N. A. Arutyunyan

Surface tension of CaO-Al2O3, CaO-SiO2, and CaO-Al2O3-SiO2 melts

A method for the approximation of the temperature-concentration dependence of the surface tension of CaO-Al2O3, CaO-SiO2, and CaO-Al2O3-SiO2 melts was suggested. The method was based on the statistical-thermodynamic model of associated solutions. A comparison of the calculated surface tensions of the melts with the available literature data showed that the suggested approach allowed the surface tension of liquid slags to be correctly predicted as a function of temperature and composition.

Effect of Microstructure and Surface Defects on the Capacity of Special Alloy Steel Round Bar for Cold Upsetting

Surface defects of special alloy steel round bar of different grades, reasons for their occurrence and degree of influence with a change in microstructure on the capacity for cold upsetting according to groups 66 and 66T by GOST 10702–78 are studied. It is established that necessary conditions for obtaining positive test results for cold upsetting are simultaneous preparation of a favorable granular pearlite microstructure and the absence of round bar surface defects more than 100 μm deep. The absence of surface defects with an unfavorable microstructure does not guarantee positive test results.

Experimental Study and Modeling of the Thermodynamic Properties of Magnesium Silicates

The thermodynamic properties of all MgO-SiO2 system phases were studied by Knudsen mass spectrometry over a wide temperature range (1571–1873 K) and the whole range of compositions. An approach based on the generation of volatile interaction products formed in the reduction of oxide components was used. The reducing agents were Nb, Ta, and Mo. The observed ion current intensity ratios I(Mg+)/I(SiO+) were used to calculate the activities and partial thermodynamic functions of the components in liquid and crystalline MgO-SiO2 mixtures and the integral thermodynamic functions of formation of magnesium ortho-and metasilicates. For the first time, direct and reliable information about the thermodynamic properties of all system phases at high temperatures was obtained. These results in combination with all the available data on the thermodynamic properties and phase equilibria in the MgO-SiO2 system were used to develop a statistical-thermodynamic model of liquid magnesium silicates based on treating them as associated liquids. Simultaneously, the problem of obtaining self-consistent data on the thermodynamic functions of all phases and conditions of equilibria between them was solved. In addition to polymeric silicon-oxygen structures of arbitrary sizes and spatial configurations, heteromolecular complexes such as MS, M2S, and M3S (S=SiO2 and M=MgO) were found to exist in liquid MgO-SiO2 mixtures. The correctness of the results obtained was substantiated by the virtually complete coincidence of the calculated thermodynamic properties and phase equilibrium conditions with experimental data and their conformity to the general patterns characteristic of binary silicate systems.

Kinetics of the Formation of Nanosize Niobium Carbonitride Precipitates in Low-Alloy Structural Steels

A detailed study is made using original methods of kinetic features of nanosize niobium carbonitride precipitate formation in relation to metal temperature and deformation regimes on the example of an industrial melt of low-alloy structural steel. It is established that in the absence of deformation there are considerable kinetic difficulties for niobium carbonitride precipitation, and for its occurrence to some significant extent a time interval of not less than 20–40 min at 900°C is necessary, even in the presence of considerable supersaturation and solid solution supercooling. With equivalent conditions, preliminary deformation considerably accelerates formation of nanosize niobium carbonitride precipitates that commences approximately after 10 sec and ceases after isothermal soaking at 900°C in 200–300 sec. A fundamental dependence is demonstrated for the amount and mechanism of nanosize niobium carbonitride precipitate formation on thermal prehistory. In addition, prior cooling to room temperature and subsequent heating to an exposure temperature of 700°C leads to a marked increase in number of nanosize carbonitride precipitates formed.

Analysis of thermodynamic properties and phase equilibria in the Si-P system

A self-consistent analysis of the available data on thermodynamic properties and phase equilibria in the Si-P system is performed. Thermodynamic properties of solid and liquid solutions of phosphorus in silicon are approximated on the basis of the concepts of dilute and ideal associated solutions. The thermodynamic properties and phase boundaries in the range of compositions 0 ≤ x(P) ≤ 0.5 are adequately described.

Thermodynamic Properties and Amorphization of Zr–Si Melts

The relationship between the thermodynamic properties of Zr–Si liquid alloys and their propensity to amorphization is studied. The temperature–concentration dependences of the thermodynamic properties of melts are presented using the concept of associated solutions. It is shown that the range of amorphization coincides with the range of the predominant concentration of Zr3Si associative groups with low formation entropy.

