Graphite Cast Iron Research Articles

Challenges and possibilities of the manual metallographic serial sectioning process using the example of a quantitative microstructural analysis of graphite in cast iron

Abstract The 3D microstructure analysis presented in this study focuses on the nodular graphite of an EN-GJS grade cast iron. The shape is analyzed based on shape factor and aspect ratio as well as average particle size and distribution. The shape of graphites in cast iron materials is critical to the mechanical properties of these alloys and is essential for the characterization of the material. Metallographic serial sectioning creates a digital twin of the material, which is removed layer by layer and visualized layer by layer under an optical microscope. From this three-dimensional twin, any number of planes can be digitally projected and analyzed. Conventional quantitative 3D analysis examines the voxel count and composition of a body in 3D space. The analysis presented here applies stereological 2D analysis methods to three spatial planes of the material. Two of the planes are digital projections of the twin. The two reconstructed planes of the material are chosen so that the direction vectors of all three planes form an angle of 90° to each other. The methodology is described in detail and the challenges and opportunities of the serial section method presented here are discussed.

Friction, wear, and anti-scuffing behaviors of zinc phosphate film on cylinder liners

Zinc phosphate chemical conversion coating possesses excellent tribological properties, which has attracted increasing attention. In this work, the friction, wear and anti-scuffing performance of zinc phosphate film applied on the cylinder liners were studied using a self-designed friction and wear experimental apparatus, which can sufficiently simulate the working conditions of the piston ring and cylinder in a real engine. The experimental results indicate that comparing with the uncoated cylinder liner, the friction force and total wear losses of friction pairs for the zinc phosphate coating are reduced by 8% and 27.5%, respectively, which is attributed to the formation of the protective film containing metal oxides and iron phosphate. In the scuffing test, uncoated cylinder liner exhibits better anti-scuffing performance because of the spalling of the cast iron graphite. On the contrary, the zinc phosphate coating particles remaining on the worn surface after oil-cut off are peeled off and acted as the abrasive at the contact interface, which accelerates the plastic deformation of friction pairs and the cast iron graphite is covered by the plastic flow of the material.

Relationships Between Macrostructure and Microstructure in Lamellar Graphite Iron Castings

AbstractSpherical sheet steel molds filled with gray iron melts of varying chemical compositions and metallurgical conditions were air-cooled until solid, followed directly by austempering to preserve the austenite grain structure. The castings were studied using a combination of cooling curves and quantitative metallography, in order to clarify control of the austenite grain structure and its impact on the local microstructure. A novel method utilizing fast Fourier transform provided visual overview of macroscopic trends in the scale of the flake graphite structure. Castings inoculated with Sr-containing ferrosilicon featured finer eutectic cell structure but coarser equiaxed structure of austenite, emphasizing that melt treatments applied to control the graphite structure may have unintended effects on the austenite grain structure. In most non-inoculated castings, the microstructure was banded, with alternating layers of coarse and fine flake graphite with distance from the casting surface. The extent of the columnar zone of austenite grains showed no correlation with the graphite structure nor the volume fraction of dendrites. The volume-to-surface ratio of dendrites was more uniform in the columnar zone, but increased toward the center in the equiaxed zone. The casting with the highest carbon equivalent (4.34), featured zones containing finer dendrites and graphite. These zones appear to be gaps in the early solidification structure which filled later by secondary dendritic growth from surrounding austenite. This highlights that high carbon equivalent may lead to poor dendrite coherency which can make the microstructure less uniform and less predictable.

“Experimental Assessment Of Microstructure And Corrosion Properties Of Sg Iron (400/15 Grade) Under As-Cast And Nitrotec Treated Condition”

