Duplex can be welded and shaped and is well suited to structures. At Nordic Steel, we often produce duplex fittings, columns, beams, crossbeams and slotted plates for bridge structures, where good strength is important in a relatively corrosive environment. We also supply many duplex steel structures to the oil and energy industry and to the aquaculture and maritime industries, which are particularly susceptible to corrosion.
Ferritic-austenitic steel is a more accurate name for Duplex. The steel type is two-phase, in that just over half of the structure is ferritic, while the rest is austenitic.
The chemical content of Duplex (ferrite-austenitic steel) should be between these values:
"Stainless steel" belonging to the Duplex category has, as mentioned above, a structure which is a mixture of ferritic and austenitic steels.
Furthermore, we can break down Duplex into three subcategories according to corrosion resistance, or PREN value. The higher the PREN value, the more resistant the steel is to corrosion. This is also reflected in the distribution of the chemical elements.
The different categories are:
C = 0.030 max, Mn = 2.00 max, Ni = 4.5-6.5, Cr 21-23%, Mo 2.5-3.5%
C = 0.030 max, Mn = 1.2 max, Ni = 6.0-8.0, Cr 24-26%, Mo 3.0-4.0%
C = 0.00 max, Mn = 0.0 max, Ni = 0.0-0.0, Cr 00-00%, Mo 0.0-0.0%
Although both Duplex and Super Duplex have better corrosion resistance than conventional austenitic alloys, in particular the resistance to local corrosion is of higher quality in Super Duplex. This is because Super Duplex has higher levels of chromium, nickel and molybdenum than Duplex has.
Super Duplex is also more expensive than Duplex. This is mainly due to higher alloying elements.
Super Duplex (25Cr) is especially suitable for:
High strength and low corrosion means that Super Duplex is often used in the following industries:
Duplex (22cr) is especially suitable for:
Duplex is often used for important industries such as:
Some common types of Super Duplex are:
Lean Duplex is part of the Duplex family and has fewer expensive ingredients, such as nickel and molybdenum.
Lean Duplex can replace 304L and 316L in several applications.
To obtain the desired corrosion properties and phase balance, other alloying elements are added to the chemical composition, such as chromium, manganese and nitrogen.
One of the main reasons for using Lean Duplex is the significant resistance to chloride stress corrosion, due to the dual phases.
The yield strength of Duplex is more than double that of 304L and 316L, and therefore the thickness of equipment and structures can be reduced. Smaller thickness also means lower weight, which is important for transport and installation, especially in remote locations or offshore.
Lean Duplex can be less expensive since nickel and molybdenum are expensive ingredients, which increases the cost of 304L and 316L. The reduction of both these elements makes Lean Duplex a good alternative. And with an almost equal cost per unit of weight, using Lean Duplex can reduce the total cost of your project.
