The theoretical analysis of dislocation-structures’ changes is carried out, and regularities of their formation in 20 metals and alloys (Mo, Fe, Fe–Si, Cu, Ni, Ti, V, Nb and others) with different types of a crystalline lattice and different quantities of a stacking-fault energy are studied experimentally. For obtaining the express information about boundaries (on a strain scale) of presence of different structure states, the justification of replotting the stress–strain curves in S–e$^{n}$ (true stress–true strain in a degree $n$) co-ordinates is made. An influence of the strain on separate parameters of deformation strengthening is considered. The TDT (true strain–temperature) diagrams for metals and alloys are plotted; each TDT diagram represents a set of the temperature dependences of critical strains of the structure-state change during a plastic deformation from the initial stages down to the fracture within the temperature interval prior right up to the beginning of dynamical recrystallization. The TDT diagrams allow directly to determine concrete regimes of thermomechanical treatment of metals, which can ensure desired values of the mechanical characteristics and, at the same time, to identify mechanisms of a plastic deformation within the given intervals of temperature, strain, and structure state.