CALCULATION OF THE FORMATION PROCESS OF TERMITIC ALLOY LAYER ON A STEEL SUBSTRATE DURING SHS PROCESS

Abstract

The most perspective directions of realization of process of self - propagating high -temperature synthesis (SHS) are considered. It is shown that in the SHS process specialattention is paid to the mechanism of structure formation and product formation in selfpropagatingthermite reactions. Іn order to obtain dense SHS material with high functionalcharacteristics, it is necessary to take into account the patterns of combustion of the reactionmixture, the formation of chemical and phase compositions of the final product and the mode ofcrystallization of the alloy. In the laboratory, the process of formation of thermite alloy layerbased on the Fe-Cr-C system on a steel substrate using self-propagating high-temperaturesynthesis is considered. It is shown that preheating of the charge components of the thermitemixture leads to an increase in the hotness of the product, reduces productivity and increasesthe cost of synthesis of the final SHS products, but does not reduce the likelihood ofnonstoichiometric compounds. Сalculations show that the concentration of chromium carbidepowders in the charge to form a layer of thermite alloy can’t be more than 13.5%. In the processof heating the termite mixture from 273 K to 873 K, 67.1% of additional iron and 24.5% ofchromium carbide are formed, which is introduced from the number of components of thetermite mixture. 2318.44 kJ of heat is used to heat the iron powder, and 3314.93 kJ of heat isused to heat the chromium powder per 1 kg of mixture. The optimal content of metal filler in thethermite mixture heated to 873 K is 40%. It is shown that the excess heat generated during aluminothermic reactions can be spent on melting an additional amount of iron powder.Metallographic studies of samples of the formed layer of thermite alloy from chromium-basedcharge showed the formation of small inclusions of corundum. These are the products of theexothermic reaction of iron oxide with aluminum, which create the effect of inoculatingmodification of thermite alloy and promote the formation of chromium carbides.