General Characteristics
Austenitic-ferritic stainless steel also referred to as duplex stainless steels, combine many of the beneficial properties of ferritic and austenitic steels. Due to the high content of chromium and nitrogen, and often also molybdenum, these steels offer good resistance to localised and uniform corrosion.
The duplex microstructure contributes to the high strength and high resistance to stress corrosion cracking. Duplex steels have good weldability. All duplex grades have the maximum service temperature restricted to 250 or 325°C according to EN10028-7 or ASME II-D 2007 respectively.
Typical Applications
Pulp and paper industry
Desalination plants
Cargo tanks and pipe systems in chemical tankers
Firewalls and blast walls on offshore platforms
Components for structural design
Boilers and water heaters
Storage tanks
Pressure vessels
Water heaters
Heat exchangers
Rotors, impellers and shafts
Bridges
Flue-gas cleaning
Chemical Composition
The typical chemical composition for this grade is given in the table below, together with composition limits given for this grade according to different standards. The required standard will be fully met as specified on the order.
| C | Mn | Cr | Ni | Mo | N | Other | |
Typical | 0.02 | 3.0 | 24.0 | 3.6 | 1.6 | 0.27 | Cu:0.40 |
AM 641 | ≤0.030 | 2.5-4.0 | 23.0-25.0 | 3.0-4.5 | 1.00-2.00 | 0.20-0.30 | Cu:0.10-0.80 |
ASME II A SA-240 | ≤0.030 | 2.5-4.0 | 23.0-25.0 | 3.0-4.5 | 1.00-2.00 | 0.20-0.30 | Cu:0.10-0.80 |
ASTM A240 | ≤0.030 | 2.5-4.0 | 23.0-25.0 | 3.0-4.5 | 1.00-2.00 | 0.20-0.30 | Cu:0.10-0.80 |
EN 10028-7 | ≤0.030 | 2.50-4.00 | 23.0-25.0 | 3.0-4.5 | 1.00-2.00 | 0.20-0.30 | Cu:0.10-0.80 |
EN 10088-2 | ≤0.030 | 2.50-4.00 | 23.0-25.0 | 3.0-4.5 | 1.00-2.00 | 0.20-0.30 | Cu:0.10-0.80 |
EN 10088-3 | ≤0.030 | 2.50-4.00 | 23.0-25.0 | 3.0-4.5 | 1.00-2.00 | 0.20-0.30 | Cu:0.10-0.80 |
IS 6911 | ≤0.030 | 2.50-4.00 | 23.0-25.0 | 3.0-4.5 | 1.00-2.00 | 0.20-0.30 | Cu:0.10-0.80 |
Mechanical Properties
The duplex stainless steels have much higher mechanical strength compared to standard stainless steels. If the high strength of the duplex grades can be utilised, down gauging can be done in many applications leading to cost efficient solutions. The allowable design values may vary between product forms.
The product types P= hot rolled plate, H=hot rolled strip and C=cold rolled coil and strip.
| Standard | Rp0.2 | Rp1.0 | Rm | Elongation | Rockwell | HB |
MPa | MPa | MPa | % | |||
Product type: Cold rolled coil and sheet | ||||||
Typical (thickness 1 mm) | 640 | 850 | 30 | |||
AM 641 | ≥ 550 | 750-900 | ≥ 25 | ≤ 290 | ||
ASME II A SA-240 | ≥ 540 | ≥ 740 | ≤ 290 | |||
ASTM A240 | ≥ 480 | ≥ 680 | ≤ 31HRC | ≤ 290 | ||
EN 10028-7 | ≥ 550 | 750-900 | ≥ 25 | |||
EN 10088-2 | ≥ 550 | 750-900 | ≥ 25 | |||
IS 6911 | ≥ 540 | ≥ 740 | ≤ 31HRC | ≤ 290 | ||
Product type: Hot rolled coil and sheet | ||||||
Typical (thickness 4 mm) | 645 | 720 | 825 | 30 | 250 | |
AM 641 | ≥ 550 | 750-900 | ≥ 25 | ≤ 290 | ||
ASTM A240 | ≥ 540 | ≥ 740 | ≤ 290 | |||
EN 10028-7 | ≥ 550 | 750-900 | ≥ 25 | |||
EN 10088-2 | ≥ 550 | 750-900 | ≥ 25 | |||
IS 6911 | ≥ 480 | ≥ 680 | ≤ 31HRC | ≤ 290 | ||
Product type: Hot rolled quarto plate | ||||||
Typical (thickness 15 mm) | 520 | 750 | 33 | 230 | ||
AM 641 | ≥ 480 | 680-900 | ≥ 25 | |||
ASME II A SA-240 | ≥ 480 | ≥ 680 | ≤ 290 | |||
ASTM A240 | ≥ 480 | ≥ 680 | ≤ 290 | |||
EN 10028-7 | ≥ 480 | 680-900 | ≥ 25 | |||
EN 10088-2 | ≥ 480 | 680-900 | ≥ 25 | |||
IS 6911 | ≥ 480 | ≥ 680 | ≤ 31HRC | ≤ 290 | ||
Physical Properties
The physical properties at room temperature are shown in the table below. Data according to EN10088 or EN10095.
| Density | Modulus of elasticity | Thermal exp. at 100 °C | Thermal conductivity | Thermal capacity | Electrical resistance | Magnetizable |
kg/dm3 | GPa | 10-6/°C | W/m°C | J/kg°C | µΩm | |
7.7 | 205 | 13.0 | 14.5 | 500 | 0.80 | Yes |
