Solidification Of Gray Cast Iron Research Articles

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

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

Density Variations during Solidification of Grey Cast Iron

As part of moving towards a sustainable production of diesel engines for heavy vehicle applications, the ability to predict casting defects has become ever so important. In order to model the solidification process for cast components correctly, it is of essence to know how the material will actually behave. To produce sound castings, often of complex geometry, the industry relies on various simulation software for the prediction and avoidance of defects. Thermophysical properties, such as density, play an important part in these simulations.Previous measurements of how the volume of liquid grey iron changes with temperature has been made with a conventional dilatometer. Measurements have also been made in the austenitic range, then on iron-carbon-silicon alloys with a carbon content lower than 1.5 wt%. Based on these measurements the density variations during solidification were calculated. The scope for this paper is to model the volume changes during solidification with the control volume finite difference method, using data from the density measurements.

Volume change during the solidification of grey cast iron: its relation with the microstructural variation, comparison between experimental and theoretical analysis

The expansion/contraction during the solidification of grey cast iron was studied using Linear Variable Differential Transformer (LVDT). The experiments were conducted with and without melt treatment. Two types of inoculant used for melt treatment: ASSC (Si, Ca, Sr & Al) and MBZCAS (Si, Ca, Zr, Ba, Mn & Al). Microstructural investigations carried out to quantify the eutectic cells, undercooled graphite, primary austenite and secondary dendritic arm spacing (SDAS). It was found that the casting shows hardly any shrinkage during early solidification but in the eutectic region, the casting expands until the end of solidification. The measured and the calculated volume changes are close to one another, but the former shows more expansion. The addition of MBZCAS promotes more flake graphite, and ASSC does not increase eutectic cells much. In addition to that, it lowers the primary austenite fraction, promotes more eutectic growth, decreases undercooled graphite and SDAS. As a result, the volume expansion changes in the eutectic region.

Formation and Utilization of Nanostructures Based on Carbon During Primary Aluminum Production

Results are given for comprehensive research concerning fields of metallurgy, nanomaterials, and ecology. Taking account of theoretical concepts and known practice of modifying gray cast iron, a new ultrafine modifier is considered containing carbon with increased chemical activity. It is established that carbon foam, electrolyzer dust from electric filters, and alumina passing through a dry gas cleaning system, have carbon nanostructures in their composition. Raw material composition for preparing modifying additive, procedures, and experimental materials are provided. Results are given from a series of cast iron melts with a different modifier content and a method for adding it with replacement of 50% of standard metallurgical graphite by the carbon-containing part of carbon foam. The effect of modifier on phase formation during gray cast iron solidification by means of cooling from a liquid condition is considered. A test cast iron sample and reference cast iron are analyzed chemically, and mechanical properties are analyzed. It is established that a modifier makes it possible to improve gray cast iron grade. Theories are proposed for carbon nanotube formation during aluminum production. A technology is provided for extracting carbon structures from starting raw material. It is shown that with preparation of one ton of aluminum using the production solutions developed for decontamination and utilization of industrial waste it is possible to produce modifier based on highly organized carbon nanostructures.

Thermal Microstructural Multiscale Simulation of Solidification and Eutectoid Transformation of Hypereutectic Gray Cast Iron

Although the gray cast iron solidification process has been the subject of several modeling studies, almost all available models appear to deal with only the more widely used hypoeutectic compositions. Models related to hypereutectic gray iron compositions with lamellar (or flake) graphite, and in particular for the proeutectic and eutectoid zones, are hard to find in the open literature. Hence, in the present work, a thermal microstructural multiscale model is proposed to describe the solidification and eutectoid transformation of a slightly hypereutectic composition leading to lamellar graphite gray iron morphology. The main predictions were: (a) temperature evolutions; (b) fractions of graphite, ferrite, and pearlite; (c) density; and (d) size of ferrite, pearlite, and gray eutectic grains; (e) average interlamellar graphite spacing; and (f) its thickness. The predicted cooling curves and fractions for castings with two different compositions and two different pouring temperatures were validated using experimental data. The differences between this model and existing models for hypoeutectic compositions are discussed.

The Effect of Inoculation on the Thermal Expansion/Contraction during Solidification of Gray Cast Iron

Inoculation of casting used to improve the microstructure and the properties of the component. Depending upon the area of application, gray cast iron has different microstructure and mechanical properties. The type and amount of the inoculation result in shape and orientation differences of the flake graphite. The Linear Variable Differential Transformer (LVDT) shows a variation in displacements change during the solidification. Temperature measurement used to analyze cooling curves and microstructural analysis of sample to examine the physical differences. Thermal analysis compared with the experimental results and microstructural study for describing the variation in area fraction and shape of graphite. The experimental result indicates contraction in austenite formation region, and expansion in eutectic formation region. The effect of the inoculant and the superheat temperature shows a variation in degree of expansion/contraction and cooling rates of the experiments. The comparisons between the experimental and the theoretical results have been done. Combining the theoretical and experimental results, it resembles a difference in eutectic formation region, and it needs carful investigation in future works.

