What is Duplex?
Duplex and Super Duplex Grades of Stainless Steel offer remarkable deterioration resistance when 316 grade just isn't enough.
Duplex Stainless Steel Fasteners (SAF 2205 or UNS https://diigo.com/0jswf3 S31803) or Super Duplex Stainless-steel Fasteners (SAF 2507 or UNS S32750) are grades of Stainless-steel often required in the fight against corrosion when 316 grade just isn't enough, such as being constantly immersed in salt-water. An important feature of Duplex stainless-steel is that its pitting and crevice rust resistance is greatly remarkable to that of 304 or 316 grade Stainless-steel.
This integrated with high mechanical strength and ductility makes it an excellent product for so many applications. Typically 316 Grade Stainless-steel plates is referred to as 'Marine grade' - and yes while it is often used and ideal for marine environments such as attachments on a luxury yacht's deck, it is by no implies the most robust alloy for high chloride environments (E.g. salt-water). Where fastener strength and stability is critical, such as for bolts in a Yacht's Keel, a Duplex or Super Duplex Fastener is required. Also where a Stainless Fastener is immersed in salt-water, Duplex would be the minimum requirement. Duplex and Super Duplex Fasteners are not usually 'off the rack' and equipped by stainless fastener suppliers. They are made to buy and ensuring the source is focused on Duplex fastener manufacture with a high degree of Quality assurance is crucial.
Duplex Production innovations
Duplex fastenersare ideally made with created heads and rolled threads, with the heating in the creating process thoroughly temperature controlled.
Duplex fasteners can be CNC machined from round or hex bar - but preferably they would be made with forged heads and rolled threads. Threads need to be rolled rather than machined to make sure smoother, stronger threads are obtained as compared with machined/CNC threads - this increases the thread's yield strength, surface finish, solidity, and wear resistance. When Hot Forging the fastener head, temperature control is crucial. When heating Duplex you must prevent prolonged time in the critical temperature level zone as this encourages undesirable Nitrides and Carbides to form. It is very important that digital control devices is utilized to rapidly heat up through this temperature zone and instantly remove from the heat source when the temperature level is maximum for creating. Any Duplex product need to then undergo laser marking to make sure traceability of the fastener through the supply chain. Test Certificates need to also constantly be acquired.
Duplex Applications - where would you utilize Super Duplex over Duplex?
Applications which can benefit from the use of these duplex steels include piping systems, pumps (where the good erosion and abrasion resistance is utilized), valves, heat exchangers, Keel Bolts, utilized with products immersed in salt-water and other equipment.
Duplex has outstanding basic rust resistance; exceptional to grade 316 in many environments, including resistance to inter-granular, pitting and crevice corrosion. Super Duplex has even higher pitting resistance. In summary - 316 is great, Duplex is great and Very Duplex is well - 'SUPER'! One of the most common methods to define resistance to pitting rust is the PRE worth, Pitting Resistance Equivalent. The PRE can be computed from the composition as: PRE = %Cr + 3.3 %Mo + 16 %N Clearly grades high in the alloying components Chromium and particularly Molybdenum and nitrogen are more resistant.