Eutectic Cast Iron Research Articles

Structural heredity in the casting of eutectic cast iron

It has been shown that the effect of structural inheritance in casting eutectic cast irons can be explained from the standpoint of nanostructured crystallization of foundry alloys. Proposed is a mechanism of structural heredity when casting eutectic cast irons. This mechanism is determined by the stability of the crystallization centers of microcrystals of austenite, graphite, cementite. This stability has been shown to depend on the concentration of adsorbed oxygen atoms. The higher this concentration, the less stable the centers of crystallization of microcrystals of austenite, graphite, cementite in melts of eutectic cast irons, and vice versa. With an increase in overheating and (or) the holding time of melts, the concentration of adsorbed oxygen atoms in them increases. As a result, structural stability during remelting of eutectic cast irons is reduced and the effect of structural heredity is disturbed.

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.

Results of study of the structure of castings from white wearresistant cast irons

The article considers white wear-resistant chrome cast iron used for making castings used in the mining industry, in particular, for parts of centrifugal grinders. Parts are made at the Navoi Machine-Building Plant (Uzbekistan). The white wear-resistant cast irons 280CrNi29 1, 300CrNiMoTi32 2 2 and experimental cast iron 330Cr17 used at the plant were studied. To conduct research on the above-mentioned cast irons, «Feeding disk» parts with a diameter of 380 mm, a thickness of 38 mm, and a weight of 35 kg were cast into earthen molds. The microstructure in the cast state of all the studied cast irons is a trostiteaustenitic metal matrix with eutectic colonies. The content of carbides in pre — eutectic cast iron 280CrNi29 1 was 30–32%, the hardness on the surface of castings 50–51 HRC, and in the center 45–46 HRC, the amount of carbides in cast iron 300CrNiMoTi32 2 2 was 35–37%, the hardness on the surface of castings 56–57 HRC, and in the center 52–53 HRC, the amount of carbides in eutectic cast iron 330Cr17 was 39–40%, the hardness on the surface of castings 53–54 HRC, and in the center 50–51 HRC. The cost of the 330Cr17 alloy is 1.3 times lower than the cost of the 280CrNi29 1 alloy, and 4.5 times lower than the cost of the 300CrNiMoTi32 2 2. To obtain parts from a cheap alloy 330Cr17, a technology for manufacturing castings using metal refrigerators is proposed, in this case, the hardness of castings from the alloy 330Cr17 is 58–61 NRC on the surface and 55–56 HRC in the center of the castings. The size of carbides is reduced by 3–4 times. By obtaining a directional structure and grinding carbides during casting using metal refrigerators, the wear resistance of cast parts increases by at least 20%. In this case, you can use cheaper grades of chromium cast iron, containing less alloying.

Calphad-based phase-field study of the interplay between spheroidal graphite growth and chemical segregation in ductile cast iron

Spheroidal graphite in ductile cast irons forms in a divorced eutectic solidification, controlled by interstitial diffusion of carbon through the enveloping austenitic shell. As technical cast irons are multicomponent alloys, carbon diffusion can strongly be affected by content and chemical gradient of other solute elements. During growth of a eutectic cell, all solute elements are partitioned at the austenite/liquid interface. Substitutional diffusion within the austenite is almost negligible, but expansion-induced spatial displacement of the iron-rich matrix and solute atoms during graphite growth significantly complicates multidimensional numerical simulation. A recently developed volumetric multi-phase-field approach, implemented in the Micress software, now accounts for the volume expansion and related matter and solute transport. In the present case study, this approach is applied to investigate the evolving chemical gradients and their potential effect on carbon diffusion during growth of a three-dimensional eutectic cast iron cell. Phase and concentration dependent thermodynamic data, partial molar volumes and diffusion coefficients are evaluated from linked Calphad-databases. The interface properties of the polycrystalline spheroidal graphite nodule are modelled based on a dedicated effective multi-facetted anisotropy function. A special target is to investigate whether increase in Si content may result in a significant reduction of the carbon flux, eventually favoring graphite degeneration and chunky growth.

Influence of Various Elements on Primary Crystal Temperature and Carbon Equivalent in Hypo Eutectic Cast Iron

Influence of Various Elements on Primary Crystal Temperature and Carbon Equivalent in Hypo Eutectic Cast Iron

Modification of wear-resistant coatings of Fe-Cr-C system based on the Cr3C2 obtained with help of SHS method

The article deals with new wear-resistant materials of the Fe-Cr-C system, designed to strengthen the working bodies of machines by high-performance inductive surfacing. Materials are presented by a mixture of powders (burden) based on high-alloy chromium-plated cast iron of type PG-USC25 (in Russian) and flux P-0.66, modified by cermet based on Cr3C2, obtained by the SHS method. The peculiarity of the modifier proposed by the authors is that the open pores of this ceramic are filled with the main, matrix material of the future wear-resistant coating - cast iron PG-CS-25 (in Russian), which is used in the SHS as an inert. X-ray diffraction studies of cermet and metallographic studies of surfaced coatings have been performed.It was shown that the introduction into the prepared burden for inductive surfacing up to 25% by weight specified cermet allows to increase hardness (up to 1320 HV) and wear resistance of the welded material. The effect is explained by formation in the hardening coating of up to 20% by vol. of new phase - the needle-shaped carbide Cr7C3 due to recrystallization and change in the composition of carbides formed from artificially introduced Cr3C2 and already available in matrix eutectic cast iron, chromium and carbon.

