DIN 1.4306 Stainless Steel: Low-Carbon Austenitic Grade for Enhanced Weldability & Corrosion Resistance
DIN 1.4306 (UNS S30403), commonly known as 304L stainless steel, is a low-carbon variant of the standard 304 grade, designed to eliminate intergranular corrosion risks in welded structures. With a maximum carbon content of 0.03%, this austenitic stainless steel maintains the mechanical properties of 304 while offering superior weldability and post-weld corrosion resistance. It is widely specified in chemical processing, pharmaceutical equipment, and heavy-gauge welded components where corrosion resistance is critical. This article covers its chemical composition, mechanical properties, production process, and industry-specific applications.
1. Chemical Composition (EN 10088-2 Standard)
| Element | Content Range | Function |
|---|---|---|
| Carbon (C) | ≤ 0.030% | Minimized to prevent chromium carbide precipitation during welding, ensuring resistance to intergranular corrosion |
| Chromium (Cr) | 17.50 – 19.50% | Forms a passive chromium oxide layer (Cr₂O₃) for corrosion resistance in oxidizing environments |
| Nickel (Ni) | 8.00 – 12.00% | Stabilizes the austenitic microstructure; enhances ductility and low-temperature toughness |
| Manganese (Mn) | ≤ 2.00% | Improves hot workability and partially substitutes nickel for cost efficiency |
| Silicon (Si) | ≤ 1.00% | Enhances oxidation resistance at high temperatures and aids in deoxidation during melting |
| Phosphorus (P) | ≤ 0.045% | Residual impurity; controlled to maintain mechanical properties and weldability |
| Sulfur (S) | ≤ 0.015% | Minimized to reduce hot cracking susceptibility during welding and improve surface quality |
| Nitrogen (N) | ≤ 0.10% | Strengthens austenite structure and improves resistance to pitting corrosion |
2. Mechanical Properties (Annealed Condition)
- Tensile Strength (Rm): 500–700 MPa (EN 10088-2 standard)
- Yield Strength (Rp0.2): ≥ 190 MPa (minimum guaranteed for structural integrity)
- Elongation (A5): ≥ 45% (superior formability for deep drawing and cold forming)
- Hardness (HB): ≤ 215 (Brinell hardness; suitable for machining and polishing)
- Impact Toughness (KV): ≥ 100 J at -196°C (retains ductility in cryogenic applications)
- Density: 7.93 g/cm³ (standard for austenitic stainless steels)
3. Manufacturing & Processing Characteristics
- Melting & Refining: Electric arc furnace (EAF) followed by argon oxygen decarburization (AOD) to achieve ultra-low carbon content (<0.03%) and precise alloy composition. Vacuum oxygen decarburization (VOD) may be used for premium grades.
- Hot Working: Hot rolling performed at 1150–1250°C, followed by rapid water quenching to prevent carbide precipitation and retain austenitic structure. Controlled cooling rates are critical for thick sections (>20mm).
- Cold Working: Cold rolling or drawing to achieve thin gauges (down to 0.3mm) with intermediate annealing at 1010–1120°C to relieve work hardening and restore ductility. Common finishes: 2B (matte), BA (bright annealed), or No.4 (brushed).
- Heat Treatment: Solution annealing at 1010–1120°C with rapid cooling (water or air) to dissolve chromium carbides and optimize corrosion resistance. Stress relieving at 400–600°C may be applied for complex fabrications.
- Surface Treatment: Pickling in nitric-hydrofluoric acid baths to remove oxide scale, followed by passivation in nitric acid to enhance the chromium oxide passive layer. Electropolishing is optional for high-purity applications (e.g., pharmaceuticals).
4. Key Application Fields
Welded Fabrications
Pressure vessels, storage tanks, and piping systems for chemical processing (e.g., acetic acid, ammonia) where post-weld corrosion resistance is critical. Compliant with ASME BPE and PED 2014/68/EU standards.
Pharmaceutical & Biotech
Sanitary tubing, fermenters, and cleanroom equipment (e.g., WFI systems) due to its smooth surface finish (Ra ≤ 0.5 µm) and resistance to microbial contamination. Meets USP Class VI and ISO 10993-5 biocompatibility requirements.
Oil & Gas
Offshore platform components, heat exchangers, and flare stacks in mild corrosive environments (e.g., sweet gas). Not recommended for H₂S-containing (sour) services—use 316L or duplex grades instead.
Food & Dairy Processing
Hygienic equipment (e.g., homogenizers, pasteurizers) and conveyors for acidic foods (tomato sauce, citrus juices). Certified to FDA 21 CFR 177.2600 and EC 1935/2004 for food contact.
Architectural & Structural
Welded structural components (e.g., bridges, stadium roofs) in coastal or urban areas where chloride-induced corrosion is a concern. Often specified with 2205 duplex for load-bearing applications.
Cryogenic Engineering
LNG storage tanks, cryogenic piping, and transport vessels operating at temperatures down to -196°C. Retains toughness and leak-tight integrity in low-temperature service.
5. Comparison with Related Grades
| Grade | Key Difference | Carbon Content | Primary Use Case |
|---|---|---|---|
| DIN 1.4301 (304) | Standard carbon (0.08% max) | ≤ 0.08% | General-purpose; non-welded or lightly welded components |
| DIN 1.4306 (304L) | Low-carbon for weldability | ≤ 0.03% | Heavy-welded structures in corrosive environments |
| DIN 1.4307 (304LN) | Low-carbon + nitrogen-alloyed | ≤ 0.03% | High-strength welded applications (e.g., pressure vessels) |
| DIN 1.4948 (304H) | High-carbon for temperature resistance | 0.04–0.10% | High-temperature service (>500°C; e.g., furnace parts) |
6. Selection Guidelines & Limitations
- Welding Best Practices: Use ER308L or ER316L filler metal for GTAW/MIG welding. Post-weld annealing (1050–1100°C) is recommended for thick sections (>6mm) to restore corrosion resistance. Avoid prolonged exposure in the 450–850°C range to prevent sensitization.
- Corrosion Resistance Limits: Not suitable for halides (e.g., seawater, bleach) or reducing acids (e.g., sulfuric acid >10%). For such environments, upgrade to 316L (1.4404) or 2205 duplex (1.4462).
- Surface Finish Selection:
- 2B: Mill finish for general fabrication (Ra 0.5–1.0 µm).
- BA: Bright annealed for decorative/pharma applications (Ra ≤ 0.3 µm).
- No.4: Brushed finish for architectural and food contact (Ra 0.8–1.2 µm).
- Certification Requirements: Request EN 10204 3.1/3.2 mill test certificates for critical applications. Verify PMI (Positive Material Identification) for alloy compliance in pharmaceutical or oil/gas projects.
- Cost Considerations: Approximately 10–15% higher cost than 304 due to stricter carbon control, but eliminates costly post-weld treatments or failures in corrosive services.
7. Request a Quote for DIN 1.4306 Stainless Steel
Need customized DIN 1.4306 (304L) stainless steel products in sheets, plates, coils, pipes, or bars? Our inventory includes hot/cold rolled coils (0.3–6.0mm), plates (6–50mm), and welded pipes (OD 6–610mm) with EN 10204 3.1 certification. Contact our team for technical specifications, lead times, or competitive pricing tailored to your project requirements.