Electroplastic effect at tension in TRIP steel

The paper presents the results of a study of electroplastic effect in metastable high-alloyed austenitic-martensitic steel in strip form with the thickness of 0.3 mm during plastic deformation with current of different modes and regimes. Choice of the research material is due to manifestation of the TRIP effect in it, caused by martensitic transformation during deformation. The ratio of volume fractions of austenite and martensite in the steel before deformation was 50:50. Deformation behavior of the steel was studied by stress-strain curves and mechanical properties at room temperature in static tension with current by short single pulses of large density, as well as multipulse current with frequency of 1000 Hz and direct current. Microstructure in the initial, before tension, state was investigated by optical and transmission microscopy. It consists of large equiaxed grains of austenite and twinned martensite up to 80 µm in size. Phase composition of the steel before and after tension with and without current was studied by X-ray diffraction. Tensile deformation without current promotes martensitic transformation and increases the volume fraction of martensite from 50 to 82 %. The introduction of single current pulses does not influence the TRIP effect, causes power surges and confirms the occurrence of electroplastic effect. Current mode has a strong influence on manifestation of the TRIP effect, suppressing it at multipulse and direct current and causing a sharp decrease in tensile strength, yield stress, and elongation to failure. Tension with current stabilizes the austenite and reduces content of the formed martensite up to 72 % in multi-pulse mode and up to 50 % when using direct current.