Duplex stainless steel
Duplex stainless steel sheets and plates
The often so-called two-phase stainless steels, also known as duplex stainless steel grades (Latin for "double"), have become in recent years an indispensable material for industry, mechanical engineering and other areas where high demands are placed on the chemical and mechanical properties of the materials, such as corrosion resistance and tensile strength.
Certain proportions of chromium, nickel, molybdenum and vanadium are added to duplex inox in order to achieve the above-mentioned and also other properties or, for example, to facilitate metal formability and the welding process.
Since duplex stainless steel sheets and plates (standard, 2205, super duplex, etc.) offer extremely interesting application possibilities for numerous mirrorINOX customers, we would like to go into more detail on this stainless steel grade here.
What is duplex stainless steel?
Duplex stainless steel is called so because it consists of two phases: an austenite phase and a ferrite phase (ideally about half ferrite and half austenite). The chemical composition of this high-tech steel contains:
- Chromium (up to 25%)
In this type of inox, the chromium and nickel proportions are providing for their high corrosion resistance. This can be further increased by adding molybdenum, which significantly improves the resistance of the material to pitting corrosion. Alloying with nitrogen also helps, as it additionally reduces the metal’s susceptibility to crevice corrosion and increases the material strength.
There are different types of duplex stainless alloys, which all have their properties and benefits according to their application.
The "Standard Duplex" is widely used. It is called stainless steel 1.4462, and is also known as:
Namely stainless steel 1.4162, and also known as S32101, "Lean Duplex" is also used as a slightly cheaper stainless steel grade.
"Super Duplex" stainless steel grades are another option. They are characterised by even better corrosion resistance and very high strength. The most common grade in this group is probably 1.4410, also known as 2507 or S31750.
The following materials also belong to the super duplex grades:
They are suitable for the most demanding applications, such as facilities for seawater desalination or chemical containers and tankers, and offer increased resistance to acids, alkalis and other chemicals.
Compared to Standard Duplex, the Super Duplex grades contain a higher percentage of chromium (approx. 25 %), nickel (up to 8 %) and molybdenum (up to 4 %).
Properties: what makes duplex stainless steel special?
Duplex stainless steel sheets have a number of outstanding technical properties, among them:
- Increased corrosion resistance against crevice, pitting and
stress corrosion cracking
- In terms of energy absorption: high resistance to erosion and abrasion over a wide temperature range
- Unique strength, surpassing that value of other chromium-nickel stainless steels: this is a very important parameter as it reduces raw material consumption compared to similar inox grades
- Combined properties of ferritic and austenitic steels, which by their very nature have high mechanical strength and excellent toughness
- Excellent impact strength properties
- Cost-effective compared to other stainless steel grades
- Easy processing
- Higher formability compared to other chromium-nickel steels
- Excellent weldability, also possible on larger cross sections
- Low thermal expansion
- Can be used in temperatures up to 300°C
Advantages of this inox grade
The above-mentioned properties of duplex make it a versatile material for a wide range of industrial applications.
Due to its unique chemical and physical properties, duplex is also used in:
- Heat exchangers
- Pressure vessels
- The chemical industry, for transporting and storing chemicals
- The manufacture of a wide range of equipment
Duplex stainless steel plates can also be used for high quality architectural applications where the material properties play an important role, e. g. for façades in aggressive sea and desert environments or in high-density urban environments.
It is a perfect material for industrial construction where extremely high demands are placed on the surface, such as Ra values in tank and container construction, etc.
However, duplex stainless steel must be professionally and properly processed, as it usually presents rather unattractive mill surfaces, such as 2E, which cannot be used for this purpose without further processing due to their extreme mattness, roughness and grit or possible further optical limitations.
This is where the versatile treatment processes by mirrorINOX come into play, making optically high-quality, visually appealing duplex stainless steel grades possible.
mirrorINOX: your partner for high-quality duplex stainless steel sheets
mirrorINOX offers a wide range of surface treatments such as polishing and grit-polishing, coating and even mirror polishing on the base of duplex stainless steel.
Thus, with its extensive know-how and many years of experience, mirrorINOX manages to transform duplex stainless steel plates from an "ugly duckling" due to their very unattractive mill surfaces into a "beautiful swan" of, for instance, Super Mirror No. 8 or other high-quality finishes.
Of course, we don’t only offer a variety of surfaces on the basis of Duplex alloy, but also of more common steel grades, such as 304 stainless steel sheets (1.4301 or V2A) and 316 stianless steel sheets (1.4404 / V4A).
We would be happy to advise you and work together to find the ideal stainless steel material for your needs or project!