Gray Iron Research Articles

Degradation of multi-layer CVD-coated cemented carbide in finish milling compacted graphite iron

Stricter regulations on emissions and higher demands on engine performance drive automotive industries to replace conventional gray cast iron with compacted graphite iron (CGI). CGI has a higher wear resistance, strength, elastic modulus, and almost double fatigue strength as to gray cast iron, yet the same positive properties make CGI more difficult to machine. This study focuses on finish milling CGI EN-GJV-450 with current industrial standard of tooling: cemented carbide with multi-layer CVD-coating of Ti(C,N)–Al2O3. At cutting speed of 150 m/min a total of 3126 cm3 of material after 190 passes was removed, while 1645 cm3 was removed after 100 passes in case of 250 m/min. Studying the wear evolution at different engagement times demonstrated an accelerated chemical wear of the Al2O3 top coating due to its reaction with MgO-containing inclusions that creates a softer reaction product of (Mg,Fe,Mn)Al2O4 spinel which is abraded and removed with the chip flow. Ti(C,N) coating layer experiences diffusional and mechanical (abrasion, debonding, micro-fracture) wear mechanisms. Exposure of cemented carbide substrate resulted in its rapid wear in the form of cratering and massive material loss on the flank where the latter eventually causes tool failure. The adherence of CGI to WC-Co facilitates diffusional loss of carbon and tungsten from WC grains. Carbon reacts with iron at the interface forming iron carbide, while residual tungsten alloys it thus forming (Fex,W1-x)3C. This phase can reduce the wear rate as it acts as a diffusion barrier, but its high brittleness enables its periodic removal by adhesive wear. Outward cobalt diffusion was also an active wear mechanism that facilitates further diffusion of carbon and tungsten but also weakens the WC-grain bonding, further facilitating adhesive wear by CGI flow. Deposition of oxide inclusions to exposed WC-Co work as an anti-stick for CGI adhesion and thus reduces the wear rate.

Effect of Copper as an Alloying Element on Microstructure and Mechanical Properties of Grey Cast Iron

Effect of Copper as an Alloying Element on Microstructure and Mechanical Properties of Grey Cast Iron

Optimization and statistical modeling of the thermal conductivity of a pumice powder and carbonated coal particle hybrid reinforced aluminum metal matrix composite for brake disc application: a Taguchi approach

Aluminum metal matrix composites have been gaining traction in recent years due to their good mechanical properties and low weight. Particulate reinforcements for the improvement of its properties have been explored. This research aimed to determine the optimal composition of the reinforcement content (pumice powder and carbonated coal particles) and processing parameters (stirring speed, processing temperature, and stirring time) on the thermal conductivity of the developed material and also to characterize the constituents using x-ray fluorescence, x-ray diffraction, and scanning electron microscope/energy dispersive x-ray. The Taguchi optimization approach and regression analysis were used for the optimization and statistical analysis, respectively. The Taguchi optimization results gave an optimum thermal conductivity of 111.5, 112.5, 111.7, 112.9, and 112.4 W m−1 °C for pumice, carbonated coal, stirring speed, processing temperature, and stirring time respectively. The optimization also revealed the optimum setting for reinforcements and stir casting process factors as regards thermal conductivity to be 2.5%, 5.0%, 300 rpm, 850 °C, and 5 min for pumice powder, carbonated coal particles, stirring speed, temperature, and time, respectively. The optimal thermal conductivity of 120.40 W m−1 °C was obtained for the hybrid composite which gives a 131.54% improvement over the conventional grey cast iron brake disc. The particulate reinforcements (pumice powder and carbonated coal particles) and the processing factors all had significant effects on the thermal conductivity of the material, with the carbonated coal particles having the highest percentage contribution of 16.51%, as established by the analysis of variance. A model for predicting the thermal conductivity was developed using regression analysis, and high prediction accuracy was established with R-Square, R-Square (adj), and R-Square (pred) values of 94.68%, 88.60%, and 79.94%, respectively. The results of the characterization show the presence of hard compounds such as silica, iron oxide, and alumina in pumice powder and carbonated coal particles.

