In this study four compacted graphite irons (CGIs) and one grey cast iron (FGI) were produced and tested in the laboratory. The molybdenum content of the four CGI grades was varied between 0 and 1··01 wt-%. The purpose of the investigations was to examine the effect of the different molybdenum contents of the CGI on the thermomechanical fatigue (TMF) behaviour. The TMF tests were performed by cycling a constrained specimen between 110 and 600°C. For every material three tests were performed on specimens machined from a ∅20 mm cylinder. Other tests were performed on specimens machined from ∅55 mm and ∅85 mm cylinders respectively. The tests showed that additions of molybdenum improved the fatigue resistance of CGI. It was observed that additions of molybdenum refined the pearlite and that the specimens with a finer metallic matrix had a higher TMF resistance.

In a previous study, the thermomechanical fatigue resistance of four compacted graphite irons (CGIs) and one grey cast iron was investigated. The molybdenum content of the four CGIs varied between 0 and 1.01 wt-%. It was observed that during thermal cycling, the maximum value of the compressive stress continuously decreased while the value of the maximum tensile stress continuously increased. The continuous decrease in compressive stresses showed that stress relaxation occurs at elevated temperatures during thermal cycling. The goal of the present investigation was to investigate the phenomenon of stress relaxation at elevated temperatures. The tests were performed at 350 and 600°C respectively. The results of the stress relaxation tests performed at 600°C showed the same trend observed at thermomechanical fatigue testing. The tests showed that additions of molybdenum improved the fatigue resistance of CGI by lowering the stress relaxation rate.

Gray cast iron has been investigated with respect to surface turbulence during mould filling. Different levels of flow velocities have been provoked in a vertically parted sand mould. The thermal resistant transparent front side of the mould permitted the observation of the flow pattern due to high speed camera registration. The registered frames including the liquid surface were investigated using image analyses. The results show good correlation between the average flow velocity and the liquid iron surface extension. Consequently it has been demonstrated that an increased absorption of hydrogen and nitrogen during mould filling is dependent on the level of liquid surface turbulence.

Purpose - The purpose of this paper is to obtain a finite difference method (FDM) solution using control volume for heat transport by conduction and the heat absorption by the enthalpy model in the sand mixture used in casting manufacturing processes. A mixture of sand and different chemicals (binders) is used as moulding materials in the casting processes. The presence of various compounds in the system improve the complexity of the heat transport due to the heat absorption as the binders are decomposing and transformed into gaseous products due to significant heat shock. Design/methodology/approach - The geometrical domain were defined in a 1D polar coordinate system and adapted for numerical simulation according to the control volume-based FDM. The simulation results were validated by comparison to the temperature measurements under laboratory conditions as the sand mould mixture was heated by interacting with a liquid alloy. Findings - Results of validation and simulation methods were about high correspondence, the numerical method presented in this paper is accurate and has significant potential in the simulation of casting processes. Originality/value - Both numerical solution (definition of geometrical domain in 1D polar coordinate system) and verification method presented in this paper are state-of-the-art in their kinds and present high scientific value especially regarding to the topic of numerical modelling of heat flow and foundry technology.

Defect formation like gas- and shrinkage porosity at cast iron component production is related to the content of gaseous elements in the liquid metal. The present work investigate the solubility of hydrogen and nitrogen in liquid iron aimed for production of lamellar and compacted graphite cast iron. The used methods and instruments are a combination of commercial measuring devices and novel experimental assemblies for measuring solubility of hydrogen and nitrogen during melting and mold filling of a complex shaped cast component. The obtained results reveal the role of the charge material and the mold filling on the solubility of the investigated elements. 

