Technical > About Duplex Stainless Steel
About stainless steels: There are four main categories of stainless steel, Ferritic, Martensitic, Austenitic & Duplex. They are distinguished mainly by their grain structure, but also by alloying element composition. All stainless steels rely on Chromium as the main corrosion resisting element, it forms Chromium Oxide on exposure to a corrosive environment. This oxide layer is sealed and tough, preventing further corrosion and repairs itself if damaged. The typical properties of each group are as follows: Ferritic Stainless Steel Ferritic Stainless Steels are typically stronger than regular structural steels, they are magnetic, and contain low quantities of Nickel which makes them generally economic and price stable. The Ferritic Stainless Steels also typically have higher yeild strengths than the Austenitic Stainless Steel, which makes ferritic stainless a good candidate for structural applications |
Austenitic Stainless Steel Austenitic Stainless Steels are typically lower yield strength than regular structural steels, and much lower than ferritic or Duplex stainless steels. They are non-magnetic and have higher quantities of nickel and sometimes molybdenmum which give them generally better corrosion resistance than the ferritic grades. The higher nickel content makes Austenic Steels more price volitile. Martensitic Stainless Steel Martensitic Stainless Steels are typically stronger and tougher than Ferritic or Austenitic, but less corrosion resistant, thanks to higher amounts of carbon. Hardening processes can be applied to Martensitic steels to make then exeptionally tough but these steels generally find little application in the construction industry. Duplex Stainless Steel Rather than being it's own class, Duplex steel is a mix of Austenitic and Ferritic grain structure in the one steel (around 50/50). The result is generally stronger and more corrosion resistant than the austenitic grades. The grain structure and higher amount of chromium give the improved corrosion resistance. |
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What is Duplex Stainless Steel? Duplex (BS EN 10088-1 grade 1.4162) is a duplex stainless steel. It has excellent corrosion resistance due to it's high chromium content and grain structure (better than austenitic grade 304) and is also very strong (yield strength of 480MPa vs 210MPa for grade 304). Isn't Duplex Stainless steel expensive? Duplex stainless steel has historically been more expensive than Austenitic Stainless steel. It has been reserved for more demanding applications such as chemical and offshore industries. However in the last decade or so the price of nickel has risen and become increasingly volitile, causing the price of the high-nickel alloys to fluctuate as well. Because of this, the price of stainless steel is now quoted (per tonne) as a base price plus an additional 'alloying elements' surcharge. The majority of this surcharge is the cost of nickel. Duplex Steel has a higher base price than 304, but it has a lower surcharge and is more price stable. When the price of 304 is low, Duplex is more expensive, but this has proven unusual in recent years. Additionally, because Duplex is so much stronger than grade 304, we can use lighter gauge steel to achieve the same effect, thus ensuring an Duplex lintel is cheaper than a 304 lintel for the same duty! What does Duplex look like? Duplex has a shiny, brushed, directional finish, very similar the background of this website. It appears to have a light 'grain' which is not present in the uniform finish on austenitic stainless such as grade 304. The brushed finish results from the descaling process used in the steel production; the scale is mechanically removed rather than chemically removed as is the case for grade 304. The chemical descaling process would be detrimental to to the high strength of Duplex stainless steels. Most people find the brushed finish of Duplex more attractive than the plain finish of 304. Duplex does not show marks such as fingerprints as easily as 304. Duplex is more corrosion resistant than grade 304 (the construction industry standard), and in some applications better than 316. Contact with contaminants can neverless stain the surface of all stainless steels, so we recommend cleaning stainless steels once they have been installed. |
Where is Duplex Used? Duplex has a established a good track record in other industries, but as far as we know we are the first to introduce Duplex into mainstream residential and commercial construction.
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