Super Duplex S32750
S32750 is a 25Cr-7Ni-4Mo super duplex stainless steel with a balanced austenite-ferrite microstructure. The high molybdenum and nitrogen content give it a PREN above 42, making it well-suited for aggressive chloride and acidic process environments.
1. Chemical Composition
The table below lists the controlled elemental ranges for S32750. Chromium, molybdenum, and nitrogen together determine its corrosion performance and phase balance.
| Grade | C | Mn | P | S | Si | Cr | Ni | Mo | N | Cu |
| S32750 | 0.03 | 1.2 | 0.035 | 0.02 | 0.8 | 24.0–26.0 | 6.0–8.0 | 3.0–5.0 | 0.24–0.32 | 0.5 |
2. Mechanical Properties
The values below are minimum mechanical requirements for S32750 in the annealed and quenched condition. They apply to both seamless and welded product forms.
| Grade | Condition | Tensile Strength Min, MPa (ksi) | Yield Strength Min, MPa (ksi) | Elongation Min, % | PREN |
| S32750 | Annealed | 800 (116) | 550 (80) | 15 | ≥41 |
3. Equivalent Grade
This table maps S32750 across major international designation systems for cross-border procurement and material verification in engineering documentation.
| GRADE | UNS | GB | JIS | ISO | DIN/EN | GOST | |
| ISC | NEW | ||||||
| 2507 | S32750 | S25073 | 022Cr25Ni7Mo4N | - | X2CrNiMoN25-7-4 | 1.4410 | — |
4. Key Technical Advantages
- Pitting and Crevice Corrosion Resistance: With a PREN >42, S32750 outperforms standard duplex (S31803/S32205) in chloride-bearing environments, including seawater and brine. The 25% Cr, 4% Mo, and 0.28% N content drives this resistance.
- High Mechanical Strength: Yield strength of ≥550 MPa is roughly twice that of austenitic grades like 316L. This allows thinner wall sections and weight savings in pressure-bearing piping systems.
- Resistance to Stress Corrosion Cracking (SCC): The duplex microstructure resists chloride-induced SCC that commonly affects austenitic grades above 60°C. S32750 holds up well in hot chloride service.
Technical Note: S32750 must be solution-annealed at 1025–1100°C and rapidly quenched to avoid sigma-phase precipitation. Prolonged exposure between 700–980°C severely degrades toughness and corrosion resistance.
5. Common Manufacturing Standards
- ASTM A790: Standardspecification for seamless and welded ferritic/austenitic (duplex) stainless steel pipe. It covers S32750 in pipe form for pressure service.
- ASTM A789: Standard specification for seamless and welded ferritic/austenitic stainless steel tubing for general service, including S32750 tubular products.
- DIN EN 10216-5: Seamless steel tubes for pressure purposes. Covers stainless steel tubes including 1.4410 (S32750 equivalent).
- JIS G3463: Not a standard designation for this alloy. The material is referenced under EN 10216-5 / ASTM A789 in most engineering specifications.
- GB/T 21833: Chinese national standard for austenitic-ferritic (duplex) stainless steel seamless pipes, covering 022Cr25Ni7Mo4N designation.
- GOST 9940 / 9941: Russian standard for seamless hot-deformed and cold-deformed stainless steel tubes. S32750 is typically procured against ASTM or EN equivalents.
Manufacturing Standards Comparison Table:
| Standard | GB | EN/DIN | JIS | GOST |
| ASTM A790 (Pipe) | GB/T 21833 | EN 10216-5 | - | GOST 9940 |
| ASTM A789 (Tube) | GB/T 21833 | EN 10216-5 | - | GOST 9941 |
6. Primary Applications
- Offshore Oil and Gas: Subsea flowlines, topside piping manifolds, and umbilical tubing where seawater injection and chloride-rich produced fluids require PREN >40 materials.
- Desalination Plants: This industry uses S32750 for high-pressure feed piping and pressure vessel components in reverse osmosis and multi-stage flash systems operating with concentrated brine.
- Chemical Process Industry: Heat exchanger tubes and process piping for sulfuric acid, phosphoric acid, and chloride-containing process streams.
- Pulp and Paper: Digesters, bleach plant piping, and washing equipment exposed to hot acidic bleaching chemicals, including chlorine dioxide.
- Subsea and Marine Structures: Hydraulic control lines and umbilicals (where high pressure and seawater exposure together require strong mechanical properties with corrosion resistance) use Super Duplex S32750.