DIN 1.4401 Stainless Steel: High-Performance Austenitic Alloy for Corrosive Environments
DIN 1.4401 (AISI 316) is a molybdenum-bearing austenitic stainless steel grade that offers superior corrosion resistance compared to standard 304/1.4301 alloys. With a minimum 2.0% molybdenum content, this grade demonstrates exceptional performance in chloride-rich environments, acidic solutions, and marine applications. Its balanced composition of 16-18% chromium, 10-14% nickel, and controlled carbon content (≤0.07%) makes it the preferred choice for chemical processing, pharmaceutical equipment, and offshore platforms where standard stainless steels would fail.
1. Chemical Composition (EN 10088-3 Standard)
| Element | Content Range | Function |
|---|---|---|
| Carbon (C) | ≤ 0.07% | Low carbon minimizes intergranular corrosion risk during welding |
| Chromium (Cr) | 16.50 – 18.50% | Forms protective Cr₂O₃ passive layer for basic corrosion resistance |
| Nickel (Ni) | 10.00 – 13.00% | Stabilizes austenitic structure; enhances ductility and low-temperature performance |
| Molybdenum (Mo) | 2.00 – 2.50% | Significantly improves pitting and crevice corrosion resistance in chloride environments |
| Manganese (Mn) | ≤ 2.00% | Improves hot working properties; partial nickel substitute in cost optimization |
| Silicon (Si) | ≤ 1.00% | Enhances oxidation resistance at elevated temperatures |
| Phosphorus (P) | ≤ 0.045% | Controlled impurity to maintain mechanical properties |
| Sulfur (S) | ≤ 0.030% | Minimized to prevent hot cracking during welding |
| Nitrogen (N) | ≤ 0.11% | Strengthens austenitic matrix without compromising ductility |
2. Mechanical Properties (Annealed Condition)
- Tensile Strength (Rm): 500-700 MPa (EN 10088-2 standard)
- Yield Strength (Rp0.2): ≥ 200 MPa (minimum guaranteed strength)
- Elongation (A5): ≥ 40% (excellent formability for complex shapes)
- Hardness (HB): ≤ 215 (Brinell hardness for machinability)
- Modulus of Elasticity: 193 GPa (consistent structural performance)
- Impact Toughness: ≥ 100 J at -196°C (superior cryogenic performance)
3. Manufacturing Process Overview
- Melting: Vacuum oxygen decarburization (VOD) or argon oxygen decarburization (AOD) processes ensure precise alloy composition and minimal gas content for enhanced corrosion resistance.
- Hot Working: Controlled rolling at 1150-1250°C followed by rapid water quenching to maintain homogeneous austenitic structure and prevent carbide precipitation.
- Cold Working: Multi-stage cold rolling with intermediate annealing (1050-1100°C) to achieve desired thickness and surface finishes (2B, BA, No.4, or HL).
- Solution Annealing: Heat treatment at 1020-1100°C followed by rapid cooling to dissolve chromium carbides and restore optimal corrosion resistance.
- Surface Treatment: Electropolishing or pickling (HNO₃ + HF) to remove oxide scale, followed by passivation to enhance the chromium oxide layer thickness.
4. Corrosion Resistance Performance
| Corrosion Type | Performance | Test Standard |
|---|---|---|
| Pitting Corrosion | PREN ≥ 25 (Pitting Resistance Equivalent Number) | ASTM G48 (Method A) |
| Crevice Corrosion | Resistant in chloride concentrations up to 1000 ppm | ASTM G48 (Method B) |
| Intergranular Corrosion | Excellent resistance in as-welded condition | ASTM A262 (Practice E) |
| Stress Corrosion Cracking | Superior to 304 in chloride environments | ASTM G36 |
| General Corrosion | Resistant to sulfuric, phosphoric, and acetic acids | ASTM G31 |
5. Key Application Industries
Chemical Processing
Storage tanks, reactors, and piping systems for sulfuric acid (up to 10% concentration), phosphoric acid, and organic chemicals. Resists corrosion from chlorine gas and hypochlorite solutions.
Marine & Offshore
Shipbuilding components, desalination plants, and offshore platform structures where saltwater exposure demands superior pitting resistance. Compliant with NORSOK M-650 standards.
Pharmaceutical & Biotechnology
Fermenters, sterile processing equipment, and cleanroom installations where surface smoothness (Ra ≤ 0.5 μm) and corrosion resistance are critical for FDA/EMA compliance.
Food & Beverage
Processing equipment for saltwater brines, vinegar production, and dairy processing where 304 would suffer from pitting. Approved under EC 1935/2004 and 3-A Sanitary Standards.
Pulp & Paper
Bleaching equipment, digesters, and recovery boilers resistant to sulfur compounds and chlorides in white liquor environments.
Architectural
Coastal building facades, handrails, and structural components in high-salinity atmospheric conditions where 304 would exhibit tea staining.
6. Comparison with Related Grades
| Grade | Key Alloying Element | Corrosion Resistance | Primary Applications |
|---|---|---|---|
| DIN 1.4401 (316) | 2.0-2.5% Mo | Excellent in chloride environments | Chemical processing, marine applications |
| DIN 1.4404 (316L) | 2.0-2.5% Mo, ≤0.03% C | Superior weldability with same corrosion resistance | Welded structures in corrosive environments |
| DIN 1.4571 (316Ti) | 2.0-2.5% Mo, Ti stabilized | Enhanced intergranular corrosion resistance | High-temperature applications (400-800°C) |
| DIN 1.4435 (316L) | 2.5-3.0% Mo, ≤0.03% C | Highest pitting resistance in the 316 family | Seawater systems, aggressive chemical environments |
7. Selection Guidelines & Best Practices
- Welding Procedures: Use ER316L filler metal for autogenous welding; maintain interpass temperature below 150°C to prevent sensitization. Post-weld pickling recommended for critical applications.
- Surface Finish Selection: Electropolished (Ra ≤ 0.5 μm) for pharmaceutical/food contact; 2B finish for general fabrication; No.4 for architectural applications requiring aesthetic appeal.
- Temperature Limitations: Continuous service up to 870°C in air; avoid prolonged exposure to 450-850°C range to prevent sigma phase formation.
- Cleaning Protocols: Use nitric acid passivation (20-30% HNO₃ at 50-70°C) for restored corrosion resistance after fabrication; avoid chloride-containing cleaners.
- Certification Requirements: Request EN 10204 3.1/3.2 mill test certificates verifying chemical composition, mechanical properties, and corrosion test results.
8. Request DIN 1.4401 Stainless Steel Quotation
For customized DIN 1.4401 (316) stainless steel products including sheets, plates, coils, pipes, or bars with specific surface finishes and dimensions, contact our technical sales team. We provide comprehensive material certification, precision cutting services, and global logistics solutions tailored to your project requirements.