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.