In situ evaluation of sensitization in the heat affected zone of supermartensitic stainless steel welded with superduplex filler metal

Supermartensitic stainless steels (SMSS) are high strength corrosion resistant alloys used in oil and gas production in deep water. Failures related to sensitization and excessive hardness in the heat affected zone (HAZ) are prone to happen in harsh environments, such as those found in oil production. To avoid dangerous types of failure, post weld heat treatments (PWHT) are necessary. Temperature and duration of PWHTs are fundamental parameters to be adjusted. In the present work, a minicell was developed to perform DL-EPR tests in different regions of a multipass welded joint of SMSS with superduplex stainless steel as filler metal. The welded joint was submitted to PWHT at 650 C-degrees for 5 and 15 min. The effects of these short duration PWHT on the HAZ and base metal were analyzed using a minicell for double loop electrochemical tests (DL-EPR), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The results indicate that both PWHTs (5 and 15 min) caused the increase in the degree of sensitization of HAZ without the reduction of hardness to acceptable values.