Super Duplex
Super Duplex stainless steels have a ‘duplex’ two-phase microstructure consisting of both austenitic and ferritic grains that gives them a combination of attractive properties. Whilst duplex alloys were developed around a 22% Cr addition level, super duplex alloys utilise a higher 25%Cr base composition to increase the level of corrosion resistance achievable.
In general, they are twice as strong as either austenitic or ferritic stainless steels. They achieve good toughness and ductility, somewhere between the two. Their corrosion resistance is also very good, assuming comparable levels of chromium, molybdenum and nitrogen in selected compositions. By increasing the level of chromium additions, combined with significant levels of molybdenum and nitrogen, super duplex stainless steels achieve a Pitting Resistance Equivalent number (PREN) >40, which will match or beat all but the most highly alloyed austenitic stainless steels and often provide comparable performance to some nickel alloys also. One further advantage over austenitic stainless steels is their resistance to stress corrosion cracking.
The addition of copper to these grades results in additional corrosion resistance in use not directly recognised by the formula used to calculate PREN. It has been shown that the presence of copper can inhibit the formation of pitting corrosion, and it also contributes to exceptional resistance to sulphuric acid. Resistance to sulphuric, nitric and phosphoric acid makes these products attractive for a number of applications in the chemical processing industry. Ferralium® has an appreciable higher copper content than other super duplex stainless steels, imparting superior corrosion resistance.
Super duplex stainless steels offer a cost effective option for many demanding applications – as their design foregoes high nickel additions which are expensive and subject to price volatility. If the application can utilise the high strength levels of these grades then components can be designed with smaller sections, using less material. This can benefit as a direct material cost saving, but can also contribute to overall design savings if the application involves suspended loads i.e. marine sensors, down-hole tooling.
| Alloy | Common Name | Related Specifications | Tensile Strength | Proof Test | Elongation | ||
| British | European | United States | N/mm2 (ksi) | N/mm2 (ksi) | (%) | ||
| Ferralium 255 (Pipe & Tube) | Alloy 255 (Super Duplex 255) |
1.4507 |
ASTM A790 ASTM A815 |
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| Ferralium 255 – SD50 | Ferralium 255 – SD50 (Super Duplex 255) |
1.4507 |
ASTM A276/A476 UNS S32550 ASME A182 F61 |
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| Ferralium 255 Welding Wire | BS EN ISO 15614:1 Group 10.1 |
AWS 5.4 E2553-XX W39553 ASME IX: Group P10H |
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| Alloy 32750 | 1.4410 |
ASTM A276/A476 UNS S32750 (Super Duplex 32750) ASME A182 Duplex F53 |
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| Ferralium 255 – 3AF Aged Grade | Alloy 255 |
1.4507 |
ASTM A276 / A476 UNS S32550 ASME A182 F61 |
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| Ferralium 255 – SD50 HS110 | Alloy 255 |
1.4507 |
ASTM A276/A476 UNS S32550 ASME A182 F61 |
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| Alloy 32760 | 1.4501 |
ASTM A276/A476 UNS S32760 (Super Duplex 32760) ASME A182 F55 |
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| Alloy 32760 (Plate) | 1.4501 |
ASTM A276/A476 UNS S32760 (Super Duplex 32760) ASME A182 F55 |
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| Ferralium 255 – 3SC for Castings | Alloy 255 CD3MCuN Grade 1C |
1.4507 |
UNS S32550 (Super Duplex S32550) |
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Ferralium 255 (Pipe & Tube):
Ferralium® 255 is a super duplex stainless steel supplied in the cold finished and annealed condition. As a 25% Chromium alloy, with significant additions of Copper, it offers excellent corrosion resistance in a wide variety of corrosive chemicals including sulphuric, nitric and phosphoric acid. In seawater and other chloride containing environments it also provides outstanding resistance to pitting and crevice corrosion, with Critical Pitting Temperature exceeding 50°C.
Ferralium 255 – SD50:
Ferralium® 255 – SD50 is a super duplex stainless steel supplied in the hot worked and annealed condition. It achieves higher strengths than most other stainless steels and alternative corrosion resistant alloys, offering the potential to reduce section size and therefore weight and cost.
As a 25% Cr alloy, with significant additions of copper, it offers excellent corrosion resistance in a wide variety of corrosive chemicals including sulphuric, nitric and phosphoric acid.
Ferralium 255 Welding Wire:
Ferralium® 255 – SD50 is produced to complement our leading super duplex stainless steel. Careful formulation of the weld wire composition ensures the optimum combination of weld strength and corrosion resistance, achieved by over-alloying the wire with Nickel to maintain the correct (austenite / ferrite) phase balance.
Alloy 32750:
Alloy 32750 is a super duplex stainless steel supplied in the solution annealed condition. As a super duplex stainless steel, it combines the desirable aspects of both austenitic and ferritic grades. The higher chromium, molybdenum and nitrogen contents result in a Pitting Resistance Equivalent number (PREN) of >41, providing pitting and crevice corrosion resistance superior to austenitic and duplex stainless steels in almost all corrosive media, and a Critical Pitting Temperature exceeding 50°C.
Ferralium 255 – 3AF Aged Grade:
Ferralium® 255 – 3AF is a super duplex stainless steel supplied in the hot worked, annealed and aged condition. By subjecting the product to an additional ageing process, it is possible to further increase the tensile strength of the product whilst retaining high levels of ductility. As a variant of our unique Ferralium® 255 – SD50 product, it is a 25% Cr alloy with significant additions of Cu, offering excellent corrosion resistance in a wide variety of corrosive chemicals including sulphuric, nitric and phosphoric acid. In seawater and other chloride containing environments it also provides outstanding resistance to pitting and crevice corrosion, with Critical Pitting Temperature exceeding 50°C.
Ferralium 255 – SD50 HS110:
Ferralium® 255 – SD50 HS110 is a higher strength super duplex stainless steel supplied in the strain hardened condition (Condition S). By precise further processing, it achieves significantly raised yield and tensile strengths whilst still retaining good levels of impact strength. Typically offered in tubular form, the machined bar will serve as coupling material, suitable for subsequent processing to coupling stock, couplings and other tubular goods as outlined in API 5CRA / 5CT. It therefore provides a cost-effective alternative for applications that previously used higher cost alloys. The production route allows smaller quantities to be economically manufactured against competitive lead times.
Alloy 32760:
Alloy 32760 is a super duplex stainless steel supplied in the hot worked and solution annealed condition. As a super duplex stainless steel, it combines the desirable aspects of both austenitic and ferritic grades. The higher chromium, molybdenum and nitrogen contents result in a Pitting Resistance Equivalent number (PREN) of >40, providing pitting and crevice corrosion resistance superior to austenitic and duplex stainless steels in almost all corrosive media, and a Critical Pitting Temperature exceeding 50°C.
Alloy 32760 (Plate):
Alloy 32760 is a super duplex stainless steel supplied in the hot worked and solution annealed condition. As a super duplex stainless steel, it combines the desirable aspects of both austenitic and ferritic grades. The higher chromium, molybdenum and nitrogen contents result in a Pitting Resistance Equivalent number (PREN) of >40, providing pitting and crevice corrosion resistance superior to austenitic and duplex stainless steels in almost all corrosive media, and a Critical Pitting Temperature exceeding 50°C.
Ferralium 255 – 3SC for Castings:
Ferralium® 255 – 3SC is a super duplex stainless steel supplied in cast form. As a 25% Cr alloy, with significant additions of Cu, it offers excellent corrosion resistance in a wide variety of corrosive chemicals including sulphuric, nitric and phosphoric acid.