Pitting potentials (Ep) of super duplex stainless steel (SDSS) grade (UNS S32760) were determined
using potentiodynamic polarization methods. The effect of chloride concentration on Ep was determined
at 130oC in an autoclave at various chloride ppm levels (15, 100, 1000, 10000) for UNS S32760. This
study also focussed on investigating the stress corrosion cracking (SCC) behaviour at + 200 mV from
the measured pitting potential (EP), using slow strain rate testing (SSRT) methods in 15 & 1000 ppm
chloride level for UNS S32760. Results show that below EP isolated small cracks initiate, around EP
small cracks start to coalesce and above EP, the attack was very rapid and appeared to be galvanic/pitting
in both phases. Slow strain rate tests indicate that applied potential (EAPP), and EP play a major role in
the failure process. Electron Back Scattered Diffraction (EBSD) and Scanning Electron Microscopy
(SEM) has shown that below Ep, SCC is associated with short cracks and selective phase attack and
above Ep pits tend to link with cracks. It was also revealed that grain size distribution of both ferrite and
austenite phases in SDSS played an important role in the final failure process. The phase morphology
and the balance of the two phases was also found to be of significance with continuous single phase
paths sometimes created along the rolling direction providing active corrosion pit paths.
Keywords: stress corrosion cracking, pitting potential, super duplex stainless steel, chloride solution