Super Duplex Corp. of America


Phone: 863-648-1236
Email: info@superduplexusa.com
P.O. Box 2717Lakeland, Florida 33807

An Introduction to Super-Duplex Stainless Steels

Super-Duplex Stainless Steels and their characteristics

The first-generation Duplex stainless steels were developed more than 70 years ago in Sweden for use in the sulfite paper industry. Duplex alloys were originally created to combat corrosion problems caused by chloride-bearing cooling waters and other aggressive chemical process fluids.

Called Duplex because of its mixed microstructure with about equal proportions of ferrite and austenite, Duplex stainless steels are a family of grades, which range in 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 steel with a pitting resistance equivalent of >40 (based on Cr% + 3.3Mo% + 16N%).

With its high level of chromium, Super-Duplex 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 steels 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 conventional stainless steels.

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 steels are graded for their corrosion performance depending on their alloy content. Today, modern Duplex stainless steel can be divided into four groups:

Composition of Duplex Stainless Steelsa

The table lists the duplex stainless steels 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

329 d

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

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Super Duplex Corp. of America


Phone: 863-648-1236
Email: info@superduplexusa.com
P.O. Box 2717Lakeland, Florida 33807