Solidification Of Cast Iron Research Articles

Investigation on effect of different types of inoculants on the solidification of ductile cast iron using thermal analysis

PurposeProducing superior-quality ductile cast iron demands the use of various intricate inoculants. In addition to iron and silicon, these materials also include alloying elements like calcium, barium, cerium, bismuth and zirconium. These elements are effective in minimizing carbide solidification and enhancing the formation of eutectic cells, thereby resulting in improved cast iron quality.Design/methodology/approachThis article discusses the findings of an investigation on how various inoculants impact critical thermal analysis parameters such as undercooling, recalescence and their correlation with the nucleation of graphite nodules and shrinkage tendency.FindingsFor the study, five distinct inoculants with varying active components in their chemical composition were utilized. The particular formulation of the inoculant has a notable impact on the extent of undercooling during the solidifying process of ductile cast iron. Investigation indicates that incorporating inoculant reduces the temperature at which austenite dendrites form and raises the eutectic freezing temperature. Upon analyzing the microstructure, it is found that the inclusion of inoculation led to a rise in the nodule count from 103 to 272 nodules.Originality/valueAn increased graphite factor, which denotes the growth of graphite nodules during the subsequent stage of the eutectic reaction, supports the benefits of inoculation. Ce and Bi-inoculation have increased the growth of graphite nodules in the cast area during solidification compared to other inoculant formulations. This enhanced production helps in decreasing the size of macroporosity.

Investigation of The Effect of Molding Material Difference on Design in GGG70 Ductile Cast Iron Production

The casting process involves filling a prepared mould cavity with molten metal, which takes the shape of the container. While the liquid metal takes the shape of the container it is in, the method is attractive, while the volumetric changes during the liquid-solid transformation reveal the importance of moulding design for the manufacture of solid parts. Especially in cast irons, moulds with the same design may produce different results depending on the changing casting and foundry conditions because the volumetric change that occurs during the solidification of ductile cast irons is affected by many parameters and develops differently than in steel and aluminium castings. This study used model wet and resin molding materials to create single and double-riser moulding and castings with different section thicknesses. The importance of the type of mold material used in castings and the number of feeders for the robust production of the cast part was evaluated using experimental and modeling techniques. When the results were examined, it was seen that the shrinkage risk was lower with resin mould than with green sand moulding. In addition, depending on the riser connection point, the importance of the riser neck has emerged.

Influence of the Rate of Cooling/Solidification on the Location of Characteristic Points on the AT and ADT Curves of Cast Iron

The paper presents the results of the analysis of cooling curves of cast iron with approximately eutectic composition rasterized at different rates of cooling and ingot crystallization. The test samples were in the form of rods with a diameter of 30,0.mm and a coagulation modulus M = 0.75 cm. They were cast in a sand mould made of furan mass placed on a chill in the form of a cast-iron plate, with which one of the front surfaces of the rod casting was in contact. In this way, a differentiated cooling rate along the rod was achieved. At selected distances from the chiller (5, 15, 25, 25 and 45 mm) thermocouple moulds were placed in the cavity to record the cooling curves used in thermal (AT) and derivation (ATD) analysis. The solidification time of the ingot in the part farthest from the chiller was about 200s, which corresponds to the solidification time in the test cup AT. An analysis of the recorded cooling curves was performed in order to determine the values of characteristic points on the AT curve (Tsol. Tliq, ΔTrecal., τclot, etc.). Relationships between cooling time and rate and characteristic points on AT and ATD curves were developed. For example, Tsol min changes in the range of 1115 - 1145 for the range of cast iron solidification times in the selected ingot zone from ~ 70 to ~ 200 s, which corresponds to the process speed from 0.0047 to 0.014 [1/s]. The work also includes an analysis of other characteristic points on the AT and ATD curves as functions of the solidification rate of cast iron of the same composition.

