Overview
Duplex stainless steels are called“duplex”because they have a two-phase microstructure consisting of grains of ferritic and austenitic stainless steel. When duplex stainless steel is melted it solidifies from the liquid phase to a completely ferritic structure. As the material cools to room temperature, about half of the ferritic grains transform to austenitic grains (“islands”). The result is a microstructure of roughly 50% austenite and 50% ferrite.
Whilst duplex stainless steel are considered resistant to stress corrosion cracking, they are not as resistant to this form of attack as ferritic stainless steel. However, the corrosion resistance of the least resistant Duplex stainless steel is greater than that for the most commonly used grades of stainless steel, i.e. 304 and 316.
Duplex stainless steel are also magnetic, a property that can be used to easily differentiate them from common austenitic grades of stainless.
Specification
ASTM A789/A789M-20 Standard Specification for Seamless and Welded Ferritic/Austenitic Stainless Steel Tubing for General Service.
Specifications | ASTM A790 / ASME SA790, ASTM A789 / ASME SA A789 |
Standards | ASTM, ASME and API |
Size | 1/2″NB TO 12″NB IN |
Schedule | SCH20, SCH30, SCH40, STD, SCH80 |
Type | Seamless / ERW / Welded / Fabricated |
Form | Round Tubes, Custom Tubes, Square Tubes, Rectangular Tubes, “U” Shape, Hydraulic Tubes |
Length | Single Random, Double Random & Cut Length. |
End | Plain End, Beveled End, Treaded |
Equivalent Grade
Grade | UNS No | Old British | Euronorm | SwedishSS | JapaneseJIS | ||
| BS | En | No | Name | ||||
| 2205 | S31803 / S32205 | 318S13 | – | 1.4462 | X2CrNiMoN22-5-3 | 2377 | SUS 329J3L |
Chemical Composition
| Grade | C | Mn | Si | P | S | Cr | Mo | Ni | N | |
| 2205 (UNS S31803) | Min Max | – 0.030 | – 2.00 | – 1.00 | – 0.030 | – 0.020 | 21.0 23.0 | 2.5 3.5 | 4.5 6.5 | 0.08 0.20 |
| 2205 (UNS S32205) | Min Max | – 0.030 | – 2.00 | – 1.00 | – 0.030 | – 0.020 | 22.0 23.0 | 3.0 3.5 | 4.5 6.5 | 0.14 0.20 |
Mechanical Properties
Grade | Tensile Strength (MPa) min | Yield Strength 0.2% Proof (MPa) min | Elongation | Hardness | |
| Rockwell C (HR C) | Brinell (HB) | ||||
| UNS S31803 / 2205 | 621 | 448 | 25 | 31 max | 293 max |
| UNS S32205 / 2205 | 621 | 448 | 25 | 31 max | 293 max |
Physical Properties
Grade | Density | Elastic | Mean Co-eff of Thermal Expansion (μm/m/°C) | Thermal Conductivity (W/m.K) | Specific Heat 0-100°C ( J/kg.K) | Electrical Resistivity (nΩ.m) | |||
| 0-100°C | 0-315°C | 0-538°C | at 100°C | at 500°C | |||||
| UNS S32205 /UNS S31803 | 782 | 190 | 13.7 | 14.2 | – | 19 | – | 418 | 850 |
Applications
1. Chemical process vessels, piping and heat exchangers
2. Pulp mill digesters, bleach washers, chip pre-steaming vessels
3. Food processing equipment
4. Oil field piping and heat exchangers
5. Flue gas desulfurization equipment
