Structure and wear of gradient steel castings

The effect of overheating of the melt over the equilibrium liquidus in the temperature range 1570 °C – 1670 °C and the rate of its cooling during crystallization and structure formation of castings on the formation of the length and morphology of the main macrostructural zones, grain dispersion, characteristics of the fine crystal structure, hardness and intensity of abrasive wear over the section of 25L steel castings with a differentiated cast structure was investigated. Regular changes of these indicators depending on thermokinetic conditions of crystallization are established. The determining influence of the melt cooling rate on the morphology and dispersion of the cast structure due to different degrees of melt supercooling during crystallization of different structural zones of castings is shown. As the distance from the rapidly cooling surface of the castings and taking into account the increase in the temperature of the melt overheat from 1570 ºC to 1670 ºC, the grain size varies from 5… 7 numbers to 1… 2 numbers, respectively. In the case of normal heat removal rate during crystallization, the grain size in the castings varies from 4… 2 to -1… -2 numbers. The determined characteristics of wear resistance of steel in different structural zones correlate with changes in the characteristics of the cast structure and the cross-sectional strength of castings. The research results open the prospect of developing new foundry technologies for the production of cast products with differential properties for special operating conditions. Keywords: gradient structure, structural zones, melt, wear.

Gradient structure and properties of steel castings

The influence of melt overheating in the range of 50-150 °C on the equilibrium liquidus and its cooling rate during crystallization of castings on the formation of macrostructural zones along their cross section, on the change of grain dispersion, dendritic structure characteristics and mechanical properties was investigated on the example of 25L steel. It is established that the macrostructure of castings in the direction of unilateral heat removal as it moves away from the cooled surface consists of four main structural zones - small coaxial crystals, columnar, branched and large coaxial crystals, the length and morphology of which naturally change depending on thermokinetic conditions of crystallization. The decisive role of the cooling rate at significant overheating of the melt to increase the number of crystallization nuclei, the formation of a more dispersed cast structure by increasing the degree of supercooling of the melt during crystallization is shown. The regularities of quantitative characteristics change of microstructure and dendritic structure depending on change of temperature-time parameters of crystallization in different structural zones of castings and their connection with characteristics of mechanical properties of steel are established. On the basis of mathematical processing of experimental data by linear regression analysis interpolation models and their graphical interpretations are obtained, which allow to quantify and predict the change of mechanical properties in different structural zones of gradient castings depending on melt overheating temperature and cooling modes within the investigated factor space. Keywords: gradient structure, structural zones, melt, mechanical properties.

THE USE OF EXTERNAL PHYSICAL INFLUENCE TO REGULATE THE FORMATION OF THE STRUCTURE OF STEEL INGOTS

В настоящей работе исследовано влияние температурных и силовых параметров внешнего воздействия на кристаллизацию и структурообразование слитков из модельных и реальных сплавов. Показано, что скоростью зарождения и роста кристаллов, а также размерами структурных зон в слитках можно управлять, изменяя температурный градиент, возникающий в жидкой фазе перед границей затвердевания. Управлять градиентом температур по сечению затвердевающего расплава можно, регулируя интенсивность теплоотвода, а также дифференцируя теплоотвод по периметру формирующегося слитка. Установлено, что от соотношения градиента температуры к скорости кристаллизации - G/R зависит формирование той или иной структурной зоны слитков. Наглядно доказана эффективность влияния вибрации на формирование структуры исследуемых слитков. Определен механизм воздействия вибрации на процессы кристаллизации и формирования структур слитков, который заключается в проявлении следующих эффектов: в разрушении и дроблении дендритов, растущих на фронте кристаллизации, под действием знакопеременных изгибающих давлений упругой волны; в зарождении кристаллов в объеме кристаллизующегося расплава вследствие кавитации; в разрушении дендритов в расплаве и на фронте кристаллизации под действием давлений, возникающих в результате схлопывания кавитационных каверн. In this paper, the influence of temperature and force parameters of external influence on the crystallization and structure formation of ingots from model and real alloys is investigated. It is shown that the rate of crystal nucleation and growth, as well as the size of the structural zones in the ingots, can be controlled by changing the temperature gradient that occurs in the liquid phase before the solidification boundary. You can control the temperature gradient along the cross-section of the solidifying melt by adjusting the intensity of the heat sink, as well as differentiating the heat sink along the perimeter of the forming ingot. It is established that the ratio of the temperature gradient to the crystallization rate - G/R depends on the formation of a particular structural zone of ingots. The effectiveness of the influence of vibration on the formation of the structure of the ingots under study is clearly proved. The mechanism of vibration influence on the processes of crystallization and formation of ingot structures is determined, which consists in the manifestation of the following effects: in the destruction and crushing of dendrites growing at the crystallization front under the action of alternating bending pressures of an elastic wave; in the nucleation of crystals in the volume of the crystallizing melt due to cavitation; in the destruction of dendrites in the melt and at the crystallization front under the action of pressures resulting from the collapse of cavitation cavities.

