AISI 304 Stainless Steel (UNS S30400): Properties & Equivalents vs AISI 316L Stainless Steel (UNS S31603): Marine-Grade Properties
Side-by-side engineering comparison of AISI 304 Stainless Steel (UNS S30400): Properties & Equivalents (ASTM A240/A276) and AISI 316L Stainless Steel (UNS S31603): Marine-Grade Properties (ASTM A240/A276). Compare mechanical properties, chemical composition, density, yield strength, international equivalents, and typical applications to select the right material for your project.
Quick Comparison
| Property | AISI 304 Stainless Steel | AISI 316L Stainless Steel |
|---|---|---|
| Standard | ASTM A240/A276 | ASTM A240/A276 |
| Category | Stainless Steel | Stainless Steel |
| Density | 8.00 g/cm³ | 8.00 g/cm³ |
| Yield Strength | 205 MPa (30 ksi) | 170 MPa (25 ksi) |
| Tensile Strength | 515 MPa (75 ksi) | 485 MPa (70 ksi) |
| Key Applications | <a href="https://ykwiki.com/materials/ss304/">AISI 304</a> (UNS S30400) is the most common austenitic stainless steel, c... | AISI 316L (UNS S31603) is a low-carbon (≤0.03%) austenitic stainless steel with 16-18% chromium, 10-14% nickel, and 2-3%... |
International Equivalents
| AISI 304 Stainless S Equivalents | AISI 316L Stainless Equivalents |
|---|---|
| EN 1.4301 | EN 1.4404 |
| X5CrNi18-10 | X2CrNiMo17-12-2 |
| SUS304 | SUS316L |
| 06Cr19Ni10 | 022Cr17Ni12Mo2 |
| AISI 304 | AISI 316L |
How to Choose
| Choose AISI 304 Stainless Steel when... | 304 is sufficient for indoor, freshwater, and food-contact applications. |
| Choose AISI 316L Stainless Steel when... | 316L adds 2-3% molybdenum for pitting resistance in chlorides—essential for marine, coastal, and chemical processing. |
Selection Guide
The decision between 304 and 316L stainless steel comes down to one question: is the application exposed to chlorides? If yes — marine, coastal, chemical processing, swimming pools, or de-icing salt environments — specify 316L. If no — indoor, freshwater, food processing, or mild chemical exposure — 304 is the more economical choice. 316L costs 25-40% more than 304, so specifying it unnecessarily wastes budget.
Key Decision Factors
- Chloride exposure — the single most important factor. 316L's PREN (24-28) significantly exceeds 304's (18-20) in chloride environments
- Cost sensitivity — 304 is 25-40% less expensive; specifying 316L without chloride justification wastes project budget
- Welding requirements — the 'L' grade (316L) with ≤0.03% carbon prevents intergranular corrosion in the heat-affected zone after welding
- Temperature — above 60°C, chloride pitting risk increases dramatically, shifting preference to 316L even in moderate chloride environments
When to Use Each
Use AISI 304 Stainless S for:
304 provides excellent corrosion resistance for indoor environments — elevator interiors, handrails, food service counters — at 25-40% lower cost than 316L.
304 is the standard for food contact surfaces (sinks, counters, brewing tanks). It resists organic acids and food-grade chemicals without the cost premium of 316L.
304 handles dilute sulfuric acid, phosphoric acid, and organic solvents at moderate temperatures where chlorides are not present.
Use AISI 316L Stainless for:
316L's 2-3% molybdenum provides critical pitting resistance in chloride environments — salt spray, seawater splash, and coastal atmospheric exposure.
316L is the standard for ASME BPE pharmaceutical piping due to its superior resistance to pitting in purified water and CIP chemical systems.
Any application involving hydrochloric acid, sodium hypochlorite, or chloride-containing process streams requires 316L to prevent pitting and stress corrosion cracking.
Frequently Asked Questions
What is the main difference between AISI 304 Stainless Steel (UNS and AISI 316L Stainless Steel (UNS?
AISI 304 Stainless Steel (UNS S30400): Properties & Equivalents (ASTM A240/A276) provides 205 MPa (30 ksi) yield strength at 8.00 g/cm³ density, while AISI 316L Stainless Steel (UNS S31603): Marine-Grade Properties (ASTM A240/A276) delivers 170 MPa (25 ksi) at 8.00 g/cm³. The choice depends on whether your application prioritizes cost-effectiveness in mild environments or chloride/corrosion resistance.
Can AISI 304 Stainless Steel (UNS be substituted for AISI 316L Stainless Steel (UNS?
In many applications, these materials can be cross-referenced, but direct substitution should always be verified against specific project specifications, especially for cost-effectiveness in mild environments, chloride/corrosion resistance, and operating environment. Consult your engineer of record.
Can 304 be used outdoors near the coast?
Not recommended. Coastal atmospheric chloride deposition causes tea staining (surface rust) and eventual pitting on 304 stainless. 316L provides significantly better coastal corrosion resistance. For coastal architectural applications within 5km of saltwater, specify 316L minimum; consider duplex 2205 for critical structural applications.
Why specify 316L instead of 316 for welded applications?
The 'L' designation means ≤0.03% carbon (vs ≤0.08% for standard 316). During welding, standard 316 can develop chromium carbide precipitation at grain boundaries in the heat-affected zone, depleting chromium and causing intergranular corrosion (weld decay). 316L's low carbon prevents this without requiring post-weld solution annealing.
Is 316L worth the cost premium for residential kitchens?
Usually not. 304 stainless steel provides excellent corrosion resistance for residential kitchen sinks, countertops, and appliances where exposure is limited to food acids and tap water. The 25-40% premium for 316L is rarely justified in residential applications unless the home is in a coastal environment.
What is PREN and why does it matter?
PREN (Pitting Resistance Equivalent Number) = %Cr + 3.3×%Mo + 16×%N. It predicts resistance to chloride pitting. 304 has PREN ~18-20; 316L has PREN ~24-28. For seawater resistance, PREN >32 is recommended (consider duplex 2205 or super-austenitic grades). PREN is a useful quick comparison tool but does not replace actual corrosion testing.
Can 304 and 316L be welded together?
Yes, they are metallurgically compatible. Use 309L or 316L filler metal for the dissimilar weld. However, the weld area will have corrosion resistance closer to 304 (the weaker grade). For critical applications, transition pieces or solid 316L is preferred to avoid creating a galvanic corrosion cell.