EN 1.4307 (European material number) and AISI 304L (American designation) refer to the same low-carbon austenitic stainless steel. The "L" stands for low carbon — capped at ≤0.03% — which prevents a damaging metallurgical phenomenon called sensitisation during welding. This single characteristic makes 304L the default grade for welded structures in food, dairy, beverage, pharmaceutical, and general process industries, where it delivers an excellent balance of corrosion resistance, formability, and cost-effectiveness compared to higher-alloyed grades such as 316L.

You may also encounter this grade listed as S30403 (UNS), SUS 304L (JIS), or Swedish Standard 2352 — all designations for the same alloy. In this guide we cover everything you need in one place: chemical composition, mechanical and physical properties, corrosion behaviour, fabrication characteristics, applicable standards, industry applications across all product forms, a data-driven comparison with related grades, known limitations, and practical maintenance guidance.

Composition and metallurgical characteristics

304L is an austenitic stainless steel, meaning its crystal structure is face-centred cubic (FCC) at room temperature — a structure that gives the alloy its characteristic ductility, toughness, and non-magnetic behaviour. The composition is built around two primary alloying elements: chromium and nickel.

Element	Minimum %	Maximum %
Chromium	17.5	19.5
Nickel	8	10
Molybdenum	—
Carbon	—	0.03
Manganese	—	2
Silicon	—	1
Phosphorus	—	0.045
Sulphur	—	0.015
Nitrogen	—	0.11
Iron	Balance	—

Chromium (17.5–19.5%) forms the self-healing passive oxide layer responsible for stainless steel's corrosion resistance. Nickel (8–10%) stabilises the austenitic crystal structure, providing ductility and toughness across a wide temperature range — from sub-zero conditions up to several hundred degrees Celsius. Carbon (≤0.03%) is the defining feature of the "L" designation and the focus of the next section. Nitrogen (≤0.11%) contributes solid-solution strengthening without compromising weldability.

A critical absence in this composition is molybdenum. Standard 304L contains no molybdenum, whereas 316L contains 2.0–2.5%. This is the primary compositional difference between the two grades and directly determines their relative pitting and crevice corrosion resistance.

The absence of molybdenum is the primary compositional difference between 304L and 316L, and it directly determines their relative pitting and crevice corrosion resistance.

 Sensitisation and Weldability

When stainless steel is heated into the 425–860 °C range — as happens in the heat-affected zone during welding — carbon atoms can combine with chromium to form chromium carbides (Cr₂₃C₆) at grain boundaries. This process, called sensitisation, depletes chromium from the metal immediately surrounding each grain boundary, creating narrow zones that have lost the passive oxide layer and are therefore vulnerable to intergranular corrosion.

Standard 304 (EN 1.4301) permits carbon up to 0.07% — enough for significant carbide precipitation in heavy welded sections. 304L limits carbon to ≤0.03%, reducing the driving force for carbide formation below the critical threshold. The practical consequences are significant:

• Excellent intergranular corrosion resistance after welding, rated "Excellent" in the corrosion performance table below.
• No post-weld heat treatment (PWHT) required — simplifying fabrication and reducing cost.
• The preferred grade for any application involving welded joints exposed to corrosive media.

This is why 304L has become the default specification for welded process equipment in the food, dairy, and beverage industries. For fabrication at temperatures between 425 and 860 °C, 304L is recommended over standard 304 precisely because of its improved resistance to carbide precipitation.

Carbon content capped at ≤0.03% prevents chromium carbide precipitation during welding, giving 304L excellent resistance to intergranular corrosion and eliminating the need for post-weld heat treatment.

Mechanical and physical properties

Room-temperature mechanical properties (annealed condition)

In the solution-annealed condition, 304L offers a well-balanced combination of strength, ductility, and hardness suitable for a wide range of structural and process applications.

Property	Value	Unit
Tensile Strength (minimum)	485	MPa
Yield Strength 0.2% proof stress (minimum)	170	MPa
Elongation at Break (minimum)	40	%
Hardness Brinell (maximum)	215	HB
Hardness Rockwell B (maximum)	95	HRB
Hardness Vickers (maximum)	220	HV

The 40% minimum elongation underscores 304L's excellent formability — it can be deep-drawn, bent, and roll-formed with relative ease, making it the dominant grade for applications such as sinks, vessels, and architectural panels.

