Research works concerning electromagnetic processing of liquid materials began very early in Europe. Through active cooperative programs between industrial companies and universities original results were obtained which gave rise to new technologies and innovative processes. Some typical examples are given relating to electromagnetic flow control of liquid metals, manufacturing of materials in cold crucible, electromagnetic stirring in continuous casting and in ladle.
The influence of electromagnetic fields on electrically conducting liquid materials is a complex phenomenon attracting more and more interests of specialists in the fields of metallurgy, technology, energetics, medicine and geophysics. The major part of the phenomena concerning the movement of electrically conducting liquid media in electromagnetic fields is studied by magnetohydrodynamics (MHD) which is comparatively a new branch of the science based on the principles of electrodynamics and mechanics of continuous media. In USSR, MHD has passed the full scale distance of the development practically covering all the known fields of the science. This discipline obliged notably, not only by its successes to the development of the MHD method for the generation of electric power, but also by the development of MHD theory and MHD technology in metallurgy and material science which have enriched MHD with new ideas and turned it into productive force helping it out of the sphere of abstractions. The current review of basic Soviet publications obviously appears for the first time in the Western journals and demonstrates the uneasy way for MHD and the main achievements along the way of MHD developed. The extremely great value of information containing in Soviet publications on hydrodynamics of conducting media can not be in essence concentrated in the style of a journal article. Nevertheless, it is possible to mark out the main fields, where the most significant results have been achieved. 1) Magneto-hydraulics and -hydromechanics including those in strong magnetic fields 2) MHD turbulence 3) MHD machinery (pumps, generators, throttles) 4) MHD technology of liquid metal Beside of these usual sections of modern MHD, there are some new sections which have appeared comparatively recently in the USSR. They are electrovortex flows where current in liquid material interacts with the magnetic field induced by the current and capillary MHD-flows which is a small-scale MHD flow with a small-scale boundary and with strong surface forces at the boundary. Appearance of such new sections is first of all obliged to penetrate into MHD and the series of engineering sciences in electrometallurgy and electric welding mutually. Such an interfusion guarantees us the development of MHD in the future.
A new process using pulse electric discharging for modification of solidification structures was investigated. If an extremely high voltage or high current is applied to solidifying metallic alloys by discharging a capacitor bank, large pressure gradients result, which produce strong local shear, and can be expected to significantly modify structures. Experiments were conducted on Sn-15wt%Pb alloy and the appropriate conditions to modify solidification structures were examined, including cooling rate, initial capacitor bank voltage, and time to discharge after onset of solidification. Solidification structures were modified from dendritic to globular (with fine grain size) under appropriate operating conditions. The critical conditions to attain the globular structures in these experiments can be expressed in terms of initial capacitor bank voltage and the fraction solid when discharging was carried out.
Anisotropic effect of magnetohydrodynamics on solidification of Pb-10%Sn alloy has been studied in a magnetic field generated by a superconducting magnet. Experimental castings have been conducted with a mold designed to solidify the alloy unidirectionally. It has been observed that equiaxed structure changes to columnar with increasing the intensity of magnetic field parallel to the solidifying direction. On the other hand, a structural change has been slightly obtained with the field perpendicular to the direction of the solidification. Transport of heat in a mercury pool examined under the various conditions of magnetic fields has revealed that temperature distribution in mercury pool is affected strongly by the direction of a magnetic field through the anisotropic effect of magnetohydrodynamics on the convection. This has demonstrated that anisotropic effect of a magnetic field gives rises to the structural change of the solidification of the metal alloy.
To clarify the mechanism of TiO2 reduction by Fe-C melt, effects of carbon and sulfur contents in liquid iron and temperature on the reduction rate of solid TiO2 were examined at temperatures of 1 350 to 1 550°C under argon atmosphere. The reduction rate of solid TiO2 was proportional to the activity of carbon in liquid iron, while it decreased by the addition of a small amount of sulfur to the liquid iron. An apparent activation energy for TiO2 reduction by carbon was calculated to be about 400 kJ mol-1. It was concluded from these experimental results that the overall rate of TiO2 reduction was controlled by the rate of chemical reaction step at the solid TiO2-liquid iron interface. The decrease in reduction rate of TiO2 by the addition of sulfur to the liquid iron was attributed to the decrease in effective reaction area by the adsorption of sulfur to the interface.
A mathematical model has been developed to predict the rod cooling behavior of steel rods under the action of water sprays in the precooling system of a Stelmor machine. The main objective of this work was to study the influence of operation parameters such as rod size, rod speed, rod temperature at the finishing mill, water flow-rate and spray cooling sequence on the final temperature distribution within the rod before it enters into the transformation conveyor. This heat transfer analysis indicates that the spray cooling sequence affects, considerably, the temperature distribution inside the rod. Besides, water flow-rate failures in the spray cooling system disturb drastically its cooling efficiency. Finally, reheating phenomena which go from 150 to 200°C at rod surface are predicted. The calculations were validated with in situ experimental measurements carried out at HyLSA's (Puebla Plant) Stelmor machine. Very good agreement was found between predicted and experimentally measured rod surface temperatures.
Study of the microstructural changes and the embrittlement behaviour of a 21/4Cr-1Mo steel with low impurity content by isothermal aging for periods of up to 10 000 h at 823, 873 and 898 K showed that although grain boundary segregation of phosphorus or other impurity elements were not recognized, considerable reduction in notch toughness occurred due to the microstructural changes associated with the precipitation and coarsening of carbides. It has been shown that the toughness degradation due to long term aging has a linear relationship with the parameter T(log t+8) where T is the aging temperature and t, the aging time. It has also been suggested that step cooling alone is not a viable method of estimating long term embrittlement. Using the above parameter, it ought to be possible to formulate a method by which the microstructural changes and toughness degradation occurring due to long term service of the order 100 000 h could be effectively simulated in the laboratory by heat treatment of a few thousand hours. An illustrative example of simulation of the changes in carbide morphologies, hardness and toughness that occurred in a 21/4Cr-1Mo steel due to 88 000 h service at 813 K has been presented.
The wettability of graphite and single crystal of α-SiC by liquid Cu-Cr alloy was investigated using the sessile drop method and the vertical plate method which was developed in this work. Main results are as follows; (1) The vertical plate method was proved to be applicable for the wetting system whose contact angle is acute. (2) The wettability of graphite by liquid Cu-Cr alloy dramatically changed at c.a. 0.3mass%Cr. (3) Electron probe microanalysis of the Cu-Cr alloy and graphite system revealed that Cr had concentrated at the interface. (4) Contact angles between liquid Cu-Cr alloys and single crystal of α-SiC were 10° and 10-20° at 0.23mass%Cr and 0.75mass%Cr, respectively.
The electron channeling, whose rate is proportional to the relativistic mass of an electron, occurs at high accelerating voltages by interaction among many simultaneously excited electron waves. As a result, the maximum observable specimen thickness markedly increases with increasing the voltage, so that essentially the same behavior of lattice defects in almost all materials can be observed dynamically as that in bulk specimens with an ultra-high voltage electron microscope (UHVEM). In situ experiments with UHVEM have been carried out in many research fields of natural science, particularly materials science. In the present article, in these experiments, only the formation process of non-equilibrium phases and its related phenomena are mentioned as one of topics in the electron beam science and engineering which has been developed recently with UHVEM.