Ferralium (UNS S32550, 1.4507, F61) is the original super duplex stainless steel, patented by Langley Alloys in 1967 and launched in 1969. As such it was the very first alloy to be captioned as ‘super duplex’ and based around a 25% chromium content. Compared with latter alternatives, it is the only grade to exceed a minimum yield strength of 85ksi, with an increased copper content for superior pitting corrosion resistance.
Alloy 32760 (UNS S32760, Zeron 100, 1.4501, F55) was developed in the 1980’s by Mather & Platt (UK) around the same 25% chromium basis. However, it contains less copper but a deliberate addition of tungsten instead, claimed to selectively improve corrosion resistance.
The final grade most commonly stocked as solid bar is Alloy 32750 (UNS S32750, 1.4410, F53) which was promoted by Sandvik as SAF2507. It contains neither copper nor tungsten as significant additions.