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JIS SUS316L Stainless Steel: Low-Carbon Molybdenum-Alloyed Austenitic Grade for Harsh Corrosive Environments
JIS SUS316L (UNS S31603) represents a premium low-carbon variant of the 316 stainless steel family, distinguished by its 2-3% molybdenum content and maximum 0.03% carbon. This alloy delivers superior resistance to pitting, crevice corrosion, and intergranular attack in chloride-rich environments while maintaining excellent formability and weldability. Certified under JIS G4304/G4305 standards, SUS316L is the material of choice for marine applications, chemical processing, and pharmaceutical equipment where standard 304 grades would fail. This technical guide examines its metallurgical properties, manufacturing specifications, and performance advantages in critical service conditions.
1. Chemical Composition (JIS G4304/G4305 Standard)
| Element | Content Range | Functional Role |
|---|---|---|
| Carbon (C) | ≤ 0.030% | Minimized to prevent chromium carbide precipitation during welding, eliminating sensitization risks |
| Chromium (Cr) | 16.00 – 18.00% | Forms passive Cr₂O₃ film; 16% minimum ensures corrosion resistance in oxidizing environments |
| Nickel (Ni) | 10.00 – 14.00% | Stabilizes austenitic microstructure; enhances ductility and low-temperature toughness |
| Molybdenum (Mo) | 2.00 – 3.00% | Critical for pitting resistance equivalent (PREN ≥ 25); forms MoO₄²⁻ ions to inhibit chloride attack |
| Manganese (Mn) | ≤ 2.00% | Deoxidizer and sulfur scavenger; partial substitute for nickel in cost-sensitive applications |
| Silicon (Si) | ≤ 1.00% | Improves high-temperature oxidation resistance; enhances scale resistance during hot working |
| Phosphorus (P) | ≤ 0.045% | Controlled impurity; excessive levels reduce corrosion resistance and toughness |
| Sulfur (S) | ≤ 0.030% | Minimized to prevent MnS inclusions that initiate pitting corrosion |
| Nitrogen (N) | ≤ 0.10% | Interstitial strengthener; improves resistance to crevice corrosion in acidic chlorides |
2. Mechanical Properties at Ambient Temperature
- Tensile Strength (σb): ≥ 485 MPa (JIS standard); typically 515-690 MPa in annealed condition
- Yield Strength (σ0.2): ≥ 170 MPa; work-hardening increases to 290+ MPa in cold-worked states
- Elongation (δ): ≥ 40% (50mm gauge length); superior formability for deep drawing and spinning
- Hardness (HB): ≤ 217 (Brinell); ≤ 95 HRB (Rockwell) in solution-annealed condition
- Impact Toughness (CVN): ≥ 100 J at -196°C; retains ductility in cryogenic applications (LNG tanks)
- Modulus of Elasticity: 193 GPa (identical to other austenitic grades; critical for pressure vessel design)
3. Manufacturing Process Flow
- Melting & Refining: Dual-process route using electric arc furnace (EAF) + vacuum oxygen decarburization (VOD) or argon oxygen decarburization (AOD) to achieve ultra-low carbon and nitrogen control. Electro-slag remelting (ESR) optional for critical applications.
- Hot Working: Hot rolling at 1150-1260°C with controlled reduction ratios to prevent centerline segregation. Water quenching from 1050°C+ to retain single-phase austenite structure.
- Cold Rolling: For thin gauges (0.3-6.0mm), multi-stage cold reduction with intermediate annealing at 1040-1120°C. Surface finishes available: 2B (standard), BA (bright annealed), No.4 (satin), and HL (hairline).
- Heat Treatment: Solution annealing at 1010-1150°C followed by rapid water quenching to dissolve intermetallic phases (σ-phase, χ-phase) that reduce corrosion resistance.
- Surface Passivation: ASTM A967-compliant nitric acid passivation (20-40% HNO₃ at 50-70°C) to enhance the chromium oxide layer. Electropolishing optional for pharmaceutical/biotech applications to achieve Ra ≤ 0.5 μm.
- Quality Control: 100% eddy current testing for surface defects; ultrasonic testing (UT) for thick plates (>10mm); positive material identification (PMI) per ASTM E1476.