THE INFLUENCE OF EXTERNAL FORCES ON THE CHARACTERISTICS OF HARDENING AND THE CHARACTER OF CONVECTIVE FLOWS DURING THE CURING OF INGOTS

The paper describes the influence of external influences on the features and nature of convective flows during the solidification of ingots. It is shown that topping up the profitable part of the ingot with hot portions of the melt changes the nature of the convective motion of the melt in the body of the model ingot. Laminar movement is observed before refilling, after turbulent. The change in the nature of the movement of the liquid in the body of the ingot contributes to an increase in the speed of the front of the solid phase, as evidenced by the results of calculating the rate of solidification throughout the solidification process of the model ingot. The analysis of the structural zones showed an increase in the zone of columnar crystals from 58.6% to 72.3% and the zone of the deposition cone, from 6.5% to 9.1% in refilled ingots compared to the classic ingot. There is also a decrease in the zone of differently oriented crystals from 26.8 to 13.7% and the crustal zone from 5.9% to 2.8%. The length of the axial zone increased from 36 to 54%, with a decrease in its diameter from 6.5 to 5.1%.

Assessment of Seismic Bedrock in Deep Alluvial Plains. Case Studies from the Emilia-Romagna Plain

The estimation of seismic shaking is essential for a realistic assessment of the local seismic hazard and the implementation of effective strategies for prevention and mitigation of the seismic risk. One of the most important aspects in the analysis of the site seismic assessment is the recognition of the seismic bedrock and its depth. Unfortunately, these data are not always easy to evaluate, especially in areas where the thickness of loose or poorly consolidated sediments is high. This article illustrates data and case studies from the Emilia-Romagna sector of the Po Plain, in order to provide examples and suggestions for the recognition of the seismic bedrock in alluvial and coastal areas characterised by significant thicknesses of unconsolidated sediments, using available data and not expensive geophysical surveys. The application of the proposed method indicates that the study area can be divided into four domains characterized by different depths of the seismic bedrock: the marginal or pede-Apennine belt, the high structural zones, the syncline/minor anticline zones, and the Po delta-coast zone.

Devising a method to parametrize the jacket style varieties through the modification of tіpological series structures

The study reported here has revealed the issue related to the inefficient scaling of the uniformity of jacket model designs in the processes involving a typical representative as a result of modification parameters uncertainty. A variant has been proposed to synchronize the critical points of silhouetted allowances by grouping the numeric series in the vector of choosing the value for an increase in the allowance according to the characteristics of style varieties. The influence of shape-forming segmentation on the formation of a classifier of the structural and technological solutions for a jacket has been determined. The built model to support modification vectors has made it possible to describe the sequence of procedures execution by the method of typical representation. The presence of one design category, the same structural parts, the uniformity of style simplifies the processes of choosing and selecting the most characteristic models of the jacket. It was found that the morphological combination of attributes of the physical appearance affects the adjustment of style preferences in a manufacturer’s products. The parameters for typical segmentation relative to the junction points of the structural zones of the optimized five-seam prototype design have been defined as the most influential vectors of jacket modification. A method for scaling the allowance for free fitting has been devised on the basis of data from empirical research. An adequate regression model has been derived for normalizing the silhouette allowance parameters. The constructed model makes it possible to scale silhouette structures by changing the increments at the corner points of the contour according to the prototype of gradation under an automated mode. Practical recommendations have been compiled on the parameters of zonal-modular modification of silhouette designs of jacket varieties: a linear character of the state silhouetted transformation relative to ASi1=5 cm. The normalized parameters for constructing functional and decorative parts have been proposed

