Material Properties Of Duplex Stainless Steel
The microstructure of duplex stainless steels features both the crystallographic structures of approximately 50% ferrite (a body-centred cubic structure) and 50% austenite (a face-centred cubic structure). The alloying elements in duplex stainless steels are either ferritisers (e.g. chromium, silicon, molybdenum) or austenitisers (e.g. carbon, nickel, nitrogen), which means they favour the formation of the ferritic and austenitic phases, respectively.
Typical duplex stainless steels show a higher yield strength than typical martensitic, austenitic and ferritic grades. However, they have a narrow range of working temperatures due to the precipitation of intermetallic phases that starts to occur above 300°C and the onset of brittleness as they approach cryogenic temperatures.
Benefits Of Duplex Stainless Steel
1. Improved Strength
Many duplex grades are as much as two-times stronger than austenitic and ferritic stainless steel grades.
2. High Toughness and Ductility
Duplex stainless steel is often more formable under pressure than ferritic grades and provides greater toughness.
3. High Corrosion Resistance
Depending on the grade in question, duplex stainless steels offer comparable (or better) corrosion resistance as common austenitic grades. For alloys with increased nitrogen, molybdenum, and chromium, steels exhibit high resistance to both crevice corrosion and chloride pitting.
4. Cost Effectiveness
Duplex stainless steel offers all of the above benefits while requiring lower levels of molybdenum and nickel. This means that it is a lower-cost option than many traditional austenitic grades of stainless steel. The higher strength and corrosion resistance also means that many parts made using duplex stainless can be thinner than their austenitic counterparts providing lower costs.
Standard And Properties Of Selected Heat Treated Duplex Steel Grades
| Duplex |
ASTM A789 Grade S32520 Heat-Treated |
ASTM A790 Grade S31803 Heat-Treated |
ASTM A790 Grade S32304 Heat-Treated |
ASTM A815 Grade S32550 Heat-Treated |
ASTM A815 Grade S32205 Heat-Treated |
|
Elastic modulus |
200 GPa |
200 GPa |
200 GPa |
200 GPa |
200 GPa |
|
Elongation |
25 % |
25 % |
25 % |
15 % |
20 % |
|
Tensile strength |
770 MPa |
620 MPa |
600 MPa |
800 MPa |
655 MPa |
|
Hardness, Brinell |
310 |
290 |
290 |
302 |
290 |
|
Yield strength |
550 MPa |
450 MPa |
400 MPa |
550 MPa |
450 MPa |
|
Coefficient of thermal expansion |
1E-5 1/K |
1E-5 1/K |
1E-5 1/K |
1E-5 1/K |
1E-5 1/K |
|
Specific heat capacity |
440 - 502 J/(kg·K) |
440 - 502 J/(kg·K) |
440 - 502 J/(kg·K) |
440 - 502 J/(kg·K) |
440 - 502 J/(kg·K) |
|
Thermal conductivity |
13 - 30 W/(m·K) |
13 - 30 W/(m·K) |
13 - 30 W/(m·K) |
13 - 30 W/(m·K) |
13 - 30 W/(m·K) |
All values taken at 20 °C.
Duplex Stainless Steel Grades And Composition
|
Type |
Example grades |
Composition |
PREN |
|||
|
Cr% |
Ni% |
Mo% |
N% |
|||
|
Lean |
S31500, S32304, S32404 |
20-24 |
1-5 |
0.1-0.3 |
0.1-0.22 |
24-25 |
|
Standard |
S31803, S32205 |
21-23 |
4.5-6 |
2.5-3.5 |
0.1-0.22 |
33-35 |
|
Super-duplex |
S32520, S32550, S32750 |
24-29 |
4.5-8 |
2.7-4.5 |
0.1-0.35 |
>40 |
|
Hyper-duplex |
S32707, S33207 |
27 |
6.5 |
5 |
0.4 |
49 |
Applications of Duplex Stainless Steel
- Offshore and near-shore operations such as oil drilling, desalination, water treatment, and other industrial operations
- Chemical and liquid processing
- Naval parts and components
- Pollution control equipment
- Pulp and paper production
- Construction
- Hot water and brewing tanks
- Chemical processing, transport and storage
Supplied Forms Duplex Stainless Steel
- Pipe
- Tube
- Plate
- Sheet
- Bar
- Fittings & Flanges
- Welding wire/rod
