SUS304L Stainless Steel: Low-Carbon Grade Properties and Applications

What Is SUS304L Stainless Steel?

SUS304L is the low-carbon version of the 18-8 austenitic stainless steel SUS304, defined in the Japanese Industrial Standards JIS G4304 (plate) and JIS G4305 (cold-rolled strip). The L stands for low carbon: the carbon content is limited to 0.030% maximum, well below the 0.08% allowed for SUS304. This simple change solves the intergranular corrosion problem that can affect SUS304 in welded or elevated-temperature service, without sacrificing the excellent general corrosion resistance and formability of the base grade.

Equivalent Grades

Standard System	Designation
JIS (Japan)	SUS304L
ASTM (USA)	304L / UNS S30403
EN (Europe)	1.4307 / X2CrNi18-9; 1.4306 / X2CrNi19-11
GB (China)	022Cr19Ni10

Because the JIS nickel range of SUS304L (9.0-13.0%) is wider than the ASTM 304L range (8.0-12.0%), SUS304L overlaps both EN 1.4307 and the higher-nickel EN 1.4306.

Chemical Composition (JIS G4304 / G4305)

Element	C	Si	Mn	P	S	Ni	Cr
Content, %	0.030 max	1.00 max	2.00 max	0.045 max	0.030 max	9.00-13.00	18.00-20.00

Mechanical Properties (JIS G4304, Annealed)

Property	Requirement
Tensile strength Rm	480 MPa min
0.2% proof stress Rp0.2	175 MPa min
Elongation A	40% min
Hardness	187 HB / 90 HRB / 200 HV max

Sensitization and Intergranular Corrosion

When austenitic stainless steel is heated into the range of approximately 425-815 degrees Celsius, as happens in the heat-affected zone of a weld, carbon diffuses to grain boundaries and reacts with chromium to form chromium carbides. The chromium-depleted zone adjacent to the grain boundaries then corrodes preferentially in many media, a failure mode called intergranular corrosion or weld decay.

SUS304L prevents this by keeping carbon below 0.030%, the solubility limit below which significant chromium carbide precipitation cannot occur. The heat-affected zone therefore keeps a uniform chromium distribution and a stable passive film, and welded components can be used without expensive post-weld annealing. This is the decisive advantage of SUS304L for large welded fabrications where post-weld heat treatment is impractical.

Cryogenic Performance

The austenitic structure of SUS304L is stable at low temperature and does not embrittle, unlike ferritic and martensitic steels. The grade retains high ductility and impact toughness down to about -196 degrees Celsius, the temperature of liquid nitrogen, and is widely used for cryogenic storage tanks and piping for liquefied natural gas, liquid nitrogen and liquid oxygen. The low carbon content also improves weld soundness at these service temperatures.

Limitations at Elevated Temperature

The low carbon content that gives SUS304L its weldability also reduces its strength at elevated temperature. Above roughly 500-600 degrees Celsius, the yield strength of SUS304L falls more quickly than that of SUS304, and the grade is not recommended for load-bearing components in hot service. For furnace parts, boiler tubes and other elevated-temperature applications, SUS304 or the higher-carbon SUS304H should be selected.

Typical Applications

Welded chemical pipelines and storage tanks.

Food processing and beverage equipment, including fermentation and storage vessels.

Cryogenic storage tanks and piping for liquefied gases.

Pharmaceutical and biotechnology process equipment.

Architectural structures and handrails where welding is extensive.

Frequently Asked Questions

Q1. What does the L in SUS304L mean?

The L stands for low carbon. The carbon content is limited to 0.030% maximum, compared with 0.08% for SUS304. This prevents chromium carbide precipitation at grain boundaries during welding, eliminating the risk of intergranular corrosion in the as-welded condition.

Q2. Why does SUS304L not require post-weld heat treatment?

With carbon at 0.030% or less, the driving force for chromium carbide precipitation is removed, so the heat-affected zone of a weld retains its corrosion resistance without annealing. For SUS304, welding into the 425-815 degrees Celsius range can sensitize the structure, and annealing would be needed to restore corrosion resistance.

Q3. Can SUS304L replace SUS304 in all applications?

No. SUS304L is the better choice for welded components that need corrosion resistance. For non-welded components requiring higher elevated-temperature strength, such as heat exchanger tubes and industrial furnace parts, SUS304 or SUS304H is preferred because of the higher carbon content and better structural stability at temperature.

Q4. How does SUS304L perform at cryogenic temperature?

Very well. The austenitic structure remains ductile and tough down to about -196 degrees Celsius, making SUS304L a standard material for LNG and liquid nitrogen storage. Unlike ferritic or martensitic steels, it does not become brittle in the cold.

Q5. Is SUS304L stronger or weaker than SUS304?

At room temperature the difference is negligible; both meet similar minimum strength requirements. The low carbon content affects the material behavior after welding and at elevated temperature, not the ambient strength of the annealed product.

Q6. What is the difference between SUS304L and SUS304H?

SUS304H is a high-carbon variant with a controlled carbon content of 0.04-0.10%, designed for elevated-temperature service where creep strength is required. SUS304L, with its low carbon, is designed for welded service where corrosion resistance after welding matters. The two grades occupy opposite ends of the carbon range for different purposes.