Abstract
The mechanism of sensitisation to intergranular corrosion in type 409L stainless steel has been investigated using both chemical etching and electrochemical potentiokinetic reacti vation tests. Specimens of a commercial type 409L stainless steel were heated at 1300°C for 1 h before subsequent sensitisation heat treatment. It was found that the time–temperature–sensitisation diagram for these annealed alloys is represented by a two step, C shaped curve. Precipitates at the grain boundaries of specimens that had been severely sensitised at 1100°C were identified as titanium compounds by analysis using energy dispersive X-ray spectroscopy. It is suggested that the sensitisation behaviour of type 409L stainless steel is influenced by microgalvanic corrosion due to the presence of concentrated Ti(C, N) precipitates in the grain boundaries, as well as by chromium depletion. Sensitisation in the lower range of temperatures is related to the precipitation of chromium carbonitrides in the grain boundaries of non-stabilised stainless steel, while in the upper temperature range it is related to the precipitation of titanium carbonitrides.
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