Following the development of duplex stainless steels, their initial specification was captured as UNS S31803. However, a number of the leading manufacturers were consistently producing this grade to the upper end of the allowable specification. This reflected their desire to maximise the corrosion performance of the alloy, aided by the development of the AOD steelmaking process that allowed tighter control of composition. In addition, it also allowed the level of nitrogen additions to be influenced, rather than just present as a background element. Therefore, the highest performing duplex grade sought to maximise the levels of chromium (Cr), molybdenum (Mo) and nitrogen (N). The difference between a duplex alloy whose composition meets the bottom of the specification, versus one that hits the top of the specification can be several points based upon the formula PREN = %Cr + 3.3 %Mo + 16 % N.
In order to differentiate the duplex stainless steel produced at the top end of the composition range, a further specification was introduced, namely UNS S32205. Duplex stainless steel made to the S32205 (F60) caption will fully meet the S31803 (F51) caption, whereas the reverse is not true. Therefore S32205 can be dual-certified as S31803.
Philips Metal stock a comprehensive range of duplex stainless steel as the preferred distribution partner of Sandvik. We stock S32205 in sizes from 5/8″ up to 18″ diameter in round bar, with most of our stock being in the Sanmac® 2205 grade, which adds ‘enhanced machinability as standard’ to the other properties. In addition, we also stock a range of S32205 hollow bar from our Mumbai Maharashtra.
How is Duplex Stainless Steel better than other Stainless Steel?
- Duplex steels offer stronger strength in addition to better corrosion resistance when compared to 300 series stainless steels.
- Type 304 stainless steel, for example, has a 0.2 percent proof strength of about 280 N/mm2 whereas a 22 percent Cr duplex stainless steel has a baseline 0.2 percent proof strength of around 450 N/mm2, and a super duplex quality has a minimal of 550 N/mm2.
- Minimum yield stress values are almost two times higher as in austenitic stainless steel.
- Because duplex grades permit for smaller sections, they are appealing when mechanical qualities at room temperature are needed.
What are the various grades of Duplex Stainless Steel?
Duplex stainless steels are often classified into three categories based on their resistance to pitting corrosion, as measured by the pitting resistance equivalent number, PREN = percent Cr + 3.3 percent Mo + 16 percent N.
Standard Duplex (PREN range: 28–38)
Normally, EN 1.4462 is the grade (also called 2205). It is characteristic of mid-range houses and is maybe the most often used nowadays.
The super-duplex (PREN range: 38-45)
Usually, grades EN 1.4410 and up to so-called hyper duplex grades (PREN: >45) were created subsequently to fulfill special needs of the oil and gas sectors, as well as the chemical industries. They have better corrosion resistance and strength, but they are more difficult to process because greater levels of Cr, Ni, Mo, N, and even W stimulate the production of intermetallic phases, which reduces the steel's impact resistance significantly. Faulty processing will lead to poor performance, hence consumers should only work with recognized suppliers/processors. Deepwater offshore oil production is one of the applications.
Grades for lean duplexes (PREN range: 22–27)
Grade EN 1.4362, for example, has recently been designed for less demanding applications, notably in the building and construction sector. Their corrosion resistance is comparable to that of normal austenitic grade EN 1.4401 (with a little advantage in stress corrosion cracking resistance), and their mechanical qualities are superior. When strength is crucial, this may be a huge benefit. This grade can be utilized for bridges, pressure vessels, and tie bars.
UNS S32205
UNS S32205 is ferritic-austenitic duplex steel having a ferritic-austenitic microstructure. In the annealed state, the alloy contains around 40-50 percent ferrite.
The duplex microstructure combines the toughness of ferritic grades with the corrosion resistance of austenitic grades. It is not unusual to see the metal employed as a realistic answer to the Achilles’ heel of stainless steel, chloride-induced stress cracking.
When compared to 317L stainless steel, UNS S32205 offers better resistance to chloride pitting and crevice corrosion. The alloy has excellent corrosion resistance to saltwater and most sulfuric acid concentrations. UNS S32205 duplex stainless steel is also resistant to sulfide stress corrosion cracking (sour-gas environments). The large concentrations of chromium, nitrogen, and molybdenum contained in UNS S32205 are largely ascribed to its excellent composition and hence efficiency.
UNS 31803
UNS S31803 is a duplex stainless steel grade with a 50:50 austenite, ferrite microstructure. The material incorporates strong mechanical strength and ductility with moderate to good corrosion resistance in a variety of settings.
This Duplex Steel UNS S31803 material is typically supplied in the annealed form. The yield strength of the material in an annealed state is roughly 450 Mpa.
The A276 S31803 Material alloy may be used effectively as a substitute to austenitic stainless steels of the 300 series. In fact, it may be utilized as a replacement in practically any application requiring great mechanical strength and low weight.
S31803 vs. S32205: Which is better?
UNS S31803 and S32205 are alloyed with more similarities than differences. For starters, they are both stainless steel with comparable elemental compositions. UNS S31803 and S32205 are both members of the duplex 2205 family, which implies they are approximately equally composed of austenite and ferrite. Second, they are both very strong and long-lasting alloys. S31803 and S32205 are both used in some of the most difficult and inhospitable manufacturing processes that need materials that can withstand repeated and continuous rides through the wringer.
The most visible difference between the two is that UNS S32205 has a larger nitrogen concentration, which adds another layer of protection to an already firm surface. The presence of treated nitrogen provides an extra layer of protection against any corrosive substances attempting to attack and eat away at the steel solution. This improved corrosion resistance offers UNS S32205 a minor but considerable advantage over its nearest competitor.
Thanks for sharing such a great article and looking forward to more articles in the future. You can visit: ASTM A240 UNS S31803 coil
ReplyDelete