Study of the sensitisation of a highly alloyed austenitic stainless steel, Alloy 926 (UNS N08926), by means of scanning electrochemical microscopy

The feedback mode of a scanning electrochemical microscope (SECM) was applied to study differences in the reactivity of a highly alloyed austenitic stainless steel, Alloy 926 (UNS N08926), in its unsensitised and sensitised state. Alloy 926 was heated at 825 °C for 1 h in an inert atmosphere in order to produce a sensitised metallurgical condition. Sensitisation was due to chromium carbide formation at the grain boundaries. The oxygen reduction reaction was used as an indicator to monitor the effect of the sensitisation process on the corrosion activity of the Alloy 926 surface in a 35 g l−1 NaCl solution. Higher oxygen consumption was observed above the sensitised sample than above the unsensitised sample due to differences in the oxide films of the two alloy conditions.

► Chromium carbide precipitation leads to differences in the electrochemical behavior of Alloy 926.
► Scanning electrochemical microscopy is used to analyse differences between the unsensitised and the sensitised Alloy 926.
► Sensitisation of Alloy 926 leads to an increase in the measured oxygen reduction rate compared to the unsensitised state.
► The passive film formation changes in Alloy 926 as a consequence of heat treatments.