Compacted Graphite Iron Research Articles

Effect of Tool Coatings on Machining Properties of Compacted Graphite Iron.

Compacted graphite iron (CGI) has become the most ideal material for automotive engine manufacturing owing to its excellent mechanical properties. However, tools are severely worn during processing, considerably shortening their lifespan. In this study, we prepared a series of cemented carbide-coated tools and evaluated their coating properties in cutting tests. Among all tested coatings, PVD coating made of AlCrN (AC) presented with the best surface integrity and mechanical properties, achieving the best comprehensive performance in the coating test. The AC-coated tool also exhibited the best cutting performance at a low speed of 120 m/min, corresponding to a 60% longer cutting life and the lowest workpiece surface roughness relative to other coated tools. In the cutting test at a high speed of 350 m/min, the CVD double-layer coated tool (MT) with a TiCN inner layer of and an Al2O3 outer layer had a 70% longer cutting life and the lowest workpiece surface roughness relative to other coated tools.

Modulation-assisted machining of compacted graphite iron with coated carbide tool in dry condition

Compacted graphite iron (CGI) is a new material replacing conventional gray cast iron (FGI) for diesel engine block applications due to its superior mechanical properties. However, widespread adoption of CGI is hindered by its poor machinability, which is reflected by the rapid tool wear especially at higher cutting speeds. In current industrial practice, CGI is usually machined with coated carbide tools at low to medium speeds (< 200 m/min). This study investigates the effect of modulation-assisted machining (MAM) on tool wear in dry turning of CGI with coated carbide tool. A new MAM turning setup is implemented for conducting the longitudinal turning experiments. Tool wear, cutting forces and tool temperature are characterized for both conventional machining (CM) turning and MAM turning at three cutting speeds: 150, 250 and 350 m/min. The results show wear reduction by MAM is not significant at the low cutting speed (150 m/min), but it is quite significant at the higher cutting speeds (250 and 350 m/min). The cutting force and temperature results can be well correlated with the wear results, revealing the dependency of the forces and temperature on the tool wear and the severity of iron adhesion. This study demonstrates the potential of MAM in enhancing the productivity of machining CGI with the coated carbide tool. The results are also useful for better understanding the wear mechanism in cutting CGI with the coated carbide tool.

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.

A study investigating the cutting mechanism of compacted graphite iron based on a novel microstructure of finite element model

Compacted graphite iron is internationally recognized as a material that has the potential to be applied for preparing high performance engine components. However, difficulties during machinability seriously limit the mass production of these. A novel method based on MATLAB image recognition and python programing was used to establish a microstructural model that included graphite and pearlite particles. The thermal conductivity and specific heat capacity at different temperatures was measured and the results were used to validate the model. Using this novel model, the chip morphology and formation mechanism, cutting surface morphology and formation mechanism and cutting temperature distribution were studied. The simulation results show that crack formation on the chip surface and generation of graphite fragments occurs during the cutting process. The crack opening angle during this is approximately 33°. Significant graphite cavities also appeared on the cutting surface. The stress concentration at the boundary of graphite and pearlite during cutting process was analyzed, and demonstrated to be the primary reason for these phenomena. The temperature of both the rake face and flank face are simulated with the highest cutting temperature concentrated in the secondary deformation zone reaching approximately 322 °C. Furthermore, the simulation results are consistent with the experimental results.

Damage mechanism and fatigue strength prediction of compacted graphite iron with different microstructures

The effects of microstructures on the tensile properties, high-cycle fatigue properties and corresponding damage mechanism of compacted graphite iron (CGI) were investigated. The results show that with the increase of pearlite content, both the tensile strength and fatigue strength show an upward trend. Fatigue cracks usually initiate at the graphite/ferrite interface and gradually propagate into the matrix under the high-frequency cyclic stress. The adjacent cracks bridge to form the main crack, leading to the final fracture. Based on the pearlite content and tensile strength, a new model for predicting the fatigue strength of CGI with high accuracy was proposed.

A Comparative Investigation on the Wear Performance of Compacted Graphite Iron (CGI) Treated with Single and Double Tempering

Compacted graphite iron (CGI) is a critical material in today's automotive and manufacturing industries. Heat treatment processes can improve CGI wear properties, related primarily to microstructural changes. In this study, single and double tempering heat treatments were used to improve the wear properties of CGI. Oil quenching was performed after 90 minutes of austenitization at 900°C, followed by 60 minutes of single and double tempering at three different temperatures (315, 350, and 375°C). The wear performance of the samples was compared using a pin-on disc test and hardness measurements. The volume loss and friction coefficient were evaluated, and wear maps were constructed to determine the samples' wear behavior. SEM and EDS analyses were carried out to worn surfaces to interpret the relationship between wear mechanism and microstructure. According to the study's findings, double tempering heat treatment may optimize wear performance better than traditional single tempering, and structures with high toughness-wear resistance combinations can be obtained.

