Papers by Author: Edward Fraś

Abstract: The mathematical model of the globular eutectic solidification in 2D was designed. Pro¬posed model is based on the Cellular Automaton Finite Differences (CA-FD) calculation method. Model has been used for studies of the primary and of globular eutectic grains growth during the ductile iron (DI) solidification. A hyper-eutectic composition has been analyzed but this model can be used in the solidification modeling of hypo- and eutectic DI. The proposed model makes possible to trace the unrestricted growth of primary grains of two phases from the liq¬uid, transition from free to cooperative solidification, and cooperative growth of globular eutectic.

Abstract: In this work an analytical solution is used to explain the mechanism of dissolved sulfur influence on the transition from graphite to cementite eutectic in cast iron. It is found that this transition can be related to (1) the nucleation potential of graphite (characterized by nucleation coefficients, Ns and b (2) the growth rate coefficient of graphite eutectic cell,  (3) the temperature range, Tsc = Ts - Tc (where Ts and Tc is the equilibrium temperature of the graphite eutectic and the formation temperature of the cementite eutectic respectively) and (4) the liquid volume fraction, fl after solidification of the pre-eutectic austenite. It has been shown that the main impact of dissolved sulfur on the transition from graphite to cementite eutectic consists in reducing the growth rate of graphite eutectic cell. Analytical equations were presented to describe the absolute chilling tendency, CT, and the chill, w of cast iron. Finally, it has been shown that as dissolved sulfur content in cast iron increases, the eutectic cell count, N, the maximum degree of undercooling at the onset of graphite eutectic solidification, ∆Tm, and the chilling tendency index, CT and chill, w increase as well.

Abstract: Modelling was carried out to investigate the internal dendrite grains structure formation from a liquid two-component solution in the area adjacent to a mould wall. For the simulation, our own model and computer program based on CAFD (Cellular Automata Finite Differences) were used. In modelling, the effect of process conditions and material-related parameters, e.g. nucleation temperature, heat exchange rate, interfacial energy, crystal orientation with respect to the casting wall, etc. on the nature of the dendritic grain growth was examined. It was demonstrated that the profile of concentration field in a near-mould-wall zone impedes the growth of the solid phase in the direct vicinity of the wall. A local melting down of the grains of a solid phase due to the segregation of admixtures reducing the alloy point of liquidus is also possible.

Abstract: The heat generation rate during austempering of ADI (Austempered Ductile Iron) for process temperatures of 250, 265, 280 and 293°C has been presented. A special measuring device was constructed. Thermal effects were quantified by analysis of the experimental temperature curves during the austempering process.

Abstract: Probability density functions of known statistical distributions (Gauss, Weibull, lognormal) have been used to describe the nucleation of grains during solidification. Empirical nucleation data for solidification of cast iron follow a model based on the lognormal distribution.

Abstract: A mathematical crystallization model in the meso scale (the intermediate dimension scale between interatomic distance in solids and grain size in metals and alloys) is presented with the use of a kinetic-diffusion cellular automaton model. The model considers the non-equilibrium character of real processes of phase transformations, where the kinetic undercooling of the solid-liquid interface is a measure of this non-equilibrium level. Anisotropy of the interface mobility is assumed. The modelling results are compared to the experimental data.