface, delivery condition and project approval. |
| ISO composition name | 4301-304-00-I | Composition-based cross-reference used within ISO's stainless grade system | ISO composition listing does not by itself establish product-form equivalence or code acceptance. |
Carbon matters most when the thermal cycle creates a sensitization opportunity.
During exposure in a susceptible temperature range, chromium carbides can precipitate at grain boundaries. The surrounding metal can become locally depleted in chromium and more vulnerable to intergranular attack in a compatible corrosive environment. Time, peak temperature, cooling rate, carbon level, prior condition and service exposure all matter.
304L reduces this risk because less carbon is available, but “L” is not a universal immunity label. Long thermal exposure, severe corrosion conditions, weld contamination, heat tint, poor shielding or an unsuitable design can still produce failures. Stabilized grades such as 321 or 347 may be considered for specific thermal duties, subject to the governing code.
- Confirm whether the drawing and welding procedure require 304, 304L or a stabilized/high-temperature grade.
- Control joint cleanliness, fit-up, travel speed, power, focus, shielding gas and backside protection.
- Inspect penetration, porosity, distortion and heat tint against the actual acceptance criteria.
- Restore the corrosion-resistant surface by the qualified cleaning, pickling or passivation route when required.
How to verify that delivered material is really 304.
Use layered evidence. No single handheld reading replaces heat traceability, the correct certificate and a test method capable of measuring the elements that distinguish the required grade.
Review the MTR
Match grade, heat number, product standard, dimensions, heat analysis, mechanical results and delivery condition to the purchase order.
Match the heat identity
Verify markings, tags, packaging and cut-piece transfer records so the certificate can be connected to the actual material.
Use XRF for Cr/Ni
Handheld XRF is effective for rapid alloy screening and can distinguish many stainless families through chromium, nickel and molybdenum.
Use LIBS or OES
When 304 vs 304L vs 304H matters, use a method qualified to measure carbon, supported by calibration, surface preparation and the inspection procedure.
Specify more than “304 stainless.”
A chemistry-only order leaves too many decisions to the seller. Define the evidence, condition and end-use requirements that determine whether the delivered material can actually be fabricated and placed in service.
Name the UNS designation when ambiguity could affect the weld, heat treatment or service case.
Plate/sheet, bar, pipe, tube, wire, forging and fastener products use different specifications.
Condition changes strength, ductility, flatness and magnetic response.
Define 2B, No. 4, BA or project finish plus surface-defect and film requirements.
Require the certificate type, heat number, chemistry and mechanical results needed by the project.
State sampling, XRF screening and carbon-capable testing where grade suffix verification is critical.
Connect material selection to welding, forming, inspection and post-weld surface restoration.
Document chlorides, temperature, cleaning chemicals, pressure rules and corrosion allowances.
Related Oceanplayer engineering guides.
Move from chemistry to identification, grade equivalence, welding behavior and weight planning.
304 stainless steel composition questions, answered directly.
These answers separate nominal shorthand, chemical limits and field-verification reality.
What is the chemical composition of 304 stainless steel?
For ASTM A240 flat products, UNS S30400 contains 18.0–20.0% chromium, 8.0–10.5% nickel, up to 0.08% carbon, 2.00% manganese, 0.75% silicon, 0.045% phosphorus, 0.030% sulfur and 0.10% nitrogen, with iron as the balance. Verify the product-specific standard and edition on the purchase order.
Why is 304 stainless called 18/8?
“18/8” describes the nominal concept of about 18% chromium and 8% nickel. It is not a complete grade specification and does not replace the permitted composition range, UNS designation, product standard or mill certificate.
What is the difference between 304 and 304L composition?
The main distinction is carbon: 304 allows up to 0.08%, while 304L limits carbon to 0.030%. Other limits can also differ by the applicable product standard. The lower carbon level reduces susceptibility to sensitization during many welding cycles.
Does 304 stainless steel contain molybdenum?
Standard 304 does not require a molybdenum addition. Type 316 intentionally contains roughly 2.0–3.0% molybdenum, which improves localized pitting and crevice-corrosion resistance in many chloride environments.
Can handheld XRF distinguish 304 from 304L?
Not reliably by itself. XRF can screen chromium, nickel and other heavier elements and can identify the 304 family, but conventional handheld XRF does not measure carbon. Carbon-capable LIBS, OES or qualified laboratory analysis is needed when the L or H suffix must be verified.
Is 304 stainless steel magnetic?
Solution-annealed 304 is normally weakly magnetic or effectively non-magnetic, but cold work and welding can create strain-induced or transformation products that increase magnetic response. Magnet response is not a dependable grade-certification test.
Is 304 stainless steel automatically food grade?
No material is made suitable for a food application by grade name alone. 304 is widely used in food equipment, but suitability also depends on finish, hygienic design, fabrication, weld quality, cleaning chemistry, passivation, contamination control and applicable regulations.
Is EN 1.4301 exactly the same as ASTM 304?
They are closely related austenitic chromium-nickel grades and are commonly cross-referenced, but their composition limits, product standards and certification requirements are not identical in every detail. Treat them as comparable grades requiring engineering and contractual review, not automatic substitutes.
Standards and first-party data behind this guide.
The visible article summarizes these sources; the final purchase decision must use the licensed standard edition and project documents named in the order.
Need to validate 304 stainless steel for laser welding?
Send the grade, thickness, joint drawing, surface condition, production target and acceptance criteria for an application-focused review.