904L vs 316L Stainless Steel: Which Grade Should You Specify?
When engineers or buyers compare 904L vs 316L stainless steel, the decision is rarely about “better.” It is about failure modes (pitting, crevice corrosion, stress corrosion cracking, acid attack), fabrication risk, and total lifecycle cost.
316L (UNS S31603) remains the default “workhorse” for many corrosive services. 904L (UNS N08904) is a high-alloy austenitic grade with elevated nickel and molybdenum plus copper, developed to perform where 316L begins to lose reliability—especially in reducing acids and more severe chloride conditions. Nickel Institute+2Nickel Institute+2
Quick selection guidance
Specify 316L when:
Chlorides are moderate, temperatures are controlled, and you can design out severe crevices.
You need widely available coil/sheet/plate with predictable fabrication and faster lead times.
Your environment is marine “adjacent,” not continuously immersed or stagnant seawater.
Upgrade to 904L when:
You face sulfuric acid (especially mid-concentration ranges) or other reducing acids where 316L’s corrosion rate becomes unacceptable.
Chloride exposure is more severe (warm, stagnant, crevice-prone geometries) and downtime or replacement is expensive.
Your ROI model supports higher alloy cost to avoid recurring failures.
Grade identity and standards
316L: UNS S31603 (low-carbon 316 family), commonly specified for flat-rolled products under ASTM A240 (Type 316L). Nickel Institute
904L: UNS N08904, also commonly specified under ASTM A240 for flat-rolled products (904L / N08904). Nickel Institute+1
For RFQs, specify both: ASTM designation + UNS + product form (coil/sheet/plate), thickness, width/length, surface finish, and testing requirements.
Chemical composition and PREN (why 904L resists localized corrosion better)
The chemistry difference is not subtle—904L carries much higher Ni and Mo and adds Cu. Nickel Institute+1
Composition snapshot (ASTM ranges) + PRE number
| Grade | UNS | Cr (%) | Ni (%) | Mo (%) | Cu (%) | PRE (typical index) |
|---|---|---|---|---|---|---|
| 316L | S31603 | 16.0–18.0 | 10.0–14.0 | 2.0–3.0 | — | 23 |
| 904L | N08904 | 19.0–23.0 | 23.0–28.0 | 4.0–5.0 | 1.0–2.0 | 32 |
What PREN means (and what it does not)
A common expression for localized corrosion ranking in chlorides is:
PRE = %Cr + 3.3×%Mo + 16×%N Nickel Institute+1
Higher PRE generally correlates with higher resistance to pitting/crevice initiation in chloride environments—but it is not a guarantee. Surface finish, crevice severity, temperature, oxidizers, and maintenance conditions can dominate real-world performance.
Note: Some producer datasheets cite 904L PRE values in the mid-30s depending on exact melt chemistry; treat PRE as a comparative index and validate with MTC chemistry for contract-critical applications.
Corrosion performance: where the real separation happens
1) Chlorides: pitting, crevice corrosion, and SCC
316/316L can pit and crevice-corrode in warm chloride environments and is susceptible to stress corrosion cracking above ~60°C in certain chloride conditions. It is often called “marine grade,” but it is not fully resistant to seawater in many practical designs—especially where crevices and rough finishes exist.
904L is described as highly resistant to chloride attack (pitting/crevice) and SCC, driven by high Ni and Mo; it is frequently chosen for more aggressive chloride duty where 316L’s failure probability becomes unacceptable.
Practical buyer takeaway: if the design includes gaskets, lap joints, deposits, intermittent wetting/drying, or warm brines, treat 316L as “possible with controls,” and treat 904L as “higher reliability”—then confirm with environment details and corrosion engineering.
2) Reducing acids (especially sulfuric acid): 904L’s differentiator
904L’s copper addition is specifically associated with improved resistance to strong reducing acids, particularly sulfuric acid, including aggressive mid-concentration ranges.
If your service includes sulfuric acid exposure (processing equipment, scrubbers, fertilizer-related systems), 904L can materially extend service life compared with 316L—often enough to offset the alloy premium when replacement downtime is costly.
3) Where 904L is not automatically better
In aggressive nitric acid, some sources note 904L can have less resistance than molybdenum-free austenitic grades such as 304L/310L. In other words: 904L is not a universal upgrade—match the alloy to the chemistry.
Mechanical properties (ASTM minimums for sheet/plate)
For most fabrication decisions, 316L and 904L are both austenitic and comparable in structural use. ASTM minimums for flat-rolled products (per common specifications) are: Nickel Institute+1
| Grade | Tensile min | Yield min (0.2%) | Elongation min |
|---|---|---|---|
| 316L | 485 MPa | 170 MPa | 40% |
| 904L | 490 MPa | 220 MPa | 35% |
Interpretation: 904L typically carries higher yield minimums in these references, but the selection decision is usually driven by corrosion, not strength.
