E. E. Baryshev

Improvement of Low-Alloy Steel Quality by Forming an Equilibrium Melt Condition

A melt’s condition before solidification is important for improving low-alloy steel metal product quality. It depends on melting method, form or type of charge materials used, melting temperature and time parameters, mixing intensity during extra-furnace treatment, and other production methods. Improvement of the level of molten steel’s physical properties as a result of some action points to the formation of more equilibrium and homogeneous melt condition, and this has a marked effect on metal product structure, properties, and quality.

Production of heat-resistant EP220 and EP929 alloys by high-temperature treatment of melt

Analysis of samples of EP220 and EP929 alloys in the liquid and solid state permits the determination of the parameters for high-temperature melt treatment in their production. On heating to specific temperatures, the structure of the liquid alloys moves closer to equilibrium. In the solidification of such melt, the cast metal formed is characterized by finer grain structure, greater dispersity of the dendrites, and greater density and microhardness of the matrix. Industrial adoption of high-temperature melt treatment will improve plasticity, increase the long-term strength, and boost the product yield. The proposed technology does not fully utilize the potential of the alloy structure obtained after high-temperature melt treatment. The effect may be amplified by more prolonged holding of the melt at 1650°C and by optimization of the vacuum-arc heating, deformation, and heat treatment, in the light of the structural changes in the experimental samples of solid metal.

Effect of Melting Conditions on Chromium-Nickel Alloy Kh20N80 Properties

Physical properties of alloy Kh20N80 in a liquid state are studied. Critical temperatures are established above which heating makes it possible to transfer melt into a micro-homogeneous equilibrium state. A timetemperature regime for liquid metal treatment is proposed and tested in industrial conditions. The use of this regime leads to a change in ingot zonal structure and more uniform distribution of alloy property values over its cross-section. At hot plastic deformation temperatures, there is a significant increase in alloy relative elongation (by 15–20%), and in this case strength properties and relative reduction of area are unchanged. In test metal, after deformation there is an increase in density and specific electrical resistance that points to increased alloy uniformity. The yield of metal after hot plastic deformation as a result of TTT increases from 66.8 to 72.3%.

Polytherms of the physical properties of metallic melts

The temperature dependence of the kinematic viscosity, electrical resistivity, surface tension, and density of liquid steels and alloys on heating and subsequent cooling is analyzed. On that basis, the polytherms of the physical properties of steels and alloys are systematized. On heating to certain critical temperatures, changes occur in the structure of the melt. Consequently, the cooling polytherms take a form more closely resembling the equilibrium classical laws and do not match the heating polytherms. Branching or hysteresis of the temperature dependences is only irreversible on heating to critical temperatures. Otherwise, partial or complete return to the primary melt structure is possible. That affects the degree of hysteresis of the polytherms. The degree of hysteresis and the data regarding the properties provide qualitative information regarding the transition of the melt structure from the equilibrium to the microhomogeneous state. The uniformity of the distribution of atoms of the alloying elements in microgroupings or clusters indicates the equilibrium of the structure, while the uniformity of the distribution of clusters that differ in structure over the melt volume reflects structural microhomogeneity. Data on the properties of multicomponent metals indicate that, after melting, the variation in melt properties on isothermal holding takes the form of familiar damping oscillations. With increase in temperature, the damping becomes aperiodic, and the relaxation time declines. The processes responsible for the isothermal variation in melt properties occur at the microscopic level. Nonequilibrium industrial metal usually contains inclusions inherited from the initial materials, such as insoluble graphite particles in the cast iron or associations and aggregations of carbide and nitride type. The melt takes a long time to reach equilibrium—usually longer than the time for diffusional mixing of the atoms within the nonequilibrium regions. With more complex chemistry and structure of the solid metal, the distance of the melt from equilibrium will be greater. In this system, new correlations are formed and broken more intensely. Cooperative interactions of the new spatial and time structures with those inherited from the initial materials occur here, as indicated by oscillating behavior of the properties of the metallic melts. Information regarding the state of the melt before solidification permits scientific analysis of the melting points and melting times of the steels and alloys. Such preparation of the melt affects its supercooling, its solidification rate, the formation of hardening phases and eutectics, the segregation of the elements, the dendrite and zonal; structure of the castings, and the overall product quality and production efficiency.

