Special Stainless Steels
| UNS Number | UNS S32750 |
| Industry Name | 2507, Super Duplex Stainless Steel, 25Cr-7Ni super duplex |
| Product Forms | Bars, Forgings, Plates,Tubes, Wires |
General Characteristics
2507 is a super duplex stainless steel. It was originally developed to address the limitations of standard duplex grades and 316L austenitic stainless steel, which exhibited insufficient pitting and crevice corrosion resistance in high-chloride brine environments.
Conventional stainless steels suffered rapid localized corrosion when exposed to seawater, brackish water and chloride-rich process media at elevated temperatures. 2507 combines high mechanical strength and outstanding chloride corrosion resistance, making it ideal for seawater piping, desalination equipment, offshore structural components, heat exchangers and process vessels in chloride service.
Compared to 2205 duplex stainless steel, 2507 has higher chromium, molybdenum and nitrogen content for superior pitting resistance, though it is more difficult to fabricate and more costly. Compared to 316L austenitic stainless steel, 2507 delivers markedly higher strength and far better resistance to chloride pitting and stress corrosion cracking, while 316L readily suffers SCC in concentrated chloride media.
Chemical compositions of Alloy 2507
C | Cr | Ni | Mo | N | Mn | Si | P | S |
≤0.030 | 24.00–26.00 | 6.00–8.00 | 3.00–5.00 | 0.24–0.32 | ≤1.20 | ≤0.80 | ≤0.035 | ≤0.020 |
Offshore & Marine||Seawater cooling systems|Riser components|Seawater pump parts
Petrochemical||Chloride rich process vessels|Heat exchangers|Reactor internals
Desalination||High pressure piping|Fasteners and valve components
Power||Flue gas desulfurization (FGD) scrubber hardware|Chloride-containing cooling circuits
Technical Standards | Product Form |
ASTM A182 / A182M | Forged Fittings, Flanges, Bars, Forgings |
ASTM A240 / A240M | Plate, Sheet, Strip |
ASTM A789 / A789M | Seamless Tube & Pipe |
ASTM A479 / A479M | Bar and Wire for high temperature service |
EN 10088-3 | Bar, Wire, Forging |
EN 10216-5 | Seamless tube |
Product form | Size range (mm) |
Forged bar | Dia.70-500 |
Rolled bar | Dia.2.0-70 |
Flat bar | T4-50*W60-300 |
Wire | Dia.0.25-18.0 |
Forged ring | OD 30-350* ID 30-350 |
Plate | 1-25 * ≤1200 * ≤1200 |
Seamless tube | OD 6.0-200 * 0.6-20 |
Q1: What is super duplex stainless steel 2507?
A1: 2507 (UNS S32750) is super duplex stainless steel with mixed austenite + ferrite microstructure (~50/50). It combines high mechanical strength and outstanding chloride pitting / crevice corrosion resistance.
Q2: Does 2507 require precipitation hardening heat treatment like PH stainless grades?
A2: No. It gains strength from duplex microstructure, not age hardening. Standard delivery condition is solution annealed and water quenched. No aging treatment is needed.
Q3: Can 2507 bar be used to manufacture fasteners?
A3: Yes. 2507 bar and wire are used for high strength fasteners for chloride / seawater environments. Hot heading is preferred; cold forming capacity is limited.
Q4: Is 2507 magnetic?
A4: Yes. Due to ferrite phase in its duplex structure, 2507 is weakly magnetic, unlike fully austenitic 316L.
Q5: What temperature limits for continuous service of 2507?
A5: Recommended maximum continuous service temperature around 300°C. Long time exposure above 300°C risks formation of brittle intermetallic phases (sigma phase).
Q6: What NDT can be supplied on 2507 bar stock?
A6: Ultrasonic testing (UT) for internal defects. Liquid Penetrant Inspection (LPI) for surface discontinuities. MPI is not reliable because it contains austenite phase.
Q7: What are the main risks during forging / machining of 2507 raw material?
A7: Overheating during forging can cause sigma phase precipitation and severe embrittlement. Controlled heating temperature and fast cooling after solution annealing are critical.
Q8: What certifications are available for 2507 raw material?
A8: Standard 3.1 MTC includes heat analysis, mechanical test, hardness and ferrite fraction report. 3.2 certification and third-party inspection available for offshore and nuclear projects.