Definition, Grades, Composition, Properties, and Applications of Duplex Stainless Steel
In the microstructure, duplex stainless steels contain both austenitic and ferritic phases in roughly equal proportions. Due to their good corrosion resistance, strength, and ease of fabrication, they are widely used in engineering applications. The acronym DSS refers to the use of Duplex Stainless Steels. Duplex Stainless Steels provide a range of benefits over traditional austenitic and ferritic stainless steels duplex 2205 density, duplex metal, 2205 stainless steel properties.
- A twofold improvement over standard stainless steel grades in terms of strength.
- A high degree of toughness and ductility
- Resistance to corrosion at a high level
- A high strength DSS material requires less pipe thickness, reducing the weight of the pipe. Nickel levels are also reduced, which reduces the cost of the pipe.
Applications of Duplex Stainless Steel
Due to its excellent corrosion resistance, increased strength, and affordable pricing, duplex stainless steel (DSS) is a popular choice for a variety of industries.
- Processing of chemicals and liquids
- Industrial operations offshore (flowlines, risers)
- Components and parts for the navy
- Production of pulp and paper
- Equipment used to control pollution
- Plants for the treatment and desalination of water
- The construction, infrastructure, and architecture industries
- Tanks for hot water and brewing
- Storage of food and beverages
- Heat exchangers, pressure vessels, and boilers
- Tanks for the marine environment
- The renewable energy sector
- Industry of the nuclear power plant
Duplex Stainless Steel Grades
Comparatively to austenitic stainless steels, duplex stainless steels have a higher chromium content, a higher molybdenum content, a higher molybdenum content, a lower nickel content, 0.05–0.50% nitrogen content. An ideal choice for resistance to pitting corrosion is DSS material. The pitting resistance equivalence number is defined as follows:
PREN = %Cr + 3.3 %Mo + 16 %N
Four grades of Duplex Stainless Steel are determined by their PREN Number values.
- There is no deliberate addition of Molybdenum to lean duplex grades (PREN range: 22–27). Usually used in bridges, pressure vessels, and tie bars. Examples include S32001, S32101, S32304, and S32202.
- Most commonly used (more than 80%) duplex stainless steel material with mid-range properties, such as S32003, S31803, and S32205.
- Specially designed for highly corrosive oil&gas and chemical industries with higher levels of Cr, Ni, Mo, N, and even W. Examples include S32750, S32760, S32950, and S32808.
- This is a duplex stainless steel with a PREN greater than 45. Examples are S32707 and S33207.
Duplex stainless steel naming convention
Duplex stainless steel is referred to by a variety of naming conventions, including:
- %Cr is denoted by 22 or 23 in DSS 2205 or 2305, while %Ni is denoted by 5 in that specific DSS material.
- DSS materials are listed in ASTM specifications under the Unified Numbering System or UNS designation.
- The AISI designation is available only for one DSS material type 329.
Duplex Stainless Steel properties
It has been previously explained that the duplex name is derived from the fact that both austenitic (FCC Structure) and ferritic (BCC Structure) components coexist in approximately equal amounts (Fig. 1). Chromium, Silicon, Molybdenum, Carbon, Nickel, Nitrogen, Manganese, Copper, Tungsten are the major alloying elements.
Duplex Stainless Steel Microstructure
As compared to stainless steel, duplex stainless steel is typically stronger. As the intermetallic phases begin to precipitate around 300 degrees Celsius, the mechanical properties and corrosion resistance decrease through embrittlement phenomena. Therefore, the DSS working temperature range is normally narrow. Several common duplex stainless steel grades are presented in the following table based on their selected properties.
Duplex stainless steel corrosion resistance
Duplex Stainless Steels exhibit a high level of corrosion resistance in a wide variety of environments because they contain a relatively high percentage of chromium, molybdenum, and nitrogen. To combat pitting corrosion, DSS is the ideal material choice. The PREN Number defined above describes DSS' resistance to localized pitting corrosion. In oxidizing, acidic, and hot alkaline environments, DSS is specifically selected for use. Increasing PREN Number increases the resistance against pitting corrosion, which is measured using Critical Pitting Temperature. Corrosion pitting is less likely to occur in materials with a high CPT.
It has been demonstrated that duplex stainless steels are better at resisting stress corrosion cracking than austenitic stainless steels.
Fabrication of Duplex Stainless Steel
As well as pipes, plates, sheets, tubes, fittings, and bars, duplex stainless steel can also be fabricated depending on the requirements. It requires special tools to fabricate duplex stainless steel materials. Due to their excellent weldability and hot forming capability, DSS materials are typically difficult to machine.
Answers to Frequently Asked Questions about DSS
How does duplex stainless steel work?
In stainless steel, the term duplex refers to the two-phase microstructure of the material. Duplex stainless steel is a family of stainless steel that contains an approximately equal amount of ferritic and austenitic phases.
What is the difference between 304 stainless steel and Duplex stainless steel?
There is no duplex stainless steel in 304 stainless steel. It is austenitic stainless steel.
What is the difference between 316 stainless steel and duplex stainless steel?
It is important to note that stainless steel 316 is not a duplex stainless steel. It is an austenitic stainless steel.
Duplex stainless steel serves what purpose?
Duplex stainless steels have roughly twice the strength of austenitic stainless steels and are more resistant to pitting corrosion, crevice corrosion, and stress corrosion cracking.
Does duplex stainless steel rust?
A very high chromium content in duplex stainless steel prevents it from rusting. Therefore, duplex stainless steel does not rust. However, it may corrode under certain conditions.
Does 2205 duplex stainless steel have a magnetic property?
The duplex stainless steels are ferritic as well as austenitic, so they are magnetic. 2205 super duplex is also magnetic. All DSS materials are magnetic.
Does duplex 2205 rust?
As a DSS, 2205 stainless steel usually does not rust. However, it may corrode in severe conditions.
In terms of stainless steel, what is the difference between duplex and super duplex?
In comparison to duplex stainless steel, super duplex stainless steel offers additional properties. As a result of its 25% chromium, 7% nickel, and 4% molybdenum content, DSS has a higher corrosion resistance and strength than duplex stainless steel.
What is the strength of duplex stainless steel?
There is more strength in duplex stainless steel than in ferritic or austenitic stainless steel.
Who invented super Duplex?
Langley Alloys developed Super Duplex stainless steel in the mid-1960s and launched it in 1969.
What grade is super duplex?
The DSS grades UNS S32760, S32750, F55, 1.4501, etc., are super-duplex grades.