IMPROVING THE SURFACE STRUCTURE OF MASSIVE PARTS BY THE PLASMA METHOD

An increase in the reliability of the operation of large-sized and massive parts by plasma hardening of their surfaces is substantiated. It has been established that the formation of several structural zones of different microhardness is observed in detail along the depth of hardening, indicating the formation of a gradient-layered structure. It has been proved that at ultrafast heating rates, which occur during surface plasma hardening, phase and structural changes move to the high temperature region, changing the kinetics of the appearance and growth of new phase nuclei. In this case, fine-grained austenite is formed, which is transformed into a highly dispersed martensitic structure, which increases the strength and reliability of the surfaces of the parts.

Parautochthonic paleooceanic and island-arc complexes of the Southern Urals

Research objects. Paleozoic (Ordovician–Middle Devonian) volcanic-sedimentary complexes of the contiguous Sakmara and Mugodzharskaya structural zones of the Southern Urals, which have a paleo-oceanic and island-arc nature. Мaterials and methods.The work was carried out on the basis of many years of personal research of the author with the involvement of literature data on other folded zones of the Southern Urals. Main results. In the early Devonian, the first intense clustering of different facies complexes of rocks took place, which determined the tectonic face of the modern western part of the fold belt. The uniformity and set of Paleozoic formations in all structures of the Urals are maintained along its entire strike and are not repeated in neighboring zones.The drilling data showed the primary character of bedding of the rocks of the Upper Devonian Zilair Formation on the dislocated volcanogenic-sedimentary deposits of the Lower-Middle Paleozoic. Thrust contacts are observed only in the marginal parts of the zone. The almost textbook views on the cover bedding of the Kraka and Kempirsai hyperbasite massifs are in contradiction with the data on the presence of “roots” up to 4–8 km deep in them. By the beginning of the Devonian, the Kempirsai massif was located within the Sakmara zone and was “cross-linked” with the surrounding effusive rocks of the Middle Ordovician by gabbro-diabase dykes. According to the results of seismometric studies, features of similarity of the deep structure of the base of the Sakmara zone with the structure of the Magnitogorsk-Mugodzharskaya zone, which also revealed a melanocratic basement, have been established. Conclusions. The formed structural zones of the Southern Urals are distinguished by a set of rocks of the same age, their stratigraphic range, and the autonomy of feeding areas. These differences have survived to this day. All subsequent tectonic episodes, including the sharpening epochs, only complicated the appearance and structure of the Southern Urals, without changing the relative position of structures that arose in the Early Devonian. There was no transfer, swarming of rocks from one zone through another in any of the subsequent stages of compression. The Early Devonian stage was the first, but at the same time the most intense, which determined the tectonic face of the modern western part of the Urals.

Healing of induced previous damage to skin under the influence of autological cells stromal-vascular fraction

In the experiment on Guinea pigs, the course of reparative skin regeneration after application of a flap wound under the influence of cellular suspensions from autologous stromal vascular fraction was studied. The material was investigated by clinical observation, light - optical studies of biopsy material, macro-and microscopic morphometry. Cell material was obtained by liposuction from the withers of the animal. Autologous adipose tissue was used to prepare a cell suspension containing a set of cells (fibroblasts, pericytes, acrophages, fat cells, endothelial cells) that make up the stromal-vascular fraction. The findings suggest that the use of cellular product leads to faster (compared with the control) healing of the defect, the formation of regenerate, morphologically similar to the surrounding intact skin. In the structure of the regenerate microscopically found restoration of the structural zones of the skin: the epidermis, dermis and subcutaneous fat. In the Central part of the regenerate, a small portion of the scar structure was preserved, the area of which is significantly less than that of the control analogues. Thus, the use of cellular products enhances the processes of reparative regeneration and is an effective way of therapeutic effects in the treatment of skin wounds.