Features of Titanium Carbide Precipitation in Low-Carbon High-Strength Steels Microalloyed with Titanium and Molybdenum

Theoretical and experimental study is carried out to establish features of all types of excessive phase precipitation in low-carbon steels microalloyed with titanium and molybdenum. It is established that the main type of precipitates controlling grain boundary and precipitation hardening mechanisms is FCCcarbide based on TiC. The optimum thermal deformation treatment regime is established providing simultaneously effective grain refi nement of steel structure and the formation of a system of nanosize carbide precipitates that control strengthening by a precipitation hardening mechanism. On the basis of the results obtained, chemical composition and heat-treatment regime are proposed for producing low-carbon TiM–Mo microalloyed steels with a ferritic microstructure and set of mechanical (tensile strength more than 850 MPa) and other service properties.

The conditions of formation and stability of quasi-crystalline phases in aluminum-manganese alloys

The conditions of formation, stability, and thermodynamic properties of the icosahedral and decagonal quasi-crystalline phases in the Al-Mn system were studied experimentally. The thermodynamic properties of equilibrium crystalline Al-Mn compositions over the composition and temperature ranges 0–26 at % Mn and 628–1193 K, respectively, and of melts over wide temperature and composition ranges (1043–1670 K and 0–50.1 at % Mn) were determined. Measurements were made by the integral variant of the effusion method under the conditions of an ultrahigh oilless vacuum and Knudsen mass spectrometry. An original technique based on the initiation and study of equilibria in reactions of the alloys with special admixtures of sodium or magnesium fluorides with the formation of volatile products was used to extend the interval of measurements to low temperatures. Complete, reliable, and consistent data on the thermodynamic properties of icosahedral and decagonal quasi-crystalline and crystalline phases based on aluminum and Al-Mn melts were obtained for the first time. Al-Mn melts were shown to contain associates of three types, AlMn, Al2Mn, and Al5Mn. The contributions of covalent interactions to the Gibbs energy and enthalpy of mixing was found to be by far predominant. The thermodynamic properties of alloys of the same chemical composition in the quasi-crystalline and equilibrium crystalline states were compared. The decagonal phase was found to be more stable than icosahedral quasi-crystals. The difference of the Gibbs energies of quasi-crystals of the two types and crystalline compositions increased as the temperature lowered. Arguments in favor of the entropy nature of the stabilization of quasi-crystals were obtained. These phases, like metallic glasses, are only an intermediate state between liquids and crystals and cannot be ground stable alloy states. The conditions of obtaining quasi-crystalline phases from melts were found to be controlled by the appearance of a substantial fraction of icosahedral short-range order in liquids in the region of compositions where associates of a certain kind (Al5Mn) were formed in substantial amounts, x(Al5Mn) ≥ 0.11.

Thermodynamic Properties of Magnesium Silicates

Being a constituent of numerous minerals, magnesium silicates are of extraordinary interest for the Earth and planetary sciences, as well as for cosmology. At the same time, they have many industrial and technological applications, including those associated with the building industry. Reliable data on the thermodynamic properties of magnesium silicates at high temperatures are necessary for the forecasting of various natural phenomena, optimization of technological parameters in a wide range of technological processes and production techniques, and for the development of novel ceramic and ceramic-metal materials, glasses, fluxes, slags and slag-forming mixtures. However, these data are at present almost entirely absent. Results from the direct measurement of thermodynamic characteristics for a magnesium-silicate melt have been reported by a single group only [1, 2]. However, these results do not agree with the data related to the phase diagram [3]. The description of the thermodynamic characteristics of intermediate phases is mainly based on low-temperature measurements and the extrapolation of temperature dependence for specific heats [4]. The present study is aimed at determining the thermodynamic properties of all phases existing in the MgO‐SiO 2 system within the wide temperature range 1571‐1873 K for the entire set of chemical compositions. The measurements were performed by the Knudsen mass-spectrometry method using the approach of [5], which was based on the generation of volatile reaction products formed as a result of the reduction of oxide components. When the MgO‐SiO 2 mixture interacts with the reducing agent R, which is, in this case, either the material of the effusion cell itself (R = Ta, Nb, Mo) or the purposefully added powders of these metals, the following chemical reactions occur: n MgO(solid, liquid) + R(solid)

Study of Principles for Creating Steel in Order to Prepare High-Strength Reliable Objects by Hot Stamping

Principles for creating a new generation of steels for preparation of objects by hot stamping with an improvement of strength properties (ultimate strength up to 2200 MPa) by a factor of three are analyzed. It is shown that first of all they should be aimed at simultaneous provision of good steel hot ductility indices, quenchability, and hardenability. It is established that boron-containing steels, and also steels of the alloy and microalloy systems Mn–Cr, Mn–Mo–Nb, Mn–Cr–Ni–(Mo–Nb–V) with an attempt to reduce carbon content are most promising for this purpose. With the aim of verifying results obtained experiments are performed for the effect of cooling rate on steel strength properties of the alloy systems selected. Adequacy of the main conclusions and the promise of using boron for alloying, and also alloying and microalloying additions C–Mn–Cr–Ni–Nb–V systems in order to create new low-alloy weldable steels for preparation of objects by hot stamping are confirmed.