Metastable versus stable solidification of silicon cast irons, effects of magnesium and tellurium

It is common knowledge that at low and ultra-low temperatures, many metals and alloys are prone to cold brittleness, which leads to the destruction of bridges, pipelines, gas-pumping compressors and other equipment. As such material, it is advisable to use high-strength, cold-resistant cast iron with nodular graphite (HCV). The importance of manufacturing technology development, properties research and implementation of cold-resistant high-strength cast iron is shown. The effect of heat treatment on its mechanical properties was studied. HF castings, compared to billets from steel casting and rolling, have a number of significant advantages. The cold resistance of structural steels does not exceed minus 40 °С. HF differs favorably from steel in terms of its casting properties, its lower cost (by 15–20 %), stronger wear resistance, higher corrosion resistance, and better machinability by cutting; lower HF density (by 8–10 %) allows to reduce the mass of parts compared to the mass of steel parts; the damping ability to extinguish vibration mechanisms arising during operation is much higher in HF than in steel. We performed a whole complex of robots on the specified topic and as a result developed technologies for obtaining unalloyed cold-resistant high-strength cast iron with spheroidal graphite – HHF – capable of working up to -80 °C; -100 °C; -150 °C, and also implemented for mass production of castings. HHF has a unique combination of physical, mechanical, operational and technological properties, namely: high strength and plasticity, high cold resistance (down to minus -100 °С, -150 °С), very high damping capacity (this is a very important factor for wind turbine parts); high corrosion resistance, manufacturability of castings during their production, as well as cheapness compared to other structural materials. This type of cast iron is an ideal structural material for responsible highly loaded parts of wind energy installations (WEE) in both northern and high-altitude versions. In order to develop and verify the effectiveness of the technology for obtaining HVC, numerous tests of HVC metal samples on mechanical properties at normal and subzero temperatures were carried out. At the same time, certain regularities were obtained, which are described in numerous publications on this subject. Prospects for development and fields of its use are described.

Hard alloys are popular materials widely used in the toolmaking industry. The refractory carbides included in their composition make carbide tools very hard (80 to 92 HRA) and heat-resistant (from 800 to 1000°С), so they can be used at cutting speeds several times higher than those used for high-speed steels. However, hard alloys differ from the latter in their lower strength (from 1000 to 1500 MPa) and the absence of impact strength; this is an urgent problem that needs to be solved. We study the influence of thermal cycling modes on the mechanical and tribological properties of VK8 (WC–8Co) hard alloy used in the manufacture of cutters and cutting inserts for metal working on metal-cutting machines. As the object of study, we select 5 × 5 × 35 mm rods made of VK8 (WC–8Co) alloy manufactured by powder metallurgy at the Dimitrovgrad Tool Plant. The following criteria are selected for evaluating the heat-treatment mode: Vickers hardness, flexural strength, and mass wear resistance (compared to the wear of as-received samples that were not heat treated). Plates in the initial state and after heat treatment (HT) are subjected to abrasion tests. Wear results are evaluated by the change in the mass of plates. Regularities of the influence of various time and temperature conditions of HT on the tribological properties of products made of VK-group tungsten hard alloys are determined. An increase in the number of thermal cycling cycles improves mechanical properties of the VK8 hard alloy such as strength and hardness. When repeating the cycle five times, an increase in abrasive wear resistance over the initial non-heat-treated sample is obtained. The elemental composition of the VK8 hard alloy changes insignificantly after thermal cycling; only a slight increase in oxygen is observed on the surface of the plates. The grain size after thermal cycling increases in comparison with the initial VK8 hard alloy. It is found that VK8 hard alloy thermal cyclic treatment leads to a change in the phase composition. X-ray phase analysis shows the presence of a large amount of α-Co with an hcp-type lattice on the surface of a hard alloy and a solid solution of WC in α-Co. A change in the cobalt modification ratio causes a decrease in microstresses. An analysis of the carbide phase structure state shows that the size of crystallites and microstresses changes after thermal cycling. The lattice constant of the cobalt cubic solid solution decreases, which may indicate a decrease in the amount of tungsten carbide and carbon dissolved in it. Statistical processing of the experimental results includes a calculation of the average value of the mechanical property, its dispersion, and standard deviation in the selected confidence interval.

