ISO X5CrNiMo17-12-2 (1.4401/AISI 316) Stainless Steel: Molybdenum-Alloyed Austenitic Grade for Corrosive Environments
ISO X5CrNiMo17-12-2 (commonly known as 1.4401 or AISI 316) is a molybdenum-bearing austenitic stainless steel designed for superior corrosion resistance in aggressive chemical and marine environments. With a balanced composition of 17% chromium, 12% nickel, and 2% molybdenum, this grade outperforms standard 304 stainless steel in chloride-rich and acidic conditions while maintaining excellent formability and weldability. This technical guide covers its metallurgical properties, manufacturing processes, industrial applications, and comparative advantages over similar grades.
1. Chemical Composition (EN 10088-3 Standard)
| Element | Content Range | Function |
|---|---|---|
| Carbon (C) | ≤ 0.07% | Minimized to prevent intergranular corrosion; enhances weldability |
| Chromium (Cr) | 16.50 – 18.50% | Forms passive Cr₂O₃ film; provides baseline corrosion resistance |
| Nickel (Ni) | 10.00 – 13.00% | Stabilizes austenitic microstructure; improves ductility and cryogenic toughness |
| Molybdenum (Mo) | 2.00 – 2.50% | Enhances pitting/crevice corrosion resistance in chloride environments |
| Manganese (Mn) | ≤ 2.00% | Deoxidizer; improves hot workability and partial Ni substitution |
| Silicon (Si) | ≤ 1.00% | Enhances oxidation resistance; aids in deoxidation during smelting |
| Phosphorus (P) | ≤ 0.045% | Controlled impurity; excessive levels reduce toughness and corrosion resistance |
| Sulfur (S) | ≤ 0.030% | Minimized to prevent hot cracking during welding and reduce inclusion formation |
| Nitrogen (N) | ≤ 0.10% | Stabilizes austenite; improves strength 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 proof strength for structural integrity)
- Elongation (A5): ≥ 40% (superior formability for deep drawing and complex shapes)
- Hardness (HB): ≤ 215 (Brinell hardness; suitable for machining and polishing)
- Impact Energy (KV): ≥ 100 J at -196°C (exceptional cryogenic toughness for LNG applications)
- Modulus of Elasticity: 193 GPa (consistent with austenitic stainless steel family)
3. Manufacturing Process Overview
- Melting & Refining: Electric arc furnace (EAF) followed by argon oxygen decarburization (AOD) to achieve ultra-low carbon content and precise alloy composition. Vacuum oxygen decarburization (VOD) may be employed for critical applications.
- Hot Working: Hot rolling at 1150-1250°C with controlled cooling to prevent sensitization. Water quenching maintains full austenitic structure and dissolves chromium carbides.
- Cold Working: Multi-stage cold rolling for thin gauges (≤ 5mm) with intermediate annealing at 1050-1100°C to restore ductility. Common finishes include 2B (matte), BA (bright annealed), and No.4 (satin).
- Solution Annealing: Heat treatment at 1020-1100°C followed by rapid water quenching to maximize corrosion resistance by dissolving precipitates and homogenizing the microstructure.
- 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 thickness.
- Quality Control: 100% eddy current testing for surface defects, ultrasonic testing for internal flaws, and spectroscopic analysis to verify chemical composition.
4. Corrosion Resistance Performance
| Corrosion Type | Performance | Test Standard |
|---|---|---|
| Pitting Corrosion | PREN ≥ 24.0 (Pitting Resistance Equivalent Number) | ASTM G48 (FeCl₃ test) |
| Crevice Corrosion | Critical crevice temperature: ≥ 15°C | ASTM G48 Method B |
| Intergranular Corrosion | Resistant in as-welded condition (≤ 0.07% C) | ASTM A262 Practice E |
| Stress Corrosion Cracking | Superior to 304 in chloride environments (≤ 100ppm Cl⁻ at 60°C) | ASTM G36 |
| General Corrosion | < 0.1 mm/year in 10% H₂SO₄ at 25°C | ISO 8407 |
5. Primary Industrial Applications
Marine & Offshore Engineering
Shipbuilding components, offshore platform structures, desalination plants, and seawater cooling systems. Resists pitting in chloride concentrations up to 1000ppm.
Chemical Processing
Reactors, storage tanks, and piping systems for sulfuric acid (≤ 10% conc.), phosphoric acid, and organic acids. Compatible with most pharmaceutical intermediates.
Oil & Gas Industry
Subsea equipment, wellhead components, and refinery heat exchangers. Performs in H₂S environments (NACE MR0175/ISO 15156 compliant).
Medical & Pharmaceutical
Surgical instruments, implant components, and bioreactors. Meets ISO 5832-1 and ASTM F138 standards for biocompatibility.
Food & Beverage Processing
High-salinity food production (soy sauce, pickles), brewery equipment, and dairy processing. FDA/EC 1935/2004 compliant for direct food contact.
Architectural & Structural
Coastal building facades, handrails, and bridge components. Maintains aesthetic appeal in C5-M (marine) atmospheric corrosion categories per ISO 9223.
6. Comparison with Related Grades
| Grade | Key Alloying Difference | Advantages | Typical Applications |
|---|---|---|---|
| X5CrNiMo17-12-2 (1.4401) | 2.0-2.5% Mo, ≤ 0.07% C | Balanced corrosion resistance and mechanical properties | General marine, chemical, and food processing |
| X2CrNiMo17-12-2 (1.4404) | 2.0-2.5% Mo, ≤ 0.03% C | Superior weldability; resistant to intergranular corrosion | Welded structures in aggressive environments |
| X5CrNiMo18-14-3 (1.4436) | 2.5-3.0% Mo, 12-15% Ni | Enhanced pitting resistance (PREN ≥ 26.5) | Seawater systems, pulp bleaching equipment |
| X5CrNi18-10 (1.4301) | No Mo, 18% Cr, 10% Ni | Lower cost; good formability | Non-chloride environments, architectural uses |
7. Selection Guidelines & Engineering Considerations
- Chloride Exposure Limits: Suitable for < 1000ppm Cl⁻ at ambient temperatures. For higher concentrations (e.g., seawater evaporation), consider 1.4436 or 1.4547 (6% Mo grades).
- Welding Procedures: Use ER316L filler metal (AWS A5.9). Post-weld annealing at 1050-1100°C recommended for maximum corrosion resistance in critical applications.
- Surface Finish Selection:
- 2B: General fabrication (mill finish with light cold rolling)
- BA: Decorative applications (bright, reflective surface)
- No.4: Architectural uses (satin finish, 150-180 grit)
- Electropolished: Pharmaceutical/food contact (Ra < 0.5 μm)
- Temperature Limitations:
- Continuous Service: Up to 870°C in oxidizing atmospheres
- Intermittent Service: Up to 925°C (avoid 425-850°C range to prevent sigma phase formation)
- Cryogenic: Maintains toughness down to -269°C (LNG applications)
- Certification Requirements: Request EN 10204 3.1/3.2 mill test certificates for critical applications. Verify PREN calculation (Cr + 3.3×Mo + 16×N) for pitting resistance validation.
8. Request a Technical Quote for X5CrNiMo17-12-2 Stainless Steel
Require precision-cut plates, coils, or custom-fabricated components in ISO X5CrNiMo17-12-2 (1.4401/316) stainless steel? Our metallurgical experts provide tailored solutions with full traceability and third-party inspection options. Submit your specifications for competitive pricing and lead times.
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