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Niobium is an important alloying element in steels. In the present work an effort has been made to investigate the effect of electropulsing on the niobium carbide (NbC) at an elevated temperature (800 °C). The results show that the electropulsing treatment can generate an evenly distributed NbC by decreasing the kinetics barriers for precipitation. It has been also found that a semitransformed pearlite structure forms in such a way that the grains are oriented toward a direction parallel to that of the electric current flow. Furthermore, the electropulsed sample benefits from refined grain size. This is thought to be due to the electropulse-enhanced nucleation rate. Tensile testing has been carried out to compare the properties of electropulsed sample with that of without electropulsing. The results show that the sample with treatment has greater yield strength and ultimate tensile stress while its elongation is only 1% less that of the unelectropulsed samples. The improved mechanical properties of the sample with pulsing are attributed to its finer grain sizes as well as the elimination of precipitation free zones caused by the electropulsing treatment. [ABSTRACT FROM AUTHOR]

Effect of electric current on the segregation of copper precipitates in the Fe–13.6Cu alloy is evaluated. Results of this approach present two stages of segregation, namely, grain-boundary segregation during the solidification and interphase-boundary segregation during the decomposition of a solid solution. The segregation becomes apparent not only because the thermodynamic barrier for segregation is decreased, but also because the diffusion is greatly enhanced. Based on the thermodynamic and kinetic aspects, the segregation process under electric current would be of great interest and of physical importance because this kind of electric current-induced segregation was much stronger than the thermal diffusion segregation. [ABSTRACT FROM AUTHOR]

Oriented sulphides parallel to the electric current direction have been experimentally observed when a pulsed electric current is passed through medium carbon steels with MnS inclusions. Two different configurations of sulphides occur after the application of the electric current: namely, oriented elongated ellipsoidal particles and oriented chain-like particles composed of two or three small spherical sulphides. Theoretical analysis indicates that this phenomenon is associated with minimization of the electrical resistance of the material. [ABSTRACT FROM PUBLISHER]

Electropulsing usually promotes a metastable phase to evolve towards its equilibrium state. This work reports an alternative case, where electropulsing promotes the decomposition of the stableδ-phase in duplex stainless steel at high temperature. This decomposition enables both theγ-phase and theσ-phase in the steel to survive and hence to strengthen it at high temperature. The hardness of the quenched sample with electropulsing treatment is 49.4% higher than that without electropulsing treatment. A fundamental understanding of the observation is developed. [ABSTRACT FROM AUTHOR]

A scheme for integrating grain growth model in phase transition and grain distortion calculation in plastic deformation is proposed, which enables the simulation of microstructure evolution in steel processing when phase transition takes place during rolling. The grain shape deformation is calculated by transforming grid coordinates according to homogeneous deformation matrix. Grain growth in phase transition is computed by phase-field model. Apart from the direct distortion effect of rolling on grain geometry, the change of interface geometry affects the interface propagation due to the anisotropic property of the interface energy. Finally, the method for integration of microstructure simulation with steel crystallography is discussed. [ABSTRACT FROM AUTHOR]

Interface stability theory predicts that the effect of stirring during solidification will decrease the stability of the solid–liquid interface and promote dendrite formation. In contrast, during semi-solid metal processing, non-dendritic particles form when stirring a casting. This apparent conflict has been resolved in the present work by taking into account the effect of turbulence. A model of stagnant diffusion boundary layer, developed by Vogel & Cantor, has been used to describe the effects of laminar flow, and has been modified to allow for the effects of turbulence. The growing of an Al5Fe2 spherical seed from an Al–Fe–Si melt under conditions of both laminar and turbulent flow has been simulated by means of a phase-field model. In pure laminar flow, the phase-field simulations agree well with the interface stability theory predictions. Under conditions of increased turbulence, the particles change from dendritic to rosettes and then to spherical morphologies as the extent of stirring increases; this result agrees well with experimental observations of semi-solid metal processing. The relative viscosities of slurries with such different particle morphologies were calculated and showed good agreement with experimental data. The effect of turbulence was explained in terms of constitutional undercooling and classical particle growth theory. [Copyright &y& Elsevier]