Suppression of trip effect in metastable steel by electrical current
The present work deals with the problem of a possible application of current in deformation processes. A literature survey has shown an existence of publications on the electroplastic effect in single-phase materials without phase transformations and the lack of works on a study of the current impact on the deformation behavior of materials undergoing a phase transformation. Therefore, the influence of current regimes (density and impulse duration) and current mode (direct, pulse or multiple-pulse) on the deformation behavior of TRIP steel in austenite-martensite and completely martensite states is studied. Methods of mechanical tests, X-ray diffraction analysis and scanning electron microscopy observations of fracture surfaces are used. In the absence of current the steel in austenite- martensite state displays a martensitic transformation during tension that leads to an excellent combination of mechanical properties - high ultimate tensile stress and preservation of the initial ductility. It is shown that in austenite-martensite state the shape of the stress-strain tension curve and the type of flow stress jumps caused by martensitic transformation and electroplastic effect depend on the current mode. Single current pulses exert practically no influence on the mechanical properties and deformation behavior in tension. The multiple-pulse and direct current cause a considerable thermal effect, decrease in the electroplastic effect and a suppression of the TRIP effect. As a result, both the ultimate tensile stress and elongation to failure decrease. The steel in martensite state displays no TRIP effect during tension with current due to the lack of a reverse transformation, and the elongation to failure sharply decreases. According to scanning electron microscopic observations, the failure mode of samples in both states, irrespective of current, corresponds to a mechanism of ductile cleavage or shear.