| This study was to investigate the effect of alloying elements i.e, nitrogen and copper on the low temperature tensile and impact properties of duplex stainless steels. Four kinds of specimens, which are the 0wt.%N, 0.13wt.% N, 0.17wt.%N and 0.19wt.%N+1.5wt.%Cu additions to the base composition of 22wt.%Cr-5.5wt.%Ni-3wt.%Mo duplex stainless steel, were prepared. From the room temperature tensile testing, it was found that the tensile strength and elongation increased with increasing the volume fraction of austenite. Tensile strengths increased with the addition of N and Cu, while for the specimen of Cu addition, the lowest elongation was shown with increasing the volume fraction of austenite. Low temperature tensile tests showed the increase in tensile strength with the addition of N and Cu. Elongation decreased after showing the maximum peak value at -50℃ and -100℃ for the nitrogen free and 0.13wt.%N alloyed specimens, respectively. On the other hand, the elongation increased continuously with decreasing the test temperature for the specimens containing 0.17wt.%N alloyed and Cu alloyed specimen. From the observation of ferrite and austenite phase after tensile deformation, the dislocations in the ferrite region were entangled leaving a relatively dislocation free region, while the extensive stacking fault and deformation twining created α` martensite in the austenite region. The volume fraction of transformed α` martensite increased with decreasing testing temperature. The N and Cu alloyed specimens appeared to decrease the volume fraction of α` martensite with decreasing the test temperature. The maximum elongation peak could be obtained when the volume fraction of α` martensite was higher than 88%. |
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