Super austenitic stainless steels are widely used for the fabrication of a wide variety of welded structures due to their attractive combination of high corrosion resistance and strength. One of the first super austenitic grades, introduced more than twenty years ago, was the 6Mo steel Avesta Sheffield 254 SMO (UNS S31254). This steel has been used successfully in several demanding applications such as offshore and pulp-and-paper industry [Ref.1].

When welding superaustenitic stainless steels, the common practice is to use nickel base fillers overalloyed with molybdenum. The main reason for this is to compensate for the segregation of molybdenum during weld solidification and to decrease the risk of forming intermetallic phases even when the weld metal is diluted to a considerable level from the base material [Ref.2]. For a weld metal with the same composition as the base metal, pitting corrosion initiates at the dendrite cores in oxidising chloride environments. This preferential attack is due to the depletion of chromium and molybdenum. The extent of segregation is less in welds with nickel base fillers and the overalloying with molybdenum ensures the minimum required level to be obtained even at the dendrite cores. The high nickel content in the weld metal helps in avoiding secondary phases to be formed in spite of the high molybdenum level.