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304 and 304L Stainless Steel: Properties, Composition and Uses
2026/08/11
304 and 304L Stainless Steel: Properties, Composition and Uses
Written by: Emma, Technical Sales Engineer | Reviewed by: Ethan, Materials Engineer | Updated: August 2026
1. What Are 304 and 304L Stainless Steel?
304 and 304L are the most widely used stainless steel grades in the world, together accounting for more than 50% of global stainless steel production. Both belong to the austenitic stainless steel family — their face-centered cubic (FCC) crystal structure is stabilized by nickel, which keeps them non-magnetic in the annealed condition and gives them excellent formability.
304 is commonly referred to as "18/8 stainless steel" because its nominal composition is approximately 18% chromium and 8% nickel. The grade is recognized globally under multiple designation systems: UNS S30400, EN 1.4301, JIS SUS304.
| Characteristic | 304 | 304L |
|---|---|---|
| UNS Number | S30400 | S30403 |
| EN Designation | 1.4301 | 1.4307 / 1.4306 |
| Family | Austenitic | Austenitic |
| Magnetic? | Non-magnetic (annealed); slightly magnetic after cold work | Non-magnetic (annealed); slightly magnetic after cold work |
| Hardenable by heat treatment? | No | No |
| Hardenable by cold working? | Yes | Yes |
Core insight: 304L is not an "upgraded" or "improved" 304. Both grades share the same chromium and nickel ranges and the same austenitic structure. The only intentional metallurgical difference is carbon content — and that single difference determines which grade is appropriate for which application.
2. Chemical Composition of 304 and 304L
The following table reflects the composition limits per ASTM A240 — the standard specification for chromium and chromium-nickel stainless steel plate, sheet, and strip for pressure vessels and general applications.
| Element | 304 (UNS S30400) | 304L (UNS S30403) | Key Difference? |
|---|---|---|---|
| Carbon (C) | ≤ 0.08% | ≤ 0.03% | Primary difference |
| Chromium (Cr) | 18.0–20.0% | 18.0–20.0% | Same |
| Nickel (Ni) | 8.0–10.5% | 8.0–12.0% | Ni slightly higher in 304L — compensates for austenite stability |
| Manganese (Mn) | ≤ 2.0% | ≤ 2.0% | Same |
| Silicon (Si) | ≤ 0.75% | ≤ 0.75% | Same |
| Nitrogen (N) | ≤ 0.10% | ≤ 0.10% | Same |
| Phosphorus (P) | ≤ 0.045% | ≤ 0.045% | Same |
| Sulfur (S) | ≤ 0.03% | ≤ 0.03% | Same |
Procurement Verification: Always cross-check the actual chemical composition on the MTC (EN 10204 3.1) against the relevant ASTM standard. Nominal composition is marketing language — only the MTC's heat analysis tells you what was actually melted. For dual-certified 304/304L material, confirm that carbon is ≤ 0.03% and mechanicals meet the higher 304 minimums.
3. Why Carbon Content Matters: Welding and Sensitization
The carbon content difference between 304 (≤ 0.08%) and 304L (≤ 0.03%) may appear trivial — 0.05 percentage points — but it is the single most important metallurgical distinction for anyone who welds the material.
During welding, the heat-affected zone (HAZ) adjacent to the weld reaches 425–870°C — the critical sensitization temperature range. At these temperatures, carbon atoms become mobile and migrate to grain boundaries, where they combine with chromium to form chromium carbides (Cr₂₃C₆). The regions immediately adjacent to these carbide precipitates become chromium-depleted — falling below the ~10.5% threshold required for passivation.
The result: grain boundaries that are locally vulnerable to intergranular corrosion (IGC), even though the bulk chemical composition appears correct on the MTC. In a corrosive environment, the weld HAZ becomes the failure initiation point — a problem that cannot be detected by visual inspection alone.
The 304L solution: By limiting carbon to ≤ 0.03%, 304L ensures that there is insufficient carbon available to form a continuous network of chromium carbides during typical welding thermal cycles. The grain boundaries retain their passivity without requiring post-weld solution annealing — a heat treatment that is often impractical for large welded fabrications.
| Situation | 304 | 304L |
|---|---|---|
| Carbon content | ≤ 0.08% | ≤ 0.03% |
| Sensitization during welding | Significant risk — IGC possible in HAZ | Very low risk — carbon too low for continuous carbide network |
| Post-weld solution anneal needed? | Yes — if welded and exposed to corrosive environment | Typically not required |
| Intergranular corrosion testing | ASTM A262 Practice E may show attack | ASTM A262 Practice E — typically passes after welding |
Procurement Decision Rule: If your component will be welded and placed in any corrosive environment — including mild atmospheric exposure — specify 304L. The cost difference between 304 and 304L is negligible in the context of the total fabrication cost. The cost of repairing or replacing a component that failed from intergranular corrosion is not.