Механизм влияния электрического поля на процесс модифицирования серого чугуна

A diagram of an experimental installation for measuring the electrical resistance of a gray cast iron melt is presented, where a gauge based on a Kelvin double bridge is used. It is shown that the value of the specific electrical resistance of gray cast iron varies depending on the type of conditioning agent. Experimental data on the difference in specific resistivity values for various gray cast iron nucleating agents are presented. Changes in the values of electrical resistance under the influence of electric field treatment of inoculated cast iron melt are also given. Comparison of the strength values of gray cast iron with its values of the electrical resistivity of the cast iron melt after the electrical field exposure showed their simultaneous change. The decrease in the values of the electrical resistance of hot iron due to the electric field exposure is shown and it corresponds to an increment in the strength of inoculated cast iron. The effectiveness of the electric field exposure on the process of inoculation is determined by thermal ionization of the chemical elements included in the conditioning agent. The maximum increase of these parameters after electric field exposure when using FS75 nucleating agent is shown. The mechanism of the influence of an electric field on the cast iron solidification for the inoculation process of FS75, containing 75 % silicon in its composition, is described. The dependence of the efficiency of electric field exposure on the composition of the nucleating agent for gray cast iron is shown. A physical model of the effect of an electric field exposure on the process of cast iron inoculation is found. The possibility of influencing the hydrodynamic situation in the melt of gray cast iron and changing the rate of dissolution of nucleating agent particles by means of electric field exposure is given

Simulation of the casting and solidification process of the brake shoes intended for rolling stock

The paper presents the results obtained from the simulation of the casting and solidification process of the phosphorous cast iron brake blocks intended for rolling stock. The simulation of the casting and solidification process was carried out using the SolidWorks and Altair inspire cast programs. A S1 type brake shoe was chosen for this process. The solidification of phosphorous cast iron brake blocks is influenced by a number of constructive and technological factors. The simulation allows analysis of technological characteristics of casting and solidification of the alloy. The solidification process influences the micro and macrostructure of the parts, their compactness, mechanical strength, dimensional accuracy and surface quality.

Microstructure and Properties Variation of High-Performance Grey Cast Iron via Small Boron Additions

A study was undertaken to investigate the effects of small boron additions on the solidification and microstructure of hypo-eutectic alloyed grey cast iron. The characteristic temperatures upon crystallisation of the treated metal melt were recorded, specifically those concerning small boron addition by using thermal analysis with the ATAS system. Additionally, a standardised wedge test was set to observe any changes in chill performance. The microstructures of thermal analysis samples were analysed using a light optical microscope (LOM) and field emission scanning electron microscopy (FE-SEM) equipped with energy dispersive spectroscopy (EDS), which reveal variations in graphite count number with the addition of boron within observed random and undercooled flake graphite. The effect of boron was estimated by the classical analytical and statistical approach. The solidification behaviour under equilibrium conditions was predicted by a thermodynamic approach using Thermo-Calc. Based on all gathered data, a response model was set with boron for given melt quality and melt treatment using the experimentally determined data. The study reveals that boron as a ferrite and carbide-promoting element under the experimental set shows weak nucleation potential in synergy with other heterogenic nuclei at increased solidification rates, but no considerable changes were observed by the TA samples solidified at slower cooling rates, indicating the loss of the overall inoculation effect. The potential presence of boron nitride as an inoculator for graphite precipitation for a given melt composition and melt treatment was not confirmed in this study. It seems that boron at increased solidification rates can contribute to overall inoculation, but at slower cooling rates these effects are gradually lost. In the last solidification range, an increased boron content could have a carbide forming nature, as is usually expected. The study suggests that boron in traces could affect the microstructure and properties of hypo-eutectic alloyed grey cast iron.