4. Corrosion Performance Metrics
| Corrosion Type | Test Method | SUS316L Performance | Comparative Advantage |
|---|---|---|---|
| Pitting Corrosion | ASTM G48 (FeCl₃) | Critical pitting temperature (CPT): ≥ 25°C | Superior to SUS304 (CPT ≤ 10°C) due to 2% Mo |
| Crevice Corrosion | ASTM G48 (Method B) | Critical crevice temperature: ≥ 15°C | Outperforms SUS316 (non-L) in welded joints |
| Intergranular Corrosion | ASTM A262 (Practice E) | No sensitization after 1-hour boil in CuSO₄-H₂SO₄ | Low carbon eliminates chromium depletion zones |
| Stress Corrosion Cracking | ASTM G36 (MgCl₂) | Threshold stress: ≥ 75% σ₀.₂ at 150°C | Resists chloride SCC better than SUS304 |
| General Corrosion | ASTM G31 (Immersion) | Corrosion rate: < 0.1 mm/year in 10% H₂SO₄ | Comparable to Alloy 20 in mild acids |
5. Primary Application Sectors
Marine & Offshore
Shipbuilding (ballast tanks, propeller shafts), desalination plants (RO membrane housings), offshore platforms (handrails, grating), and submarine pipelines. Certified by DNV, ABS, and Lloyd’s Register for seawater exposure.
Chemical Processing
Reactors for acetic acid, formaldehyde, and sulfuric acid (≤80%); heat exchangers in chloride-cooled systems; storage tanks for hypochlorite and hydrogen peroxide. Compliant with ASME BPE for hygienic design.
Pharmaceutical & Biotech
WFI (water-for-injection) systems, fermenters, and cleanroom piping. Electropolished surfaces (Ra ≤ 0.38 μm) meet USP Class VI and EPA sterilization requirements. Resists microbial adhesion per ASTM E2197.
Oil & Gas
Subsea umbilical tubes, wellhead components, and sour gas processing equipment (NACE MR0175/ISO 15156 compliant). Resists H₂S-induced cracking in environments with ≤150,000 ppm chloride.
Food & Beverage
Saltwater processing equipment, soy sauce fermentation tanks, and high-salinity food production lines. FDA/EC 1935/2004 approved; resists lactic acid and fruit juice corrosion.
Architectural
Coastal building facades, swimming pool structures, and monument cladding. 316L’s PREN ≥ 25 ensures longevity in tropical marine atmospheres (ISO 9223 C5-M classification).
6. Comparison with Related Grades
| Grade | Key Alloying | Carbon Content | PREN Value | Optimal Use Case |
|---|---|---|---|---|
| SUS316L | 17Cr-12Ni-2.5Mo | ≤ 0.03% | 25-30 | Welded structures in chloride environments; pharmaceutical equipment |
| SUS316 | 17Cr-12Ni-2.5Mo | ≤ 0.08% | 25-30 | Non-welded components where sensitization isn’t a concern |
| SUS316Ti | 17Cr-12Ni-2.5Mo-0.5Ti | ≤ 0.08% | 25-30 | High-temperature applications (400-800°C) where Ti stabilizes carbon |
| SUS317L | 19Cr-13Ni-3.5Mo | ≤ 0.03% | 30-35 | More aggressive chloride environments (e.g., pulp bleaching) |
| 904L | 20Cr-25Ni-4.5Mo-1.5Cu | ≤ 0.02% | 35-40 | Sulfuric acid service; replaces high-nickel alloys in some cases |
7. Selection Guidelines & Engineering Considerations
- Welding Procedures: Use ER316L or ER316LSi filler metal (AWS A5.9). Maintain interpass temperature ≤150°C to avoid hot cracking. Post-weld pickling (HNO₃ + HF) mandatory for full corrosion resistance restoration.
- Chloride Limits: Continuous exposure should not exceed 1,000 ppm Cl⁻ at ambient temperature or 150 ppm at 60°C. For higher concentrations, consider SUS317L or duplex 2205.
- Surface Finish Selection:
- 2B: Standard for industrial applications (Ra 0.5-1.0 μm)
- BA: Mirror finish for decorative/pharma (Ra ≤ 0.1 μm)
- No.4: Satin finish for architectural (Ra 0.8-1.2 μm)
- Electropolished: Critical for cleanability in GMP environments
- Temperature Limitations:
- Continuous service: -196°C to 450°C (avoid 450-850°C range due to σ-phase precipitation)
- Short-term exposure: Up to 900°C in non-sulfidizing atmospheres
- Certification Requirements: Demand EN 10204 3.1/3.2 mill test certificates with actual chemistry and mechanical test results. For pressure vessels, ASME SA240/SA479 certification may be required.
- Cost Optimization: Consider 316L dual-certified plates (316/316L) for non-welded applications where carbon content flexibility exists. Thin gauges (<3mm) may use 316L coil for cost savings.
8. Request a SUS316L Stainless Steel Quote
Require JIS SUS316L stainless steel in custom forms—sheets, plates, coils, pipes, or fittings? Our metallurgical experts provide tailored solutions for marine, chemical, and pharmaceutical applications with full traceability and third-party inspections. Submit your specifications (grade, dimensions, surface finish, and quantity) for a competitive quote within 24 hours.
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