Hard alloys are popular materials widely used in the toolmaking industry. Refractory carbides included in their composition make carbide tools very hard (80 to 92 HRA) and heat-resistant (800 to 1000 °С) so as they can be used at cutting speeds several times higher than those used for high-speed steels. However, hard alloys differ from the latter by lower strength (1000 to 1500 MPa) and the absence of impact strength, and this constitutes an urgent problem. We studied the influence of thermal cycling modes on the mechanical and tribological properties of VK8 (WC–8Co) hard alloy used in the manufacture of cutters and cutting inserts for metal working on metal-cutting machines. As the object of study, we selected 5×5×35 mm billets made of VK8 (WC–8Co) alloy manufactured by powder metallurgy methods at Dimitrovgrad Tool Plant. The following criteria were selected for heat treatment mode evaluation: Vickers hardness, flexural strength, and mass wear resistance (as compared to the wear of asreceived samples that were not heat treated). Plates in the initial state and after heat treatment were subjected to abrasion tests. Wear results were evaluated by the change in the mass of plates. Regularities of the influence of various time and temperature conditions of heat treatment on the tribological properties of products made of VK group tungsten hard alloys were determined. An increase in the number of thermal cycling cycles improved such mechanical properties of the VK8 hard alloy as strength and hardness. When repeating the cycles five times, an increase in abrasive wear resistance was obtained compared to the initial nonheat-treated sample. The elemental composition of the VK8 hard alloy changed insignificantly after thermal cycling, only a slight increase in oxygen was observed on the surface of plates. The grain size after thermal cycling increased in comparison with the initial VK8 hard alloy. It was found that VK8 hard alloy thermocyclic treatment leads to a change in the phase composition. X-ray phase analysis showed the presence of a large amount of α-Co with an hcp-type lattice on the surface of a hard alloy and a solid solution of WC in α-Co. A change in the cobalt modification ratio causes a decrease in microstresses. An analysis of the carbide phase structure state showed that the size of crystallites and microstresses changed after thermal cycling. The lattice constant of the cobalt cubic solid solution decreased, which may indicate a decrease in the amount of tungsten carbide and carbon dissolved in it. Statistical processing of experimental results included the calculation of the average value of the mechanical property, its dispersion and standard deviation in the selected confidence interval.

This manuscript summarizes recent investigation of the authors into the solidification and shrinkage defect formation of ductile and compacted graphite cast irons. The study makes use of the DAAS (direct austempering after solidification) technique, developed earlier by some of the authors, to reveal the solidification grains. In addition, color metallography is used to reveal the microsegregation pattern. The formation of shrinkage defects is related to both the solidification macrostructure and the microsegregation pattern. The examination of the macrostructure shows that large solidification grains, composed by dendritic austenite and graphite, characterize the solidification of compacted graphite irons of carbon equivalent values ranging from hypoeutectic to hypereutectic. Similar results are observed for ductile iron, but in this case, the hypereutectic irons display a finer macrostructure. The characteristics of the primary austenite dendrites are revealed by the microsegregation pattern, which is exposed by the color etching reagent. This pattern also clarifies the nature of the interaction between the growing austenite and the compact and spheroidal graphite particles. The microshrinkage cavities in both ductile and compacted graphite irons form at the interior of the austenite grains, where fluid feeding cannot compensate the contraction of the last-to-freeze portions of the melt. Schematics of the solidification of ductile and compacted irons are proposed, accounting for the experimental observations.

Tribological Characterization of Centrifugally Cast Graphite Cast Iron under Dry and Wet conditions

Two types of compacted vermicular graphite (CVG) cast iron having ferritic and pearlitic structures have been studied to determine the effects of CVG on fatigue strength, fatigue crack growth rate and fracture appearance of cast iron. The results obtained were compared with those of two types of spheroidal graphite (SG) cast iron (corresponding to JIS FCD) having ferritic and pearlitic structures. The significant conclusions obtained are as follows: The fatigue limit of the CVG cast iron was lower than that of the SG cast iron independent of matrix structure. This tendency was prominent for ferrite matrix. However, the fatigue limit ratio of the CVG cast iron was not less than that of the SG cast iron regardless the shape of graphite. The fatigue crack growth rate of the CVG cast iron was higher than that of the SG cast iron. This trend was significant for the CVG cast iron having ferritic matrix. This could be due to the fact that the fatigue crack propagation in the CVG cast iron occurs through a zig-zag path between graphites more than that in the SG cast iron when compared at the same level of Kmax.

