The effect of long heat treatments on the structure and degree of sensitization of the DAZ in an austenitic stainless steel weld joint were studied. In the literature review sensitization as a phenomenon and the various metallurgical factors that affect sensitization are presented. Sensitisation that occurs at temperatures well below the normal sensitization range, the so called low temperature sensitization (LTS), is described and the various variables affecting the susceptibility to LTS are considered. Transmission electron microscopy revealed that M23C6 carbides precipitate on grain boundaries in the EJA7. After welding the carbides are small and the degree of sensitization is low, but aging at temperatures below the precipitation range caused the growth of previously nucleated carbides. At the same time the degree of sensitization increased considerably. The degree of sensitization was evaluated with various intergranular corrosion tests. The electrochemical EPR-test proved to be suitable for measuring small changes in the degree of sensitization.