Cast Iron Solidification Structure and how it is Related to Defect Formation

In this work, the meaning of the solidification structure and how it is related to defect formation in grey cast iron will be discussed. The work also confirms observations made earlier. In previous work the formation of shrinkage porosity in grey cast iron cylinder heads was investigated. It was found that the defect is located around solidification units resembling primary austenite grains. The solidification of grey cast iron starts with the formation of primary austenite grains, followed by the eutectic solidification. The primary grains nucleate and grow either as columnar or equiaxed grains, creating a columnar to equiaxed transition between the two zones. Based on the presence of a migrating hot spot, and other characteristics found on the cylinder heads, a geometry was developed that promote the formation of shrinkage porosity. The primary solidification structure, normally transformed during the solid state transformation, was preserved using a technique called Direct Austempering After Solidification (DAAS). After solidification, the samples were cut and prepared for investigation using a Scanning Electron Microscope (SEM) equipped with a detector for Electron Back Scattered Diffraction (EBSD). Individual grains were identified and the primary solidification structure around the defects was revealed. The investigation shows how shrinkage porosity is formed and located between primary austenite grains. This confirms that the primary solidification structure has a large influence on the formation of defects in grey cast iron. The investigation also confirms the correctness of earlier results as well as the validity of the DAAS technique.

Influence of Primary Austenite on the Nucleation of Eutectic Cells

The solidification of gray cast iron starts with the precipitation of primary austenite. This phase nucleates either as columnar or equiaxed dendrites depending on whether nucleation occurs on the mould wall or on particles and impurities in the melt. In this work, the nucleation of primary austenite and its influence on the eutectic solidification has been investigated using different amounts of iron powder as inoculants. Besides, the influence of different cooling rates was also examined. Within each austenite grain there is a microstructure, and this microstructure was investigated using a color etching technique to reveal the eutectic cells and the dendritic network. It is shown how the cooling rate affects the dendritic network and the secondary dendrite arm spacing, and how the microstructure can be related to the macrostructure through dendrite arm spacing. The secondary dendrite arm spacing is a quantification of the primary austenite belonging to the primary solidification, and it will be shown how the eutectic cell size is related to the secondary dendrite arm spacing. The total amount of oxygen influences the microstructural dimensions. This effect, on the other hand, is influenced by the cooling rate. The number of eutectic cells versus eutectic cell size show two distinct behaviors depending on whether being inoculated with iron powder or a mixture of iron powder and commercial inoculant. The addition of a commercial inoculant decreases eutectic cell size and increases the number of cells, while iron powder almost only changes cell size.

Inoculation and its effect on primary solidification structure of hypoeutectic grey cast iron

The solidification of grey cast iron is controlled by the addition of inoculants. This is done in order to provide nucleation sites and hence facilitate the formation of eutectic cells and decrease the degree of undercooling. The number of eutectic cells and the graphite morphology affect the final properties of the casting. Preceding the nucleation of graphite and the eutectic cells is the nucleation of the primary austenite. It was found that the addition of inoculants also influences the primary solidification. The largest effect on the primary dendrites is obtained by inoculation using pure iron powder. It was also shown how the columnar to equiaxed transition (CET) depends on the number of equiaxed dendrites per unit volume. In addition, the primary structure was found to influence the eutectic solidification. The relationship between the secondary dendrite arm spacing and the eutectic cell size was found to correlate well with the work of others.

Influence of duplex melting process on melt quality and solidification of grey cast iron

The quality of molten iron produced by two melting processes, the medium frequency induction furnace melting process and the shortcut duplex melting process with blast and medium frequency induction furnaces, has been studied comparatively. The shortcut melting process contributes to a higher undercooling tendency of base iron, and the extent of this tendency depends on other processing parameters such as ratio of charges, fluctuation in composition, superheating temperature and holding time, etc. When the shortcut melting process is used in the production of grey cast iron, there are no essential differences, with subsequent proper inoculation, in the microstructure and mechanical properties of castings compared with the conventional medium frequency induction melting process. Inoculation is a very effective method to alleviate and/or eliminate the negative effect when the shortcut melting process is used.

On the effect of natural convection on the thermal-microstructural evolution in gray cast-iron solidification

A coupled analysis involving natural convection, thermal balance, and microstructural evolution that take place in the solidification process of a hypoeutectic gray cast iron is presented in this work. The microstructural formulation used in this study includes classical models of primary-austenite and eutectic (gray and white) transformations. The influence of both natural convection and heat-transfer conditions on the thermal-microstructural response is particularly assessed in a simple cylindrical casting system. The evolutions of temperature and different microstructural variables are compared and validated with available experimental measurements.

