F316
F316 is an austenitic stainless steel containing molybdenum, which is widely used in harsh environment because of its excellent corrosion resistance (especially chloride corrosion resistance) and comprehensive properties. The following is a systematic analysis from six dimensions: standard, code, composition, performance, heat treatment and application:
I. Standards and brand system
1. Core Standards
F316 mainly follows ASTM standards:
- ASTM A182: Regulates forged/rolled stainless steel flanges, pipe fittings, and valve components for high temperatures (corresponding to the “F316” grade).
- ASTM A240: Standard for stainless steel plates/strips (corresponding to “S31600” plates).
- ASTM A312: Standard for seamless/welded stainless steel tubes (corresponding to tube applications).
Other related standards: JIS G4303 (Japan), EN 10088 (Europe), GB/T 20878 (China), etc., all have corresponding specifications for type 316 stainless steel.
2. International Grade Correspondence
| Region/System | Grade | Description |
|---|---|---|
| US UNS | UNS S31600 | Basic type F316 |
| European EN | EN 1.4401 | Equivalent to F316 |
| Japanese JIS | SUS316 | General – purpose grade |
| China GB (Old) | 0Cr17Ni12Mo2 | Has been updated to the new national standard |
| China GB (New) | 06Cr17Ni12Mo2 | Low – carbon revision |
3. Variant Grades
- 316L (UNS S31603): Low – carbon type (C ≤ 0.03%), with stronger resistance to intergranular corrosion, suitable for structures that cannot undergo heat treatment after welding.
- 316H (UNS S31609): High – carbon type (C ≥ 0.04%), improving high – temperature strength, used in working conditions above 500°C (such as boiler pipelines).
- 316F: Free – cutting type (containing sulfur), used for processing precision parts such as screws and nuts.
II. Chemical composition (ASTM standard, mass fraction%)
The core alloy design of F316 is “synergistic effect of Cr – Ni – Mo”: Chromium resists oxidation, nickel stabilizes austenite, and molybdenum enhances resistance to pitting/crevice corrosion.
| Element | Content Range | Function Analysis |
|---|---|---|
| C | ≤0.08 (316L≤0.03) | Controls carbide precipitation and reduces the risk of intergranular corrosion |
| Si | ≤1.00 | Improves oxidation resistance and assists in deoxidation |
| Mn | ≤2.00 | Improves workability and stabilizes austenite |
| P | ≤0.045 | Impurity element that needs strict control |
| S | ≤0.030 (higher in 316F) | Improves machinability in 316F; low sulfur is required in ordinary types |
| Cr | 16.0~18.0 | Forms a passivation film and resists uniform corrosion |
| Ni | 10.0~14.0 | Stabilizes austenite and enhances corrosion resistance/toughness |
| Mo | 2.0~3.0 | Inhibits pitting/crevice corrosion caused by chloride ions |
III. Mechanical properties (room temperature after solution treatment)
F316 has both high strength and high plasticity, suitable for cold working and welding:
| Performance Indicator | Typical Value (ASTM Requirement) | Remarks |
|---|---|---|
| Tensile Strength | ≥520 MPa | Can reach 600 – 700 MPa in actual production |
| Yield Strength (σ₀.₂) | ≥205 MPa | Austenitic stainless steel has low yield strength and relies on work hardening |
| Elongation (δ₅) | ≥40% | Gauge length 50mm, excellent plasticity |
| Hardness | ≤217 HB (or ≤95 HRB) | Non – aged state, can be hardened by cold working |
Physical Properties
- Density: 7.98 g/cm³ (slightly higher than 7.93 g/cm³ of 304, because molybdenum atoms are heavier).
- Thermal conductivity: 15.1 W/(m·K) at 100°C (lower than 16.2 W/(m·K) of 304, molybdenum reduces heat transfer).
- Thermal expansion coefficient: 16.0 μm/m·°C (20 – 100°C), close to that of 304, suitable for dissimilar metal connection.
IV. Heat Treatment Requirements
The heat treatment of F316 centers on “solution annealing”, whose purpose is to dissolve carbides and restore corrosion resistance:
- Solution Treatment:
- Temperature: 1010 – 1150°C (adjusted according to product form, for example, 1050 – 1100°C is commonly used for tubes).
- Cooling: Rapid water cooling (quenching) to prevent carbide precipitation and ensure a single austenitic structure.
- Application: Must be done before all F316 products leave the factory. Re – solution treatment is required after welding (especially for thick – walled parts) to avoid sensitization (staying in the 450 – 850°C range leads to grain boundary carbide precipitation and reduced corrosion resistance).
- Special Treatment (Optional):
- Stabilization treatment: Only used for variants containing titanium/niobium (such as 321, 347). F316 generally does not need it because the presence of molybdenum has reduced the risk of sensitization.
V. Main application fields (focusing on the scene due to the “specialty” of corrosion resistance)
The “molybdenum advantage” of F316 makes it outperform 304 in environments containing chloride ions, high temperatures, and strong corrosion. Typical applications:
- Marine Engineering
- Seawater desalination equipment (membrane modules, pipelines), ship propellers, offshore platform supports: Resistant to seawater scouring and chloride ion pitting.
- Chemical Industry
- Acid – base storage tanks (sulfuric acid, phosphoric acid, acetic acid), reactor linings, desulfurization pipelines: Resistant to chemical medium corrosion.
- Food and Medical
- Food processing equipment (sterilization tanks, conveying pipelines): Resistant to disinfectants (such as sodium hypochlorite) and meets hygiene standards.
- Medical devices (surgical instruments, implant substrates): Good biocompatibility and resistant to liquid corrosion.
- Energy Field
- Nuclear power auxiliary systems (condenser tubes, pump bodies): Resistant to high – temperature water and radiation environments.
- Hydrotreating reactors in refineries: Resistant to high – temperature sulfide corrosion (316H is used in high – temperature sections).
- High – end Manufacturing
- Precision instruments (optical equipment, sensors): Corrosion – resistant + low magnetic permeability (austenite is non – magnetic).
- Aerospace components (fuel pipelines): Resistant to aviation fuel corrosion and suitable for lightweight processing.
VI. Key Contrast and Precautions
- vs 304: F316 contains molybdenum, and its resistance to chloride ion corrosion is increased by 2 – 3 times, but the cost is 15 – 20% higher. Selection should be based on the environment.
- Corrosion risks: It still corrodes in high – concentration hydrochloric acid and hydrofluoric acid, so nickel – based alloys need to be replaced; avoid staying in the 450 – 850°C range for a long time in chlorine – containing environments (to prevent sensitization).
- Processing tips: Cold working can strengthen it (for example, cold – rolled plates have higher strength), and it has good weldability, but solution treatment is required after welding thick plates.
In summary, F316 is a “corrosion – resistant upgraded austenitic stainless steel”. It breaks through the chloride corrosion bottleneck of 304 through Mo element and becomes a core material in fields such as marine, chemical, and medical. Its variants (316L, 316H, etc.) further cover 细分 scenarios and are a classic choice for “corrosion – resistant 刚需” in the industrial field.