To increase the wear resistance of the flat surfaces of the wedge of the DN20 PN160 gate valve made of EOS PH-1 stainless steel powder with a particle size from 20 to 50 μm by selective laser melting (SLM) on the EOSINT M280 machine, we studied the effect of post-processing by ultrasonic burnishing on the ULTRASONIC 20 machine with a tool with a natural diamond tip with a radius of 2 mm, oscillating with a frequency of 35 kHz and moving with a linear speed of 10 m/min under loading conditions with a static force of 400 N. We found that at feed rates of 0.04...0.08 mm/pass the greatest hardening of steel by 11-13 % relative to the initial microhardness of 430 HV0.05 before post-processing occurs at depths from 60 to 300 μm. Increasing the feed rate to 0.12 mm/pass ensures the formation of the maximum hardened zone in a thin surface layer with a microhardness of 489...502 HV 0.05 at a depth of 20 to 100 μm. Further increasing the feed rate to 0.2 mm/pass leads to a significant reduction to 440 HV 0.05 and microhardness instability at depths greater than 100 μm. The minimum value of the roughness parameters occurs at a feed rate of 0.06 mm/pass and is Ra = 57.67 nm. If we increase the feed rate to 0.12 mm/pass, the roughness increases to Ra = 176.44 nm and stabilizes at feed rates of 0.16 and 0.2 mm/pass. We plotted the Abbott-Firestone curves and histograms of the distribution of the wedge surface microprofile heights after post-processing at the investigated tool feed rates.