Fabrication and welding
Forming and machining
904L is weldable and formable, but it is a high-alloy grade and may not machine as easily as more common stainless grades; plan tooling and cycle times accordingly.
Welding risk: hot cracking and filler selection
Because 904L solidifies fully austenitic, it can be more susceptible to hot cracking in constrained weldments, requiring better heat input control and procedure discipline.
For welding consumables, common references list ER385 wire / E385 electrodes for 904L (N08904). Nickel Institute
Buyer checklist (welding):
Require a documented WPS/PQR for 904L joints in critical service.
Specify filler metal explicitly (do not leave to shop default).
For chloride + crevice critical duty, consider post-fabrication cleaning and passivation requirements in your PO.
Temperature capability: avoid a common specification mistake
316/316L oxidation resistance: good oxidation resistance is often cited to 870°C intermittent and 925°C continuous service (subject to application constraints).
904L caution: despite having good oxidation resistance, it should not be used above ~550°C due to structural instability (brittle phase precipitation).
Also note the frequent misunderstanding:
904L solution anneal temperatures (e.g., ~1090–1175°C) are heat-treatment parameters, not allowable service temperatures.
Typical applications (where each grade is commonly justified)
316L typical uses
Food processing equipment, laboratory equipment, architectural panels/trim, boat fittings, chemical containers, heat exchangers (with chloride constraints).
904L typical uses
Processing plants for sulfuric/phosphoric/acetic acids, pulp and paper processing, gas scrubbing, seawater cooling equipment, refinery components.
Cost and availability: how to justify 904L commercially
904L contains substantial amounts of nickel and molybdenum, which are high-cost alloying elements; this is the primary reason 904L typically carries a significant price premium and can be less commonly stocked than 316L.
A practical way to make the decision is replacement interval economics:
If 316L’s corrosion risk leads to predictable replacement or frequent maintenance, 904L can reduce total cost of ownership even with higher initial material cost.
If your environment is well-controlled and failures are unlikely, 316L usually wins on total delivered cost and procurement speed.
Alternative note (often overlooked): in many applications historically served by 904L, duplex 2205 may meet the duty at lower cost (with different temperature/forming constraints).
RFQ checklist
Include the following in your inquiry to prevent re-quotes and spec mismatch:
Grade + standard
ASTM A240 Type 316L (UNS S31603) or ASTM A240 904L (UNS N08904). Nickel Institute+1
Product form
Coil / sheet / plate, plus thickness, width, length, coil ID/OD if applicable.
Surface finish and post-processing
2B, BA, No.4, HL, pickled, polished, protective film, etc. (Add processing tolerance requirements.)
Testing and documents
Require Mill Test Certificate (MTC) with chemistry and mechanicals; define any third-party inspection needs.
Service conditions (minimum needed for alloy confirmation)
Chloride level (or seawater/brine), temperature range, pH, presence of oxidizers/reducing acids, stagnant vs flowing, and whether crevices/deposits are expected.
Why source from LYH Steel (built for specification-driven buyers)
LYH Steel supports stainless buyers with:
Standard supply formats in sheet/plate and strip/coil, with optional processing services (slitting, shearing, surface finishing). LYH Steel+2LYH Steel+2
Quality controls oriented to export supply, including inspection workflows suitable for contract delivery. LYH Steel
Tools for faster engineering alignment during RFQ: PREN calculator and weight calculators. LYH Steel+1
If you share your environment details and drawing/spec (or current material grade + failure history), we can recommend a grade shortlist and quote the right supply form for your fabrication route.
CTA: Request pricing and lead time through the LYH Steel contact page. LYH Steel
FAQ
1) Is 904L “better” than 316L?
Not universally. 904L is typically chosen for higher-risk chloride duty and reducing acids (notably sulfuric acid), while 316L is usually the best-value choice for general corrosion resistance with manageable chlorides.
2) What are the key chemical differences between 904L and 316L?
904L has much higher Ni and Mo and adds Cu; 316L has lower Ni/Mo and no Cu. These differences drive higher PRE and improved acid performance for 904L. Nickel Institute+1
3) What PRE values should I expect for 316L vs 904L?
Common references list PRE ≈ 23 for 316L and 32 for 904L (exact values depend on melt chemistry and nitrogen). Nickel Institute+2Nickel Institute+2
4) Does 316L resist seawater indefinitely?
Not necessarily. It can suffer crevice/pitting in marine service, particularly with crevices, deposits, warm temperatures, or rough finishes.
5) Is 904L suitable for high-temperature service?
It is generally not recommended above ~550°C due to structural instability, even though its solution annealing temperatures are much higher (heat treatment ≠ service temperature).
6) What welding filler is typically used for 904L?
Common references list ER385 wire and E385 electrodes for 904L (N08904). Nickel Institute