Study of desulphurization processes at heat treatmet of iron ore pellets

Main reactions of iron ore pellets desulphurization are considered in details in a number of papers, in which the results obtained refer only to their isothermal heating. Therefore studies of authors were concentrated on desulphurization kinetics of nonfluxed and fluxed Sokolov-Sarbai and Kostomuksha pellets, having different content of initial Sulphur in concentrate at nonisothermal heating.Regime peculiarities of sulphuric pellets thermal treatment in a layer considered. Recommendations on roasting regime of pellets layer elaborated, which enable to decrease the sulfates decomposition degree. The mechanism and kinetics of calcium sulfate dissociation at temperatures and gas content, typical for conveyer and sintering machines, studied. The temperature level determined, at which maximum dissociation velocity of calcium sulfate is reached. Simulation of the process of pellets thermal treatment in air and in helium media realized. It was shown that at roasting in a lowoxidizing atmosphere the sulphur content in pellets, roasted at correspondent temperatures, was decreased considerably. Rational iron ore pellets roasting regimes elaborated aimed at their acceptable properties both by strength and by Sulphur content.

Experimental Study of the Interaction between Recrystallization and Precipitation Processes of an AA8011 Commercial Alloy

Phase changes in a commercial AA8011 alloy from different initial microstructure conditions were studied using thermoelectric power (ΔS), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM) techniques with the purpose of obtaining evidence of the interaction between recovery-precipitation and recrystallization-precipitation processes occurring during nonisothermal heating at different rates. Thermoelectric power and its thermal derivative reflect this evidence by a displacement of the characteristic precipitation peaks, the recovery and recrystallization contributions remaining masked by the strong incidence of the iron precipitation on that property, while DSC measurements detect the emergence of new peaks not observed on thermograms of homogenized samples. An exhaustive study of these peaks permits direct differentiation between precipitation and recovery-recrystallization contributions. TEM confirms the interaction between both processes by means of local observations.

Analysis of soft impingement in nonisothermal precipitation

The effects of soft impingement on precipitation are considered. A physically realistic analytical treatment of soft impingement has been developed for solid-state precipitation in a nonisothermal heating/cooling process following the basic assumptions (i.e., a two-stage transformation including site saturation of nucleation, isotropic growth and linear approximation for a concentration gradient in front of the precipitate/matrix interface). Furthermore, both one- and three-dimensional precipitations have been described using a compact expression which is analogous to Zener’s model but with a temperature-dependent growth coefficient. A detailed description for the model parameters has been given for the model application. Good agreement with published experimental data, for example, the decomposition of austenite in a 0.038–0.30wt%Mn plain carbon steel, has been achieved.