The paper highlights a number of problems, which can explain a mechanism of the effect of hydrogen on the physicochemical and mechanical properties of solids. Among them, the most important is identification of the impact of various forms of hydrogen on such processes as elastic and plastic deformations and various types of brittle fracture. In nature, the hydrogen can exist in the molecular, atomic, and ionic states. In connection with the various forms of state of hydrogen, diverse phenomena of its interaction with the deformable metal take place. Typically, changes in the processes of deformation and fracture of iron alloys are attributed to the interaction of the metal with hydrogen, which is in the ionic or atomic states, while the hydrogen in a molecular state does not affect these processes. As noted, the study of the phenomena occurring in the interaction of hydrogen and its active forms with deformable metal is of interest not only in connection with metal machining, but also for the use of this interaction in order to achieve the desired positive results in the protection of structural metals against the negative sequences of these processes. The results of investigation of the microstructure of titanium surface after its machining in hydrogen atmosphere and in the air, and the proof of the plasticization effect of hydrogen in titanium machining are presented. As shown, the hydrogen does not substantially change elastic deformation, but facilitates the plastic deformation.