Abstract <p>The aim of the work is to study the distribution of oxygen in the contact layer of C45 steel during pin-on-ring dry friction against St3 steel under high-density electric current (&gt;100 A/cm²). The formation of a transfer layer on the contact surface of the counterbody and the formation of a melt on the contact surface of the transfer layer were shown by the electron microscopy method. The melt has weak signs of adhesive interaction, which is an indicator of high melt viscosity. X-ray spectral microanalysis of the contact surface of the transfer layer showed an oxygen content of 30 at %, which serves as an indicator of FeO formation. The oxygen corresponds to a concentration of about 60 vol % FeO. The oxygen concentration in the cross-section of the transfer layer at a distance of 3 μm from the contact surface was about 10 at % that corresponds to about 20 vol % FeO. The X-ray phase analysis method established the predominance of FeO and α-Fe in the contact surface of the transfer layer of C45 steel, i.e., about 90 vol % FeO. These data indirectly prove the existence of a FeO concentration gradient directed into the depth of the transfer layer and allow us to state that the melt consists of neutral atoms or ions of iron and oxygen. An increase in the current density in the contact leads to an increase in the electrical conductivity of the contact and to a decrease in the friction coefficient. This allows us to assume an increase in the amount of melt in the contact space with an increase in the current density. An increase in the current density also leads to an increase in the sliding stage (“slip”) during sliding in the stick–slip mode and to a decrease in the friction coefficient. The obtained data can serve as a guideline in the design of current-collecting friction units for powerful electric motors and generators.</p>