4. 304 Stainless Steel Properties
Corrosion Resistance
304 offers good atmospheric corrosion resistance and resistance to a wide range of organic and inorganic chemicals at moderate temperatures. It performs well in food processing environments, fresh water, rural and urban atmospheres, and many mildly acidic conditions.
However, 304 has clear corrosion boundaries that the buyer must understand:
- Chloride environments: 304 is susceptible to pitting and crevice corrosion in chloride-containing environments — including coastal atmospheres, de-icing salt exposure, and any process fluid containing significant Cl⁻ ions. PREN of 304 is approximately 18–20
- Warm seawater: Not recommended for seawater immersion at any temperature. Even coastal atmospheric exposure may cause pitting without regular washing by rain
- Strong acids: 304 resists many organic acids but is attacked by hydrochloric acid, sulfuric acid above certain concentrations and temperatures, and hydrofluoric acid
Mechanical Properties (Annealed Condition, per ASTM A240)
| Property | 304 (S30400) |
|---|---|
| Tensile Strength (min) | 515 MPa |
| Yield Strength 0.2% offset (min) | 205 MPa |
| Elongation in 50mm (min) | 40% |
| Hardness (max) | 201 HBW / 92 HRB |
| Density | ~8.0 g/cm³ |
| Melting Range | 1400–1455°C |
| Modulus of Elasticity | ~193 GPa |
| Thermal Conductivity (at 100°C) | ~16.2 W/m·K |
Note on Strength Values: The values above are ASTM A240 minimums for annealed plate/sheet. Actual mechanical properties vary with product form (plate vs. sheet vs. bar), thickness, and processing condition. Cold-worked 304 can reach substantially higher strength — up to 1000+ MPa in heavily worked condition (e.g., spring temper), though this comes with reduced ductility and increased magnetism.
Fabrication Properties
304 is among the most formable stainless steels: excellent deep-drawing, bending, and stretch-forming capability. It can be welded by all common processes (TIG, MIG, SMAW, SAW, resistance welding). Surface finishing options range from mill finish to mirror-polished, making it suitable for architectural and decorative applications alongside industrial uses.
5. 304L Stainless Steel Properties
304L maintains essentially the same corrosion resistance and mechanical properties as 304 in the unwelded condition. The chromium and nickel ranges overlap substantially, and both grades form the same austenitic structure with the same passive film behavior.
Where 304L distinguishes itself is in welded fabrication:
- Weld zone corrosion resistance: The low carbon (≤ 0.03%) prevents sensitization in the HAZ, maintaining intergranular corrosion resistance without post-weld heat treatment. This is 304L's defining advantage
- Code compliance: Many design codes and client specifications — particularly for pressure vessels, chemical tanks, and hygienic equipment — specifically require low-carbon grades for all welded construction. Using 304 in these applications may result in non-compliance
- Dual certification availability: Much 304L material is actually supplied as 304/304L dual certified, meeting both grade specifications simultaneously. This provides procurement flexibility — one heat of material satisfies both specification requirements
| Property | 304L (S30403) |
|---|---|
| Tensile Strength (min) | 485 MPa |
| Yield Strength 0.2% offset (min) | 170 MPa |
| Elongation in 50mm (min) | 40% |
| Hardness (max) | 201 HBW / 92 HRB |
Clarification on Strength: ASTM A240 lists slightly lower minimum strength for 304L vs 304 — 170 MPa vs 205 MPa yield, 485 MPa vs 515 MPa tensile. However, modern AOD-refined 304L routinely meets or exceeds the higher 304 minimums, which is why 304/304L dual-certified material is the industry norm. When ordering 304L for load-bearing applications, verify the actual mechanical properties on the MTC — the reported values will almost certainly exceed the 304L minimums and likely meet 304 minimums.