A Review of Dendritic Austenite in Cast Irons

Solidification of cast irons usually involves dendritic growth of austenite. This article presents a literature survey about the dendrites in cast irons, their consequences and how they may be manipulated. The literature review is supplemented with relevant micrographs from our research. While austenite usually transforms into ferrite or pearlite, the dendrites limit where liquid flows, where eutectic grows, and where segregated elements go. The amount and shape of dendrites show correlations with tensile strength in pearlitic gray and compacted graphite irons. There are also indications that a coarse dendrite grain structure may be beneficial to tensile strength. The dendrite grain structure depends on melting process parameters and shows sensitivity to melt treatment. The evolution of scale of dendrite arms and their spacing under isothermal condition is by now fairly well-understood; however, work remains to better understand its evolution during cooling and its interaction with the eutectic. The amount and shape of dendrites are less understood in irons of near-eutectic and hypereutectic composition, in particular mixtures of dendrites of distinct scales, associated with regions of distinct graphite morphology. While significant advances have been made in recent years, the role and control of dendrites remain a relatively unexplored area of research with potential to improve production and properties of cast irons.

Certain investigation on feasibility of developing riser less ductile iron castings

The solidification mechanism of ductile iron is a bit complex due to the precipitation of graphite and silicon. These elements change the solidification pattern of cast iron. Density of these elements is less than iron leads to occupying more volume consequently increase the overall metal volume. There are two aspects on this increase in metal volume. One is, reducing this volume increase to reduce the creation of porosities at the earlier stage of solidification and second is, using this volume increase to remove porosity at the later stage of solidification. Proper understanding of this graphite expansion in cast iron solidification will bring insights on reducing or removing of the risers. The current study focus on correlating the net contraction and austenitic liquidus point with shrinkage. The average contraction found through this study is 1.36 % which is more than the net expansion of 0.25 % (without riser) reported in literature. The study found that properly balancing graphite precipitation, pouring temperature and mold strength can enable riserless casting of ductile iron by compensating for liquid contraction through graphite expansion.

Термодинамічні закономірності структуроутворення високоміцного чавуну при модифікуванні та різних умовах кристалізації розплаву

The article presents the results of the analysis of thermodynamic regularities of structure formation of high-strength cast iron during modification and under different conditions of melt crystallization. The concept of the formation of graphite nuclei in high-strength cast iron is proposed. It has been established that during the modification of molten iron, as a result of a significant redistribution of all elements dissolved in it, impurities (sulfur, phosphorus, etc.) are removed, which makes it possible to obtain the structure of cast iron with nodular graphite with the use of modifiers. During the crystallization of cast iron with the release of austenite, direct microliquation of silicon with a distribution coefficient less than one is characteristic, manganese is more evenly distributed in the metal, and carbide stabilizing elements are treated in the liquid phase. A thermodynamic calculation of the thermal effects of the reactions of the release of graphite from carbon dissolved in iron, the transition of silicon and manganese from a liquid state to a solid state in the process of forming high-strength cast iron is presented. The physical and latent heat of crystallization of high-strength cast iron was determined by the enthalpy method. Thermodynamic calculations were performed and the thermal effects of reactions (9) in the melt of high-strength cast iron were determined, depending on their concentrations and the temperature of the melt. Using the results of thermodynamic calculations makes it possible to study the crystallization process by changing the number and composition of phases that are formed under the influence of heat release of phase transformations. It was found that the introduction of Si into pre-eutectic alloys (from 1 to 5% at.) leads to a slight decrease in the latent heat ΔН of crystallization of primary graphite (up to 3% for each atomic percentage of Si). As a result of the change in the temperature interval, its release causes a decrease in the total physical heat of crystallization Qf. It is shown that the thermodynamic analysis of the processes that occur during the crystallization of cast iron based on the data on the change in enthalpy for the system Fe-C-Xi (Xi = Si, Mn) indicates that with an increase in carbon, the change in enthalpy in the crystallization interval changes approx lyzno by 16 kJ/mol. The physical heat of crystallization has a significant effect on the change in the value of the total heat of crystallization of cast iron Qkr Fe-C-Xi (Xi = Si, Mn) in comparison with the Fe-C alloy. The latent heat of crystallization during solidification of high-strength cast iron is between 245 and 275 kJ/kg.