Wear behaviors of cubic boron nitride tools with various binders in high-speed turning of compacted graphite irons

Compacted graphite iron (CGI) is a promising material as diesel engines in automotive industry, but the poor machinability and low machining efficiency have further hindered the employment of CGI in the potential applications. Cubic boron nitride (cBN), possessing extreme hardness and chemical inertness, is the best candidate as tools to machine ferrous metals. In this paper, we attempt to explain the disparities in wear behaviors of cBN tool with different binders by implementing high-speed turning of CGI. The effects of various binders on cBN tool flank wear, cutting force, cutting temperature, and machined surface roughness was systematically investigated. Additionally, the response relationship among flank wear, cutting force, temperature and surface roughness was obtained. Further, the underlying reasons of the wear mechanism of cBN tool were revealed. The results indicated that the cBN tool performances strongly depend on the affinity of binders with CGI. The contributions of binder phases, cBN content, and cBN grain size under the employed machining conditions: the binders are dominated, and followed by cBN grain size or cBN content in the high-speed cutting of CGI. The small cBN grain size, and TiCN, TiC, TiN binders of cBN tools have superior cutting performance than the Co binders.

Thermal debonding of inclusions in compacted graphite iron: Effect of matrix phases

This paper investigates graphite decohesion as the primary fracture mechanism of compacted graphite iron (CGI) subjected to thermal load. Despite CGI’s extensive industrial use and considerable research on its mechanical behaviour, thermal debonding is not yet fully understood, nor is the influence of matrix phases on it. After thermal cycling to confirm the occurrence of the phenomenon, a numerical approach is developed: a 2D unit cell is constructed, with a single graphite particle, represented as an ellipse embedded in a metallic matrix. The inclusion is surrounded by an extra layer that accounts for either pearlite or ferrite, in order to study their effect on thermal debonding. An elastoplastic behaviour is assumed for all constituents, described with a classical J2 flow theory of plasticity, and the models are analysed employing a finite-element approach. The proposed numerical strategy focuses on the influence of matrix phases on thermal debonding, identifying numerical schemes to assess it. The obtained results can provide significant knowledge on the response of CGI to thermal load at the microscale, contributing to the understanding of its macroscopic thermomechanical behaviour.

Influence of Plasma Arc Current on the Friction and Wear Properties of CoCrFeNiMn High Entropy Alloy Coatings Prepared on CGI through Plasma Transfer Arc Cladding

High-entropy alloys receive more attention for high strength, good ductility as well as good wear resistance. In this work, CoCrFeNiMn high-entropy alloy (HEA) coatings were deposited on compacted graphite iron through plasma transfer arc at different currents. The microstructure and wear properties of the CoCrFeNiMn HEA coatings were investigated. The coatings are composed of single phase with FCC structure. The CoCrFeNiMn HEA coating had the highest microhardness of 394 ± 21.6 HV0.2 and the lowest wear mass loss when the plasma current was 65 A. All of the HEA coatings had higher friction coefficients than that of the substrate. There were adhesive, abrasive and oxidation wear forms in the HEA coatings with the wear couple of N80 alloy. The HEA coating presented higher friction coefficient and better wear resistance than compacted graphite iron.

Microstructure, Inclusions, and Elemental Distribution of a Compacted Graphite Iron Alloyed by Ce and La Rare Earth (RE) Elements

This work investigates the microstructure and inclusions of a compacted graphite iron (CGI) alloyed by Ce and La rare earth (RE) elements. In our study, alloying elemental distribution and solute segregation were characterized by methods of secondary ion mass spectrometry (SIMS) and a three-dimensional atom probe (3DAP) with high sensitivity and spatial resolution. RE sulfide, MgS, carbide, and composite inclusions formed during solidification and provided heterogeneous nucleation cores for the nucleation of the graphite. Significant solute clustering in the matrix, coupled with the segregation of solute to grain boundaries, was observed. C, Mn, Cr, and V were soluted in cementite and promoted the precipitation of cementite, while Si was found to be soluted in ferrite. Cu is usually distributed uniformly in ferrite, but some Cu-rich atom clusters were observed to segregate towards the interface between the ferrite and cementite, stabilizing the pearlite. In addition, P, as a segregation element, was enriched along the boundaries continuously. The RE elements participated in the formation of inclusions, consuming harmful elements such as As and P, and also promoted the heterogeneous nucleation of the graphite and segregated, in the form of solute atoms, at its interfaces.