6. 304 vs 304L: Complete Comparison
| Property | 304 | 304L |
|---|---|---|
| UNS Number | S30400 | S30403 |
| Carbon Content | ≤ 0.08% | ≤ 0.03% |
| Corrosion Resistance (unwelded) | Good | Good — equivalent to 304 |
| Corrosion Resistance (welded, HAZ) | Possible IGC without PWHT | Excellent — resistant to IGC |
| Sensitization Resistance | Lower | Higher |
| Weldability | Weldable; PWHT may be needed for corrosive service | Weldable; typically no PWHT required |
| Strength (ASTM min.) | TS ≥ 515 MPa; YS ≥ 205 MPa | TS ≥ 485 MPa; YS ≥ 170 MPa (note: dual-certified meets 304 minimums) |
| Formability | Excellent | Excellent — equivalent to 304 |
| Typical Cost | Baseline | Marginal premium; often same as 304 in practice |
| Best Application | Non-welded general fabrication | Welded fabrication for corrosive service |
7. Common Applications of 304 and 304L
| Industry | Typical Applications | Recommended Grade | Reason |
|---|---|---|---|
| Food processing | Storage tanks, piping, conveyor systems, work tables | 304 / 304L | Non-toxic, easy to clean, good corrosion resistance to food acids |
| Architecture & building | Handrails, cladding, elevator panels, column covers | 304 | Aesthetic finish options, adequate for indoor/urban environments |
| Chemical processing | Welded storage vessels, reactor bodies, heat exchanger shells | 304L | Welded construction; IGC resistance in HAZ is essential |
| Pharmaceutical | WFI tanks, process piping, cleanroom equipment | 304L | All components are welded; surface finish and IGC resistance critical |
| Kitchen & catering | Sinks, worktops, cookware, appliances | 304 | Good formability, hygienic, adequate corrosion resistance |
| General sheet metal | Brackets, enclosures, formed parts, fasteners | 304 | Excellent formability, no welding required in most cases |
| Pressure vessels | ASME-coded tanks and vessels | 304L | Code typically mandates low-carbon grade for all-welded pressure boundaries |
| Brewing & dairy | Fermentation tanks, milk storage, sanitary tubing | 304L | All sanitary systems are fully welded with orbital TIG; IGC resistance mandatory |
8. Limitations of 304 and 304L
304 is the most versatile stainless steel — but it is not universal. Understanding its limitations is as important as knowing its strengths:
| Condition | Is 304/304L Suitable? | Recommended Alternative |
|---|---|---|
| Freshwater, ambient, no chlorides | Yes | — |
| Indoor atmosphere, urban | Yes | — |
| Coastal atmosphere, sheltered | At risk — pitting likely over time | 316L |
| De-icing salt exposure | No — will pit | 316L |
| Seawater immersion | No — rapid pitting and crevice corrosion | 2205 duplex or 2507 super duplex |
| High temperature (> 500°C) under load | No — insufficient creep strength | 304H, 321, or 347 |
| Strong reducing acids (HCl, H₂SO₄) | No — uniform corrosion | 904L, duplex, or higher alloys |
9. How to Select Between 304 and 304L
Question 1 — Will the component be welded?
If yes → choose 304L unless post-weld solution annealing at 1040–1120°C followed by rapid quenching will be performed and verified for every weld. In practice, this means 304L is the default choice for any welded fabrication exposed to any corrosive environment.
Question 2 — Will your service environment contain chlorides?
If the chloride concentration is significant (coastal atmosphere, salt spray, any process fluid with Cl⁻) → evaluate whether 304/304L is even the correct grade family. 316L may be the minimum requirement regardless of the 304 vs 304L decision.
Question 3 — Is elevated-temperature strength required?
If the component operates above ~500°C under sustained load → 304L is not suitable due to low carbon = low creep strength. Evaluate 304H (0.04–0.10% C) or stabilized grades 321 (Ti-stabilized) or 347 (Nb-stabilized).
Question 4 — Is there a compelling reason NOT to use L-grade?
If there is no specific reason to avoid L-grade, and the material will be welded, default to 304L or dual-certified 304/304L. The cost difference is negligible; the technical risk of using 304 for welded corrosion service is real and avoidable.
10. Procurement Guidance: Ordering 304 and 304L Correctly
| Specification Element | Example (304L) | Why It Matters |
|---|---|---|
| Grade | 304L | Specifies carbon grade; "304" alone may default to standard carbon unless explicitly stated |
| UNS | S30403 | Unambiguous — eliminates any grade confusion across international standards |
| Product Standard | ASTM A240 (plate/sheet) or ASTM A312 (pipe) | Different standards = different requirements. A generic "304L" without the product standard is incomplete |
| Product Form | Plate / Sheet / Coil / Pipe / Bar | Determines applicable dimensional tolerances and available surface finishes |
| Surface Finish | 2B / BA / No.4 / No.8 | 2B is mill finish; BA is bright annealed; No.4 is brushed; No.8 is mirror — specifies appearance and cleanability |
| Dimensions | 3 mm × 1500 mm × 3000 mm | Complete dimensions prevent quoting the wrong thickness or format |
| Certification | EN 10204 3.1 MTC | Confirms chemical composition and mechanical properties from the specific heat |
| Supplementary Testing | PMI; IGC per ASTM A262 Practice E (if welded) | Verifies grade identity and corrosion resistance of welded condition |
Common Procurement Error — Avoid: Stating only "304 stainless steel sheet, 3mm" on a purchase order. This is fundamentally incomplete. It does not specify: (1) whether 304 or 304L, (2) which product standard applies, (3) surface finish, (4) MTC type, (5) whether the material will be welded. The supplier can legitimately deliver standard 304 with an uncoated mill finish — which may be perfectly correct per the PO but entirely wrong for your application. A properly written specification prevents this.
