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It is usually difficult to quantitatively determine the mass fraction of each type of precipitates in steels using transmission electron microscopy and traditional X-ray powder diffraction analysis methods.Traditionally,electrolysis extraction-chemical separation-wet chemical test were combined to quantitatively analyze precipitation phases.By chemical dissolution or selective electrolysis,sometimes,different precipitations could be separated and the mass of individual alloying elements of each precipitation phase could be determined.However,due to some precipitation phases were very similar and firm coalescent,they could not be separated totally by chemical method.Typically,our previous research had demonstrated that σphase was formed on the basis of χ phase in duplex stainless steel,and they were not separated independently but coexisting.In this paper,the Rietveld full-pattern fitting algorithm was employed to calculated the relative mass fractions of the precipitates in duplex stainless steel.The results suggested that the fractions of σphase,χ phase,carbide phase and nitride phase were evaluated precisely and relatively quickly.In addition,it was found that the cubic crystal χ phase was the molybdenum-rich inter-metallic compound phase,which was formed earlier thancrphase.The χ phase was metastable,and its amount gradually decreased with the prolonging of aging time.Furthermore,the σ phase was developed from nothing and then gradually increased.