Spheroidal Graphite (SG) iron castings (conforming to IS 400/15 grade) are made in green sand moulds. Test specimens are then machined from the castings. One set of Specimens is then subjected to Nitrotec Treatment, treating the surface with nitrogen atmosphere which resulted in the formation of Fe3N layer. The Nitrotec temperature selected is 5700C and 6300C. Specimen is held at this temperature for a fixed duration of 180 minutes and then quenched in quench bath (water based quenchant) maintained at 500C. The effect of Nitrotec Treatment on microstructure and corrosion is studied and compared with as-cast ones. The results of the research indicate the Graphite nodules are more or less uniform and distributed evenly in the ferritic matrix. The nodules count shows an average of 90 nodules/mm2. Corrosion or rusting is essentially a process of oxidation in which iron combines with water and oxygen to form rust, the reddish-brown crust that forms on the surface of the iron. Nitrotec treated specimen treated at 570º C exhibit lower corrosion rate compared with the ones treated at 630º C. This may be due to the higher hardness values obtained for low Nitrotec temperature treated ones. From the above investigation it is clear that the Nitrotec treatment has an effect on the microstructure and corrosion properties of SG iron castings leading to further investigation on Nitrotec treated SG iron by changing different parameters.

Michael James Stowell. 10 July 1935—27 February 2022

Mike Stowell was a Bristol physicist turned metallurgist who led the development of practical aluminium-based superplastic alloys by showing how to retain grains small enough, at temperatures high enough, to allow almost unlimited shape changes in forming operations. He can be regarded as the father of SUPRAL alloys, as these are now called. At the Tube Investment laboratory in Hinxton Hall, Essex, he led teams that made effective use of the novel electron-optical equipment invented there to solve numerous fascinating problems of technical importance, among them the sequence of growth by evaporation of thin metallic films and the mechanisms controlling the precipitation of graphite in cast iron. He was dedicated to science at the heart of industrial metallurgy, so that when the laboratory closed, rather than retire, he became research director at Alcan, interacting with a laboratory in Italy as well as managing disparate laboratories in England and Canada to develop coatings for the electrodes used in aluminium production. He was a founder member of what we now know as the ‘Cambridge Phenomenon’, the close interaction between innovative, high-tech industry and the university. In connection with these activities, he made long-lasting fundamental contributions to the understanding of precipitation both of two-dimensional islands in the growth of thin films and in three dimensions in the bulk solid state.

Automatic Measurement in Metallography

Quantitative analysis of the structure of metals and alloys is an important part of modern metal science. To obtain quantitative data and build dependencies, metallographic image processing programs are used, oriented both for scientific research and for use in industry. Programs capable of automatically performing metallographic analysis are of great interest to consumers. When advertising such programs, it is often claimed that they allow quantitative analysis of the structure with virtually no time. The purpose of this work was to determine the time spent on quantitative metallographic analysis in some image processing programs presented on the Belarusian market. Connected and unconnected metallographic objects were considered. It is shown that automatic quantitative analysis is possible for unconnected objects (powders, cast iron graphite). The time required is within a minute. For connected objects (structures of metals and alloys after metallographic etching), the time required to detect objects and obtain digital data is 10–40 min or more, depending on the complexity of the object, which is unacceptable for factory laboratories that analyze a large number of samples per shift. Therefore, it is recommended that potential users of metallographic image processing software always require a substantive demonstration of the automatic measurement capabilities of the proposed software.

Influence of Structural Parameters - the Shape of Graphite and Matrix on Change of Ultrasonic Wave Propagation Rate and Value of Attenuation in Graphitic Cast Irons

Abstract Despite the tendency of the current industry, especially the automotive industry, it is to use modern, light and super-strong materials based on Al or HSLA steels, the application of classic materials such as cast iron still makes sense, especially concerning price and excellent castability. The article presents one of the possible ways of using the ultrasonic non-destructive method in quality control and simplification of the identification of the type of cast iron concerning the change of parameters of ultrasound propagation in materials. The main criteria for assessing the quality and determining the type of graphite cast iron were considered to be the rate of propagation of ultrasound - cL and the value of attenuation - α, which vary depending on the shape of the graphite and matrix. Graphitic cast irons with different graphite shapes (lamellar, vermicular, and globular shapes) and a matrix with different ferrite/perlite ratios were used as experimental material. Along with the ultrasonic tests, a metallographic analysis was also performed to quantify the microstructure of cast irons.

