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DIN 1.4404 Stainless Steel: High-Performance Austenitic Alloy for Corrosive Environments
DIN 1.4404 (AISI 316L, UNS S31603) is a low-carbon, molybdenum-bearing austenitic stainless steel renowned for its superior corrosion resistance, particularly in chloride-rich and acidic environments. With a balanced composition of 16-18% chromium, 10-14% nickel, and 2-3% molybdenum, this grade outperforms standard 304/304L in marine, chemical, and pharmaceutical applications. This article explores its metallurgical properties, fabrication characteristics, industrial applications, and performance advantages over competing alloys.
1. Chemical Composition (EN 10088-3 Standard)
| Element | Content Range | Function |
|---|---|---|
| Carbon (C) | ≤ 0.030% | Minimized to prevent intergranular corrosion during welding |
| Chromium (Cr) | 16.50 – 18.50% | Forms chromium oxide passive layer; enhances oxidation resistance |
| Nickel (Ni) | 10.00 – 13.00% | Stabilizes austenitic structure; improves ductility and cryogenic toughness |
| Molybdenum (Mo) | 2.00 – 2.50% | Increases pitting resistance equivalent (PREN ≥ 24); critical for chloride environments |
| Manganese (Mn) | ≤ 2.00% | Enhances hot workability; partial nickel substitute for cost optimization |
| Silicon (Si) | ≤ 1.00% | Improves high-temperature oxidation resistance; aids deoxidation |
| Phosphorus (P) | ≤ 0.045% | Controlled impurity; excessive levels reduce corrosion resistance |
| Sulfur (S) | ≤ 0.015% | Minimized to prevent hot cracking and improve machinability |
| Nitrogen (N) | ≤ 0.10% | Strengthens austenite; improves pitting resistance when combined with molybdenum |
2. Mechanical Properties (Annealed Condition)
- Tensile Strength (Rm): 480-620 MPa (EN 10088-2-2005)
- Yield Strength (Rp0.2): ≥ 170 MPa (minimum for structural integrity)
- Elongation (A5): ≥ 40% (superior formability for deep drawing and cold forming)
- Hardness (HB): ≤ 215 (Brinell); ≤ 95 HRB (Rockwell)
- Impact Strength (KV): ≥ 100 J at -196°C (excellent cryogenic performance)
- Density: 8.0 g/cm³ (standard for austenitic stainless steels)
3. Manufacturing Process & Metallurgical Features
- Melting & Refining: Electric arc furnace (EAF) + argon oxygen decarburization (AOD) + vacuum oxygen decarburization (VOD) for ultra-low carbon content and inclusion control.
- Hot Working: Hot rolled at 1150-1250°C with controlled cooling to prevent sigma phase precipitation; solution annealed at 1020-1100°C followed by rapid quenching.
- Cold Working: Cold rolled to achieve 2B, BA, or No.4 finishes; intermediate annealing required for heavy reductions to maintain ductility.
- Heat Treatment: Solution annealing at 1010-1120°C with water quenching to dissolve intermetallic phases (e.g., chromium carbides, sigma phase).
- Surface Treatment: Pickling in nitric-hydrofluoric acid bath; electropolishing for medical/pharmaceutical applications to achieve Ra ≤ 0.5 µm.
4. Corrosion Resistance Performance
| Corrosion Type | Performance | Test Standard |
|---|---|---|
| Pitting Resistance (PREN) | PREN ≥ 24 (excellent in chloride environments up to 1000 ppm) | ASTM G48 (Method A) |
| Crevice Corrosion | Resistant in seawater (≤ 35°C); avoid stagnant conditions | ASTM G78 |
| Intergranular Corrosion | Highly resistant due to ≤ 0.03% carbon (no sensitization) | ASTM A262 (Practice E) |
| Stress Corrosion Cracking (SCC) | Superior to 304/304L in chloride solutions (≤ 60°C) | ASTM G36 |
| General Corrosion | Resistant to sulfuric acid (≤ 10%), acetic acid, and phosphoric acid | ISO 3651-2 |
5. Primary Industrial Applications
Marine & Offshore
Shipbuilding components, desalination plants, offshore platform piping, and seawater cooling systems — resistant to saltwater spray and biofouling.
Chemical Processing
Reactors, storage tanks, and heat exchangers for acetic acid, chlorine dioxide, and organic chemicals — compliant with ASME BPE for hygienic design.
Pharmaceutical & Biotech
Fermenters, clean-in-place (CIP) systems, and surgical implants — electropolished surfaces meet FDA 21 CFR 177.2600 and ISO 10993-1.
Food & Dairy Processing
High-salinity food production (e.g., soy sauce, pickling), dairy evaporation equipment, and hygienic pipelines — compliant with EC 1935/2004 and 3-A Sanitary Standards.
Architectural & Structural
Coastal building facades, handrails, and bridges in high-humidity regions — resistant to atmospheric corrosion and staining (e.g., “tea staining”).
Oil & Gas
Subsea pipelines, wellhead equipment, and refinery components for sour gas (H₂S) environments — NACE MR0175/ISO 15156 compliant.
6. Comparison with Related Grades
| Grade | Key Alloying Elements | Advantages | Limitations |
|---|---|---|---|
| DIN 1.4404 (316L) | 17% Cr, 12% Ni, 2.2% Mo, ≤ 0.03% C | Superior chloride resistance; weldable without sensitization | Higher cost than 304L; lower strength than 316H |
| DIN 1.4401 (316) | 17% Cr, 12% Ni, 2.2% Mo, ≤ 0.07% C | Higher strength than 1.4404; wider temperature range | Risk of intergranular corrosion if welded |
| DIN 1.4435 (316Ti) | 17% Cr, 12% Ni, 2.2% Mo, Ti-stabilized | Resists intergranular corrosion in welded structures | Ti carbides may reduce corrosion resistance in some environments |
| DIN 1.4571 (316Ti) | 16.5% Cr, 11% Ni, 2% Mo, Ti-stabilized | Enhanced high-temperature strength (up to 450°C) | Higher cost; limited availability in thin gauges |
7. Fabrication & Handling Guidelines
- Machining: Use carbide tools (e.g., KC720 grade); maintain slow speeds (60-90 m/min) and high feed rates to avoid work hardening. Coolants recommended to prevent galling.
- Welding: Preferred methods: TIG (GTAW) or MIG (GMAW) with ER316L filler. Pre-weld and post-weld cleaning essential; passivate welds with 20-30% nitric acid for 30-60 minutes.
- Forming: Cold forming requires intermediate annealing for reductions > 50%; springback compensation needed due to high ductility. Use stainless steel-specific lubricants.
- Cleaning: Avoid chloride-containing cleaners; use alkaline or citric acid-based solutions. For electropolished surfaces, use deionized water rinses to prevent water spotting.
- Storage: Store in dry, ventilated areas; separate from carbon steel to prevent galvanic corrosion. Use VCI (volatile corrosion inhibitor) packaging for long-term storage.
8. Request a DIN 1.4404 Stainless Steel Quote
For customized DIN 1.4404 (316L) stainless steel products — including sheets, plates, coils, pipes, and bars — contact our technical team. We provide mill-certified materials with full traceability, precision cutting, and surface finishing options to meet your project specifications.
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