СИСТЕМАТИЗАЦИЯ ПОЛИТЕРМ ФИЗИЧЕСКИХ СВОЙСТВ МЕТАЛЛИЧЕСКИХ РАСПЛАВОВ

Abstract

The analysis of the research results of temperature dependences of the kinematic viscosity, electrical resistivity, surface tension and density of liquid steels and alloys during heating and the subsequent cooling was performed. The identified characteristics formed the basis for systematization of physical properties polytherms of steels and alloys. It was established that the changes occur in the melt structure during heating up to certain critical temperatures. As a result, the cooling polytherms acquire a different view, more close to equilibrium classical patterns and do not coincide with heating polytherms. The branching of the temperature dependences of the physical properties or hysteresis of polytherms is irreversible only when heating up to a temperature not lower than the critical ones. If these conditions are not met the partial or full return to the primary structure of melt can occur and it has an impact on the value of the polytherms hysteresis. Therefore, the hysteresis value, along with the data on the properties, is a qualitative characteristic of the melt structure and its deviations from the equilibrium and micro homogeneous state. The uniformity of distribution of alloying elements atoms into micro groups or clusters indicates the equilibrium of the structure and uniformity of clusters distribution, different in structure in the melt volume, reflects its structural micro-homogeneity. In the process of studying the properties of multicomponent metal materials it was found that after melting the change of melt properties at isothermal holding is a typical pattern of damped oscillations. With the increase of temperature the damping mode approaches the aperiodic one, and the relaxation time decreases. The processes responsible for kinetics of isothermal change in the melt properties occur at the micro level. Non-equilibrium industrial metal typically contains inclusions from the initial materials in the form of undissolved particles of graphite in the cast iron, association and aggregation of carbides, nitrides, etc. Bringing such melt into equilibrium state requires a lot of time, normally much more than for the diffusion transfer of atoms within the disbalanced zones. The more complex is the chemical and structural interactions of solid metal, the greater is the separation between the equilibrium and the obtained melt. In such system the new correlations are formed and broken most intensely. In this case the cooperative processes of interaction of new spatial and temporal structures with inherited from the initial materials take place occur, which is reflected by oscillating dependences of the properties of metal melts. The information about the state of the melt prior to solidification enables a scientific foundation for temperature and time regimes of smelting of steel and alloys. Such melt preparation affects its capacity for supercooling, the crystallization rate and the formation of eutectic reinforcing phases, elements segregation, dendrites structure and zonal structure of castings, and in general – the quality and efficiency of steel production. © 2017, National University of Science and Technology MISIS. All rights reserved.