Effect of Secondary Melt Refining on the Properties of an EP602 Nickel Superalloy

The influence of argon blowing of the EP602 alloy melt in a ladle is considered. Ladle treatment during the manufacture of nickel superalloys is shown to form a more equilibrium and homogeneous structure of a melt, which leads to changes in the structure and properties of the solid metal.

Influence of the chromium concentration on structure formation in liquid chromonickel alloys

The electrical resistivity of liquid nickel–chromium alloys is studied as a function of the temperature and concentration. Experimental data indicate that the dependence of the alloys’ electrical-resistance isotherms on the concentration is nonlinear. On the basis of the temperature and concentration dependence of the electrical resistivity of nickel and chromium alloys, the optimal conditions for the formation of microhomogeneous and equilibrium structure in the melt may be determined. The electrical-resistance isotherms of chromonickel alloys may be qualitatively explained on the basis of percolation theory and a quasi-chemical model of the microheterogeneous structure of molten metal alloys. The structure formation of chromonickel melts with increase in chromium concentration is characterized by the successive formation of clusters with different structure and dimensions.

ВЛИЯНИЕ КОНЦЕНТРАЦИИ ХРОМА НА ПРОЦЕСС СТРУКТУРООБРАЗОВАНИЯ ЖИДКИХ ХРОМОНИКЕЛЕВЫХ СПЛАВОВ

The temperature and concentration dependences of the electrical resistivity of the nickel-chromium alloys in the liquid state have been studied. Experimental data suggest a nonlinear concentration dependence of the electrical resistivity isotherms of the studied alloys. The results of studies of the temperature and concentration dependencies of the electrical resistivity of nickel-chromium alloys allow determining the optimal conditions for the formation of microhomogeneous and the equilibrium structure of the melt. Using of percolation theory and quasichemical model of microheterogeneous structure of liquid metal alloys gives the possibility to explain the nature of the isotherms of the electrical resistivity of nickel-chromium melts. The process of structure formation of nickel-chromium melts with increasing chromium concentration has been presented in the form of schemes, reflecting the gradual formation of different clusters, featuring by their structure and size.

Special features of structural changes of amorphizing nickel alloys in liquid and heterogeneous state

Polytherms of kinematic viscosity of nickel-based alloys with Cr, Si, Fe and B additives have been studied. It was found out that the first liquid phase volumes appear when temperatures are well below the tabular values of the solidus temperature ts. The critical temperature of the alloy was defined. The ways of obtaining materials of higher amorphization ability were suggested.

Production feature of soft magnetic amorphous alloys

Methods for making nanocrystalline alloys have been discussed. Temperature dependences of the surface tension (σ), electric resistivity (ρ), magnetic susceptibility (χ) and kinematic viscosity (ν) have been obtained. Comparison of the properties of amorphous ribbons obtained by the pilot and serial technologies has been conducted. Science-based technology of multi-component alloy smelting makes it possible to prepare equilibrium smelt, the structure of which has a significant effect on the properties of the amorphous ribbon before spinning and kinetics of its crystallization has been offered.

Improvement of the qualitative characteristics of low-alloy steels by the formation of an equilibrium state in a melt

The state of melt before solidification is of great importance for the properties of metal products made from low-alloy steels. It depends on the melting method, the type of charge materials, the temperature-time parameters of melting, the intensity of mixing during out-furnace treatment, and other technological parameters. The improvement of the physical properties of liquid steel as a result of various actions demonstrates the formation of a more equilibrium and homogeneous state of melt, which substantially influences the structure, properties, and quality of metal products.