11. How Shangyou Ensures Correct 304/304L Supply
- ASTM Specification Verification: Every order is confirmed against the applicable ASTM standard — A240 for plate/sheet, A312 for pipe, A276 for bar. We do not accept "close enough" — the material either complies with the specified standard or it does not ship
- Carbon Content Confirmation: For 304L and 304/304L dual-certified orders, carbon content is verified from the MTC heat analysis. ≤ 0.03% is the pass/fail criterion — no exceptions
- UNS Grade Verification: Every MTC is cross-checked to confirm the correct UNS number — S30400 for 304, S30403 for 304L. A grade listed as "304" without UNS verification is ambiguous
- Chemical Composition Review: Beyond carbon, we verify all alloying elements — Cr, Ni, Mn, Si, P, S, N — against the specified ASTM standard's composition limits. Any out-of-spec element triggers a rejection before the material reaches your facility
- PMI Testing Coordination: Positive Material Identification using XRF confirms major alloying elements (Cr, Ni, Mo) and screens for grade mix-ups — particularly important when multiple grades are present in the same shipment
- MTC 3.1 Documentation: Every shipment includes an EN 10204 3.1 MTC with full chemical composition and mechanical properties traceable to the specific heat number. We do not ship on "typical" or nominal values
- Surface Inspection: Visual inspection for surface defects, finish conformity, and dimensional accuracy before dispatch — catching issues before they arrive at your facility
- Third-Party Inspection Coordination: Pre-shipment inspection with SGS, Bureau Veritas, TÜV, or Intertek — including MTC review, PMI, dimensional check, and surface condition verification against your purchase order
12. Frequently Asked Questions
Q1: What is 304 stainless steel?
304 is an austenitic chromium-nickel stainless steel — the most widely used stainless steel grade worldwide. Its nominal composition is approximately 18% chromium and 8% nickel, giving it the common name "18/8 stainless steel." Under UNS, it is designated S30400. 304 offers good atmospheric corrosion resistance, excellent formability and weldability, and is non-magnetic in the annealed condition. It cannot be hardened by heat treatment but can be strengthened by cold working. Typical applications include kitchen equipment, food processing, architectural components, and general sheet metal fabrication.
Q2: What does 18/8 stainless steel mean?
"18/8" is a traditional shorthand referring to the approximate composition of 304 stainless steel: ~18% chromium and ~8% nickel. It is a convenient way to distinguish 304 from 18/10 (higher nickel, typically found in higher-quality cookware but still within the 304 composition range) or 18/0 (ferritic 430, no nickel). However, 18/8 is not a formal grade designation — it should not appear on a purchase order or MTC. Always specify the full grade (304 or 304L) and the relevant ASTM standard.
Q3: What is the difference between 304 and 304L stainless steel?
The only intentional metallurgical difference is carbon content: 304 allows ≤ 0.08% C; 304L limits to ≤ 0.03% C. This reduces the risk of sensitization (chromium carbide precipitation at grain boundaries) during welding. In the unwelded condition, 304 and 304L have equivalent corrosion resistance. The choice is driven by welding: if the component will be welded and placed in any corrosive environment, choose 304L. For non-welded general fabrication, 304 may be adequate.
Q4: Is 304L better than 304?
Not in the sense of universally "better." 304L is specifically optimized for welded corrosive service. If your application does not involve welding, 304 and 304L perform equivalently — there is no measurable benefit to paying extra for 304L. If your application does involve welding, 304L is the technically correct choice because it prevents intergranular corrosion without requiring post-weld solution annealing. "Better" depends entirely on whether welding is part of your fabrication route.
Q5: Why is 304L preferred for welding?
During welding, the heat-affected zone reaches 425–870°C — the sensitization range. At these temperatures, carbon combines with chromium to form chromium carbides at grain boundaries, depleting the surrounding areas of chromium and destroying their corrosion resistance. 304L limits carbon to ≤ 0.03%, which is insufficient to form a continuous network of carbides. The result: 304L's weld HAZ retains its corrosion resistance without requiring post-weld solution annealing — a process that is expensive, energy-intensive, and often physically impossible for large fabrications.
