SAF2906duplex stainless steel was nitrided at 610 ℃for 60

90

120

150 and 180min

respectively

then followed by the same post-oxidation process with heating temperature at 400℃for 30 min.The microstructure and wear resistance of the treated samples were investigated by means of OM（optical microscope）

SEM（scanning electron microscopy）

XRD（X-ray diffraction）

microhardness test and wear resistance test.Microstructure observation indicates that the surface layer of the samples after QPQ treatment is composed of oxide layer

compound layer and diffusion layer from the surface to the center.The oxide layer is composed of Fe3O4.The main phase of the nitrided layer

such as compound layer and diffusion layer

consists of CrN

α-N

Fe2-3N and Sphase.With nitriding time increase

the growth rate of the compound layer is gradually slowed down

and the loose microstructure exhibits more serious.Porosity of the surface layer is increased with the extension of time

and its relative density is declined.The surface hardness of QPQ treated samples is 3times more than the substrate

which is first increased and then decreased with increasing in nitriding temperature

and the optimum hardness is1164HV0.2at 120 min.The dry sliding results show that the wear resistance of QPQ treated samples reaches at least 20 times than that of the substrate

and the desirable wear resistance is presented at 120 min.The worn surface morphology observation reveals that the abrasion form of the substrate belongs to plough cutting

while the abrasion form of QPQ treated samples belongs to micro-cutting.