On modification of eutectic cast iron graphite

It has been shown that elementary crystalline cells of graphite and basic products of iron modification do not correspond to the principle of structural and dimensional correspondence of Dankov –Konobeevsky. Modifying elements Al, Ca, Mg, Ba, Ce increase the phase tension melt‑graphite by binding surface‑active oxygen and sulfur. Modifying cast iron eutectic graphite is a nanostructured process in which modifying elements refine elemental graphite nanocrystals from adsorbed oxygen and sulfur atoms. This contributes to an increase in the concentration of graphite nuclei upon solidification of the cast iron melt. The modification reduces the concentration of dissolved hydrogen, which increases the effectiveness of the modifying effect. Reduced concentrations of demodifying surface‑active elements, melt degassing, increased heat removal contribute to increasing the degree of branching and compactness of graphite dendrites during iron crystallization. The strongest modifying element of eutectic cast iron graphite is magnesium.

Risk Evaluation for Coating Thickness Conformity Assessment.

This paper presents the conformity assessment process of the epoxy coating thickness applied on water pipes made of gray cast iron with the specifications given for this kind of coating appliance. An epoxy coating was applied to prevent a special form of corrosion called the graphitization of cast iron. In order for the pipe to withstand its designed service life, it is necessary to ensure the required thickness of the applied coating. In accordance with the EN 877 norm, the thickness of the epoxy coating on the pipes for the projected corrosiveness of the environment C4 and the durability of 20 years is at least 70 μm and this indicates the required accuracy of the product. To achieve the desired product quality, statistical control of the coating application process was carried out and the impact of uncertainty associated with the measurement result was analyzed. Considering the quality of the coating application process and the quality of the measuring system, and to ensure the quality of products and to reduce consumer risk, the optimal thickness of the coating was determined.

P – T – х диаграмма состояния системы Al – Ba

Intermetallic compounds formed in Al – Ba system are stable at temperatures above the melting point of both barium and aluminum, which allows to consider barium as a promising element for aluminum alloys operating at high temperatures and characterized by relatively high vapor pressure of barium. On the other hand, aluminum-barium ligature is widely used in various fields of metallurgy for the preparation of alloys and complex modification of steels and cast irons: aluminum improves the quality of steels, acting as a reducing agent for iron in its oxide compounds, and barium contributes to the graphitization of cast irons, which leads to an improvement in the pearlite and ferritic structures. The study of the aluminum-barium system (Al – Ba) demands taking into account the high vapor pressure of Ba, which requires analysis of the system in the pressure-temperature-concentration coordinates (p – T – x diagrams), which is the aim of the present paper. The results obtained in this work can be successfully used in the development of ternary and more alloys containing aluminium and barium.

Multi-Scale Modeling of the Thermo-Mechanical Behavior of Cast Iron

This work presents a multi-scale modelling framework for thermo-mechanical behaviour of Compacted Graphite Iron cast iron. A general thermo-elasto-visco-plastic model is developed to describe the matrix (pearlite) behavior under thermo-mechanical cyclic loading, for which the parameters are identified from tests on pearlitic steel. The pearlite model takes into account the temperature dependent rate-dependency and kinematic hardening. The importance of properly accounting for the graphite anisotropy is emphasised, for which a numerical procedure for estimating the local anisotropy directions from the graphite particle geometry and experimental observations is proposed. A high quality conforming finite element mesh is generated on a representative volume element using discrete voxelized microstructural data in combination with signed distance functions from the interfaces. For fully constraint thermal cyclic loading conditions with different holding times, the capabilities of the developed multi-scale model are demonstrated at both scales: the macroscale, where the simulation results are in very good agreement with the experimental data, and the microscale, providing the evolution of local fields.

