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Duplex Stainless Steel

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Duplex Stainless Steel

Duplex stainless steel is a type of stainless steel that contains a combination of both austenitic and ferritic microstructures in its metallurgical structure. This unique combination of phases gives duplex stainless steel its name and imparts a range of beneficial properties. Duplex stainless steel offers a balance of corrosion resistance, strength, and other mechanical properties, making it suitable for a variety of applications.

A few examples of commonly used duplex stainless steel grades:

Duplex 2205 (UNS S31803 / UNS S32205)

904L (UNS N08904 / S39042)

254SMO (UNS S31254)

Duplex 2304 (UNS S32304)

Duplex 2507 (UNS S32750)

Duplex 4501 (UNS S32760)

Duplex 2101 (UNS S32101)


● Duplex 2205 (UNS S31803 / UNS S32205):

2205 is a ferritic-austenitic stainless steel which combines many of the beneficial properties of both ferritic and austenitic steels. As a result of high chromium and molybdenum contents, the steel has very good pitting and uniform corrosion resistance to stress corrosion cracking as well as high mechanical strength.

2205 has good weldability and can be welded using most of the welding techniques for stainless steels.

Due to the balanced composition, when welded correctly, the heat affected zone contains sufficient austenite to avoid the risk of localized corrosion.

The chemical composition of Duplex 2205 is balanced to give a microstructure containing roughly equal amounts of ferrite and austenite.

Chemical Composition

CCrFeMnMoNNiPSSi
MaxMaxMaxMaxMax
0.03021.0-23.00Bal2.02.50 – 3.500.08 – 0.204.50 – 6.500.030.021.0

Design Features

  • ● High strength.
  • ● Low thermal expansion and higher heat conductivity than austenitic steels.
  • ● High resistance to stress corrosion cracking, corrosion fatigue and erosion.
  • ● High uniform corrosion resistance.
  • ● High pitting and crevice corrosion resistance.
  • ● Good sulfide stress corrosion cracking resistance.

Typical Applications

  • ● Heat exchangers, tubes and pipe for production and handling of gas and oil
  • ● Heat exchangers and pipes in dasalination plants
  • ● Pressure vessels, pipes, tanks and heat exchangers for processing and transport of various chemicals
  • ● Pressure vessels, tanks and pipes in process industries handling chlorides
  • ● Rotors, fans, shafts and press rolls where the high corrosion fatigue strength can be utilized
  • ● Cargo tanks, piping and welding consumables for chemical tankers

Features: Good general corrosion resistance, high strength, and excellent resistance to stress corrosion cracking and pitting.

Applications: Oil and gas industry, chemical processing, marine environments, desalination plants, structural components.


● 904L (UNS N08904 / S39042):

904L is a high quality austenitic stainless steel with low carbon content. The grade is intended for use under severe corrosive conditions.

It has been application proved over many years and was originally developed to resist corrosion in dilute sulfuric acid. It is standardized and approved for pressure vessel use in several countries.

Structurally, 904L is fully austenitic and is less sensitive to precipitation ferrite and sigma phases than conventional austenitic grades with high molybdenum content. Characteristically, due to the combination of relatively high contents of chromium, nickel molybdenum and copper, 904L has good resistance to general corrosion, particularly in sulfuric and phosphoric conditions.

Chemical Composition

CCrCuMnMoNiPSSi
MaxMaxMaxMaxMax
0.0219.0 – 23.01.0 – 2.02.04.0 – 5.023.0 – 28.00.0450.0351.0

Design Features

  • ● Good resistance to pitting and crevice corrosion.
  • ● Very good resistance to stress corrosion cracking
  • ● Good resistance to intergranular corrosion.
  • ● Good formability and weldability.
  • ● Maximum service temperatures of 450 C (824 F).

