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

Abstract

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 σ content after annealing for long times. These results were correlated with the nitrogen content and microstructure of the weld metals. The effect of σ 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.