Methodology of technological design in the restoration of parts

In the work, from the standpoint of a systematic approach, a methodology for technological design of repair and restoration of worn parts using methods to improve the quality of the working layer is proposed. For the stages of the product life cycle, solving the problem of extending the service life after repair and restoration of worn parts, a general scheme and structure of information support for technological design were developed using restoration methods that ensure and improve the quality of the working layer. A variant of the technological process for the restoration of cylinder liners from modified gray cast iron by a combination of surface plastic deformation (SPD) and finishing antifriction non-abrasive treatment (FANT) is proposed.

Dilatation of New Progressive Hybrid Sand and Its Effect on Surface Structure, Roughness, and Veining Creation within Grey Cast Iron.

The constant effort of all metal alloy manufacturing technologies and processes is to improve the resulting quality of the processed part. Not only the metallographic structure of the material is monitored, but also the final quality of the cast surface. In foundry technologies, in addition to the quality of the liquid metal, external influences, such as the behaviour of the mould or core material, significantly affect the cast surface quality. As the core is heated during casting, the resulting dilatations often lead to significant volume changes causing stress foundry defects such as veining, penetration and surface roughness. In the experiment, various amounts of silica sand were replaced with artificial sand and a significant reduction in dilation and pitting of up to 52.9% was observed. An important finding was the effect of the granulometric composition and grain size of the sand on the formation of surface defects from brake thermal stresses. The specific mixture composition can be considered as an effective prevention against the formation of defects instead of using a protective coating.

Исследование антифрикционных и противоизносных свойств смазочных материалов судового назначения, содержащих слоистый модификатор трения

The paper highlights the results of anti-friction and anti-wear tests of samples of lubricating media containing a layered friction modifier - molybdenum diselenide. The main variable test conditions are the load on the test samples, volume concentration of the layered friction modifier in the lubricating oil, preliminary storage time of the lubricating composition before testing. The main evaluation criteria are the mass wear of samples, wear intensity, friction coefficient. Each of the eight test cycles was implemented on a tribotechnical installation of an original design using a cylindrical contact type. The resource indicators transferred from the model conditions of the tests to the real tribological unit “ring-cylinder” of a marine diesel engine 6ChSP 18/22 were evaluated. According to the results of tribological studies, the effect of increasing the load on the model friction unit of the installation, containing a cylindrical wear pair of alloyed gray cast iron, was revealed, as a result of which the mass wear of the annular movable sample increases, and the resource transferred to the real tribological interface of the marine diesel engine “ring-cylinder” decreases in 1.13-1.23 times. The greatest influence on the wear indicators of model samples and the resource transferred to the real “ring-cylinder” interface of a marine diesel engine is the time of preliminary storage of a lubricant composition containing molybdenum diselenide as an additive. It has been proven that the deterioration of anti-friction properties (an increase in the average surface temperature of a segment sample and the friction force) is largely affected by a decrease in the volume concentration of an anti-wear additive in the oil. It has been found out that serious changes in the indicated estimated parameters are valid for the smallest loading step on the samples. General recommendations are formulated for the use of antiwear additives considered in the studies. It has been proved that storing lubricating compositions with additives is possible for a period of no longer than 3-4 days at given volume concentrations in the range of 0.5-1.0%, since if this period is exceeded by 25-40%, the diesel CPG resource may be halved with increased wear of its piston rings and cylinder liners.

