SUS304 vs SUS304L: Key Differences in Corrosion Resistance

When selecting stainless steel for corrosive environments, SUS304 and SUS304L are two of the most commonly used austenitic stainless steel grades. While their compositions are nearly identical and they appear interchangeable, subtle differences in carbon content significantly impact their corrosion resistance, especially in welded structures or high-temperature environments.
This guide, tailored to buyer needs, provides authoritative data and answers frequently asked questions to help you choose the appropriate grade and make more informed purchasing decisions.
 

SUS304 stainless steel, also known as A2 or 18/8 stainless steel, is a standard 18% chromium/8% nickel stainless steel with a carbon content of ≤0.08%. It exhibits excellent corrosion resistance in general environments. It cannot be hardened by heat treatment and is typically used in the annealed condition. It is weldable and machinable and is commonly used in sinks, food storage tanks, surgical instruments, and exhaust systems.

 

SUS304L stainless steel is a strong, silver-gray alloy, a low-carbon version with a carbon content of ≤0.03%, lower than 304 stainless steel. It is designed to minimize sensitization (precipitation of chromium carbides at grain boundaries during welding/heating), thus maintaining corrosion resistance in the welded area. It is primarily used in industries such as chemical processing, food and beverage manufacturing, and construction.

 

 

During welding or prolonged heating in the sensitization range​ (approx. 450–850 °C), carbon in SUS304 combines with chromium to form Cr₂₃C₆ at grain boundaries, depleting local Cr below the passive threshold (~12 %), leading to intergranular attack. SUS304L's ultra‑low carbon (<0.03 %) suppresses this reaction, preserving the Cr‑rich passive layer.

SUS304 vs SUS304L:Corrosion Resistance Deep Dive​

Corrosion Type	SUS304	SUS304L
General corrosion (oxidizing environments)	Excellent	Excellent
Intergranular corrosion (welded or heated 400–850 °C)	Prone to sensitization without solution annealing	Highly resistant due to low C
Pitting resistance (PREN ≈ 18–20)	Similar baseline	Similar baseline
Stress corrosion cracking (chloride environments)	Good resistance	Good resistance
Acid resistance (dilute organic/inorganic acids)	Good	Good

 

SUS304 vs SUS304L: Chemical Composition Comparison​

Element	SUS304 (Typical)	SUS304L (Typical)
Carbon (C)	≤ 0.08 %	≤ 0.03 %
Chromium (Cr)	18.0–20.0 %	18.0–20.0 %
Nickel (Ni)	8.0–10.5 %	8.0–12.0 %
Manganese (Mn)	≤ 2.0 %	≤ 2.0 %
Silicon (Si)	≤ 1.0 %	≤ 1.0 %
Phosphorus (P)	≤ 0.045 %	≤ 0.045 %
Sulfur (S)	≤ 0.030 %	≤ 0.030 %
Nitrogen (N)	≤ 0.10 %	≤ 0.10 %

Authority Source: ASTM A240/A480, JIS G4303/G4304, EN 10088‑1/2.

 

SUS304 vs SUS304L: Mechanical Properties (Annealed Condition)​

Property	SUS304	SUS304L
Tensile Strength (MPa)	515–690	485–655
Yield Strength @0.2% (MPa)	≥ 205	≥ 170
Elongation (%)	≥ 40	≥ 40
Hardness (HBW)	≤ 201	≤ 187
Density (g/cm³)	7.93	7.93
Modulus of Elasticity (GPa)	~193	~193

 

SUS304 vs SUS304L: Applications ​

Application	SUS304 Preferred	SUS304L Preferred
Architectural panels (unwelded)	✅	✅
Food processing equipment (welded joints)	⚠️ Risk of sensitization in welds	✅ Safer for long-term hygiene
Chemical storage tanks (welded seams)	⚠️ May need PWHT	✅ Better for corrosive chemicals
Heat exchangers (welded tubes)	⚠️ Consider 304L	✅ Recommended
Marine/Chloride environments (welded)	⚠️ Possible localized attack	✅ Reduced risk

 

Is SUS304L more expensive than SUS304?​
Yes, typically 5–15 % higher​ per kg due to extra refining steps, but lower lifecycle cost in welded corrosive service.

 

Can I use SUS304 instead of SUS304L for welded structures?​
Only if post‑weld solution annealing is performed; otherwise, risk of intergranular attack exists.

Which grade is better for pharmaceutical equipment?​
SUS304L is preferred for fully welded assemblies to ensure cleanability and corrosion resistance.

 

 

At GNEE, SUS304 is available in various forms to meet diverse industrial needs:
Plates and Sheets (cold rolled and hot rolled)
Bars and Rods (round, square, hexagonal)
Tubes (seamless and welded)
Wires and Strips (for springs, fasteners, electrical applications)
Forgings and Custom Parts (according to drawings or specifications)
Testing and Documentation: Mill Test Certificates, EN 10204 3.1, Chemical Reports, Mechanical Reports, Destructive Testing Reports, Non-Destructive Testing Reports, PMI Test Reports, Visual Inspection Reports, Third-Party Inspection Reports, NABL Certified Laboratory Reports.
Packaging: Wooden crates, bubble wrap, steel strapping, or packaged according to customer requirements.