Prospective refractory materials for vacuum electrometallurgy

Abstract

Scientific--technical progress and the rapid development of modern industries required the creation of metal alloys that possess special properties. This made it necessary to create essentially new steelmelting processes --vacuum-induction melting, vacuum arc~ electronbeam, and electroslag remelting processes.At present vacuum induction furnaces are used to melt various grades of steelandalloys from nickel, magnesium, and cobalt bases, alloys of complex composition practically from any materials, with the metal composition being regulated during the melting, ensuring high composition reproducibility from melt to melt. In technically advanced countries in recent years we have noted a tendency to increase the capacity of vacuum furnaces.To obtain practical utilization of all the advantages of the above-mentioned methods of exceptional importance is the choice of the refractory lining for the crucible which should be resistant to the action of metallic melts. The presence of surface contact between the liquid metal and crucible lining explains the possibility of mutual transfer of the components at the boundary of the phases, and this in itself either reduces or reinforces the refining action of the melt in vacuum.The intensity of the reduction reactions on the metal-lining boundary depends on the chemical composition of the metal being melted, and the physicochemical properties of the refractory used for lining the crucible. An important role is played also by the temperature schedule of the process and its duration, and the depth of the vacuum.The lining material used in crucibles for vacuum induction furnaces should have a high chemical inertia to molten metallic and metal penetration, and be resistant to sublimation and dissociation, and the thermal shock resistance should be high and the linings should have adequate strength.An examination of the state of the problem at the present time in regard to the trends leading to the creation of lining materials with the maximum degree of satisfying the above demands is the subject of the present article.The East Institute of Refractories in collaboration with the Elektrostal' Plant has done some work* [i, 2] on the development of a technology for making monolithic rammed linings for vacuum induction furnaces of capacities 0.5, 1,0, 1.3, and 2.5 tons. As a result it was established that the highest resistance is possessed by crucibles made on the basis of fused periclase with additions of electrocorundum. The finely dispersed corundum was added to the ramming body in order to compensate the shrinkage of the periclase constituent. The volume constancy of the crucible, it was assumed, could be attained as a result of the expansion of the grains of spinel. However, the process of spinel formation, was completed during the period of several early meltings. The developed spinel, as for the periclase matrix, during sintering, was subjected to shrinkage as a result of recrystallization. The thermal stresses developing during the cooling of the crucible led to the formation of ...