F53
F53 (core code UNS S32750, commercial name 2507 super duplex stainless steel) is a highly alloyed duplex steel. With the synergistic advantages of “chloride corrosion resistance 3 times that of austenitic steel + strength twice that of it”, it has become a core material in extreme corrosion and high – pressure scenarios. The following is a systematic analysis from six dimensions:
Ⅰ. Standard System and Grade Codes
1. Core Executive Standards
- Forgings/Flanges: ASTM A182 (grade “F53”, specifying high – temperature pressure – bearing components such as valves and flanges);
- Plates/Pipes: ASTM A240 / ASME SA – 240 (pressure vessels, heat exchanger liners/pipes);
- International Compatibility:
- European EN: 1.4410;
- Chinese National Standard: 022Cr25Ni7Mo4N (low – carbon, highly alloyed design to enhance corrosion resistance).
2. Global Grade Correspondences
| System/Region | Grade | Description |
|---|---|---|
| U.S. UNS | UNS S32750 | Core identification (benchmark of super duplex steel) |
| Commercial Name | 2507 Duplex Steel | Abbreviated due to Cr≈25% and Ni≈7%, most commonly used |
Ⅱ. Chemical Composition (Mass Fraction %, ASTM Standard)
F53 achieves performance breakthroughs through “high Cr – Mo – N synergy + duplex structure (ferrite 40 – 60% + austenite 60 – 40%)”, and the roles of elements are precise:
| Element | Content Range | Core Role |
|---|---|---|
| C | ≤0.03 | Strictly control carbides, avoid intergranular corrosion (very low sensitization risk) |
| Cr | 24.0 – 26.0 | Ferrite is rich in Cr, forming Cr₂O₃ passive film, resisting pitting/uniform corrosion |
| Ni | 6.0 – 8.0 | Austenite is rich in Ni, stabilizes duplex structure, improves toughness and stress corrosion resistance |
| Mo | 3.0 – 5.0 | Enhance resistance to chloride pitting/crevice corrosion (synergizes with N, PREN≈40 – 45, far exceeding F51’s 32 – 36) |
| N | 0.24 – 0.32 | Stabilize austenite, significantly increase strength (duplex steel strength ≈ twice that of austenite, about 15% higher than F51) |
| Mn | ≤1.20 | Improve workability, assist in stabilizing duplex proportion |
| Si | ≤0.80 | Assist in deoxidation, optimize hot working performance |
Ⅲ. Mechanical Properties (After Solution Treatment, Room Temperature)
Due to the duplex structure + high N strengthening, the performance of F53 far exceeds that of conventional duplex steels (such as F51/2205):
| Performance Index | Typical Value (ASTM Requirement) | Comparison with F51 (2205) |
|---|---|---|
| Tensile Strength | ≥795 MPa | 28% higher (2205≥620 MPa) |
| Yield Strength | ≥550 MPa | 22% higher (2205≥450 MPa) |
| Elongation (δ₅) | ≥15% | Slightly lower (2205≥25%), still meets formability |
| Hardness | 250 – 310 HB | Higher (2205≤270 HB) |
| Physical Properties | Density 7.85 g/cm³, thermal conductivity is better than austenite | Suitable for high – temperature heat exchange |
Ⅳ. Heat Treatment Requirements (Activating Duplex Advantages)
- Solution Treatment (Mandatory):
- Temperature: \(1020 – 1100^\circ\text{C}\) (hold for 1 – 2 hours to homogenize the duplex structure and dissolve carbides / nitrides);
- Cooling: Rapid water quenching (inhibit the precipitation of harmful phases such as \(\sigma\) phase and \(\chi\) phase, and retain stable ferrite + austenite);
- Role: Maximize corrosion resistance and strength, laying the foundation for processing / service.
- Welding and Post – treatment:
- Welding Materials: Select ER2594 welding wire (match the high Cr – Mo – N composition to ensure the duplex proportion of the weld);
- Process: Strictly control heat input (avoid ferrite coarsening). For thick – walled parts, short – term solution treatment at \(1050^\circ\text{C}\) is required after welding (restore corrosion resistance and prevent embrittlement in the weld heat – affected zone).
Ⅴ. Main Application Fields (Extreme Corrosion + High – Pressure Scenarios)
Relying on “chloride corrosion resistance × ultra – high strength”, F53 (2507) dominates the following fields (performance exceeds F51, close to nickel – based alloys):
- Marine Engineering:
- Seawater desalination (high – pressure membrane shells, deep – sea water pipes): Resistant to pitting corrosion in 5 – 10% NaCl seawater (service life 3 times that of 316L, 1.5 times that of F51);
- Offshore platforms (drilling equipment, mooring systems): Resistant to seawater + high – pressure impact, reducing cost by 40% compared with titanium alloys.
- Energy and Chemical Industry:
- Acid oil and gas fields (wellhead valves, transmission pipes): Resistant to stress corrosion cracking by H₂S + high Cl⁻ (complying with NACE MR0175, temperature resistance up to 300°C);
- Flue gas desulfurization (absorption towers, spray pipes): Resistant to HCl + sulfuric acid dew point corrosion (perforation resistance 2 times that of F51).
- Nuclear Power and Environmental Protection:
- Nuclear power (nuclear waste tanks, cooling pipelines): Resistant to radiation + high – temperature water corrosion, with long – term stability;
- Waste incineration (heat exchangers, flues): Resistant to short – term high temperature of 800°C + chloride corrosion (superior to F51’s upper limit of 600°C).
- High – end Manufacturing:
- Papermaking bleaching (digesters, bleaching towers): Resistant to corrosion by chlorine – containing chemicals, avoiding pulp pollution;
- Food and pharmaceutical (high – concentration pickling liquid tanks): Resistant to organic acids + hygienic compliance (replacing Hastelloy, reducing cost by 30%).
Key Summary
- Core Advantages:
- Corrosion Resistance: PREN ≈ 45, the ability to resist chloride pitting is 30% higher than that of F51, close to nickel – based alloys;
- Mechanical Properties: Strength is 20% + higher than that of F51, and the structure can be thinned by 25%, reducing weight and saving energy;
- Cost Ratio: Performance is close to that of Hastelloy C – 276, while the cost is only 1/3 of it.
- Limitations:
- Long – term service temperature ≤ 300°C (σ phase is prone to precipitate at high temperatures, leading to embrittlement);
- High difficulty in cold working (high strength requires customized molds/processes).
F53 (UNS S32750/2507) is the “benchmark of super duplex steel”. It breaks through the performance bottleneck of F51 through ultimate alloy design (high Cr – Mo – N). In extreme environments such as marine, energy, and chemical industries, it becomes the “ultimate solution for high – pressure and strong corrosion scenarios”, balancing performance and cost, and replacing austenitic stainless steel and some nickel – based alloys.