The high-cycle fatigue fracture mechanism and fatigue strength prediction of compacted graphite iron

The tensile properties, high-cycle fatigue (HCF) properties and corresponding fatigue fracture mechanism of compacted graphite iron (CGI) were investigated. It is found that the tensile strength, yield strength and fatigue strength of CGI decrease as the temperature increases. At 25 °C, the fatigue cracks of CGI are mainly caused by local cleavage fracture at ferrite around the tip of vermicular graphite. At 400 °C and 500 °C, the gradual occurrence of grain boundary softening and oxidation may reduce the difficulty of fatigue crack propagation. Similar to temperature, the change of microstructure content also has a significant effect on the fatigue properties of CGI. By analyzing the damage characteristics of fatigue fracture morphology, it is shown that the fatigue crack initiation of CGI is mainly dependent on the damage localization caused by the ferrite and vermicular graphite inside the graphite cluster and the pearlite and spheroidal graphite outside the graphite cluster under cyclic loading. Based on those results, a fatigue strength prediction model associated with tensile strength, yield strength and microstructure area percentage was proposed. This model can provide a reasonable prediction of HCF strength of CGI at different temperatures.

Wear Study of Cubic Boron Nitride (cBN) Cutting Tool for Machining of Compacted Graphite Iron (CGI) with Different Metalworking Fluids

Due to its desirable mechanical properties, compacted graphite iron (CGI) has been used to replace conventional gray cast iron (CI) in various applications, such as automotive engine blocks and cylinder heads. However, the poor machinability of CGI can lead to excessive tool wear and consequently high manufacturing costs. Various strategies have been developed to improve the machinability of CGI, including optimizing machining parameters and the development of novel metalworking fluids. In this study, machining of CGI was conducted using cubic boron nitride (cBN) tools under different cutting speeds, with both soluble and full-synthetic water-based metalworking fluids at different levels of sulfur addition and water dilution. The effects of the metalworking fluids on the tool wear behavior were examined. Results showed that at 200 m/min cutting speed, the soluble metalworking fluid at 4% dilution and 0.3% sulfur compound exhibited the best performance, with a cutting distance reaching 23.8 km. In contrast, the least effective soluble metalworking fluid at 9% dilution and 0.3% sulfur compound resulted in a 28.6% decrease in the cutting distance (17.0 km) compared to the best one. At a higher speed (300 m/min), the cutting distance for all metalworking fluids dropped to less than 6.0 km, with the full-synthetic metalworking fluid showing the shortest cutting distance of 4.8 km.

Wear Properties of Iron-Based Alloy Coatings Prepared by Plasma Transfer Arc Cladding

Plasma transfer arc cladding technology has been widely utilized in surface engineering, repairing and remanufacturing. In the present work, multiple cladded thick claddings were prepared on compacted graphite cast iron (CGI) substrates with iron-based powders through plasma transfer arc cladding technology using different plasma arc currents to improve the surface wear resistance. The coatings’ phase and microstructure were analysed through XRD, SEM and EDS. The coatings’ microhardness and wear resistance were characterized. There were pearlite, graphite, austenite and secondary carbides in the iron-based alloy coatings. Due to the heat influence during the multiple cladding process, a spheroidal graphite transition zone appeared between the substrate and the coating. The microhardness of the claddings varied from 363 to 402 HV as the plasma arc current was changed from 45 to 60 A. With the increase of plasma arc current, the cladding’s microhardness increased. The iron-based coating’s minimum friction coefficient and wear mass loss were about 0.48 and 4.2 mg, respectively, when the plasma arc current was 60 A, which are lower values than those of the compacted graphite iron substrate with the friction coefficient and wear mass loss of 0.55 and 8.2 mg. Compared with the substrate, the iron-based alloy claddings achieved the effect of reducing friction and wear resistance simultaneously, which resulted from the self-lubricating effect of graphite and high wear-resistance of carbides in the claddings. The iron-based coatings had a similar abrasive wear mechanism to the CGI, which should be helpful to repair or remanufacture CGI workpieces.

Effect of Elemental Segregation on the Microstructure and Mechanical Properties of Heavy Section Compacted Graphite Iron

Effect of Elemental Segregation on the Microstructure and Mechanical Properties of Heavy Section Compacted Graphite Iron

Control of Compacted Graphite Iron Production Process by Using the Thermal Analysis System

The objective of this paper is to describe the major principles of controlling production of compacted graphite iron, aka vermicular graphite iron, using thermal analysis (TA) of cast iron melts as a means of control. The paper goes on to show the engineering implementation of the above principles and the results of how one of a Russian foundry applied them.

