Langley Alloys for super duplex

Langley Alloys are the original inventor of super duplex stainless steels and have specialised in these attractive, highperformance alloys ever since. We invented the very first super duplex stainless steel, Ferralium 255, in 1967. In addition, we are the distribution partner of Sandvik for duplex and super duplex grades, meaning we hold unrivalled stocks of these alloys.

Super duplex stainless steels benefit from a combined microstructure of austenite and ferrite, which provides an optimum mix of mechanical and physical properties. The term super duplex is typically applied to duplex stainless steels with a chromium content of 25% and a PREN value >40. Pitting Resistance Equivalent Number (PREN) is a quick reference to the corrosion resistance of stainless steels and other corrosion resistant alloys (CRA), which are most likely to be impacted by pitting and crevice corrosion. For Alloy 316L, the PREN is only 25, and for duplex grades it is 34, so the uplift for super duplex stainless steels (SDSS) is significant.

As a very crude ‘rule of thumb’, Alloy 316L can be used successfully in rural, urban and estuary environments, but is limited in more exposed coastal settings; 2205 duplex can be comfortably used in estuary, marine and offshore environments; but for applications with long-term immersion then a super duplex may be necessary.

However, when discussing PREN and corrosion resistance, we are overlooking the other significant benefits of super duplex stainless steels. Firstly, the strength levels are twice those of regular duplex grades, and three to four times those of Alloy 316L. This means that not only can more applications fall within the scope of these alloys, but also end users can exploit this virtue to use less metal, saving cost, reducing component size and decreasing the suspended weight.

All duplex grades resist the effect of stress corrosion cracking, again making them suitable for application in a number of aggressive environments. Their higher strength will contribute to this resistance, but the duplex microstructure of austenite and ferrite grains helps to prevent the propagation of cracks through the alloy.

Finally, for an alloy family with this very favourable combination of physical and mechanical properties, alternative metals are generally more highly-alloyed and significantly more expensive. Super duplex stainless steels benefit from a lower nickel content, reducing their cost and limiting their price volatility.

In addition to Ferralium 255-SD50, we carry the following grades from ˝″ to 16″ diameters.

32750 (F53, SAF2507, 1.4410, UNS S32750)

32760 (F55, 1.4501, UNS S32760, Zeron 100)

2205 (F51, Sanmac 2205, 1.4401)

Tel: 01782 610250

Spring 2020 // Issue 52
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