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

Duplex stainless steels were gas tungsten are welded without filler materia l in various Ar-N-2 mixed gas atmospheres. Weld metals having different nit rogen contents were annealed at 900-1300 K to examine the single effect of nitrogen on the sigma transformation. Nitrogen content of the weld metal di d not influence the nose temperature and the time for sigma initiation in t ime-temperature-precipitation diagrams for sigma, but did decrease the sigm a content after annealing for long times. These results were correlated wit h the nitrogen content and microstructure of the weld metals. The effect of sigma on the fracture toughness of the weld metal was evaluated by the sma ll punch (SP) test. A small amount of sigma in the weld metal led to a mark ed decrease in the SP energy.