Effect of high-temperature thermomechanical treatment on the microstructure, mechanical properties and fracture features of ferritic-martensitic steel Ep-823

The effect of high-temperature thermomechanical treatment (HTMT) with plastic deformation in the austenitic region on the microstructure and mechanical properties under the conditions of tensile tests at temperatures (-70 ¸ -40 °C), 20 °C, (650-720 °C) and fracture features of 12% chromium ferritic - martensitic steel EP-823 were investigated. It is shown that HTMT leads to the formation of a heterophase microstructure with a high dispersion of nanoscale particles of the MX type ((V, Nb, Mo) (C, N)) and an increased dislocation density. These features of the microstructure provide an increase in mechanical properties relative to traditional heat treatment in the studied temperature range. At low temperatures (-70 ¸ -40 °C) the yield strength increases by ≈ 100-200 MPa, at elevated temperatures (650-720 °C) the changes are insignificant (up to 14 MPa). The values of the relative elongation of steel after HTMT at low temperatures are in the range of 12.7-14.3%. In the studied temperature range,fracture occurs with the formation of a neck. At elevated temperatures, a viscous cup fracture is observed; at room temperature in addition to the viscous fracture, elements of brittle fracture and microcracks are observed. At low temperatures, the proportionof brittle fracture in fractures increases significantly, and the size and number of microcracks increase.

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