Investigation on effect of carbon equivalent and inoculation on the solidification and shrinkage tendency of ductile cast iron using thermal analysis

PurposeThe foundry industry incurs additional costs as a result of defective castings. Shrinkage defects are a frequent problem in ductile iron castings. It is still essential to understand how shrinkage porosity varies in size when the ductile iron composition changes. This information can be used to produce high-quality cast parts and determine the best processing conditions. The objective of this research paper is to examine the effect of carbon equivalent and inoculation on the morphology of the shrinkage defect using thermal analysis.Design/methodology/approachThis study focuses on certain thermal analysis parameters, such as the angle of the first derivative curve at the solidus temperature, recalescence and its relationships to graphite nucleation and shrinkage tendency. The results of thermal analysis in terms of the cooling curve and its derivative parameters, and thorough characterizations of the shrinkage observed in cup castings produced with various melt compositions and inoculation are presented in the current study.FindingsThe proportion of caved surfaces and macro shrinkage porosity defects has been reduced as the carbon equivalent of melt increases from hypoeutectic to a hypereutectic composition. The composition that is slightly hypereutectic has the lowest shrinkage propensity. Although inoculation reduces shrinkage, the importance of this parameter differs depending on the carbon equivalent.Originality/valueThe percentage of macro shrinkage porosity and the angle that the cooling rate curve forms are strongly correlated. It is found that the macro shrinkage size decreases as the angle of the first derivative curve at the solidus temperature is reduced. Further, lower macroporosity is produced by a metal that has a higher nodule count in association with a greater cooling rate toward the end of the solidification process.

Analyzing the effect of inoculant addition on the solidification of ductile cast irons using thermal analysis

PurposeThe final properties of ductile iron are decided by the inoculant processing while pouring the melt. The shape and size of nodules generated during solidification are of paramount importance in solidification of ductile cast iron. The purpose of this study is to examine the effect of different inoculant addition on the solidification of ductile cast iron melt through thermal analysis.Design/methodology/approachThermal analysis has recently grown as a tool for modeling the solidification behavior of ductile cast irons. Iron properties will be predicted by analyzing the cooling curve patterns of the melts and predicting the related effectiveness of inoculant processing. In this study, thermal analysis is used to evaluate the need for inoculation.FindingsThe amount and type of inoculation will affect the amount of undercooling during the solidification of ductile cast iron. It is found that the addition of 0.1 to 0.4 Wt.% inoculant lowers the austenite dendrite formation starting temperature while increasing the eutectic freezing temperature. Microstructure analysis revealed that the addition of inoculation increases the nodule count from 103 to 242 nodules. The beneficial effects of inoculation are sustained by an improved graphitization factor, which shows the formation of graphite nodules in the second phase of the eutectic reaction.Originality/valueThe inoculation treatment has improved metallurgical occurrences such as carbide to graphite conversion, graphite microstructure control, graphite nodule count at the start of solidification and the last stage of solidification, which determines the soundness of casting. The foundry industry can follow these steps for monitoring the solidification of ductile iron castings.

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

Cast iron is a material with a unique combination of design flexibility, mechanical properties, wear resistance, recyclability, low life cycle energy consumption and low cost. The optimization of current production and the development of new material variants with improved properties rely on the control of the melt throughout the process, from charge selection to casting. Thermal analysis just prior to pouring the molds has been developed over the years for melt control, e.g., for composition verification or for graphite shape prediction. Since minor additions of tellurium prevent graphite growth, thermal analysis with Te-coated cups is commonly used for compositional control of slightly hypereutectic alloys. The present study was designed to test the feasibility of using Te-coated cups to monitor the magnesium content of melts after a full or partial spheroidizing treatment leading to spheroidal or compact graphite, respectively. In the course of this work, it was realized that thermal analysis could give unreliable results when the microstructure of the casting is not homogeneous, i.e., it exhibits a mixture of metastable and stable eutectics. Tellurium has been shown to have an ambivalent effect on solidification of Mg-bearing melts.

Density change upon solidification of silicon cast irons

Amongst the possible defects that can appear during casting, voids due to solidification shrinkage is certainly the most usual and important in the case of cast irons. For any predicting work, the knowledge of the density of the phases of interest, namely liquid, austenite and graphite, is a prerequisite. The density of liquid and austenite in silicon cast irons are here assessed as function of composition and temperature based on the literature review. Estimate of theoretical expansion upon solidification are then derived for lamellar and spheroidal graphite cast irons and compared to reported experimental values obtained in near-equilibrium conditions.