Iron-based alloys (steel and cast iron) are currently the main structural materials that provide a high level of mechanical and technological properties along with a relatively low cost. Increasing the performance characteristics (tensile strength, hardness, wear resistance, corrosion resistance and, ultimately, service life) of cast irons and steels is an urgent task. The quality of castings made of cast iron and steel depends on many technological parameters that affect the processes of crystallization of the melt (casting temperature, molding mixture, chemical composition, volume of casting, overheating of the metal during smelting, etc.). It is possible to improve the quality of castings without changing the technology of smelting and pouring metal into molds, if you learn how to manage the crystallization process. The laboratories have grown defect – free iron crystals with a tensile strength of more than 1000 kg/m2 (strength of carbon steel-40 kg/m2). Attempts to improve the mechanical properties by creating a single crystal are not justified, so you have to go the opposite way-to influence the crystallization process to get a lot of small crystals (grains), which also allows you to achieve high mechanical properties. The dependence of the strength characteristics on the grain size is well described by the law of Hall-Petch, according to which when the average grain size is reduced by 3...5 times there is an increase in the hardness of the material, with a further decrease in the average grain size by more than 10 times – an increase in plasticity. Influence on the processes of crystallization of iron and steel melts (change the size of metal grains, change the shape, size and distribution of graphite inclusions) can be the introduction of small additives substances (modifiers), not chemically interacting with the matrix. The use of modifiers to increase the rate of crystallization, reduce the structural heterogeneity of castings has good prospects. In addition, unlike doping, modification does not require a large number of expensive additives and, accordingly, slightly increases the final cost of production.

THE ANALYSIS OF COOLING CURVES FOR GREY CAST IRON AND ITS MECHANICAL PROPERTIES

Purpose. Improving the mechanical and operational properties of details of internal combustion engines by managing the structure formation of phosphorous cast irons.
 Research methods. Graphitized and bleached phosphorous cast irons with lamellar and globular graphite of laboratory and industrial melts, melted in electric induction furnaces with alloying modification and fractional casting into dry sand molds were investigated. Chemical composition, microstructure, physical and mechanical properties were determined using standard methods. Non-destructive quality control of engine parts, statistical analysis of experimental data and deterministic factor analysis of the influence of structural components on the properties of the cast irons were carried out according to the methods developed with the participation of the authors. Bench and road motor tests of optimal composition cast irons details were carried out in engines according to standard and factory methods in accordance with state standards.
 Obtained results. The general laws and principles of the formation of the microstructure of cast irons with lamellar and nodular graphite are determined depending on the degree of their alloying with phosphorus and the influence of the scale factor. It has been established that phosphide eutectic in an amount of up to 5.8 % is a strengthening structural component and increases strength, hardness, wear resistance, heat resistance, and machin-ability of phosphorous cast irons with blade tools. The negative effect of phosphide eutectic on plastic properties and cyclic fracture toughness is less significant than the effect of increasing amounts of ferrite, its grain size and graphite. Optimal chemical compositions and microstructures of phosphorous cast irons for internal combustion engines details are recommended.
 Scientific novelty. For the first time, a comprehensive system for managing the properties of phosphorous cast irons has been developed, including the analytical determination of the required characteristics of structural components and the technology for their production.
 Practical value. Methods and technologies for melting, alloying, modifying, heat treatment and surface hardening of phosphorous cast irons have been developed. They make it possible to provide the required level of mechanical and operational properties of internal combustion engines details.

The thermal transport properties of five predominately pearlitic grades of grey, compacted graphite and spheroidal graphite iron have been investigated by the laser flash technique. Samples have been taken from cylinders cast in controlled thermal environments designed to produce three dissimilar cooling rates. Digital image analysis has been utilised in order to characterise the different graphite morphologies. The results indicated linear relationships between the thermal transport properties and the roundness of the graphite and the nodularity for compacted graphite and spheroidal graphite iron. A pronounced decrease in the thermal conductivity occurred when the lamellar graphite structure was transformed into compacted graphite. The thermal conductivity of compacted and spheroidal graphite iron has been recalculated with good accuracy over a temperature range of 25–500°C by means of regression analysis.

