Orientation (EBSD) and transmission electron microscopy have been used to study the structure and orientation relationships of α' and γ-phases in medium-carbon steels during rotational friction welding. It is shown that, as a result of phase recrystallization, martensite with interlayers of the γ phase is formed in the structure of the welded joint. The formation of secondary (reverted) austenite was established by the form of the spectrum of angular deviations of interfacial boundaries. It is shown that, in this case, an orientation relation close to the Bein one is realized between the crystals of the α and γ phases.