ТЕРМОЦИКЛИЧЕСКАЯ ОБРАБОТКА (ТЦО) МЕТАЛЛОВ – ПУТЬ К ПОЛУЧЕНИЕЮ ОПТИМАЛЬНЫХ СТРУКТУРЫ И СВОЙСТВ

Abstract

The aim of this work is to study the basic principles of thermal cyclic processing (TCТ) of metals to obtain structures that determine the optimal complex of mechanical properties. The basic provisions of metal heating centers using periodically repeated heating and cooling cycles are given. The TCТ method, as a heat treatment method, is based on constant accumulation from cycle to cycle of positive changes in the structure of metals. Studies have shown that with rapid heating, the growth of austenitic grain occurs slowly and, therefore, heating to high temperatures (up to 10000C) does not lead to an intensive increase in grain. It has been established that grain size increases at a variable heating temperature 3 times slower than under isothermal conditions at the corresponding temperature. Provided that the growth rate of the new phase (austenite) is small and the nucleation rate of grains is significant, it turns out that by the end of the a®g transformation, a fine-grained structure is retained. Further heating or holding at a constant temperature leads to a rapid coarsening of austenite grains. If cooling (for example, in air) of rapidly heated steel is performed 10–150C higher than the temperature of the Ас1 point, then fine perlite grain is formed due to reverse recrystallization. With one thermal cycle, ferrite in subeutectoid steels almost does not undergo changes. But if several such heating and cooling are performed, then the entire ferrite-pearlite structure undergoes a change. It has been established that the higher the heating rate during heating and heating and the less overheating above Ас1, the finer the grain in carbon structural steel. However, this increases the need to increase the number of heat treatment cycles. The mechanism of structure formation explaining these phenomena and practical recommendations on the implementation of the process of the technical and economic process are presented. This approach makes it possible to form the optimal metal structure. At the same time, opportunities can be significantly expanded in terms of obtaining materials with desired properties and improving on this basis machines, structures, individual units and parts. All this puts TCТ in the category of promising areas in metalworking.