PREPARATION OF MOLTEN CAST IRON FOR MODIFICATION BY MEANS OF REFINING TREATMENT IN THE FURNACE

Refining issues of molten metal are still actual in modern conditions of foundry. In manufacturing process of ductile and vermicular graphite iron castings with required microstructure and mechanical properties one of the essential conditions is the control of sulfur content in the base iron. Increased sulfur concentration (over 0,02%) can destabilize the production process of ductile and vermicular graphite iron castings and decrease the efficiency of modifying treatment. An additional factor reducing the efficiency of modification, which is not mostly controlled and not taken into account in foundry is oxidation of cast iron; average content is 1200–1600 ppb depending on charge materials. In this regard, in the production of ductile castings, the stage of metal pretreatment in the furnace, which consists in refin-ing the metal from sulfur and oxygen, is important. The iron foundry factories do not often have the opportunity to buy the modern equipment for refinement of liquid metal due to its high cost. In this case, in addition to existing traditional methods of refining, it is interesting to use specially developed compositions of complex materials and modifiers, improvement of methods of their input into the liquid metal. A possible variant of metal pretreatment for subsequent modification was presented. The complex briquetted material Refloy®F based on ferrosilicon FS45 has in its composition such active elements as alkaline-earth and rare-earth metals. The chemical composition of briquette Refloy®F and mechanism of its influence on cast iron melt was presented and practical experience of its application was provided. The technology of introducing briquettes depending on applied smelting unit, its consumption characteristics, results of reduction of oxygen and sulfur concentration in pig iron in the course of tests at different plants are presented. The advantages of iron desulfurization technology with Refloy®F briquettes are provided.

A two-scale model of degenerated graphite in cast iron

A two-scale model for clusters of degenerated graphite in gray cast iron is presented. The novelty of the model is that, at the mesoscale, a single cluster is described as a spheroidal inclusion made of porous materials. At the microscale, the porous material contains a random distribution of randomly oriented spheroidal voids modeling the graphite precipitates. To calculate the stress state inside and at the outer surface of the cluster, two different approaches are presented. In the first approach, the effective elastic properties of the porous material at the microscale are obtained using Pan and Weng homogenization scheme, based on Eshelby’s equivalent principle and the Mori-Tanaka’s estimate; at the mesoscale, the stress distributions inside and at the outer surface of the cluster are calculated using Eshelby’s solution applied to an inclusion made of equivalent porous material. The second approach is based on a finite element analysis of a cluster embedding 216 randomly oriented and randomly distributed spheroidal voids. A comparison between the numerical results obtained with the two approaches indicates good agreement in terms of average (elastic and stress distribution) properties. The equivalent elastic properties (Young’s modulus) calculated at the microscale in the two approaches are also compared with some experimental results available in the scientific literature.

Wear behaviour of graphitic aluminium composite sliding under dry conditions

Abstract A modified mixing and casting procedure was used for the preparation of Al-1.2 Si-0.8 Fe–Gr composite (wt.%). Graphite and gray cast iron powders were blended and dispersed in Al-1.2 Si matrix alloy melt and poured in a cast iron mould. Gray cast iron powder worked as carrier for graphite particles. The presence of graphite improves the ultimate tensile strength, tensile and compressive stress but beyond 1 % of graphite all properties deteriorate. However, hardness continuously increases and percentage elongation reduces with graphite. In wear studies, different mechanisms: mild-oxidative, oxidative-metallic and severe-metallic, are operative in the different combinations of sliding velocities and applied loads.

Successive steps of growth of compacted graphite in cast irons

Successive steps of growth of compacted graphite in cast irons

Growth mechanisms of vermicular graphite in cast iron

To steadily produce high-quality vermicular graphite cast iron (VGI), it is essential to have a deep understanding of the growth mechanism of vermicular graphite. The morphology and microstructure of graphite in VGI were studied using various techniques, including both experimental and theoretical methods. An abnormal graphite structure with an anomalous layer distance of 6.60 Å was observed by transmission electron microscopy (TEM) imaging, which is approximately two times larger than the normal structure (3.40 Å). The theoretical simulations of possible trace elements added (approximately 34 different elements) to the graphite basal planes were studied and analyzed individually to understand the observed phenomenon and their effects on graphite growth. The theoretical calculations (6.56 Å) show good agreement with the experimental results (6.60 Å), which proves that the lattice anomaly is caused by Mg. The abnormal graphite was believed to be the remains of the transition state during the growth of graphite. Based on the investigation, a mechanism is proposed to describe the influence of Mg during the growth process of vermicular graphite.