Typical Applications

  • ● Production and transport of sulfuric acid Metal pickling in sulfuric acid
  • ● Production and concentration of phosphoric acid
  • ● Use in seawater, brackish water, condensers, heat exchangers and pipe work in general
  • ● Paper and allied industries
  • ● Gas washing
  • ● Chemical and pharmaceutical industries


● 254SMO (UNS S31254):

254SMO is an austenitic stainless steel designed for maximum resistance to pitting and crevice corrosion. With high levels of chromium, molybdenum, and nitrogen, 254SMO is especially suited for high chloride environments such as brackish water, seawater, pulp mill bleach plants and other high chloride process streams. 254SMO offers chloride resistance superior to that of Alloy 904L, Alloy 20, Alloy 825 and Alloy G. 254SMO is compatible with the common austenitic stainless steels. It is often used as a replacement in critical com- ponents of larger constructions where Type 316L or 317L has failed by pitting, crevice attack, or chloride stress corrosion cracking. In new construction, 254SMO has been found in many cases to be a technically adequate and much less costly substitute for nickel-based alloys and titanium.

254SMO is substantially stronger than the common austenitic grades, but is also characterized by high ductility and impact strength. 254SMO is readily fabricated and welded.

Chemical Composition

CCrCuMnMoNNiPSiS
MaxMaxMaxMaxMax
0.0219.5 – 20.50.5 – 1.01.06.0 – 6.50.18 – 0.2217.5 – 18.50.030.801.01

Design Features

  • ● High resistance to pitting, crevice and general corrosion.
  • ● Very high resistance to chloride stress corrosion cracking.
  • ● 50% stronger than 300-series austenitic stainless steels.
  • ● Excellent impact toughness.
  • ● Excellent workability and weldability.

Typical Applications

  • ● Seawater handling equipment
  • ● Pulp mill bleach systems
  • ● Tall oil distillation columns and equipment Chemical processing equipment
  • ● Food processing equipment
  • ● Desalination equipment
  • ● Flue gas desulfurization scrubbers
  • ● Oil and gas production equipment


● Duplex 2304 (UNS S32304):

Duplex 2304 is a 23% chromium, 4% nickel, molybdenum-free duplex stainless steel whose structure is a balance of ferrite and austenite

It has high mechanical strength, good weldability, good corrosion resistance, high resistance to stress corrosion cracking, good machinability, low thermal expansion, good fatigue properties, high thermal conductivity and easy fabrication.

Chemical Composition

CCrCuMnNNiPSiS
MaxMaxMaxMaxMax
0.0321.5-24.50.05-2.02.50.05-2.017.5 – 18.50.041.01.0

Features

Good corrosion resistance, especially in chloride-containing environments. Higher strength than standard austenitic stainless steels.

Applications

Chemical and petrochemical industry, marine applications, heat exchangers, food and beverage processing.


● Duplex 2507 (UNS S32750):

Duplex 2507 is a super-duplex stainless steel designed for applications requiring superior strength and corrosion resistance

Chemical Composition

CCrCuMnMoNNiPSiS
MaxMaxMaxMaxMax
0.0324-260.5 – 1.01.23.0-5.00.24-0.326.0-8.00.0350.800.02

Features

  • ● High corrosion resistance
  • ● Superior strength
  • ● Excellent resistance to chloride-induced pitting and crevice corrosion.

Applications

  • ● Oil and gas industry
  • ● Offshore platforms
  • ● Chemical processing
  • ● Desalination plants
  • ● Marine engineering.


● Duplex 4501 (UNS S32760):

Alloy 32760 is a super duplex stainless steel supplied in hot worked and solution annealed conditions. As a super duplex stainless steel

Chemical Composition

CCrCuMnMoNNiPSiS
MaxMaxMaxMaxMax
0.0324-260.5 – 1.01.03.0-4.00.2-0.36.0-8.00.030.10.01

Features

High corrosion resistance, excellent mechanical properties, and resistance to sulfide stress corrosion cracking.

Applications

Oil and gas industry, marine applications, chemical processing, pulp and paper industry.


● Duplex 2101 (UNS S32101):

S32101 is a duplex (austenitic-ferritic) stainless steel with relatively low content of alloying elements. The grade has high mechanical strength

Chemical Composition

CCrMnMoNNiPSiS
Max-MaxMaxMax
0.0421-224.0-6.00.1-0.80.2-0.251.35-1.790.041.00.03

Features

Good corrosion resistance and higher strength than austenitic stainless steels. Lower nickel content for cost savings.

Applications

Structural components, architectural applications, transportation industry.