The pitting corrosion resistance of three types of lean duplex stainless steels (grades UNS S32003, UNS S32101 & UNS S32304) along with duplex stainless steel grades (UNS S31803 & UNS S32550) and super duplex stainless steel (grades UNS S32750 & UNS S32760) were investigated using the potentiodynamic polarisation technique. Results are discussed based on data generated in an autoclave for wide range of chloride concentrations (15-22,000 ppm) and
temperatures (600C-1700C) in 8ppm dissolved oxygen. Super duplex stainless steel (SDSS) showed superior pitting resistance in all the conditions tested and demonstrated the highest pitting potentials (EP). But among all the lean duplex stainless steel (LDSS) grades tested, UNS S32003 with higher pitting resistance equivalent number (PREN) value has shown high resistance to pitting than corresponding LDSS (UNS S32304 & UNS S32101) for the conditions tested. A full scale evaluation of corrosion mechanisms was performed using Electron Back Scattered Diffraction (EBSD) techniques to characterise the damage initiation processes and the behaviour of austenite and ferrite phases in corrosive conditions. It is observed that the ferrite phase is preferentially attacked in LDSS. But in case of DSS the
austenite phase is selectively attacked, whereas in SDSS both austenite and ferrite phases are attacked.
Keywords: Lean duplex, duplex, super duplex stainless steel, chloride concentration, PREN,