Investigation on the Thermal Fatigue and Microstructure Evolution Mechanism of Compacted Graphite Iron under Elevated Temperature

Investigation on the Thermal Fatigue and Microstructure Evolution Mechanism of Compacted Graphite Iron under Elevated Temperature

High-temperature deformation and interfacial damage in CGI: 3D numerical analysis

Compacted graphite iron (CGI), a type of cast iron, forms an integral part of the industry worldwide thanks to its good thermal and mechanical properties, excellent wear resistance, and competitive price. Despite the extensive research on cast irons since the 1950s, their thermomechanical behaviour and, especially, their fracture at the microscale is not yet fully understood. Interfacial debonding is the main mechanism of fracture in compacted graphite iron. Such features of interfacial-debonding initiation, thermal interfacial damage and deformation between graphite inclusions and a surrounding matrix are investigated in this work. A three-dimensional unit cell comprising the matrix and a graphite inclusion is developed to simulate thermal deformation and damage under pure thermal loading; both phases were assumed to have elastoplastic behaviours. Different fracture mechanisms were analysed under fully fixed and periodic boundary conditions. The results could provide a deeper understanding of the mechanisms of thermal deformation and fracture in compacted graphite iron.

CGI 주철 소재 극저온 밀링 공정 절삭성 분석 연구

Compacted graphite iron (CGI) has been widely used in the automobile industry because of its good mechanical properties. CGI has better strength as compared to grey iron due to its internal structure. It includes graphite particles, which enhance the adhesion between graphite and iron. However, the material characteristics can negatively affect the machinability. In this study, cryogenic milling was performed for CGI450. It is well known that cryogenic machining is effective in improving the machinability. The process included spraying liquid nitrogen as a cryogenic coolant, and the influences on machinability were experimentally investigated with a focus on the cutting force and surface roughness. When liquid nitrogen was sprayed, the cutting force was slightly increased due to the cold-strengthening effect. On the other hand, surface roughness was dramatically decreased by 44.7% as compared to dry milling because brittleness of work material was increased by cryogenic coolant spraying.

Thermal debonding in compacted graphite iron: effect of interaction of graphite inclusions

This paper focuses on investigation of the interaction effect of graphite inclusions on failure of compacted graphite iron (CGI) subjected to thermal load. Although CGI has been used extensively in industrial applications and studied for many years, its failure under pure thermal load has not yet been fully understood, nor has the influence of interacting graphite particles on it. To analyse this phenomenon, a finite-element two-dimensional unit cell is constructed, consisting of two graphite particles presented as ellipses embedded in a metallic matrix. Each inclusion is surrounded by a thin layer that accounts for its interface in order to study its decohesion from the surrounding matrix. An elastoplastic behaviour is assumed for both graphite and matrix material, described by classical J2 flow theory of plasticity, whereas a traction-separation law is applied to the interface. The model is analysed numerically, with an emphasis on the influence of different parameters such as the inclusion size, the distance between the particles, and the combination of their shapes on thermal debonding, identifying critical combinations that either deteriorate or relieve the effect. The obtained results can provide significant knowledge on the response of CGI under thermal load at the microscale, contributing also to understanding of its macroscopic behaviour at elevated temperatures.

Three-dimensional transient cutting tool temperature field model based on periodic heat transfer for high-speed milling of compacted graphite iron

The new material, compacted graphite iron, plays a key role in the reliability of engine and the realization of high emission standard, but it is a difficult-to-machine material. In high-speed milling process of compacted graphite iron, thermal crack induced by thermal stress is the main reason for tool breakage and chipping. In order to reveal the initiation and propagation mechanisms of thermal cracks, and improve tool life by controlling the formation of thermal crack, it is necessary to study the three-dimensional transient cutting tool temperature field under the condition of periodic heat transfer in intermittent cutting. In this paper, the three-dimensional transient FEM cutting tool temperature field model for high-speed milling of compacted graphite iron was established by using the heat source method. The uneven spatial distribution of the heat flux on the rake face of the tool, and the changes of heat flux density due to the transient cutting thickness and tool-chip contact length over time were considered, and the influence of boundary conditions in the cutting stage and the non-cutting stage were also all taken into account. The heat flux action time and the ratio of cutting time and non-cutting time in the model were set according to the experimental conditions of actual milling process. The established three-dimensional transient cutting tool temperature field model was finally verified by measuring the real temperature in high-speed orthogonal turning experiment. The results showed that the predicted value of the model was consistent with the experimental value, and the predicted error was less than 6.0%, indicating that the model has high accuracy for simulation. This model has great theoretical significance for the development of new tool materials for compacted graphite iron processing, studying the mechanism of thermal crack, controlling and preventing tool failure caused by thermal crack.