The first-generation duplex stainless steel were developed more than 70 years ago in Sweden for use in the sulfite paper industry. Duplex alloy were originally created to combat corrosion problem caused by chloride-bearing cooling water and other aggressive chemical process fluid. Called duplex because of its mixed microstructure with about equal proportion of ferritic andaustenitic. Duplex stainless steel are a family of grade, which corrosion performance depending on their alloy content.
The term “Super-Duplex” was first used in the 1980’s to denote highly alloyed, high-performance Duplex stainless steel with a pitting resistance equivalent of >40 (based on Cr% + 3.3Mo% + 16N%). With its high level of chromium, Super duplex stainless steel provides outstanding resistance to acids, acid chlorides, caustic solutions and other environments in the chemical / petrochemical, pulp and paper industries, often replacing 300 series stainless steel, high nickel super-austenitic stainless steel and nickel based alloys.
The chemical composition based on high contents of chromium, nickel and molybdenum improves intergranular and pitting corrosion resistance. Additions of nitrogen promote structural hardening by interstitial solid solution mechanism, which raises the yield strength and ultimate strength values without impairing toughness. Moreover, the two-phase microstructure guarantees higher resistance to pitting and stress corrosion cracking in comparison with conventiona stainless steel. From the introduction of its first-generation, Duplex steel has seen a steady increase in popularity.
Recently, the production of high-strength, corrosion resistant super-duplex coil has been implemented in the marine and chemical industries, architecture and mast riggings, wire lines, lifting and pulley equipment and well service strands. In fact, development of wire processing techniques has enabled the production of steel wires down to 1mm in diameter.
The various Alloys Super-Duplex falls under the Duplex stainless steel grouping. Duplex stainless steel are graded for their corrosion performance depending on their alloy content. Today, modern Duplex stainless steel can be pided into four groups:
- Lean Duplex such as 2304, which contains no deliberate Mo addition;
- 2205, the work-horse grade accounting for more than 80% of duplex usage;
- 25 Cr duplex such as Alloy 255 and DP-3;
- Super-Duplex; with 25-26 Cr and increased Mo and N compared with 25 Cr grades, including grades such as 2507, Zeron 100, UR 52N+, and DP-3W
Composition of Duplex Stainless Steel The table lists the duplex stainless steel covered in ASTM specifications for plate, sheet, and bar products.
UNS Number Duplex Grades | Typeb | C | Mn | P | S | Si | Cr | Ni | Mo | N | Cu | Other |
S31200 | … | 0.030 | 2.00 | 0.045 | 0.030 | 1.00 | 24.0-26.0 | 5.5-6.5 | 1.20-2.00 | 0.14-0.20 | … | … |
S31260 | … | 0.03 | 1.00 | 0.030 | 0.030 | 0.75 | 24.0-26.0 | 5.5-7.5 | 2.5-3.5 | 0.10-0.20 | 0.20-0.80 | W0.10-0.20 |
S31803 | … | 0.030 | 2.00 | 0.030 | 0.020 | 1.00 | 21.0-23.0 | 4.5-6.5 | 2.5-3.5 | 0.08-0.20 | … | |
S32001 | … | 0.030 | 4.0-6.0 | 0.040 | 0.030 | 1.00 | 22.0-23.0 | 1.00-3.00 | 0.60 | 0.05-0.17 | 1.00 | |
S32205 | 2205 | 0.030 | 2.00 | 0.030 | 0.020 | 1.00 | 19.5-21.5 | 4.5-6.5 | 3.0-3.5 | 0.14-0.20 | … | |
S32304 | 2304 | 0.030 | 2.50 | 0.040 | 0.030 | 1.00 | 21.5-24.5 | 3.0-5.5 | 0.05-0.60 | 0.05-0.20 | 0.05-0.60 | |
S32520 | … | 0.030 | 1.50 | 0.035 | 0.020 | 0.80 | 24.0-26.0 | 5.5-8.0 | 3.0-4.0 | 0.20-0.35 | 0.50-2.00 | |
S32550 | 255 | 0.04 | 1.50 | 0.040 | 0.030 | 1.00 | 24.0-27.0 | 4.5-6.5 | 2.9-3.9 | 0.10-0.25 | 1.5-2.5 | |
S32750 | 2507 | 0.030 | 1.20 | 0.035 | 0.020 | 0.80 | 24.0-26.0 | 6.0-8.0 | 3.0-5.0 | 0.24-0.32 | 0.50 | |
S32760 | … | 0.030 | 1.00 | 0.030 | 0.010 | 1.00 | 24.0-26.0 | 6.0-8.0 | 3.0-4.0 | 0.20-0.30 | 0.50-1.00 | c |
S32900 | 329d | 0.06 | 1.00 | 0.040 | 0.030 | 0.75 | 23.0-28.0 | 2.5-5.0 | 1.0-2.0 | … | … | |
S32950 | … | 0.03 | 2.00 | 0.035 |
a Weight percent, maximum unless otherwise noted.
