QPQ（ Quench-Polish-Quench） treatment was carried out on 316 L stainless steel by nitriding at 600 ℃for varied time（ 60

90

120

150 and 180 min）. The microstructure

phase constituent

hardness and wear resistance of modified surface layer of the 316 L stainless steel were investigated by means of optical microscopy

SEM

XRD

micro-hardness testing and wear resistance testing. The results reveal that after QPQ treatment for316 L stainless steel

Fe3O4 oxidized layer is formed on the top of the compound layer

and middle compound layer consists of Fe2

3N、Fe4N、Cr N and α-N

while the diffusion layer is composed of Cr N and γN. The thickness of the compound layers is increased from 16. 54 μm to 34. 94 μm with the increase of nitriding time from 60 min to180 min

and the thickness of the compound layer exhibits parabolic relation with the nitriding time. The microhardness of QPQ treated samples is increased by 4

6 times higher than that of the untreated sample

and the maximum microhardness value of 1 040. 1 HV0. 2can be obtained after nitriding for 150 min. With prolonging nitriding time

the surface hardness is decreased due to the porosity in the surface layer. The wear resistance of316 L stainless steel can be improved significantly by QPQ treatment

and the optimum nitriding duration for improving the wear resistance is 150 min. The worn surface morphology reveals that the un-treated samples are characterized by adhesive wear

so wear rate is the higher.