Physical properties

Property	Value	Unit
Density	7.93	g/cm³
Melting Range	1400–1450	°C
Thermal Conductivity at 20 °C	15	W/m·K
Thermal Conductivity at 100 °C	16	W/m·K
Thermal Expansion Coefficient 20–100 °C	16	10⁻⁶/K
Thermal Expansion Coefficient 20–300 °C	17	10⁻⁶/K
Specific Heat Capacity	500	J/kg·K
Electrical Resistivity	0.73	µΩ·m
Elastic Modulus	200	GPa
Magnetic Permeability (annealed)	1.02	—

With a magnetic permeability of 1.02, 304L is essentially non-magnetic in the annealed condition. Cold working can induce a degree of magnetic response due to partial martensite transformation.

High-temperature mechanical properties

Mechanical properties degrade progressively with rising temperature. The following table quantifies this degradation from 20 °C to 600 °C, giving designers the data they need to de-rate accordingly.

Temperature (°C)	Tensile Strength (MPa)	Yield Strength 0.2% (MPa)	Elongation (%)
20	485	170	40
100	450	145	40
200	420	130	40
300	390	120	40
400	370	115	40
500	350	110	40
600	300	100	40

At 600 °C, tensile strength drops to 300 MPa and yield strength to 100 MPa — roughly 62% and 59% of the room-temperature values respectively. Elongation remains stable at 40% throughout the range, confirming that 304L retains its ductile character even at elevated temperatures.

At 600 °C, tensile strength drops to 300 MPa and yield strength to 100 MPa — roughly 62% and 59% of the room-temperature values — requiring careful de-rating in elevated-temperature design.

Corrosion resistance

304L's corrosion behaviour varies significantly depending on the type of attack and the environment. The table below summarises performance across the main corrosion mechanisms.

Corrosion Type	Performance Rating	Notes
General / Uniform Corrosion	Excellent	Good resistance in mild environments
Pitting Corrosion	Moderate	No molybdenum; lower resistance than 316L
Crevice Corrosion	Moderate	Susceptible in chloride environments
Intergranular Corrosion	Excellent	Low carbon content prevents sensitisation
Stress Corrosion Cracking	Moderate	Risk above 60 °C in chloride environments
Galvanic Corrosion	Depends on couple	Assess against coupled material

General corrosion resistance is excellent because the high chromium content (17.5–19.5%) maintains a stable, self-healing passive oxide layer in mild atmospheric and aqueous environments. Intergranular corrosion resistance is equally strong — a direct benefit of the ≤0.03% carbon cap that prevents sensitisation, as discussed above.

Pitting and crevice corrosion resistance, however, is only moderate. Without molybdenum, 304L achieves a Pitting Resistance Equivalent Number (PREN) of just 18. PREN is calculated as %Cr + 3.3 × %Mo + 16 × %N — and with zero molybdenum, the formula leaves a significant gap compared to 316L's PREN of 25. In practice, even moderate chloride concentrations can initiate localised attack.

Stress corrosion cracking (SCC) is a concern above 60 °C in chloride-containing fluids. This threshold is a critical decision point: if your process fluid contains chlorides and operates above 60 °C, 304L may not be the right specification.

Stress corrosion cracking risk rises sharply above 60 °C in chloride-containing environments — a hard threshold that often determines whether 304L or 316L is the right specification.

Standards, designations, and product forms

304L appears under different designations depending on the standards body. The cross-reference table below helps procurement staff and engineers match specifications across international projects.

International designations

Standard Body	Designation
European Norm (material number)	1.4307
American Iron and Steel Institute	304L
ASTM (sheet and plate)	A240
ASTM (bar and rod)	A276
ASTM (seamless pipe)	A312
American Society of Mechanical Engineers (plate)	SA-240
Japanese Industrial Standard	SUS 304L
Swedish Standard	2352

Product forms and dimensional standards

304L is produced in virtually every standard product form. The governing European standards ensure dimensional accuracy and material traceability across the supply chain.

Product Form	Relevant Standard
Sheet and Plate	EN 10088-2
Bar and Rod	EN 10088-3
Seamless Tube and Pipe	EN 10216-5
Welded Tube and Pipe	EN 10217-7
Fittings	EN 10253-4

Compliance with EN 10217-7 is particularly relevant for European process equipment because it facilitates conformity with the Pressure Equipment Directive (PED). Within the dairy and food processing sectors, hygienic tubes and fittings manufactured from 1.4307 (304L) are commonly specified with an internal surface finish of Ra < 0.8 µm and delivered with 3.1 certificates in accordance with EN 10204 — ensuring full material traceability from mill to installation.

