Passing one electric-current pulse through deformed pearlitic steel wires at room temperature causes the formation of cementite particles around 30 nm in size. This is found not only in some particular locations but throughout the cementite area, which reveals a different mechanism from traditional spheroidization of cementite plates because the latter leads to the formation of particles with much large size. Transmission electron microscopy images show electropulse-induced strain relief and formation of fine precipitations. Differential scanning calorimetry analysis demonstrates the additional stored free energy by electropulsing treatment. The raised free energy accounts the increased interface area in finer microstructure of materials. The experiment evidences that the passing electric current in metal has alternated the free energy sequence of various microstructures in comparison with that of current-free system.

Application of high intensity electric pulse (HIEP) to a severely deformed eutectoid microstructure in high carbon steel wire has resulted in spheroidized microstructure. The observed spheroidization on electropulsing is compared with that reported for isothermal/ thermo-mechanical annealing of the pearlite structure. The faster kinetics observed in this study has been rationalized in terms of accelerated kinetics induced by HIEP.Pearlitic steel in severely cold drawn condition is an important structural material, which meets the needs of high strength requisite applications such as suspension cables, tire cords, springs, etc. Fine pearlitic structures are known to sustain cold drawings of extreme reduced cross-sectional area without fracture. 1-5 It has been recognized that cold working results in progressively increasing alignment of pearlite colonies along the direction of drawing, reduction in interlamellar spacing, thinning and mechanical fragmentation of lamellae, and development of step bands in some pearlite colonies. [1][2][3][4][5][6][7][8][9] To improve the machineability of this high strength steel spheroidization heat treatments are conventionally used. 10-13 It has been reported that during static annealing, the regions of faults in the cementite break up into smaller segments leading to diffusion-controlled spheroidization. 14 Application of electric current pulse (ECP) of high intensity to materials has been known to accelerate diffusion-controlled solid-state phase transformations in many alloy systems. [15][16][17] In Cu-Zn alloys, diffusive a þ b 0 ! b transformation was observed on electropulsing, whereas the same transformation was not observed when similar temperature and heating rates were maintained employing laser heating; hence, a dramatic increase in diffusion coefficient was attributed to be due to electropulsing. 16 Furthermore, in the Cu-Zn alloy with Pb inclusions an accelerated rate of diffusion of Pb to the boundaries has been reported, on application of ECP of amplitude higher than a critical value. In this work, we report the spheroidization observed in highly deformed pearlitic steels when subjected to high intensity electric pulses (HIEP) and the observed process is compared with that reported in the literature for isothermal and thermomechanical processing.The pearlitic steel wires containing 0.8 wt% carbon were cold drawn to true strains of 3.00, which correspond to percentage reduction in the area of 95% (specimen-A). Microstructure of the as-received alloy in the heat treated and cold drawn condition was heavily deformed to fully pearlitic structure, free of any proeutectoid precipitation. The high degree of cold drawing had resulted in fine pearlite structure, which is severely elongated along the direction of drawing (Fig. 1). HIEP of amplitudes 7.73 Â 10 9 (denoted as EP-1), 9.82 Â 10 9 (EP-2), and 1.07 Â 10 10 (EP-3) A/m 2 and peak pulse width of 150 ms were used across 30 mm length of the specimen. To differentiate the influence of prior deformation on electropulsing,...