Effect of Admixtures of Surface-Active Elements in Fe – C – Si Alloys Under Rapid Solidification of Melt on the Quality of Structural Articles

Computer and experimental studies of the effect of admixtures of Te and H2 surface-active elements (s.a.e.) on the kinetics of nucleation of crystallization centers and phase growth under accelerated crystallization of eutectic cast iron are performed. It is shown that under quenching cooling with decelerated diffusion processes the admixtures of s.a.e. in the melt play the role of initiators of diffusion redistribution of elements in formation and growth of new phase fragments affecting the structure and properties of the formed material.

Transient Directional Solidification of Cast Iron: Microstructure Formation, Columnar to Equiaxed Transition and Hardness

A number of applications may require cast iron. Engine cylinder blocks, flywheels, gearbox cases, machine-tool bases may be manufactured by using grey cast iron while bearing surfaces with white cast iron. Thus, understanding the solidification behaviour of eutectic cast iron becomes an essential task, with certain points to be accomplished. Transient directional solidification may provide particular advantages in order to deal with these items, such as the large variation of growth rate (V) and cooling rate (T) values, which may allow a variety of microstructures and morphologies to be studied. The aim of this work is to examine the macrostructure regions, scale of the dendritic microstructure, proportions of the formed phases and hardness of samples obtained by transient directional solidification of a eutectic cast iron (Fe-3.5wt%C-2.5wt%Si). It was shown that a CET criterion should be based on a critical V value at the solidification front of about 0.6 mm/s. The effects of the formed phases, their proportions and λ2 on hardness of the cast alloy are assessed.

Preparation of lead-free free-cutting graphite brasses by graphitization of cementite

Graphite brasses were prepared by graphitizing annealing of cast brasses containing cementite particles, which were in-situ formed during the fasting process. The eutectic cast iron as carbon source was added into common brasses by casting. SEM and EDS were used to analyze the microstructure of graphite brasses, and the relationship between the microstructure and machinability was investigated. The results show that graphite particles are formed by the decomposition of cementite particles in cast brasses. The graphite particles are uniformly dispersed in the brass matrix with the average size of 5.0 μm and the volume fraction of ∼1.1%. The machinability in the graphite brass is dramatically increased relative to the common brass, because of the lubricating properties of graphite particles and its role in chip breaking. The workpiece surface of the graphite brasses chips is smooth and burr-free, and the chips of graphite brasses are short (C-shape) and discontinuous, which is much better than that of the long spiral chips of common brasses.

Modelling of the Density Changes of Nodular Cast Iron During Solidification by CA-FD Method

Formation of the shrinkage defects in ductile iron castings is far more complicated phenomenon than in other casting alloys. In the presented paper changes the ductile iron density during solidification is analyzed. During the solidification path the influence of the temperature, phase fractions and phase composition is taking into account. Computer model, using cellular automata method, for estimation of changes in density of ductile iron during its solidification is applied. Results of the solidification modeling for Fe-C binary alloys with different composition in the castings with a different wall thickness are presented. As a result of calculations it was stated that after undercooling ductile iron below liquidus temperature volumetric changes proceed in three stages: pre-eutectic shrinkage (minimal in eutectic cast iron), eutectic expansion and the last shrinkage.

Cellular Automaton Modeling of Ductile Iron Density Changes at the Solidification Time

Abstract Formation of the shrinkage defects in ductile iron castings is far more complicated phenomenon than in other casting alloys. In the paper one of the aspects of formation of porosity in this alloy was considered - changes in cast iron's density during crystallization caused by varying temperature, phase fractions and phase's composition. Computer model, using cellular automata method, for determination of changes in density of ductile iron during crystallization was applied. Simulation of solidification was conducted for 5 Fe-C binarie alloys with ES from 0.9 to 1.1 for the estimation of the eutectic saturation influence on the ductile iron shrinkage and expansion. As a result of calculations it was stated that after undercooling ductile iron below liquidus temperature volumetric changes proceed in three stages: preeutectic shrinkage (minimal in eutectic cast iron), eutectic expansion (maximum value equals to about 1.5% for ES = 1.05) and last shrinkage (about 0.4% in all alloys regardless of ES).

