Duplex stainless steel Microstructure of base metal of the duplex stainless steel, 2205, 250X original magnification. Austenite phases are present as white island in blue sea of ferrite. Duplex stainless steels have a two-phase microstructure of austenite and ferrite grains. The picture shows the yellow austenitic phase as “islands” surrounded by the blue ferritic phase.
Introduction
Stainless steels are high-alloy steels. These steels are available in four groups that include martensitic, austenitic, ferritic and precipitation-hardened steels. These groups are formed based on the crystalline structure of stainless steels.
Stainless steels contain larger amounts of chromium in comparison with other steels and thus have good corrosion resistance. Most of the stainless steels contain about 10% of chromium.
Grade 2205 stainless steel is a duplex stainless steel whose design enables combining improved resistance to pitting, high strength, stress corrosion, crevice corrosion and cracking. Grade 2205 stainless steel resists sulfide stress corrosion and chloride environments.
Chemical Composition
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Table.1
Chemical Composition
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Element
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Content (%)
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Iron, Fe
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63.75-71.92
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Chromium, Cr
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21.0 – 23.0
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Nickel, Ni
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4.50 – 6.50
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Molybdenum, Mo
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2.50 – 3.50
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Manganese, Mn
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2.00
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Silicon, Si
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1.00
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Nitrogen, N
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0.080 – 0.20
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Carbon, C
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0.03
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Phosphorous, P
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0.03
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Sulfur, S
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0.02
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The duplex structure gives this family of stainless steels a combination of attractive properties:
Strength: Duplex stainless steels are about twice as strong as regular austenitic or ferritic stainless steels.
Toughness and ductility: Duplex stainless steels have significantly better toughness and ductility than ferritic grades; however, they do not reach the excellent values of austenitic grades.
Corrosion resistance: As with all stainless steels, corrosion resistance depends mostly on the composition of the stainless steel. For chloride pitting and crevice corrosion resistance, their chromium, molybdenum and nitrogen content are most important. Duplex stainless steel grades have a range of corrosion resistance, similar to the range for austenitic stainless steels, i.e from Type 304 or 316 (e.g. LDX 2101©) to 6% molybdenum (e.g. SAF 2507©) stainless steels.
Stress corrosion cracking resistance: Duplex stainless steels show very good stress corrosion cracking (SCC) resistance, a property they have “inherited” from the ferritic side. SCC can be a problem under certain circumstances (chlorides, humidity, elevated temperature) for standard austenitic such as Types 304 and 316.
Cost: Duplex stainless steels have lower nickel and molybdenum contents than their austenitic counterparts of similar corrosion resistance. Due to the lower alloying content, duplex stainless steels can be lower in cost, especially in times of high alloy surcharges. Additionally, it may often be possible to reduce the section thickness of duplex stainless steel, due to its increased yield strength compared to austenitic stainless steel. The combination can lead to significant cost and weight savings compared to a solution in austenitic stainless steels.
Mechanical Properties
Table 2. Mechanical Properties of Duplex Stainless Steel / UNS S31803 / AISI 2205
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Table 2.
Mechanical Properties
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Properties
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Metric
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Imperial
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Tensile strength at break
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621 MPa
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90000 psi
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Yield strength (@strain 0.200 %)
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448 MPa
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65000
psi |
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Elongation at break (in 50 mm)
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25.0%
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25.0%
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Hardness, Brinell
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293
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293
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Hardness, Rockwell c
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31.0
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31.0
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Equivalent materials to grade 2205 duplex stainless steel are:
- ASTM A182 Grade F51
- ASTM A240
- ASTM A789
- ASTM A790
- DIN 1.4462
Applications :
- Fuel gas filters
- Chemical tanks
- Heat exchangers
- Acetic acid distillation components
References:
- https://en.wikipedia.org/wiki/Duplex_stainless_steel
- https://www.imoa.info/
- https://www.steeltank.com/
- http://www.corrosionlab.com/
- http://mit.imt.si/Revija/izvodi/mit114/tehovnik.pdf
FOR FUTHER INFORMATION ABOUT DUPLEX STAINLESS STEEL PLEASE CONTACT :