Interlaboratory Study on Brake Particle Emissions Part II: Particle Number Emissions

The Particle Measurement Programme (PMP) informal working group co-ordinated a global interlaboratory study (ILS) on brake wear particle emissions with the participation of 16 laboratories in 2021. Two articles present the results of the ILS: (I) particulate matter mass (PM) and (II) particle number (PN) emissions. The test matrix covered different brake systems, including ECE and NAO pad materials with grey cast iron discs and a drum brake. Regarding PN, the study measured the total particle number from approximately 10 nm to 2.5 µm (TPN). Some testing facilities measured solid particle number emissions (SPN) in parallel. The mean TPN concentrations ranged from 9.1 × 108 #/km/brake to 1.1 × 1010 #/km/brake. TPN and SPN emission levels were comparable, except for one lab that measured very high volatile particle emissions for one brake system. The minimum and maximum SPN emissions for a given brake differed by a factor of 2.5 ± 0.5, comparable to data from exhaust SPN ILS measurements. This article provides an overview of lessons learned and subsequent measures incorporated in an upcoming global technical regulation to reduce measurement variability when sampling and measuring brake particle emissions for light-duty vehicles up to 3.5 t.

Wear Behavior of Nb Alloyed Gray Cast Iron for Automotive Brake Disc Application

Gray cast iron (GCI) with a pearlitic matrix and type-A graphite remains the most widely used material in the manufacturing of brake discs. To reduce the environmental impact of disc wear during braking, alternative materials and/or compositions to the standard ones are being studied. In this study, the effect of variation in niobium content (0–0.7 wt%) on microstructure and wear behavior of samples machined from brake discs made of hypoeutectic gray cast iron was investigated. The wear behavior of GCI was examined through pin-on-disc (PoD) wear tests using low-metallic-friction material discs as the counterparts. Microstructural analyses and hardness measurements were also conducted to evaluate the effect of Nb addition on the morphology of graphite, eutectic cells, and distribution of carbides. In addition, the wear mechanisms of different samples were evaluated using scanning electron microscope analysis. The results revealed that adding 0.3% of Nb promotes the highest wear resistance of the alloys.

Effect of Ni and Mo on microstructure and mechanical properties of grey cast iron

ABSTRACT Alloying elements (Ni, Mo) were added to grey cast iron, and the effect of Ni, Mo on microstructure and mechanical properties were analysed in this study. When Ni was added alone, the precipitation of graphite was inhibited at the early stage of solidification, and part of graphite was formed between the dendrites, resulted in an uneven distribution of graphite. Ni played a role of solution strengthening and reduced the pearlite interlammer spacing, improved the mechanical properties. The addition of Mo refined the austenite dendrites and made the carbon unevenly distributed, which led to the abnormal growth of graphite. Mo increased the eutectoid supercooling degree, reduced the pearlite interlammer spacing and improved tensile strength. When Ni and Mo were added together, the elements beneficial to strength (Mo, Sn) were not uniformly distributed, and the influence on graphite size and pearlite interlammer spacing was not obvious, resulted in poor mechanical properties.

Effect of increased mechanical strength on the machinability of graphite cast irons in face milling

Due to the low cost and high vibration damping capacity, gray cast irons are commonly used in machine tool bases, in addition to applications with noise restrictions, such as engine blocks, housings, and brakes. The matrix’s graphite, sulfides, and ferrite/pearlite ratio are some of the most important parameters governing the machinability of the gray cast irons. This work aims to evaluate the machinability of high-resistance gray cast irons of the FC 300 grade, in two versions, with the addition of molybdenum (FC 300 (Mo)) and with refined graphite and addition of molybdenum (FC 300 (Mo+RG)), for use in cylinder heads and engines blocks, compared to materials that have been used for this purpose, gray cast iron FC 250 and the compacted graphite cast iron FV 450. The materials were characterized according to the cementite interlayer spacing and microhardness of the perlite matrix, the number of eutectic cells, and the distribution of manganese sulfide inclusions, with those characterizations being correlated with the machinability results. The face milling process was chosen for the tests with uncoated cemented carbide tools without cutting fluids; the cutting speed and feed rate varied in addition to the type of cast iron. Analysis of tool life, wear mechanisms, and machined surfaces’ quality (Ra roughness parameter) were the output variables considered. Using harder materials such as FC 300 (Mo) or FC 300 (Mo+RG) for the engine would bring benefits such as increased durability, reduced weight, and improved efficiency, but it has a cost in machining. These harder materials have a shorter tool life compared to the commonly used gray cast iron FC 250, but the difference in performance is less pronounced under more extreme cutting conditions, such as high cutting speed and feed rate. When analyzing the surface roughness, FC 250 produced a smoother surface at low cutting speeds but performed worse than FC 300 (Mo) and FC 300 (Mo+RG) at higher cutting speeds.

