Effect of nitrogen on σ transformation in duplex stainless steel weld metal

Duplex stainless steels were gas tungsten arc welded without filler material in various Ar-N₂ mixed gas atmospheres. Weld metals having different nitrogen contents were annealed at 900-1300 K to examine the single effect of nitrogen on the σ transformation. Nitrogen content of the weld metal did not influence the nose temperature and the time for σ initiation in time-temperature-precipitation diagrams for σ, but did decrease the a content after annealing for long times. These results were correlated with the nitrogen content and microstructure of the weld metals. The effect of a on the fracture toughness of the weld metal was evaluated by the small punch (SP) test. A small amount of σ in the weld metal led to a marked decrease in the SP energy.