Cast iron is one of the oldest technical alloys used for creating objects. Foundrymen from the very beginning of casting was fighting to avoid casting defects. In the beginning a successfully performed casting was associated with witchcraft. Cast component producers suffer yearly substantial expenses due to rejecting or repairing castings. The present work will summarize research efforts to understand formation mechanisms of defects, performed in collaboration with Swedish foundries during the last years. The presented work will focus on defects, specific casting of gray iron components. Studied defects are gas porosity, shrinkage porosity and metal expansion penetration. Novell experimental set up has been developed or existing methods has been improved to study defect formation mechanisms. Today we can realize that casting without defects are possible only by approaching the defect formation mechanism with multidisciplinary science.

Lamellar graphite cast iron was investigated with carbon equivalents varied between CE = 3.4 and 4.26, cast at various cooling rates between 0.195 and 3.5 °C s−1 covering the limits used for technical applications in the production of complex-shaped lamellar graphite cast iron. Registered cooling curves displaced in two positions in the casting were used to predict the solidification and microstructure formation mechanisms. The predicted volume fraction of primary austenite was compared with the fraction of primary austenite measured on colour micrographs with the help of image analyses. A good correlation has been obtained for medium and slow cooling conditions, while a less good correlation at fast cooling condition was attributed to the used protective environment to preserve thermocouples. The observed fraction and the predicted fraction of primary austenite were in good correlation and followed a consequent variation dependent on the carbon equivalent. Furthermore, the quality of the prediction was dependent on the used numerical algorithm involving cooling information from either one or two thermocouples.

Primary austenite has been underestimated in general when the theories of nucleation, solidification, microstructure formation and mechanical properties were established for cast iron and particularly for lamellar cast iron. The present work aims to investigate the primary austenite morphology of as cast samples of a hypoeutectic lamellar cast iron produced with different cooling rates. Morphological parameters as the area fraction primary austenite, the secondary dendrite arm spacing, the dendrite envelope surface, the coarseness of the primary dendrite expressed as the relation between the volume of the dendrite and its envelope surface and the coarseness of the interdendritic space also known as the hydraulic diameter are measured. Furthermore, the role of the size of the investigation area is revealed to be sequential investigation. A strong relation between all measured morphological parameters and the solidification time has been established, except the volume fraction of primary austenite, which is constant for all cooling conditions.

The fracture mechanism of gray cast iron was investigated on tension loaded samples produced under different conditions. The parameters studied included the graphite morphology, the carbon content, the inoculation and the cooling condition. The observations made reveal the role of the microstructure on crack propagation. The cracks were found to always propagate parallel with the graphite flakes. The interaction between the metallic matrix precipitated as primary austenite and graphite has been interpreted by a simplified model of the austenite reinforced eutectic cell. The geometrical transcription gave a standard crack component configuration with known mathematical solution. The microstructure observed in the experiments has been analysed by means of a novel interpretation. The fictitious stress intensity at yield and the fictitious maximum stress intensity at failure are strongly related to the relative shape of the eutectic cell and the fraction primary austenite. A different slope is observed for the material cooled at high rate when the precipitation of primary carbide reduces the stress intensity. The observed relations indicate that the tensile strength of the grey cast iron is the result of the collaboration between the toughness of the metallic matrix precipitated as primary austenite and the brittleness of the graphite phase. The shape and distribution of the primary austenite and graphite can be influenced by chemical composition, by inoculation or by the cooling condition, but they will maintain equilibrium with respect to the stress intensity.

Primary austenite has been underestimated in general when the theories of nucleation, solidification, microstructure formation and mechanical properties was established for cast iron and particularly for lamellar cast iron. After extensive use of colour etching during the last two decades it has been found that primary austenite dendrites can be characterized using general morphology parameters like those used for other technical cast alloys with dendritic structure. The present work aims to investigate the primary austenite morphology of as-cast samples of a hypoeutectic lamellar cast iron produced with different cooling rates. Morphological parameters as the area fraction primary austenite, the secondary dendrite arm spacing, the dendrite envelope surface, the coarseness of the primary dendrite expressed as the relation between the volume of the dendrite and its envelope surface and the coarseness of the interdendritic space also known as the hydraulic diameter are measured. Furthermore the role of the size of investigation area is revealed be sequential investigation. A strong relation between all measured morphological parameters and the solidification time have been established excepting the volume fraction of primary austenite which is constant for all cooling conditions.

