Automotive exhaust systems must meet increasingly stringent lifetime requirements, and thus the incorporation of stainless steels (primarily ferritic) has increased. One of the failure mechanisms that is rarely encountered, but does occur, is intergranular corrosion. Intergranular corrosion of ferritic stainless steels is believed to occur via a similar mechanism as is observed in austenitic stainless, namely precipitation of chromium-carbonitride (Cr-C/N) particles at the grain boundaries leading to Cr-depleted regions. In the present study, the effect of thermal history (including heat treatment, welding and post- weld heat treatment) and alloy chemistry on the level of sensitization of Type 409SS were examined. Keywords: intergranular corrosion, ferritic stainless steel, stabilization, welding, heat treatment