Microstructural and local electrochemical characterisation of Gr. 91 steel welded joints as function of post-weld heat treatments

Welded gr. 91 steel is widely used for structural components in the energy production field, where it suffers from selective corrosion near welded joints. In this work, Gr. 91 plates were welded using a gas tungsten arc welding technique and subjected to two different post-welding heat treatments (tempering or normalising plus tempering). Localised corrosion measurements performed with a microcell, coupled with microstructural characterisations, showed that corrosion was very active in the heat-affected zone (HAZ) in the as-welded condition and was worsened by the tempering treatment. In contrast, after a normalising treatment, the electrochemical behaviour of the welded joint was uniform.