GB/T 022Cr17Ni12Mo2 (316) Stainless Steel: Molybdenum-Enhanced Austenitic Grade for Corrosive Environments
GB/T 022Cr17Ni12Mo2, internationally designated as AISI 316 stainless steel (UNS S31600), represents a premium austenitic grade distinguished by its 2-3% molybdenum addition. This alloy modification significantly enhances resistance to chloride pitting, crevice corrosion, and general atmospheric attack compared to standard 304 grades. With a balanced composition of 16-18% chromium, 10-14% nickel, and controlled carbon content (≤0.08%), it delivers superior performance in marine, chemical processing, and pharmaceutical applications where standard austenitic steels would fail. This technical guide examines its metallurgical properties, processing characteristics, industrial applications, and selection criteria for engineering professionals.
1. Chemical Composition (GB/T 20878 & ASTM A240 Standards)
| Element | Content Range (wt%) | Metallurgical Function |
|---|---|---|
| Carbon (C) | ≤ 0.08% | Minimized to prevent sensitization and intergranular corrosion during welding; lower variants (316L) reduce to ≤0.03% |
| Chromium (Cr) | 16.00 – 18.00% | Forms passive Cr₂O₃ film (minimum 10.5% Cr required for stainless classification); enhances oxidation resistance |
| Nickel (Ni) | 10.00 – 14.00% | Stabilizes austenitic microstructure at room temperature; improves ductility and cryogenic toughness |
| Molybdenum (Mo) | 2.00 – 3.00% | Critical for pitting resistance equivalent (PREN ≥ 24); 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 rolling |
| Phosphorus (P) | ≤ 0.045% | Controlled impurity; excess reduces corrosion resistance and weldability |
| Sulfur (S) | ≤ 0.030% | Minimized to prevent MnS inclusions that initiate pitting corrosion |
| Nitrogen (N) | ≤ 0.10% | Optional addition in 316N variant to enhance strength via interstitial solid solution hardening |
2. Mechanical Properties at Ambient and Elevated Temperatures
| Property | Room Temperature (20°C) | Elevated Temperature (300°C) | Test Standard |
|---|---|---|---|
| Tensile Strength (σb) | ≥ 520 MPa | ≥ 450 MPa | GB/T 228.1, ASTM A370 |
| Yield Strength (σ0.2) | ≥ 205 MPa | ≥ 170 MPa | GB/T 228.1 |
| Elongation (δ5) | ≥ 40% | ≥ 35% | ASTM E8 |
| Hardness (HB) | ≤ 217 | ≤ 187 | ASTM E18 |
| Impact Toughness (CVN) | ≥ 100 J (-196°C) | ≥ 80 J | ASTM E23 |
| Modulus of Elasticity | 193 GPa | 186 GPa | ASTM E111 |
3. Corrosion Resistance Performance
- Pitting Resistance Equivalent Number (PREN): PREN = %Cr + 3.3×%Mo + 16×%N ≥ 24 (vs. 18-20 for 304), quantifying superior chloride resistance
- Critical Pitting Temperature (CPT): ~25°C in 1M NaCl (vs. ~10°C for 304), measured per ASTM G150
- Crevice Corrosion Resistance: Withstands 10ppm Cl⁻ at 50°C (ASTM G48 Method A), suitable for flange connections and gasketed joints
- Intergranular Corrosion: Resistant when solution-annealed (1010-1120°C); 316L variant preferred for welded structures (ASTM A262 Practice E)
- Stress Corrosion Cracking (SCC): Superior to 304 in chloride environments; maximum service temperature 60°C in aerated NaCl solutions
- Oxidation Resistance: Continuous service to 870°C in air; scaling rate <0.1mm/year at 760°C (ASTM A268)
4. Manufacturing and Processing Characteristics
- Melting Practice: Electric arc furnace (EAF) + AOD (argon oxygen decarburization) or VOD (vacuum oxygen decarburization) to achieve ultra-low carbon and nitrogen levels for 316L/316H variants. Continuous casting ensures homogeneous microstructure.
- Hot Working: Forging/rolling temperature range 1150-1260°C; avoid 425-850°C to prevent sigma phase precipitation. Water quenching required to retain austenitic structure.
- Cold Working: Work hardening rate ~160 MPa per 10% reduction (higher than carbon steel). Intermediate annealing at 1050-1100°C recommended for >30% deformation to restore ductility.
- Machinability: Relative machining rating 60% (vs. 100% for 1212 carbon steel). Use carbide tools (e.g., KC720 grade), sulfurized oils, and slow speeds (60-90 sfm) to mitigate work hardening.
- Welding: Fully austenitic weld metal achieved with ER316L filler (AWS A5.9). Preheat not required; post-weld annealing at 1050-1100°C for critical corrosion applications. Shielding gas: 98%Ar/2%O₂ for GMAW.
