CRUST | Browsing by Author "Meniailo, Helena V."

Browsing by Author "Meniailo, Helena V."

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Graphitizing Modification of the Axial Zone of Cast Iron Rolling Rolls in the Liquidus-Solidus Temperature Range
(Dnipro University of Technology, Dnipro, Ukraine, 2023) Khrychikov, Valerii E.; Meniailo, Helena V.; Semenov, O. D.; Aftandiliants, Y. G.; Gnyloskurenko, S. V.
ENG: Purpose. To develop a method for calculating a process of graphitizing modification of unsolidificated liquid-solid zone to reduce transcrystallinity of the macrostructure and the amount of cementite in the center of castings. Methodology. The duration of solidification of the castings was determined by the kinetic curves of liquidus, solidus and pouring boundary in coordinates of relative thickness of the solidified metal layer – the parametric criterion of Gulyaev. Findings. A methodology for the process of modification of the axial zone of rolling was developed, the mass and time of adding aluminum were determined according to the amount of liquid-solid phase that remains after the solidification of the working layer. On the example of a rolling roll weighing 1115 kg, 0.488 kg of aluminum was added into liquid-solid zone after the working layer solidified. Movement of aluminum to the front of crystallization is provided by centrifugal forces and adding of aluminum along the height of the roll. Originality. For the first time, the kinetic curves of liquidus, solidus and pouring boundary have been plotted in coordinates of the relative thickness of the solidified metal layer x/R and τ/R2 – the parametric criterion of Gulyaev for rolled cast iron alloys cooled in chill-sand molds of various sizes. A methodology was developed for calculating the process of aluminum modification of the axial zone of rolling rolls after solidification of the working layer in the barrel which was set at the pouring boundary. The amount of aluminum depends on the remains of the liquid-solid phase. Practical value. Graphitizing modification reduces transcrystallinity of the macrostructure and the amount of cementite in the axial zone of castings. A promising direction for further development is the development of new methods for manufacturing castings due to physical and mechanical effects on the two-phase zone, deoxidation and alloying of the central zones of castings.
Influence of K2ZrF6 and SiO2 on Refining Ability of Flux for Manufacturing Bimetallic Castings
(Latvia University of Life Sciences and Technologies, Jelgava, 2024) Aftandiliants, Yevhenii; Gnyloskurenko, Svyatoslav; Meniailo, Helena V.; Khrychikov, Valerii Ye.; Lomakin, Viktor
ENG: Bimetallic material is considered as an advanced functional material due to the unique physical and mechanical properties varied over the layers. Formation of bimetallic castings with steel base greatly depends on diffusion coupling with the second material working layer at elevated temperatures. The common technological problem is to remove the oxide films from the solid steel surface while its heating prior pouring melt of the working layer. This work studies the protective refining fluxes matching the selected requirements of good wetting the surfaces of solidified metal, effective protection against oxidation in the working temperature range, easy separation after pouring liquid metal and high refining capacity for oxides. The most effective fluxes based on Na2B4O7 and B2O3 compounds were used. To improve their ability to enhance wetting, work of adhesion and reduce surface decarbonization addition of K2ZrF6 and SiO2 to the flux in the amount of 3-4 wt.% was proposed and investigated. It was established that such additions increased wettability up to 9 and 20%, respectively and reduced the average rate of decarburization in the temperature range from 800 to 1000 ºС on 57 and 37%. The complete reduction of iron from scale on the steel surface was observed, while in the case of Na2B4O7 – B2O3 system it achieved 30-40% only. The mechanism explaining such a result is proposed to be due to the prevailing effect of zirconium in protecting the surface of the steel base from the oxidation and decarburization. The important result of the study is the recommendation of optimal flux composition (wt.%): Na2B4O7 – from 60 to 80; B2O3 – from 10 to 30; K2ZrF6 - from 3 to 4; SiO2 from 3 to 4. Thus, such flux could improve the production of steel based bimetallic castings and increase their properties.
Influence of Melt Properties on the Dendritic Structure of Steel Castings
(The Katowice Branch of the Polish Academy of Sciences, Poland, 2024) Aftandiliants, Y.; Gnyloskurenko, S.; Meniailo, Helena V.; Khrychikov, Valerii Ye.