On the characterization of eutectic grain growth during solidification

ABSTRACTThe purpose of this work is to compare the results obtained from three methodologies intended to estimate kinetic parameters describing quantitatively the grain growth during equiaxed eutectic solidification in order to identify the best procedure to characterize grain growth kinetics. A heat transfer / solidification kinetics model is implemented to simulate the cooling and solidification of eutectic Al-Si and eutectic cast iron in sand molds. Using simulated cooling curves and volume grain density data generated by the model, the three methods are applied to obtain their predicted grain growth coefficients. The predicted results are compared with the grain growth coefficients used in the model. The outcome of this work suggests that two of the three methods under study represent the best option to obtain the kinetic parameters of equiaxed growth during eutectic solidification.

Thermal analysis of nodular and lamellar eutectic cast iron under different cooling rates

Thermal analysis was performed on near-eutectic nodular and lamellar cast iron alloys under different cooling rates. In a DTA setup, cooling rates from 0.08 K/sec to 0.35 K/sec were used, while in a mirror furnace setup cooling rates up to 55 K/sec were reached. At low cooling rates, the solidification behaviour was analyzed by interrupting the process through quenching. The volume fraction of each phase and substructure was evaluated together with the latent heat at different solidification times. It was observed that the growth rate of the nodules decreases with time. Measurements on the number of nodules indicate that the nucleation rate is constant through the solidification process.The measured latent heat of fusion varies along the solidification process for nodular cast iron but not for lamellar cast iron. This difference in the solidification behaviour may be explained by different diffusion kinetic laws.It was also found that the measured latent heat of fusion decreases when the cooling rate increases. Alloys with nodular graphite showed lower latent heat in comparison with the alloys with lamellar graphite at high cooling rates. This effect is explained by means of thermodynamics of lattice defects, such as vacancies, formed in the austenite and graphite phase during solidification.

A Model for Equiaxed Eutectic Solidification with Melt Convection and Solid-Phase Transport

This paper presents a method to track microstructural evolution during eutectic solidification using a coupled fluid flow—mass transport model. The continuum formulations were used to describe the macroscopic transports of mass, energy, and momentum, associated with the microstructural evolution, for two-phase systems. It was assumed that the liquid flow is driven by thermal and solutal buoyancy, as well as solidification contraction. The eutectic cell (grain) of cast iron was assumed to have a spherical morphology. The microstructural model includes the gray-to-white eutectic transition and the influence of microsegregation on the eutectic temperature. A continuous nucleation law was used in calculation. Rules for grain movement have been developed to track the nucleation, growth and movement of grains because of melt convection. Three test cases are discussed to demonstrate the influence of melt convection and solid phase transport on microstructure evolution for eutectic cast iron.

Microstructures and superplastic behavior of eutectic Fe-C and Ni-Cr white cast irons produced by rapid solidification

Superplastic behavior of two commercial grade white cast irons, eutectic Fe-C and Ni-Cr white cast irons, was investigated at intermediate temperatures (650 to 750 °C). For this purpose, rapidly solidified powders of the cast irons were fully consolidated by compaction and rolling at about 650 °C. The volume fractions of cementite in the eutectic cast iron and in the Ni-Cr cast iron were 64 pct and 51 pct, respectively, and both cast irons consisted of fine equiaxed grains of cementite (1 to 2 μm) and ferrite (0.5 to 2 μm). The cast iron compacts exhibited high strain-rate sensitivity (strain-rate-sensitivity exponent of 0.35 to 0.46) and high tensile ductility (total elongation of 150 pct to 210 pct) at strain rates of 10-4 to 10-3 s-1 and at 650 °C to 750 °C. Microstructure evaluations were made by TEM, SEM, and optical microscopy methods. The equiaxed grains in the as-compacted samples remained unchanged even after large tensile deformation. It is concluded that grain boundary sliding (e.g., along cementite grain boundaries in the case of the eutectic cast iron) is the principal mode of plastic deformation in both cast irons during superplastic testing conditions.

Undercooling and Flake Graphite-Undercooled Graphite Structural Transition in Unidirectionally Solidified Eutectic Cast Iron

Undercooling and Flake Graphite-Undercooled Graphite Structural Transition in Unidirectionally Solidified Eutectic Cast Iron

仕上面加工層に関する研究(第5報)

The Effects of shot peening on the typical structures of such iron alloys as ferrite, pearlite, pearlite-cementite, martensite, pearlite-graphite, and martensite-carbides, were investigated. The above mentioned structures were obtained from 0.12% carbon steel (ferrite), 0.64% carbonsteel (pearlite), 0.99% carbon steel (pearlite and cementite), quenched 0.99 carbon steel (martensite), eutectic cast iron (pearlite and graphite), quenched and tempered highspeed steel (martensite-carbides) respectively. The test pieces were blasted with #20 cast iron shot under the compressed air pressure of 3.0 kg/cm2 for 3.0 minutes.For measuring the induced stresses in the surface layer and checking the hardening effect, the same method as described in the 4th report was adopted.The results were as follows :1. Among the three typical structures, the greatest effect of shot-peening is seen on martensite, then on pearlite, and the smallest effect on ferrite.2. The effect on martensite-carbide is smaller compared to that on martensite due to the existence of carbides.3. Pearlite-graphite has comparatively smaller surface compressive stress than pearlite due to the existence of graphite.