Although lamellar cast iron has been used in advanced applications for about 20 years, our knowledge about the mechanisms affecting microstructure and defect formation is relatively limited. The present paper summarises some solidification-related phenomena from a series of recently published peer-reviewed papers and scientific theses and suggests a mechanism of defect formation which is dependent on the shape of the solidifying casting geometry. When shrinkage porosity or metal expansion penetration occurs, evidence of material transport in the intergranular zone of primary equiaxed austenite grains in the casting and in the intergranular regions between the sand grains in the mould material is seen. Material transport occurs across the casting-mould interface, where the existence of or the permeability of the primary columnar zone determines if material transport can take place.

Microsegregation is closely related to the solidification characteristics and microstructure development of a material. In this paper, the microsegregation of Si, Cu, Mn, and P was investigated on a spheroidal and a compacted graphite iron using a modified EPMA equipped with WDS spectrometers. On the basis of the approximated local equilibrium eutectic temperature, the solidification sequence of the matrix was estimated. The inferred microstructure development appeared to correspond well to published interrupted solidification experimental results. Solute profiles and effective partition coefficients were constructed using the solidification sequence. While the spatial microsegregation patterns clearly differed between the two materials, solute profiles and effective partition coefficients were very similar. For Si, Cu and Mn, the solute profiles corresponded reasonably with simulation results produced using the Scheil-Gulliver module of the Thermo-Calc software with the TCFE7 databank, indicating back-diffusion of these elements is negligible for SGI and CGI with solidification times up to 10 min. The effective partition coefficients for Si, Cu and Mn were fairly constant until about 90% of the matrix had solidified, after which they appeared to approach unity.

Microsegregation is intimately coupled with solidification, the development of microstructure, and involved in the formation of various casting defects. This paper demonstrates how the local composition of the metal matrix of graphitic cast irons, measured using quantitative electron microprobe analysis, can be used to determine its solidification chronology. The method is applied in combination with Fourier thermal analysis to investigate the formation of micropores in cast irons with varying proportions of compacted and spheroidal graphite produced by remelting. The results indicate that micropores formed at mass fractions of solid between 0.77 and 0.91, which corresponded to a stage of solidification when the temperature decline of the castings was large and increasing. In 4 out of the 5 castings, pores appear to have formed soon after the rate of solidification and heat dissipation had reached their maximum and were decreasing. While the freezing point depression due to build-up of microsegregation and the transition from compacted to spheroidal type growth of the eutectic both influencing solidification kinetics and the temperature evolution of the casting, the results did not indicate a clear relation to the observed late deceleration of solidification.

This paper presents an unconventional etching technique to reveal the microstructure in a hypoeutectic lamellar graphite iron that has been quenched after isothermal heat treatment in the proeutectic semi-solid temperature region. A technique for quantifying the dendrite microstructure using the aforementioned etching technique involving a combination of a raster graphics editor and an image analysis software is outlined. The agreement between this quantification technique with regard to volume fraction and surface area per unit volume of the dendritic austenite and corresponding point counting and line intercept techniques is analyzed. The etching technique was found useful but sporadic tinting of martensite was problematic. Some measurements showed significant systematic disagreement which correlated with the coarseness of the measured dendrites. Most systematic disagreement is attributed to difficulties in defining the dendrite boundary in the analogues and much of the random disagreement to easily identified discrepancies between the analogue and the micrograph.

