What is duplex stainless steel?
Duplex stainless steel grades have a ferritic-austenitic microstructure, with a phase balance of approximately 50% ferrite and 50% austenite. They combine many of the beneficial properties of ferritic and austenitic stainless steels. The duplex microstructure contributes to the high mechanical strength and high resistance to stress corrosion cracking.
The high strength of duplex steel grades is also a result of alloying with nitrogen. Other characteristic properties of duplex steel grades include good abrasion and erosion resistance, good fatigue resistance, high-energy absorption and low thermal expansion.
Duplex stainless steel grades generally have good weldability and they can be welded using most of the welding methods used for austenitic stainless steels:
- Shielded metal arc welding (SMAW)
- Gas tungsten arc welding TIG (GTAW)
- Gas metal arc welding MIG (GMAW)
- Flux-cored arc welding (FCW)
- Plasma arc welding (PAW)
- Submerged arc welding (SAW)
- Laser welding
- Resistance welding
- High-frequence welding
Superior corrosion resistance
Duplex stainless steel grades are superior to standard austenitics with regard to stress corrosion cracking resistance. They are also good in a number of acidic and alkaline environments.
Outokumpu's duplex offering is unique: for a given austenitic stainless steel grade there is a duplex counterpart that not only provides similar corrosion resistance but also twice the strength.
Lean duplex stainless steel grades
The duplex stainless steel grades Forta LDX 2101, Forta DX 2304, Forta EDX 2304 and Forta LDX 2404 are referred to as lean duplex steel grades. Typical applications are storage tanks, bridges, water heaters and reinforcement bars. The corrosion resistance is comparable to the standard austenitic steel grades like 304/304L (4301/4307) and 316/316L (4401/4404) respectively high alloyed ferritics like 444 (4521).
Super duplex stainless steel grades
Our duplex steel grades 2507 and 4501 are regarded as super duplex stainless steel grades. They are highly alloyed and have a corrosion resistance comparable to high performance austenitics like 254 SMO®. Typical applications for super duplex steels are desalination plants, seawater systems, flue-gas cleaning, umbilicals, storage tanks and pressure vessels.
By lowering total material weight, you also lower the transportation and assembly costs. This reduces the environmental impacts even further, making duplex stainless steel a genuine material of the future.