The Role of Selenium on the Formation of Spheroidal Graphite in Cast Iron

Sulfur, an element that belongs to group 16 (chalcogens) of the periodic table, is an excellent promoter of nucleation substrates for graphite in cast iron. In ductile iron, sulfur favors a higher nodule count, which inhibits the risk of carbides and of microporosity. It is reasonable to expect that other elements from group 16, such as selenium or tellurium, play similar roles in the nucleation of graphite. The objective of this paper was to investigate the effect of selenium on the process of graphite formation. Thermal analysis cups were poured to evaluate the nodule count and size distribution. Some of the cups were not inoculated, while others were inoculated with a Ce-bearing inoculant, or with the Ce inoculant and additions of Se. Cross-shaped castings were also poured to quantify the microporosity regions by tomography. It appears that selenium additions modify the number and size of graphite particles, as well as the volume of microshrinkage. Direct correlations between these three parameters were found. Advanced Extensive Field Emission Gun Scanning Electron Microscope (FEG-SEM) techniques were used to identify the nature of the main nucleation compounds. Selenides, combined with Mg and rare earths, were observed to serve as nuclei for graphite. Their presence was justified by thermodynamics calculations.

On a possibility of replacing grey cast iron for manufacturing cast elements of electrolyzer gas collecting bell

The main process leading to the destruction of the cast elements of gas-collection bell of electrolyzer, made of grey cast iron, is the oxidation of iron by oxygen, SO2 gas and sulfur vapors to form magnetite, hematite and pyrrhotin. The simultaneous formation of iron oxides and sulfides does not prevent further corrosion, since scale is formed with a loose structure that does not have protective properties. Reducing the length of the interfacial boundaries inside the material of the cast enables to reduce the rate of corrosion destruction, which can be achieved by modifying the cast iron to change the shape of graphite inclusions, i.e. obtaining high-strength cast iron with a spherical shape of graphite inclusions. However, the obtaining spherical graphite in cast iron using magnesium modification does not exclude the access of aggressive gases to the surface of the products and the possibility of their diffusion along the grain boundaries. It was shown that alloying can be an alternative, which leads not only to the exclusion of lamellar secretions of graphite in the structure of cast iron, but also to the formation of surface oxide layers based on the alloying element preventing the corrosion. Alloying with chromium gives cast iron high abrasive resistance due to the presence of a carbide component in the structure, as well as corrosion resistance due to the alloying of the metal base, heat resistance due to increasing the electrochemical potential of the metal base and creating a strong neutral oxide film on the surface of the castings, heat resistance, etc. An experimental comparative analysis of the corrosion resistance of cast iron used for manufacturing of gas collecting bell of electrolyzers showed that chromic cast iron ЧХ3 has a higher corrosion resistance than high-strength cast iron with spherical graphite ВЧ50 and much higher than grey cast iron with lamellar graphite. However, chromic cast iron ЧХ3 has low casting properties, is very sensitive to the cooling rate and has a large heterogeneity in structure, which makes it difficult to use it for the manufacture of gas collecting bell of electrolyzers.

EFFECT OF COOLING RATE ON MICROSTRUCTURE AND HARDNESS IN GRAY CAST IRON CASTING PROCESS

This study aims to investigate the thermal conditions of the molds, changes in microstructure and hardness of casting products using sand mold and permanent mold. The use of sand mold and permanent mold results in different cooling rates. Thermal analysis was performed using a thermocouple to obtain a temperature versus time curve. Metallographic observations were carried out using a Scanning Electron Microscope equipped with Energy-Dispersive X-ray Spectroscopy. The Vickers hardness test was carried out in three areas with different thicknesses. The results showed a constant temperature at 691 oC where the eutectoid phase reaction occurred. Testing with sand mold showed that cast iron with flake graphite was finer and spreader than graphite in cast iron produced by permanent mold. Meanwhile, gray cast iron from a casting process with a permanent mold has a higher hardness than gray cast iron from a casting process using a sand mold.

Phase Quantification of Regular and Turbo-stratified Graphite in Cast Iron by X-ray Diffractometry/Rietveld Refinement

Phase Quantification of Regular and Turbo-stratified Graphite in Cast Iron by X-ray Diffractometry/Rietveld Refinement