What is Duplex?
Duplex and Super Duplex Grades of Stainless Steel deal superior rust resistance when 316 grade simply isn't enough.
Duplex Stainless Steel Fasteners (SAF 2205 or UNS S31803) or Super Duplex Stainless Steel Fasteners (SAF 2507 or UNS S32750) are grades of Stainless Steel frequently required in the battle versus rust when 316 grade just isn't enough, such as being constantly submerged in salt-water. A crucial feature of Duplex stainless steel is that its pitting and crevice deterioration resistance is considerably exceptional to that of 304 or 316 grade Stainless Steel.
This integrated with high mechanical strength and ductility makes it an outstanding material for so many applications. Frequently 316 Grade Stainless Steel is described as 'Marine grade' - and yes while it is often used and perfect for marine environments such as attachments on a private yacht's deck, it is by no indicates the most robust alloy for high chloride environments (E.g. salt-water). Where fastener strength and integrity is vital, such as for bolts in a Luxury yacht's Keel, a Duplex or Super Duplex Fastener is needed. Likewise where a Stainless Fastener is submerged in salt-water, Duplex would be the minimum requirement. Duplex and Super Duplex Fasteners are not generally 'off the rack' and stocked by stainless fastener suppliers. They are made to buy and making sure the source is concentrated on Duplex fastener manufacture with a high degree of Quality Control is crucial.
Duplex Production technologies
Duplex fastenersare ideally made with created heads and rolled threads, with the heating in the creating procedure carefully 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 ensure smoother, more powerful threads are gotten as compared to machined/CNC threads - this increases the thread's yield strength, surface area finish, hardness, and wear resistance. When Hot Forging the fastener head, temperature control is important. When heating Duplex you should avoid extended time in the critical temperature level zone as this motivates undesirable Nitrides and Carbides to form. It is very important that digital control devices is utilized to quickly heat through this temperature level zone and instantly eliminate from the heat source when the temperature level is optimum for forging. Any Duplex product need to then go through laser marking to make sure traceability of the fastener through the supply chain. Test Certificates ought to also always be gotten.
Duplex Applications - where would you use Super Duplex over Duplex?
Applications which can benefit from the use of these duplex steels include piping systems, pumps (where the excellent erosion and abrasion resistance is employed), valves, heat exchangers, Keel Bolts, http://www.bullionpipe.com/our-product/alloy-steel-products/ http://www.bbc.co.uk/search?q=steel used with items submerged in salt-water and other devices.
Duplex has excellent general rust resistance; superior to grade 316 in most environments, including resistance to inter-granular, pitting and crevice corrosion. Super Duplex has even greater pitting resistance. In summary - 316 is good, Duplex is great and Incredibly Duplex is well - 'SUPER'! One of the most typical methods to specify resistance to pitting rust is the PRE value, Pitting Resistance Equivalent. The PRE can be computed from the structure as: PRE = %Cr + 3.3 %Mo + 16 %N Clearly grades high in the alloying components Chromium and specifically Molybdenum and nitrogen are more resistant.