b Unless otherwise indicated, a common name, not a trademark, widely used, not associated with any one producer, as listed in ASTM A 240.
c W 0.50-1.00; Cr+3.3Mo+16N=40 min.
d AISI designation BENEFITS
- High strength,
- High resistance to pitting, crevice corrosion resistance.
- High resistance to stress corrosion cracking, corrosion fatigue and erosion,
- Excellent resistance to chloride stress-corrosion cracking
- High thermal conductivity
- Low coefficient of thermal expansion
- Good sulfide stress corrosion resistance,
- Low thermal expansion and higher heat conductivity than austenitic steels,
- Good workability and weldability,
- High energy absorption.
Applications
- Duplex Stainless Steel Pipes and duplex Stainless Steel tubes for production and handling of gas and oil,
- Heat exchanger and duplex Stainless Steel pipes in desalination plants,
- Mechanical and structural components,
- Power industry FGD systems,
- Duplex Stainless Steel pipes in process industries handling solutions containing chlorides,
- Utility and industrial systems, rotors, fans, shafts and press rolls where the high corrosion fatigue strength can be utilized,
- Cargo tanks, vessels, piping and welding consumables for chemical tankers.
- High-strength, highly resistant wiring.
Seamless Duplex Stainless Steel Pipes 1. ASTM A789/A789M 12.7-1016x 0.5-25.4mm 2. ASTM A790/A790M 10.3-1016x 0.5-36mm 3. API 6L EFW Duplex Stainless Steel Pipes 1.ASTM A789/A789M:12.7-323.9×0.5-12.7mm 2:ASTM A790/A790M 10.3-610×0.5-18mm 3.ASTM A928/A928M 10.3–610x 0.5-18mm Material: UNS S31500 S32304 S31803 S2205 S2760 S2750,S 32205, S 32550, S32750, S 32760. | |
Specifications: | Seamless Duplex Stainless Steel Pipes 1. ASTM A789/A789M 12.7-1016x 0.5-25.4mm 2. ASTM A790/A790M 10.3-1016x 0.5-36mm EFW Duplex Stainless Steel Pipes 1.ASTM A789/A789M:12.7-323.9×0.5-12.7mm 2:ASTM A790/A790M 10.3-610×0.5-18mm 3.ASTM A928/A928M 10.3-610x 0.5-18mm Material: UNS S31500 S32304 S31803 S2205 S2760 S2750,S 32205, S 32550, S 32750, S 32760. Duplex Stainless Steel have a structure that contains both ferrite and austenite. Duplex alloys have higher strength and better stress corrosion cracking resistance than most austenitic alloys and greater toughness than ferritic alloys, especially at low temperatures. The corrosion resistance of duplex alloys depends primarily on their composition, especially the amount of chromium, molybdenum, and nitrogen they contain. Duplex alloys are often pided into three sub-classes: Lean Duplex (AL 2003 alloy), Standard Duplex (AL 2205 alloy), and Superduplex (AL 255 Alloy and UNS S32760). |
Standard Met: | Duplex Stainless Steels: Part One Abstract: Microstructure |
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