An SGI was machined into 400 g cylindrical pieces and remelted in an electrical resistance furnace protected by Ar gas to produce materials ranging from SGI to CGI. The graphite morphology was controlled by varying the holding time at 1723 K (1450 °C) between 10 and 60 minutes. The discrete sectional size distribution of nodules by number density was measured on cross sections of the specimens and translated to volumetric distribution by volume fraction. Subpopulations of nodules were distinguished by fitting Gaussian distribution functions to the measured distribution. Primary and eutectic graphite, were found to account for most of the volume of nodular graphite in all cases. For holding times of 40 minutes and greater, corresponding to nodularity roughly below 40 pct, the primary subpopulation was very small and difficult to distinguish, leaving eutectic nodules as the dominant subpopulation. The mode and standard deviation of the two subpopulations were roughly independent of nodularity. Moreover, the nodular and vermicular graphite were segregated in the microstructure. In conclusion, the results suggest that the parallel development of the vermicular eutectic had small influence on the size distribution of eutectic graphite nodules.

Cylinder heads have an extremely complex shape with large areas of concave casting surfaces. The concave casting surfaces are often associated with metal expansion penetration problems or other surface defects, e. g. surface shrinkage. The defects cause high production costs due to component rejection and increased fettling time. This report presents an investigation of the microstructure in grey cast iron close to the sand-metal interface affected by metal penetration in a complex shaped casting. The dominant penetration defect observed in the cylinder heads was expansion penetration. Even pre-solidification penetration and sand crack defects were observed. The microstructure found in the non penetrated areas is typical for solidification of grey iron cast in sand moulds.

The mechanism of metal expansion penetration of grey cast iron components is dependent on both solidification anomalies at the metal – mould interface and the inclination of the sand mould to permit the metal liquid to penetrate between the sand grains. The present work utilizes the latest development of primary austenite inoculation in combination with classic eutectic inoculation to limit the metallurgical contribution to metal expansion penetration. A solid shell containing the primary austenite dendrite network constitutes the barrier between the liquid metal and mould interface. Inoculants of both the primaryand eutectic phase control the permeability of the dendrite network.

In the present paper the oxygen balance during a temperature decrease and especially at temperatures close to the liquidus temperature has been studied for lamellar, compacted and nodular cast irons. Extrapolated data from the full scale trial results show that there are significant differences in the level of dissolved oxygen before start of solidification. Earlier research suggest the influence of the dissolved oxygen on the graphite shape, while the present work draws the attention on how the different shaped lamellar-, compacted- and nodular graphite is incorporated in the austenite matrix based on the differences in the dissolved oxygen content. Predicted differences in the dissolved oxygen are also suggested to influence the growth mechanism of the eutectic colonies and the graphite morphologies in the lamellar cast irons.

In this work, the influence of cooling rate, chemical composition and inoculation practice on the solidification of grey cast iron has been examined. The primary solidification structure, referred to as the macrostructure, was preserved using a special heat treatment, DAAS (Direct Austempering After Solidification). These samples were etched and the number of equiaxed and columnar crystals as well as the transition between these areas, CET, was examined quantitatively. Samples considered As-Cast were colour etched to reveal the microstructural constituents. On these samples the number of eutectic cells, fraction of primary austenite and DAS (Dendrite Arm Spacing) was investigated. The relationship between CET and the number of equiaxed crystals was confirmed, and decreases with increasing number of equiaxed crystals per unit volume. It was also found that the number of equiaxed chemical composition. Furthermore, there is a relationship between eutectic cells and DAS; where the eutectic cell size increases with increasing DAS. DAS, on the other hand, depends on inverse cooling rate and the number of equiaxed crystals.

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.

The amount of dissolved oxygen, as well as oxygen available as oxides, is considered to affect the nucleation and growth of porosity defects in gray iron castings. Therefore, the influence of melting process on oxygen content was investigated in the production at two foundries. The importance of temperature on the equilibrium between the melt and its surrounding was especially examined. It was found that the amount of dissolved oxygen decreased with decreasing temperature, but the total amount of oxygen remained unchanged, meaning that the amount of oxygen found as oxides increased as the temperature decreased.