ENG: The paper presents the experimental results on the determination of melt parameters such as the energy of the boundary, contact angle, density and kinematic viscosity of low and medium alloy steels at different temperatures, as well as the dispersion of their dendritic structure in solidified castings. The analysis of the data obtained allowed revealing using mathematical models the influence of the chemical composition and temperature of melts on their properties and the dendritic structure of castings. It was established the variation of the melt parameters depending on the particular chemical elements of steels as C, Si, Mn, O, P, V, Cr. The established analytical dependences shown that increasing density and viscosity contributes to the dispersion of the dendritic structure and viscosity is of the major effect. The derived quantitative patterns allows to evaluate structure formation of cast structural low and medium alloy steels.
Influence of Technological Factors on Formation Process of Bimetallic Castings
(Latvia University of Life Sciences and Technologies, Jelgava, 2023) Aftandiliants, Yevhenii; Gnyloskurenko, Svyatoslav; Meniailo, Helena V.; Khrychikov, Valerii Ye.
ENG: The analysis of the modern state of wear-resistant metallic material production showed that one of the promising directions for improving their quality is the use of bimetallic steel-cast iron castings, which have a complex of properties differentiated over the volume and surface of the products. However, the problem of obtaining a high-quality joint of the steel base and the working cast iron layers is not completely solved at present. So, the research aims to determine the quality criterion of a good diffusion joint and to study the selected technological factor influence on the formation process of bimetallic castings using the developed mathematical model. The paper examines the effect of the steel base temperature at liquid cast iron pouring over it, the temperature of pouring cast iron, as well as the ratio of liquid cast iron mass to the unit surface of the steel base on the contact surface temperature as selected quality criteria, and the structure of the transition diffusion layer of bimetallic castings. It was determined that a high-quality joint is realized when this temperature is larger than the solidus temperature of the cast iron. Moreover, the results of the mathematical model application showed maximum contribution of the liquid cast iron mass/steel unit surface ratio, less effect of the pouring iron temperature and minimum influence of the solidified steel base temperature onto the quality criteria. The metallographic analysis established the diffusion joint formation in the transition steel-cast iron layer consisting of pearlite on the side of the steel base and without the carbide matrix area on the side of the working iron layer. The results obtained are of great importance for the designing bimetallic machine parts worked under intensive wear conditions.
Kinetics of Solidification and Crystallization of Liquid Axial Zone of Fe-C Alloys in Cylindrical Molds
(The Katowice Branch of the Polish Academy of Sciences, Poland, 2024) Khrychikov, Valerii Ye.; Semenov, Oleksandr D.; Aftandiliants, Y.; Gnyloskurenko, S.; Semenova, Tetіana V.; Meniailo, Helena V.
ENG: According to the results of digitization of the experimental studies carried out in the past concerning Fe-C alloys solidification in cylindrical molds of castings with a carbon content of 0.04%, 0.1%, 0.4%, 0.93%, 1.42%; 2.44%, 3.28%, 4.45%, 4.83% and their subsequent interpolation in the range of 0.04 ÷4.83%С there were obtained the curves of the advancement of the pour point, liquidus and solidus in the coordinates of the relative thickness of the solidified metal layer x/R and the parametric criterion τ/R2. Their usage is proposed for the development of modes of physical and chemical influence on the liquid metal in the axial zone of the casting after solidification of its calculated layer. Calculation of the mass of modifiers or deoxidizers for introduction into the axial zone was performed in relation to the total mass of metal in the liquid and liquid-solid zones of the casting. The technique for calculating the mass and time of introduction a graphitizing modifier into the axial zone of rolling rolls made of hypereutectoid steel with 1.7%C is proposed to reduce the negative impact of cementite, chromium and molybdenum carbides on the structure of the axial zone of the rolls. The obtained curves can also be used to assess the accuracy of computer modeling of the processes of Fe-C alloys solidification and further adaptation of mathematical models by the correction of thermophysical coefficients, the values of which are not always known in the liquidus-solidus temperature range.