Fabrication data : welding, forming, and working

One of 304L's greatest practical advantages is its fabrication-friendly nature. The table below consolidates the key parameters.

Parameter	Detail
Weldability	Excellent; no post-weld heat treatment required
Recommended Filler Metal	308L or 304L
Forming	Excellent cold and hot formability
Machinability	Approximately 50% of carbon steel reference
Solution Annealing Temperature	1010–1120 °C, water quench
Hot Working Range	1150–1260 °C
Cold Working	Work hardens; intermediate annealing may be required

Welding: 304L is compatible with TIG, MIG, resistance welding, and orbital welding techniques. The low carbon content means heavy welded sections do not require post-weld annealing — a step that is often necessary with standard 304. Recommended filler metals are 308L or 304L.

Forming: Excellent formability in both cold and hot states makes 304L suitable for deep drawing, bending, roll forming, and spinning. It is the dominant grade for pressed and formed components such as sinks, vessels, and architectural panels.

Cold working and work hardening: 304L work hardens significantly during cold deformation. For complex, multi-stage forming operations, intermediate annealing may be required to prevent tearing or cracking. A full solution anneal at 1010–1120 °C followed by water quench restores the original microstructure and optimises corrosion resistance.

Hot working: Should occur after uniform heating to 1150–1260 °C, followed by rapid cooling to retain maximum corrosion resistance.

Machinability: Rated at approximately 50% of a free-cutting carbon steel reference. Keep cutting edges sharp, use adequate coolant, and ensure feeds are deep enough to cut below the work-hardened surface layer rather than riding on it.

Industries and applications

304L's combination of corrosion resistance, weldability, formability, and cost-effectiveness makes it one of the most widely specified stainless steels across multiple industries. Its applications extend well beyond any single product form.

Food, dairy, and beverage: Processing vessels, storage tanks, piping systems, heat exchangers, and CIP (clean-in-place) installations. 304L is the standard grade wherever chloride exposure remains low and the environment is classified as mild.

Pharmaceutical and cosmetics: Vessels, transfer lines, and processing components for standard-duty applications. Where ultra-high purity or elevated chloride resistance is required, 316L may be specified instead.

Chemical processing: Reactors, mixing tanks, and piping for mild chemicals and solvents where aggressive acids or high chloride levels are not present.

Architectural and construction: Cladding, handrails, structural supports, decorative panels, kitchen fixtures including sinks, splashbacks, and countertops. The alloy's excellent surface finish and atmospheric corrosion resistance make it a natural choice for visible installations.

General fabrication: Springs, screws, nuts and bolts, fasteners, and structural components. The widely available product forms — sheet, strip, plate, coil, bar, rod, wire, seamless and welded tube and pipe, fittings, and forgings — ensure that designers can specify 304L for virtually any geometry.

Grade comparison: 304 vs. 304L vs. 316L and higher grades

Choosing the right austenitic grade comes down to a few measurable factors: carbon content, molybdenum content, PREN, and the specific environment the material will face. The two tables below lay out the data.

304, 304L, and 316L

Property	1.4301 / 304	1.4307 / 304L	1.4404 / 316L
Carbon Maximum (%)	0.07	0.03	0.03
Chromium (%)	17.5–19.5	17.5–19.5	16.5–18.5
Nickel (%)	8.0–10.5	8.0–10.0	10.0–13.0
Molybdenum (%)	None	None	2.0–2.5
Pitting Resistance Equivalent Number	18	18	25
Weld Sensitisation Risk	Moderate	Low	Low
Corrosion Resistance vs Chlorides	Moderate	Moderate	Good
Typical Application	General purpose	Welded structures	Marine, pharma

Higher-alloyed 316L variants

Property	1.4432 / 316L+	1.4435 / 316L
Carbon Maximum (%)	0.03	0.03
Chromium (%)	16.5–18.5	17.0–19.0
Nickel (%)	10.0–13.0	12.5–15.0
Molybdenum (%)	2.5–3.0	2.5–3.0
Pitting Resistance Equivalent Number	26	27
Weld Sensitisation Risk	Low	Low
Corrosion Resistance vs Chlorides	Good	Very Good
Typical Application	Aggressive media	High purity pharma

The PREN progression — 18 → 25 → 26 → 27 — gives a clear, quantifiable basis for grade selection. With a PREN of 18, 304L provides reliable corrosion protection in mild environments. Where chloride concentrations increase, the jump to 316L and its PREN of 25 represents a measurable step up in pitting resistance. For aggressive media or high-purity pharmaceutical applications, 1.4432 (PREN 26) or 1.4435 (PREN 27) offer further protection at a correspondingly higher material cost.

