Super-Duplex Steel & Duplex Steel

Super duplex steel is used regularly at IBS Penstocks. For a good reason: Duplex steels are acid and rust resistant and are used in particular where other stainless steels no longer meet the high requirements.


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Penstock RSG T4 made Super Duplex Steel

The special attributes of Super-Duplex Steel

These special steels consist of a two-phase structure consisting of ferrite and austenite. Due to its high content of chromium and nitrogen, and often also molybdenum, this steel offer good resistance to pitting and uniform corrosion. The duplex micro-structure contributes to their high strength and high resistance to stress corrosion cracking.

As a result, they have a significantly higher strength compared to ordinary chrome-nickel steel and are nevertheless very ductile and deformable during processing. Super Duplex is particularly appreciated for its features:

  • excellent resistance to pitting corrosion, crevice corrosion, stress corrosion cracking, uniform corrosion, erosion corrosion and corrosion fatigue.
  • good fatigue resistance
  • acid-resistant
  • high energy absorption
  • hardly any erosion and abrasion
  • low thermal expansion
  • good weldability
Penstock RPS T8 made of Super Duplex Steel

Penstocks made of Super Duplex Steel

Among other things, we manufacture penstocks or caseless fittings made of the special steels Duplex (1.4462 / EN: X2CrNiMoN22-5-3 / AISI: 318LN) or Super Duplex Steel (1.4410 / EN: X2CrNiMoN25-7-4 / AISI: F53).

With our highly trained workers, our experience and the corresponding machines, IBS Penstocks can process the difficult-to-process materials in the best possible way. IBS Penstocks explicitly qualifies and trains their employees on these duplex and super duplex steels.

Our quality department is especially checking our welding and bending processes to secure our quality standards for our penstocks and stop logs. Please feel free to contact our sales team if you have any questions. Please send us your request for quote and we will send you an offer briefly.

IBS Penstock in action

Fields of application for Super Duplex Steel

Due to the special properties, these steels qualify for countless fields of application. Even those in which the steel is in contact with a variety of materials in an extremely demanding environment. Our penstocks made of Duplex and Super Duplex Steel can be found in:

  • chemical industry
  • petrochemical
  • power plants, especially cooling towers
  • galvanization facilities
  • water treatment plants, especially desalination plants
  • offshore facilities (gas, oil, wind energy)

Fabrication & forming of Super Duplex Steel

Hot forming should be carried out in the temperature range 1200-1000 ° C. It should however, be observed that the strength of the duplex material is low at high temperatures. Hot working should normally be followed by solution annealing.

Due to the high proof strength of duplex material, greater working forces than those required for austenitic steel are usually needed for cold forming of duplex steel. The spring back is relatively high because of the high yield point. Solution annealing is normally recommended after more than 10 % cold deformation.


Characteristic temperatures of Super Duplex Steel

Temperature in °C
Solidification range 1445 - 1385
Scaling temperature in air 1000
Hot forming 1200 - 1000
Solution annealing 1040 - 1120
Stress relief annealing (max 5h) 1040 - 1120
Use in pressure vessels (-10) - 250

Machining Super Duplex Steel

Super Duplex stainless steels, such as EN 1.4410, are generally more difficult to machine than conventional austenitic steels and have different machining properties than those of high-alloy austenitic steels. The main difference is that duplex steels are relatively easier to machine with highspeed tools than with cemented carbide tools compared to austenitic stainless steels with similar alloy content.

Welding Super Duplex Steel

EN 1.4410 has generally a good weldability and can be welded using most of the welding methods used for stainless steels: Due to the balanced composition, the heat affected zone obtains a sufficiently high content of austenite to avoid the risk of localised corrosion. Welding shall be performed without preheating, and cooling between passes to below 150ºC. Filler material ISO 25 9 4 NL or similar shall be used to ensure weld properties comparable to those of the parent metal.

Mechanical properties

Tensile strength Rm 730 - 930 N/mm2
Proof strength Rp0,2   Min 530 N/mm2
Elongation A5 Min 25 %
Impact energy KV20ºC Min 100 J/cm2
Impact energy KV-40ºC Min 40 J/cm2
Hardness Max 290 HB
Machining Super Duplex Steel at IBS Penstocks
Super Duplex Steel has good weldability

Corrosion resistance & different types of corrosion

Uniform corrosion

Uniform corrosion is characterised by a uniform attack on the steel surface that has come into contact with a corrosive medium. The corrosion resistance is generally considered good if the corrosion attack is less than 0,1 mm/year. Due to the high content of chromium and molybdenium the Super Duplex steel EN 1.4410 offers excellent corrosion resistance in many media.

Intercrystalline corrosion

The Super Duplex microstructure and the low carbon content gives EN 1.4410 very good resistance to intercrystalline corrosion. The composition of the steel ensures that austenite is reformed in the heataffected zone after welding. The risk of undesirable precipitation of carbides and nitrides in the grain boundaries is thus minimized.

Stress corrosion cracking

Conventional steels of the 1.4301 and 1.4401 type can be attacked by stress corrosion cracking (SCC) in chloride environments at high temperatures in combination with tensile stress. Due to their continuous ferritic phase, stainless steels of the Duplex type are much less sensitive to this type of corrosion.
EN 1.4410 is also an approved material according to NACE MR0175 “Standard Material Requirements Metals for Sulfide Stress Cracking and Stress Corrosion Cracking Resistance in Sour Oilfield Environments”.

Pitting and crevice corrosion

Resistance to pitting corrosion and crevice corrosion increases with the content of chromium, molybdenum and nitrogen in the steel. This is often illustrated by using the pitting resistance equivalent (PRE) for the material, which can be calculated using the formula: PRE = %Cr + 3.3 x %Mo + 16 x %N or by measuring the critical crevice corrosion temperature (CCT) at which corrosion occurs in a well-defined solution.

Chemical details

EN 1.1440 Typical analysis %
C 0,02
Cr 25
Ni 7
Mo 4
Other N