Q6: Is 304 stainless steel corrosion resistant?
304 offers good corrosion resistance in many common environments: fresh water, rural and urban atmospheres, food acids, and many organic chemicals at moderate temperatures. However, 304 is not resistant to chlorides — it will pit in coastal atmospheres, de-icing salt exposure, and any chloride-containing process fluid. It is not suitable for seawater immersion. 304's PREN (Pitting Resistance Equivalent Number) is approximately 18–20, the lowest among commonly used austenitic grades. Always match the specific corrosion environment to the grade — "corrosion resistant" does not mean "immune to all corrosion."
Q7: Can 304 stainless steel be used in seawater?
No. 304 should not be used for seawater immersion or in direct, continuous contact with seawater. With PREN of approximately 18–20 and no molybdenum, 304 will pit rapidly in seawater chloride concentrations (~19,000 ppm). Even 304L — which solves the welding-related corrosion problem — does not change the fundamental chloride pitting susceptibility. For seawater immersion, 2205 duplex (PREN ~33–36) is the minimum practical option; 2507 super duplex (PREN >40) or 6Mo super austenitics are the standard recommendation for seawater service.
Q8: Is 304 stainless steel magnetic?
In the fully annealed condition, 304 is non-magnetic — its austenitic (FCC) crystal structure is paramagnetic. However, cold working (bending, forming, drawing) transforms some austenite to martensite, which is ferromagnetic. This means cold-worked 304 can be slightly magnetic — a formed sink bowl, a deep-drawn container, or a heavily cold-rolled strip may attract a magnet. This is normal and not a defect. If non-magnetic behavior is required after forming, specify solution annealing after fabrication to revert the martensite to austenite.
Q9: What is the UNS number of 304 and 304L?
304 is UNS S30400 and 304L is UNS S30403. The UNS (Unified Numbering System) designation is the most unambiguous way to specify a stainless steel grade — it eliminates confusion between national standards (AISI, EN, JIS) and ensures all parties in the supply chain are talking about the same material. Always include the UNS on your purchase order alongside the common grade name.
Q10: What documents should I request when purchasing 304 or 304L stainless steel?
Request the following as a minimum: (1) EN 10204 3.1 MTC with full chemical composition (including carbon — verify the grade suffix) and mechanical properties traceable to the heat number; (2) Product standard compliance statement (e.g., ASTM A240 for plate/sheet); (3) UNS number confirmation (S30400 or S30403); (4) If welded fabrication is planned — IGC testing per ASTM A262 Practice E to confirm sensitization resistance; (5) PMI report if supplementary grade verification is required. Review these documents before the material is shipped — not after it has arrived at your facility.
Related Reading
- [What Is Stainless Steel? Types, Properties, Manufacturing and Uses]
- [Stainless Steel Grades Chart: AISI, UNS, EN and JIS Cross-Reference Guide]
- [L, H and Dual-Certified Stainless Steel Grades Explained]
- [Does Stainless Steel Rust? Causes, Corrosion Types and Prevention]
- [PREN Explained: Formula, Grade Comparison and Selection Limits]
- [304 vs 316 Stainless Steel: Differences and Applications]
Technical References
- ASTM A240 — Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip
- ASTM A276 — Standard Specification for Stainless Steel Bars and Shapes
- ASTM A312 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Pipe
- ASTM A262 — Standard Practices for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels
- Outokumpu Stainless Steel Handbook — 304/304L datasheets and corrosion data
- ASM Handbook Volume 1 — Properties and Selection: Irons, Steels, and High-Performance Alloys
- British Stainless Steel Association (BSSA) — Grade 304/304L Technical Datasheet
Need 304 or 304L Stainless Steel?
Whether you need standard 304 for general fabrication or 304L for welded equipment in corrosive service, our technical team verifies ASTM compliance, carbon content, and complete MTC documentation before every shipment. Send us your specifications for a quotation — typically within one business day.
Include in your inquiry: Grade + UNS (304/S30400 or 304L/S30403) / product standard (ASTM A240, A312, A276) / product form and dimensions / surface finish / quantity / MTC type / supplementary testing requirements / delivery terms.
Contact Shangyou Stainless Steel — correct grades, verified chemistry, complete documentation.
Disclaimer: This article provides educational and procurement reference information. Material selection for specific applications should be confirmed by a qualified engineer reviewing actual service conditions, applicable design codes, and the material MTC from the specific heat to be used.