This article presents a comprehensive analysis of the industrial relevance and manufacturing processes of grinding balls produced from high-quality cast iron. Owing to its superior mechanical characteristics, high density, hardness, and cost-effectiveness, cast iron has long been a material of choice across multiple industrial sectors. In particular, its application in the production of grinding balls is driven by its excellent wear resistance and durability under high-pressure and high-friction operating conditions. Surface-hardened cast irons are extensively utilized for manufacturing crushing and grinding components in mineral processing industries. Beyond these applications, grinding balls made from high-quality surface-hardened cast irons demonstrate outstanding mechanical performance in equipment such as spreader shafts, sand handling machinery, and refractory material workshops. The study first explores the chemical composition and physical properties of cast iron, highlighting how carbon content and the incorporation of alloying elements influence hardness, toughness, and operational suitability. Enhancements to the cast iron matrix, through the addition of chromium, molybdenum, and other alloying elements, further improve resistance to wear and corrosion. The production process encompasses casting molten iron into molds followed by detailed microstructural analysis and optimization of the grinding balls. The technological parameters at each stage play a crucial role in determining the final mechanical properties, wear resistance, and overall service life of the products. Keywords: cast iron, grinding balls, microstructure, surface hardening, wear resistance, mechanical properties, industrial applications.

The progress in the development of composites with natural fibers for various applications in different sectors witnesses remarkable success worldwide in the last decade. Among the various natural fibers existing worldwide, pineapple leaf fibers (PALFs) possess remarkable mechanical properties because of the maximum content of cellulose (∼80%) among all natural fibers. In spite of having few limitations such as hydrophilicity, its advantages such as low cost, low weight, and biodegradability overweigh their limitations. The PALFs are poorly reported in the literature as a reinforcement in epoxy material. Bagasse, wheat straw, and coir have been successfully reinforced with epoxy resin; but inspite of having highest tensile strength among all natural fibers, PALF’s are seldom used. PALF has been characterized chemically, morphologically, and thermally. Using thermal analysis, the models were fitted to calculate its activation energies at different fraction levels using different heating rates. PALF epoxy composites have been prepared using the hand layup method. The effect of fiber loading has also been studied for morphological, chemical, mechanical, and thermal properties of composites. Composites with 10% fiber loading have better mechanical properties in comparison to composites with other fiber loading. Scanning electron microscopic micrographs of fractured surfaces have been analyzed for all fiber loading composites, and the results have been successfully studied linking the stated work of other distinguished researchers of this arena.

Although the main concern of consumers is to reduce the cost of energy consumption, zero-energy buildings are the main concern of governments, which reduce the carbon footprint of the residential sector. Therefore, homeowners are motivated to install distributed renewable energy resources such as solar energy, which includes photovoltaics (PVs), solar concentrators, and energy storage systems (ESSs); these installations are intended to maintain the homeowners’ energy consumption, and the excess energy can be sold to the grid. In light of the comfort consumption suggestions made by users, this paper presents an optimal home energy management (HEM) for zero-energy buildings and low energy consumption. Firstly, this paper proposes a new optimization algorithm called random integer search optimization (RISO). Afterwards, we propose a new objective function to enable zero energy consumption from the grid and lower costs. Therefore, in this study, the primary energy resources for homes are PVs and ESSs, while the grid is on standby during the intermittency of the primary resources. Then, the HEM applies the RISO algorithm for an optimal day-ahead load schedule based on the day-ahead weather forecast and consumers’ comfort time range schedule. The proposed HEM is investigated using a schedule of habits for residential customers living in Hong Kong, where the government subsidizes the excess clean energy from homes to the grid. Three scenarios were studied and compared in this work to verify the effectiveness of the proposed HEM. The results revealed that the load schedule within the comfort times decreased the cost of energy consumption by 25% of the cost without affecting the users’ comfort.

The article shows the relevance of the use of alloyed cast iron in mining and metallurgical engineering. The article discusses the technologies for producing naturally alloyed cast iron. For working bodies and friction units of mining machines, such as pumps, coal pumps, hydrocyclones, crushers and mills. The main type of wear for them is abrasive. To increase the wear resistance of cast iron the production of cast iron has not been sufficiently studied yet. Although the use of cast iron in a complex alloyed with manganese, silicon, chromium, titanium and vanadium has been studied. The article studies the influence of manganese, titanium and vanadium on the mechanical properties and performance of machine parts and products of mining and metallurgical production in contact with high-temperature and highly abrasive media. The rational content of titanium and vanadium in gray cast irons is established in the range of 0.05-0.1%, which ensures their heat resistance and increases their wear resistance. The content of these elements can be increased to 0.07-0.12%. Bushings made of this cast iron have the required wear resistance and can increase the operational reliability of the equipment in the conditions of mining and metallurgical production. They also replace non-ferrous metals, as well as products obtained by powder metallurgy methods.

Spheroidal graphite coalescence during thermal cycling in the ferritic domain of a high-silicon cast iron studied by optical microscopy and X-ray computed tomography