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This paper studies the influence of mechanical tensile loads in the range of 0–300 MPa on the nature of γ → α transformation in cold-rolled maraging steel in the temperature range of –20...–60°С. Based on the kinetic curves of the electrical resistance, critical temperatures Mbeg and Mend were determined and the diagrams of the isothermal decomposition of supercooled retained austenite annealed in the two-phase region after two cycles at a temperature of 650°C for 6 h were plotted. It has been established that mechanical loads in the range of 20–300 MPa affect the parameters of the gamma-alpha transformation ambiguously, shifting the isothermal diagrams in temperature and time and significantly changing the stability characteristics of austenite. Resistance of austenite to supercooling Ts varies from –25 to –55°С, incubation period τinc from 2 to 8 min, and decay period τdec with two extremes (50 and 100 MPa) from 51 to 518 min depending on the load level. The recorded maximum duration of the annealing austenite decomposition at low loads (20–100 MPa) is explained by the structural and chemical inhomogeneity of the phases, as well as the stress level of the initial state of the samples under study. The threshold stress is determined, loading up to which leads to a decrease by ∼15°С in the beginning of the γ → α transformation in the interval of subzero temperatures (from –40° to –55°C). It can be assumed that the shift of the diagrams to the range of low temperatures is due to a change in the mechanism of the γ → α transformation. It is shown that cyclic heat treatment in the two-phase region at a temperature of 650°C for 6 h at loads up to 100 MPa delays the isothermal decomposition of supercooled retained austenite in the steel under study. [ABSTRACT FROM AUTHOR]

In this paper, the γ → α transformation kinetics in cold-rolled maraging steel is studied in the temperature range of 0...–100°C. Based on electrical-resistivity kinetic curves R = f(τ), critical temperatures Mbegin and Mend have been determined and isothermal transformation diagrams have been constructed for overcooled retained austenite formed during annealing and quenching with preliminary annealing. It is shown that the martensitic γ → α transformation of retained austenite formed during annealing in the two-phase (α + γ) region at the temperature of 500°C during 50 h, which is close to the critical temperature Abegin, takes place in the temperature range of –8...–16°C; the temperature of the minimal stability (the "nose" of the C-curve) is –12°C, at which the incubation period is 4 min and the transformation period is 11 min. The martensitic γ → α transformation of retained austenite formed during quenching with preliminary annealing takes place in the temperature range of –86...–96°C. In this case, the incubation period increases by more than a factor of 10 and the transformation period increases by more than a factor of 8. The maximal shift of the diagrams to the side of low temperatures is ~80°C and is not associated with the preliminary annealing influence since the stability characteristics of retained austenite of quenching with preliminary annealing and without it are similar. The shift of the diagrams to the side of low temperatures is due to the processes occurring at heating for quenching, and according to the resistometry results, preliminary annealing does not influence the above processes. [ABSTRACT FROM AUTHOR]