In this research the effect of deep cryogenic treatment on tribological behavior of 1.7147 steel was investigated. At first, the samples were carburized for 6 hr at 920 ?C. Austenitizing were done at 930 ?C for 1 hour and the samples were quenched in oil. To finde the effect of deep cryogenic treatment time, the samples were submerged in liquid nitrogen for 1, 24, 30 and 48 hours and then heated to room temperature; then they tempered at 200 ?C for 2 hours. After surface preparation the wear test was carried out at force of 80 and 110 N. The hardness before and after of tempering were measured in 30 Kg force. The worn surfaces were cleaned by acetone and studied by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Derbies also were studied by Energy Dispersive Spectrometry (EDS). For phase characterization the Xpert software was used. The XRD patterns show that the amount of retained austenite is reduced by deep cryogenic treatment and by more holding time, no picks were observed. The SEM and optical microscopy images show that the amount of carbides is increased and their distribution became homogenous. The percent of hardness increment is 4 – 33% by deep cryogenic treatment and up to 24 hours holding time in liquid nitrogen, wear resistance increases to 191.39%. By more holding time, the wear resistance decreases; the cause of hardness increment is retained austenite – martensite transformation. Also the cause of wear resistance decrement is carbides growth and nonhomogeneous distribution in matrix and weakening it. So 24 hours deep cryogenic treatment is the best time duration for 1.7147 steel. Keywords: Cryogenic Treatment, Retained austenite, Carbide, Wear resistance, Hardness
