SUS304 vs SUS304L: Carbon Content & Weldability Review

Carbon Content Comparison

SUS304: Max 0.08% carbon.

SUS304L (Low Carbon): Max 0.03% carbon.

Weldability & Corrosion Resistance

< The Problem (Sensitization): When standard 304 is welded, the heat causes carbon to combine with chromium, forming chromium carbides at grain boundaries. This depletes the surrounding area of chromium, making it vulnerable to intergranular corrosion (corrosion between grains).

304L Solution: The low carbon in 304L prevents significant carbide formation, even after welding, preserving its corrosion resistance in the heat-affected zone.

304 Weldability: Moderate; suitable for thinner sections or where post-weld annealing (heat treatment) is performed to re-dissolve carbides.

304L Weldability: Excellent; preferred for thick-section welding (over 5mm) and critical applications like chemical tanks, pressure vessels, and high-temperature piping.

Strength & Applications

Strength: 304 is slightly stronger (higher yield/tensile strength) than 304L due to its higher carbon content, according to some specs.

304 Applications: General architectural, kitchenware, and food processing where welding isn't the primary concern.

304L Applications: Chemical processing, food/beverage tanks, pharmaceutical equipment, and marine parts where welding is essential for fabrication.

In essence, choose 304L for welding and corrosion-critical uses; choose 304 for general strength and formability without heavy welding.