A phenomenological concept of austenite strengthening due to both the formation of e martensite on cooling and the development of the γ → ε → α′ deformation-induced transformation in low-carbon 05G20-type manganese steels was considered on the basis of literature and experimental data. The dependences of σ0.2 and hardness of these steels on the ε-martensite content before tests were obtained and the effect of the structural evolution of austenite and ε martensite during tensile tests on mechanical properties was considered.