What grade is super duplex?

Super duplex stainless steels are grades that have a combination of austenitic and ferritic microstructures, based upon a chromium content of 25%. There have been a large number of grades developed over the last 50 years that meet this basic classification. However, the most popular ones are described below.

ASTM A182 F51 equates to UNS S31803 or DIN 1.4462. This was the original caption for a 22% Cr duplex stainless steel. However, manufacturers optimised the composition towards the top end of the limits to improve pitting corrosion resistance. This grade, with a tighter specification, is captioned as F60, equating to UNS S32205. Consequently, S32205 can be dual-certified as S31803 but not vice-versa. It accounts for around 80% of overall duplex stainless steel production. Langley Alloys stocks S32205 from 5/8” (15.87mm) up to 450mm diameter solid bars, plus plate up to 3” (76.2mm) thick, pipes in scheduled sizes, hollow bars, flanges and fittings.

ASTM A182 F53 equates to UNS S32750 or DIN 1.4410. This is the 25% Cr super duplex stainless steel originally developed by Sandvik (now Alleima) and marketed as SAF2507. With an increased chromium content compared with F51 it offers improved pitting corrosion resistance.  The yield strength is also higher, allowing component designers to reduce section size for load-bearing applications. Langley Alloys stocks S32750 solid bars in sizes from 5/8” to 20” (15.87-508mm) diameter, plate up to 3” (76.2mm) thick, plus pipes in scheduled sizes, fittings and flanges.

ASTM A182 F55 equates to UNS S32760 or DIN 1.4501. The origins of this grade can be traced back to the development of Zeron 100 by Platt & Mather, Manchester UK. It is another super duplex stainless steel based upon a 25% Cr composition, but with an addition of tungsten. Langley Alloys stocks S32760 solid bars in sizes from 5/8” to 20” (15.87-508mm) diameter, plate up to 3” (76.2mm) thick, plus pipes in scheduled sizes, fittings and flanges.

ASTM A182 F61 equates to UNS S32550 or DIN 1.4507. This is an approximation of Ferralium 255, the original super duplex stainless steel invented by Langley Alloys. Launched in 1969, it has now provided more than 50 years of successful service in a wide range of demanding applications. Compared with F53 and F55 it delivers increased strength and corrosion performance. Its minimum yield strength exceeds 85ksi, whereas other grades are limited to 80ksi. In addition, it contains up to 2.0% of copper, which aids in pitting corrosion resistance. Langley Alloys stocks Ferralium 255-SD50 in sizes from 5/8” to 14” (15.87-355.6mm) diameter solid bar, plus plates up to 3” (76.2mm) thickness plus pipes, flanges and fittings.


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