Optimization of Production Process of Structural Steel Modified with Nitrogen and Vanadium
(Latvia University of Life Sciences and Technologies, Jelgava, 2022) Aftandiliants, Yevhenii; Gnyloskurenko, Svyatoslav; Meniailo, Helena V.; Khrychikov, Valerii Ye.
ENG: Structural steels are the most promising material, particularly in machine design. An important issue is to match their properties with the exploitation demands. It can be achieved by the optimization of the steel production process, i.e. formation of the primary and secondary structure under modification with nitrogen and vanadium, proposed in this research. At the experiments the structural steels were melted, modified with nitrogen and vanadium, subsequently deoxidized with aluminium, cerium and lanthanum. The steel samples were tested to reveal the mechanical properties and study the effect of modifying processing. The results have shown that some decrease in plastic properties, the impact strength and an increase in the critical temperature of brittleness is not due to vanadium nitride hardening of steel, but could be associated with imperfect technology. The final deoxidation of steel is often performed with aluminum of at least 0.05% in order to stabilize the grain of the structure during austenitizing heating. It was established that the necessary condition for the effective influence of nitrogen and vanadium should be a higher formation temperature of vanadium nitrides than aluminum nitrides in steels. Calculations showed that this condition is realized when the content of aluminum in steel is less than 0.03% and vanadium - 0.10%. The results of the performed experiments have shown that in this case there is a simultaneous increase in the strength properties and impact toughness of steel. Based on the obtained results the recommendations for the industrial process of steel making was formulated as below. In foundry shops with inductional melting furnaces it is necessary to additionally deoxidize steel with cerium and lanthanum. So, comprehensive optimization of the content of nitrogen, vanadium and deoxidizers in steel, as well as the temperature of austenitizing heating ensure increase in mechanical properties without reduction in plasticity and toughness.
The Process of Vacuum Formation in the Shrinkage Cavity at Castings Crystallization
(The Katowice Branch of the Polish Academy of Sciences, Poland, 2022) Khrychikov, Valerii Ye.; Semenov, Oleksandr D.; Meniailo, Helena V.; Aftandiliants, Y.; Gnyloskurenko, S.
ENG: The formation process of one of the most common casting defects, a shrinkage depression concerned to shrinkage cavity, was studied. The methodology, device and the experimental set up were developed to study the shrinkage cavity growth. The kinetics of vacuum formation in the cavity of the spherical casting of Al-Si-Mg alloy at its solidification in the sand-and-clay form was investigated. The data were analysed taking in mind the temperature variation in the centre of crystallizing casting. The causes of the shrinkage depression in castings were clarified. It was determined that atmospheric pressure leads to the retraction and curvature of metal layer on the surface of the casting with lower strength below which the shrinkage cavity is formed. To avoid such defects it was recommended to use the external or internal chills, feeders and other known technological methods. Deep shrinkage cavities inside the castings could be removed with an air flow through a thin tubular needle of austenitic steels for medical injections.
Regularities of Crystallization Heat Release During Solidification of Alloyed Cast Irons
(The Katowice Branch of the Polish Academy of Sciences, Poland, 2023) Aftandiliants, Y.; Gnyloskurenko, S.; Meniailo, Helena V.; Khrychikov, Valerii Ye.; Lomakin, V.
ENG: The chemical composition of alloys plays an important role at their crystallization and influences the solid phase formation, and thus, microstructure and properties. The present paper studies the release of the heat of crystallization of alloyed wear-resistant cast irons in order to determine the quantitative patterns of the chemical composition influence to the kinetics of crystallization. The differential thermal analysis was applied to get the data of heat release, its rate at cast iron temperature decrease. The normalized dependence of the amount of crystallization heat over time was obtained. The main temperature parameters were analyzed and four stages at irons crystallization were established and characterized with their duration and released heat. The multiple correlation analysis allowed considering a numerous physical and chemical factors and distinguishing their role at crystallization of irons. As a result, the quantitative regularities are determined of influencing the content of alloying elements, impurities and carbides on a heat and time of crystallization at the different stages of solidification, which are of great importance in developing alloyed irons with required quality and properties.

Browsing by Author "Meniailo, Helena V."

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