Stainless Steel 304 / 304L & 316 / 316L Material & Sourcing Guide

1. Material Overview: 304 / 304L vs 316 / 316L in One Page

Austenitic stainless steels 304 / 304L and 316 / 316L are by far the most widely used grades in process equipment, pipelines and fabricated stainless structures.

In simple terms:

• 304 / 304L is the “workhorse” grade for many indoor and mildly corrosive environments, offering a good balance of cost, corrosion resistance and fabricability.
• 316 / 316L adds molybdenum (Mo), significantly improving resistance to chlorides (salt, de-icing chemicals, many process streams) and certain chemicals – at a higher alloy and purchase cost.
• The L variants (304L, 316L) limit carbon to ≤0.03% to improve resistance to weld sensitisation and intergranular corrosion in welded heavy sections.

For Sunhyings customers, material selection is usually a trade-off between corrosion risk, life-cycle cost and code compliance. This guide is written to help engineers and buyers justify that decision with clear technical reasoning.

2. Chemistry & International Designations

Both 304 and 316 are chromium-nickel austenitic stainless steels. The key difference is the deliberate addition of 2–3% Mo in 316 / 316L, plus slight adjustments to Ni to maintain the austenitic structure.

2.1 Designations at a glance

2.2 Typical chemical composition ranges (% by weight)

Note: Many plates are supplied dual-certified (e.g. 304/304L or 316/316L), combining low-carbon weldability with the minimum strength of the parent grade. Always confirm on the MTC if you have strict code requirements.

3. Mechanical & Physical Properties

Both grade families share the characteristic high toughness and ductility of austenitic stainless steels. At room temperature, mechanical properties in solution-annealed plate are broadly comparable, with 316 often showing slightly higher tensile strength in practice.

3.1 Typical mechanical properties (plate, room temperature)

3.2 Physical properties (typical)

In fully solution-annealed condition, both grade families are essentially non-magnetic. Cold work (bending, forming) can introduce slight magnetism without significantly affecting corrosion resistance.

4. Corrosion Behaviour in Real Environments

The most important practical difference is corrosion resistance – especially in chloride-bearing environments (sea salt, de-icing salts, many process streams, cleaning chemicals).

4.1 Pitting & crevice corrosion (chlorides)

Engineers often use the Pitting Resistance Equivalent Number (PREN) as a quick indicator:

PREN ≈ %Cr + 3.3 × %Mo + 16 × %N

• 304 / 304L typically gives PREN around 18–20.
• 316 / 316L, with Mo, typically gives PREN around 24–26.

In practice this means:

• For dry indoor environments and many mildly corrosive services, 304L is completely adequate.
• In coastal atmospheres, splash zones, salt-spray areas or hot chloride cleaning solutions, 316L usually offers significantly better margin against pitting and tea-staining.
• In warm, stagnant seawater or heavily contaminated crevices, even 316L can still pit; duplex or higher-alloy grades may be needed.

4.2 Intergranular corrosion & the role of “L” grades

When welded material spends time in the 425–860°C range, chromium carbides can precipitate at grain boundaries, locally depleting Cr and creating paths for intergranular attack. This is called weld sensitisation.

• 304L and 316L limit carbon to 0.03% max, minimising carbide formation and providing much better resistance to intergranular corrosion in welded heavy sections, without needing post-weld solution annealing in most thicknesses.

4.3 Stress corrosion cracking (SCC)

All austenitic stainless steels, including 304L and 316L, can suffer chloride stress corrosion cracking when tensile stress + chlorides + elevated temperature (usually >60°C) act together. 316L is somewhat better than 304L, but SCC risk remains. For high-risk combinations, duplex stainless steels are normally preferred.

5. How to Decide: 304L or 316L for Your Project?

Many buyers ask a simple question: “Can I save cost by staying with 304L, or do I really need 316L?” The answer depends on the medium, temperature, environment and cleaning regime.

5.1 Situations where 304 / 304L is usually sufficient

• Indoor process equipment in dry, clean industrial atmospheres.
• Food & beverage equipment handling low-chloride products at moderate temperatures (for example many dry foods, sugar, beer, milk).
• Architectural components not exposed to sea spray or de-icing salts, with reasonable cleaning.
• Structural brackets, frames and supports where cosmetic appearance is important but exposure is mild.

5.2 Situations where 316 / 316L is strongly recommended

• Coastal and offshore environments (marine hardware, ladders, cable trays, coastal façade panels).
• Equipment exposed to chloride-bearing cleaning chemicals or CIP media at elevated temperature.
• Process streams containing chlorides, reducing acids or fertiliser solutions where 304L test coupons show early pitting.
• High-value installations where downtime or repair access is difficult and a conservative corrosion allowance is justified.

Sunhyings can review your actual service conditions – not just the alloy name – to recommend whether 304L or 316L is the more economical choice over the whole life of the equipment.

6. Fabrication & Welding Considerations

304L and 316L behave very similarly in workshop operations. Both are readily formed, machined and welded with appropriate procedures.

6.1 Welding

• Suitable for all common processes (TIG/GTAW, MIG/GMAW, MMA/SMAW, SAW).
• Use matching low-carbon filler metals (e.g. 308L for 304L, 316L / 316LSi for 316L) to maintain corrosion resistance in the weld metal.
• Control heat input and interpass temperature to avoid excessive distortion and preserve toughness.
• Thorough post-weld cleaning (pickling, passivation, removal of heat tint) is essential to restore full corrosion resistance, especially in aggressive environments.

6.2 Machining & forming

• Both families work-harden more rapidly than carbon steel. Use sharp tools, positive feed and adequate cutting fluids.
• For deep drawing or complex forming, generous radii and polished tools help reduce galling and surface damage.
• Cold-worked areas will have increased strength and hardness and may show slight magnetism.

7. Typical Applications for 304L & 316L

Both grade families appear side-by-side across many industries. In practice, the “right” choice is often a mixed strategy: 304L for less exposed parts, 316L where chloride or chemical attack is concentrated.

8. Quality Assurance, MTCs & Supply Scope from Sunhyings

For B2B projects, documentation and traceability are just as important as the material itself. Sunhyings maintains a controlled supply chain with mill-backed documentation suitable for export projects.

• Standards: ASTM A240 / A480, ASME SA240, EN 10088-2, EN 10028-7, GB/T 3280 as required by project.
• MTCs: EN 10204 3.1 Mill Test Certificates with full chemistry and mechanical test data, linked to heat numbers and plate markings.
• Product forms: Hot rolled plate (No.1), cold rolled sheet & coil (2B, BA), strip and blanks cut to drawing (laser, plasma, waterjet), with optional surface protection films.
• Processing services: Cutting to size, edge preparation, basic forming and packing tailored to sea or land transport.

9. FAQ – 304 / 304L vs 316 / 316L

10. Downloads & Talk to a Sunhyings Engineer