- Surface Finishes:
- 2B: Cold-rolled, heat-treated, pickled; Ra 0.3-0.5μm (standard for industrial equipment)
- BA: Bright annealed; Ra 0.1-0.2μm (mirror finish for decorative applications)
- No.4: Unidirectional satin; Ra 0.5-0.8μm (architectural panels, anti-fingerprint)
- HL: Hairline; Ra 0.2-0.4μm (elevator interiors, luxury appliances)
5. Industrial Application Domains
Marine & Offshore Engineering
Ship propellers, desalination plant piping, offshore platform handrails, and ballast water systems. Resists seawater corrosion (Cl⁻ ~19,000ppm) and biofouling. Compliant with DNVGL-OS-B101 for marine structures.
Chemical & Petrochemical Processing
Reactors for acetic acid (≤99% conc.), sulfuric acid (≤10% conc.), and caustic soda (≤50% conc.) production. Heat exchanger tubes in fertilizer plants (urea/ammonia synthesis). Meets NACE MR0175/ISO 15156 for H₂S environments.
Pharmaceutical & Biotechnology
ASME BPE-compliant piping, fermentation tanks, and cleanroom equipment. Electropolished surfaces (Ra ≤0.38μm) to prevent bacterial adhesion (e.g., Pseudomonas aeruginosa). Validated per USP for total organic carbon (TOC) leachables.
Food & Beverage Processing
Wine/beer fermentation vessels, dairy processing equipment (CIP systems), and hypochlorite-resistant conveyors. FDA 21 CFR 177.2600 compliant; resists lactic acid (pH 3.5-4.5) and fruit juice corrosion.
Architectural & Structural
Coastal building facades, swimming pool components, and urban furniture in high-salinity zones (e.g., Miami, Dubai). EN 10088-4 certified for exterior applications with ≤0.1mm/year corrosion rate in C4 environments.
Medical Devices
Surgical implants (temporary; ISO 5832-1), dental instruments, and MRI-compatible components. Non-magnetic (μr <1.005) with biocompatible surface passivation per ASTM F86.
6. Comparison with Related Grades
| Grade | Key Alloying Addition | PREN Value | Primary Advantage | Typical Application |
|---|---|---|---|---|
| GB/T 022Cr17Ni12Mo2 (316) | 2-3% Mo | 24-26 | Balanced corrosion resistance and cost | General chemical processing, marine hardware |
| 316L | 2-3% Mo, ≤0.03% C | 24-26 | Superior weldability; ASME IX P-No. 8 | Welded pressure vessels, pharmaceutical tanks |
| 316Ti | 2-3% Mo, 5×%C Ti | 24-26 | Stabilized against sensitization (425-850°C) | High-temperature weldments (e.g., exhaust systems) |
| 316H | 2-3% Mo, 0.04-0.10% C | 24-26 | Enhanced creep resistance (>500°C) | Refinery furnaces, heat exchangers |
| 316N | 2-3% Mo, 0.10-0.16% N | 28-30 | Higher strength (σb ≥ 550 MPa) | Thinner-section structural components |
| 904L | 4-5% Mo, 1.5% Cu | 35-37 | Superior to 316 in sulfuric acid | Acid production, flue gas desulfurization |
7. Selection Guidelines and Engineering Considerations
- Chloride Exposure Limits: For continuous immersion in seawater (Cl⁻ ~19,000ppm), limit operating temperature to <30°C; use 316L for welded joints to avoid knife-line attack.
- Welding Procedures: For >6mm thickness, use low-heat-input processes (e.g., GTAW with ≤1.5 kJ/mm heat input). Post-weld pickling (20% HNO₃ + 2% HF at 50°C) restores corrosion resistance.
- Surface Passivation: ASTM A967 nitric acid passivation (20-40% HNO₃ at 50-70°C for 30-120 min) recommended for pharmaceutical/food contact surfaces to achieve Cr/Fe ratio >1.3 in passive film.
- Galvanic Compatibility: Avoid coupling with carbon steel (galvanic potential difference ~0.5V in seawater). Use insulating gaskets or select cathodic materials (e.g., titanium) for mixed-metal systems.
- High-Temperature Service: Above 425°C, sigma phase (FeCr) may precipitate after 1000+ hours, reducing toughness. 316H preferred for 500-800°C applications due to stabilized carbon content.
- Quality Certification: Verify material test reports (MTRs) per EN 10204 3.1/3.2 for critical applications. Third-party NDT (PT/UT) recommended for pressure-containing components.
- Cost Optimization: For non-welded components in mild environments (e.g., indoor architectural), 304 may suffice. Reserve 316 for Cl⁻ >50ppm or pH <3 environments.
8. Request a Technical Quote for GB/T 022Cr17Ni12Mo2 (316) Stainless Steel
Require precision-cut 316 stainless steel plates, coils, or custom-fabricated components? Our metallurgical team provides tailored solutions for marine, chemical, and pharmaceutical industries—including electropolished surfaces, dual-certified 316/316L materials, and NACE-compliant documentation. Submit your specifications (dimensions, tolerances, surface finish) for a competitive quote with lead times as short as 10 days for stock sizes.