In practice, many component suppliers have standardised on 1.4404 (316L) rather than 1.4435 for their corrosion-resistant product lines. Years of field experience across the process industries have confirmed 1.4404 as an effective cost-performance match for the majority of applications requiring molybdenum-alloyed stainless steel.

With a PREN of 18, 304L provides reliable corrosion protection in mild environments — but where chloride concentrations increase, the jump to 316L and its PREN of 25 represents a measurable step up in pitting resistance.

Grade selection decision guide

Limitations and when to choose an alternative

304L is a versatile grade, but it has clearly defined boundaries. Understanding these limits helps avoid costly failures.

Chloride pitting and crevice corrosion: With no molybdenum and a PREN of only 18, 304L is susceptible to localised attack in environments with even moderate chloride concentrations. If chlorides exceed trace levels, evaluate 316L as a minimum.

Stress corrosion cracking: Risk increases significantly above 60 °C in chloride-containing fluids. This is a hard threshold — crossing it often makes 316L or a duplex grade the safer choice.

Marine environments: Coastal or marine applications demand the superior salt-water resistance of 316L. 304L is not recommended where exposure to sea spray or marine water is ongoing.

Strong acids: While 304L handles mild acids and low-concentration salt solutions well, strong mineral acids and high-concentration salt solutions require higher-alloyed grades.

Sustained elevated temperature: Although 304L retains useful properties up to 600 °C and beyond, continuous service between 425–860 °C remains the sensitisation-prone temperature range. 304L's low carbon mitigates this risk, but for sustained high-temperature strength requirements, grades such as 304H should be evaluated.

The decision rule is straightforward: if any of the above conditions apply, step up to 1.4404 (316L) as the minimum. For aggressive media or high-purity pharmaceutical applications, 1.4432 or 1.4435 provide further insurance through higher molybdenum content and PREN values of 26–27.

Maintenance, cleaning, passivation, and preserving corrosion resistance

Day-to-day care of 304L components is straightforward. Routine cleaning with a mild detergent and warm water is sufficient for most applications. Avoid chloride-containing cleaning agents, which can initiate localised corrosion.

Passivation with nitric or citric acid should be performed after fabrication, grinding, or any operation that disrupts the passive oxide layer. This restores the chromium oxide film and optimises long-term corrosion resistance.

Cross-contamination prevention is important: always use tools dedicated to stainless steel. Contact with carbon steel tooling or work surfaces can embed iron particles into the surface, creating rust spots.

Electropolishing enhances the chromium-to-iron ratio at the surface, further improving corrosion resistance and reducing bacterial adhesion — a key consideration in hygienic applications.

In chloride-containing environments, periodic inspection of weld zones and crevice-prone areas is recommended to catch any early signs of localised attack.

Electropolishing promotes a chromium-enriched surface layer that maximises corrosion resistance and minimises bacterial build-up on surface cavities.

Summary 

EN 1.4307 / AISI 304L is the weld-friendly workhorse of the austenitic stainless steel family. Its ≤0.03% carbon cap prevents sensitisation in welded structures, delivering excellent intergranular corrosion resistance without post-weld heat treatment. With a minimum tensile strength of 485 MPa, 40% elongation, and excellent formability, it serves a vast range of product forms and industries — from food processing vessels and architectural cladding to pharmaceutical transfer lines and general structural components. Its limitations are equally well defined: no molybdenum, moderate chloride resistance (PREN 18), and stress corrosion cracking risk above 60 °C in chloride-containing fluids. When these boundaries are crossed, upgrading to 316L (PREN 25) or higher grades is a straightforward engineering decision based on quantifiable data.

If you are evaluating whether 304L or 316L is the right specification for your process environment, our team at Euroflow is here to help. As Alfa Laval Master Distributor for southern Germany (postal code areas 66–99 and 07–08), we provide technical support for component selection across pumps, valves, heat exchangers, tubes, fittings, and tank equipment — serving the dairy, food, beverage, cosmetics, and pharmaceutical industries. Reach out to us with your process conditions, and we will help you identify the grade and product configuration that fits.