EVALUATION OF LATENT HEAT OF SOLIDIFICATION OF GREY CAST IRON FROM COOLING CURVES

The temperature history in the casting obtained from cooling curves can be used to determine some information related to latent heat release during alloy solidification. This work presents a procedure for the evaluation of latent heat of primary and eutectic solidification of grey cast iron from cooling curves based upon the Newtonian cooling principle. The thermal data obtained from quik-cups are processed with the Mathcad code in order to obtain the cooling curve, its first and second derivatives and the first derivative of the fictitious neutral body generated according to the principles of Newtonian cooling assumption. The cooling curves of seven different alloys of hypoeutectic, eutectic and hypereutectic compositions were investigated with special emphasis on the amounts of latent heat released during primary and eutectic solidification. The values obtained are consistent with the statement that the latent heat of eutectic solidification should increase as the composition of the cast iron comes closer to the eutectic point, but the methodology is found to be unreliable for the estimation of latent heat of primary solidification.On peut utiliser l’histoire thermique dans le moulage, obtenue à partir des courbes de refroidissement, pour déterminer l’information reliée au relâchement de chaleur latente lors de la solidification de l’alliage. Ce travail présente une procédure d’évaluation de la chaleur latente de solidification primaire et eutectique de la fonte grise, à partir des courbes de refroidissement, basée sur le principe de refroidissement newtonien. Les données thermiques obtenues de coupelles sont traitées avec le code Mathcad afin d’obtenir la courbe de refroidissement, sa première et sa seconde dérivées ainsi que la première dérivée du corps neutre fictif, engendré d’après les principes de l’hypothèse de refroidissement newtonien. On a étudié les courbes de refroidissement de sept alliages différents de compositions hypoeutectiques, eutectiques et hypereutectiques, avec emphase particulière sur les quantités de chaleur latente relâchées lors de la solidification primaire et eutectique. Les valeurs obtenues sont consistantes avec l’énoncé disant que la chaleur latente de solidification de l’eutectique devrait augmenter à mesure que la composition de la fonte s’approche du point eutectique, mais on trouve que la méthodologie n’est pas fiable pour l’estimation de la chaleur latente de solidification primaire.

Comments on “Eutectic solidification of gray cast iron”

Applying a new technique for studying the orientation of austenite at room temperature, where it would normally transform to martensite, Rivera et al. have studied the solidification of gray cast iron. Their conclusions are in general agreement with the classical work in this field.

Reply to comments on the solidification of gray cast iron

The discussion is focused on the differences between what Hillert calls “classical work in the field” and the more recent bibliography. The authors prove that the role of austenite dendrites on the solidification of eutectic and hypereutectic gray iron has been overlooked over recent years, and that the picture of the solidification mechanism was not clear.

Solidification of gray cast iron

This article investigates the solidification of hypo, eutectic and hypereutectic gray cast irons, using novel techniques developed by the authors. The nature of the revealed macro and microstructure suggests that the solidification mechanism is different from that usually accepted.

A 2D stochastic micro-macro model of equiaxed eutectic solidification

We propose a model of equiaxed eutectic solidification that couples macroscopic heat diffusion with a microscopic description of nucleation and growth of the eutectic grains. The heat equation is solved numerically by means of an implicit finite difference method. The evolution of solid fraction is deduced from a stochastic model of nucleation and growth which uses the local temperature (interpolated from the FDM mesh) to determine the local grain density and the local growth rate. The model predicts the evaluations of both temperature and solid fraction at any point of the sample. Moreover, a realistic appearance of the recalescence on the cooling curves, as well as a detailed picture of the microstructure, are predicted. We apply the model to the solidification of grey cast iron.

Influence of low-gravity solidification on heterogeneous nucleation in stable iron-carbon alloys

The processes of nucleation and growth of alloys during solidification are linked to the level of gravitational force. In a low-gravity environment, buoyancy-induced convection becomes negligible, resulting in lower convection as compared to normal or high gravity. In this paper, heterogeneous nucleation and grain multiplication during solidification of gray cast iron, and the effect of gravitational level on them, have been studied by means of directional solidification on ground and under low-gravity (low-g) and high-gravity (high-g) conditions obtained by aircraft parabolic flights. It has been assumed that the final number of eutectic grains results from the contribution of heterogeneous nucleation,Nh, heterogeneous nucleation induced by inoculation,Ni, and heterogeneous nucleation induced by convection,Nc. In turn,Nc has two components, a grain multiplication component,Ncm, and a kinetics of chemical reactions component,Nck. In all cases, it was found that a higher number of grains are obtained when solidifying in highg as compared with lowg. This was attributed to higher convection in highg. It was demonstrated that grain multiplication due to convection can contribute 20 to 23 pct from the total number of grains resulting from heterogeneous nucleation of uninoculated samples. For the case of inoculated samples, it was shown that the contribution to the convection-induced nucleation of the kinetics of chemical reactions can be as high as 30 pct but can be zero at very low or very high grain numbers. A possible mechanism and an explanation have been given to those findings. The silicon distribution, graphite morphology, and the influence of soak time on experimental results have also been discussed.

Influence of Carbon Equivalent on the Volume Change during Solidification of Gray Cast Iron

Influence of Carbon Equivalent on the Volume Change during Solidification of Gray Cast Iron