Duplex stainless steels are based around a composition of 22% chromium, whereas super duplex stainless steels are based around a composition of 25% chromium. By increasing the chromium content, the level of pitting corrosion resistance is also increased. However, in order to retain the favourable balance of austenitic and ferritic microstructures, it is also necessary to increase the content of nickel and other elements, which also increases the cost. Hyper duplex stainless steels are now being developed, based around a composition of 27% and 29% chromium, but as yet are only available in tube form, not bar or plate due to difficulties in forging and rolling them.
If you have any more questions about duplex and super duplex stainless steels, please contact us today.