MODELLING AND VALIDATION OF EFFECT OF BINDER TYPE ON FEEDING BEHAVIOUR OF SPHEROIDAL GRAPHITE CAST IRON

ABSTRACT In the casting method, it is crucial to properly make the moulding design to produce sound parts. Volumetric change, especially during the solidification of spheroidal graphite cast irons, may show different behaviour compared to steel and aluminium castings. In this study, castings were carried out with single and double feeders with varying casting parameters of green sand and resin mould sand containing different cross-sectional thicknesses. Depending on the chemical composition, mould rigidity and inoculation efficiency, and the importance of the feeder path was evaluated by experimental and modelling techniques. Consequently, it was observed that the risk of shrinkage in resin moulds is less than in green sand castings in the same moulding design. In addition, it has been found that the number of feeders and neck connection is an important parameter in pore formation.

Experimental Verification of the Cast Iron Solidification Model

Experimental Verification of the Cast Iron Solidification Model

Effect of solutes on the formation of primary carbides during solidification of hypereutectic high chromium cast irons through thermodynamic modeling

Effect of solutes on the formation of primary carbides during solidification of hypereutectic high chromium cast irons through thermodynamic modeling

Unraveling compacted graphite evolution during solidification of cast iron using in-situ synchrotron X-ray tomography

In spite of many years of research, the physical phenomena leading to the evolution of compacted graphite (CG) during solidification is still not fully understood. In particular, it is unknown how highly branched CG aggregates form and evolve in the semi-solid, and how local microstructural variations at micrometer length scale affect this growth process. We present here the first time-resolved synchrotron tomography combined with a bespoke high-temperature environmental cell that allows direct observation of the evolution of CG and relates this dynamic process to the local surrounding microstructures in a cast iron sample during repeated melting and solidification. Distinct processes are identified for the formation of CG involving the nucleation, growth, development of branches and interconnection of graphite particles, ultimately evolving into highly branched graphite aggregates with large sizes and low sphericities. CG is found to nucleate with a spheroidal or a plate-like shape, developing branches induced by high carbon concentration, e.g. thin melt channels. Additionally, CG grows much faster than spheroidal graphite during subsequent cooling in solid state. The direct visualization of the dynamic solidification process provides unprecedented new insights into formation mechanisms of CG and correlating factors such as local microstructural variations, and guides the development of CG iron solidification models.

Microstructural Observation of Dendrite and Its Surrounding Regions Formed during Solidification of Gray Cast Iron

Microstructural Observation of Dendrite and Its Surrounding Regions Formed during Solidification of Gray Cast Iron

Effects of High-Concentration Cu and Sn on the Nucleation and Growth Behavior of Graphite on Rare-Earth Compounds During the Solidification of Cast Iron

Effects of High-Concentration Cu and Sn on the Nucleation and Growth Behavior of Graphite on Rare-Earth Compounds During the Solidification of Cast Iron

An Integrated Approach for the Characterization of the Solidification Structure of Free Graphite Cast Irons

Abstract Over the years, the majority of the studies that addressed the study of the solidification of free graphite cast irons have focused primarily on explaining the influence of graphite morphology on the solidification mechanism, but instead, have dedicated much less attention to the influence of the metallic phase that grows together with graphite, which is the austenite. However, the combined use of the direct autempering after solidification technique and color etching makes it possible today to extend the study of the solidification of these materials by considering the growth of the austenite. The objective of the present study is to demonstrate how these two techniques can be exploited to understand the solidification macro and microstructure and the microshrinkage cavities formation in free graphite cast irons. The results show that these techniques find potential application in studies aimed at developing procedures to refine both the macroscopic and microscopic solidification structures, such as those investigating the use of inoculants to refine the austenitic grain structure, and its consequences on the microsegregation pattern, the eutectic solidification and the tendency to form microshrinkage.