AISI 304L Stainless Steel: Low-Carbon Grade for Welded Corrosion-Resistant Applications
AISI 304L / UNS S30403 · Published: 2026-07-15 · Updated: July 2026
AISI 304L is the low-carbon version of Type 304 stainless steel, with carbon content limited to 0.03% maximum (versus 0.08% for standard 304). This single chemistry difference is critical: with ≤0.03% carbon, 304L does not sensitize during...
AISI 304L is the low-carbon version of Type 304 stainless steel, with carbon content limited to 0.03% maximum (versus 0.08% for standard 304). This single chemistry difference is critical: with ≤0.03% carbon, 304L does not sensitize during welding — carbide precipitation at grain boundaries (which causes intergranular corrosion in standard 304 weld HAZs) is effectively eliminated. This makes 304L the correct grade specification whenever 304-type stainless will be welded and subsequently exposed to corrosive environments, particularly: chemical process vessels and piping, food and beverage equipment (dairy, brewing, processing tanks), pharmaceutical clean-in-place systems, architectural exterior applications in coastal/marine environments, and water treatment equipment. The tradeoff: 304L has marginally lower yield strength (170 MPa vs 205 MPa for 304) and slightly lower maximum service temperature (425°C vs 870°C for intermittent exposure) due to the reduced carbon. For non-welded applications or welded applications in non-corrosive environments, standard 304 is acceptable and slightly less expensive. For applications requiring both welding and high-temperature service, 321 or 347 (stabilized grades) should be specified instead of 304L.
Quick Facts
| Category | Stainless Steel |
| Standard | AISI 304L / UNS S30403 |
| Density | 7.95 g/cm³ |
| Yield Strength | 170 MPa (25 ksi) annealed |
| Tensile Strength | 485 MPa (70 ksi) annealed |
Detailed Mechanical Properties
| Elongation | 40% minimum |
| Hardness | 70-85 HB (annealed) |
| Charpy V Notch | >100J at -196°C (excellent cryogenic toughness) |
| Modulus Of Elasticity | 193 GPa |
Physical Properties
| Melting Range | 1400-1450 °C |
| Thermal Conductivity | 16.2 W/m·K at 100°C |
| Electrical Resistivity | 0.000072 Ω·cm at 20°C |
| Specific Heat | 500 J/kg·K at 20°C |
| Coefficient Of Expansion | 17.3 µm/m·°C (20-100°C) |
Global Equivalents & Cross-Reference
| Alternative Standard / Grade | Action |
|---|---|
| X2CrNi18-9 (EN 1.4307) | Compare |
| SUS304L (JIS) | Compare |
| 03Cr18Ni10 (GB) | Compare |
Heat Treatment & Processing
| Annealing | 1010-1120°C, rapid cool (water quench or air blast) |
| Stress Relieving | 400-425°C for 1-2 hours (do not exceed 425°C to avoid sensitization risk) |
| Note | 304L cannot be hardened by heat treatment; strength is achieved only by cold work. Full annealing after welding restores maximum corrosion resistance. |
Welding & Fabrication
| Preheat | Not required (austenitic stainless; preheat is counterproductive) |
| Filler Metal | ER308L (GTAW/GMAW) — the 'L' filler matches the base metal low carbon; E308L-16 (SMAW) |
| Interpass Temp | Max 150°C (low interpass essential to prevent carbide precipitation and distortion) |
| Pwht | Solution anneal at 1010-1120°C for maximum corrosion resistance; stress relief at 400-425°C acceptable |
| Weldability Rating | Excellent — superior to 304 for welded corrosive service due to low carbon |
Related Materials
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Frequently Asked Questions
Is 304L always better than 304 for welded applications?
In corrosive environments, yes — 304L eliminates intergranular corrosion risk in the weld HAZ. However, 304 is acceptable for welded applications when: (1) the service environment is mild (atmospheric exposure, pure water) — sensitization occurs but corrosion is negligible, (2) the weldment will be solution-annealed after welding (1050-1100°C, water quench) — this dissolves carbides and restores corrosion resistance, (3) the component operates below 425°C where sensitization kinetics are extremely slow. 304L costs 5-10% more than 304. For critical corrosion applications (chemical processing, marine), the small cost premium of 304L is always justified over post-weld annealing of 304.
When should I use 321 instead of 304L?
Specify 321 (titanium-stabilized) instead of 304L when: (1) service temperature exceeds 425°C — 304L's very low carbon reduces high-temperature creep strength, while 321's titanium stabilization maintains both corrosion resistance and creep resistance to 870°C, (2) the component experiences prolonged exposure in the sensitization range (425-870°C) during operation — e.g., exhaust systems, furnace components. 304L is the better choice for: ambient-to-moderate temperature welded applications (<425°C), food/pharma equipment, and architectural applications. 304L is more readily available and 5-10% less expensive than 321.
References & International Standards
- ASTM International. Standard Specifications for Steel & Metal Alloys. astm.org
- International Organization for Standardization (ISO). Metallic Materials — Cross-Reference Database. iso.org
- American Iron and Steel Institute (AISI). Steel Grade Designations & Equivalents. steel.org
- European Committee for Standardization (CEN). EN Steel Standards & Numbering System. cencenelec.eu
Specialty Metals — Engineering Reference
Non-ferrous metals — aluminum, copper, titanium, zinc, magnesium — serve applications where steel cannot: electrical conductivity, thermal management, weight reduction, corrosion resistance in specific chemical environments. Each metal family has its own classification system and selection logic.
ASTM B209/B221 (Al), ASTM B152/B187 (Cu), ASTM B265/B348 (Ti), ASTM B86 (Zn), ASTM B90/B91 (Mg)
Electrical wiring and busbars (Cu), aircraft structures and automotive bodies (Al), medical implants and aerospace fasteners (Ti), die-cast consumer products (Zn), lightweight electronic enclosures (Mg)
Galvanic corrosion is the #1 failure mode in multi-metal assemblies. When joining dissimilar metals, consult the galvanic series: the more anodic metal will corrode preferentially. Use isolating washers, protective coatings, or select metals close together on the galvanic series.