Comparative Study on the Friction Behaviour and the Particle Formation Process between a Laser Cladded Brake Disc and a Conventional Grey Cast Iron Disc

Brake-wear particle emissions are the result of the components of a friction brake being in tribological contact, and they are classified as non-exhaust emissions. Since most of the emitted particles belong to the size classes of particulate matter (≤10 μm) and differ significantly in terms of their physico-chemical properties from automotive exhaust emissions, this source is of particular relevance to human health and, therefore, the focus of scientific studies. Previous studies have shown that coated brake discs offer significant wear and emission reduction potential. Nevertheless, no studies are available that describe the specific particle formation process, the contact conditions, the structure of the friction layer and the differences compared to conventional grey cast iron discs. The aim of this study is to describe those differences. For this purpose, the tribological behaviour, the structure of the friction layer and the associated particle dynamics within the friction contact between a laser cladding coated disc and a conventional grey cast iron disc are compared. The required investigations are carried out both ex situ (stationary) and in situ (dynamic). Parallel to the tribological investigations, the particle emission behaviour is determined on an inertia dynamometer using a constant volume sampling system (CVS) and equipment for particle number and particle size distribution measurement. The results show that, for two different brake pads, the laser cladding brake disc has lower wear and less particulate emissions than the grey cast iron brake disc. The wear behaviour of the coating varies significantly for the two brake pads. By contrast, the grey cast iron brake disc shows a significantly lower influence.

Influence of FeS2 and FeSi75 in Double-Chamber Sample Cup on Thermal Analysis Curve and Graphite Morphology of Molten Iron

In the production of vermicular graphite cast iron, the allowable range of residual magnesium content in molten iron after treatment is very narrow, amounting to only 0.008%. Therefore, thermal analysis technology was used to quickly evaluate the vermiculation and inoculation level of molten iron at the furnace itself, thus allowing the molten iron to be adjusted in time. The additives in the sample cups play a crucial role in obtaining cooling curves with remarkable characteristics. In this study, either FeS2 or FeSi75 additives were added to one chamber of a double-chamber sample cup made of resin sand, in which the cavities of the double chambers were spherical with diameters of 30 mm. The thermal analysis curves of molten iron in the double-chamber sample cup were acquired using a double channel temperature recorder, and the solidified spherical samples were analyzed quantitatively. The influence of FeS2 or FeSi75 additives on both the cooling curves of molten iron and the graphite morphology were investigated. The experiment’s results indicated that when 0.05% FeS2 is added to one chamber of the sample cup, the cooling curve changes to the solidification pattern of gray cast iron. The continuous increase in the FeS2 additive has little influence on the shape of cooling curves, and the graphite changes form from vermicular to flaked. When the amount of FeS2 is increased from 0.05% to 0.10%, the resulting graphite changes from D-type and E-type to A-type and B-type. When the amount of FeS2 reaches 0.20%, the morphology of graphite is short and thick. With the increase in the amount of FeSi75 additive, the amount of spherical graphite in the sample cup increases gradually, and the vermicularity decreases gradually from 89% to 46%. With the increase in FeSi75 additive from 0 to 0.45%, we observed that the average diameter of graphite decreases from 23 μm to 19 μm and then increases to 22 μm. The eutectic recalescence temperature shows a decreasing trend, and the cooling curve gradually changes from a hypoeutectic to a eutectic pattern. The addition of 0.05% FeS2 or 0.45% FeSi75 to one chamber is more appropriate for a double-chamber sample cup with two spherical cavities with diameters of 30 mm. This lays a foundation for the optimization of additives when using the double-chamber sample cup for thermal analysis of vermicular graphite cast iron.

Full-scale determination of pipe wall and bulk chlorine degradation coefficients for different pipe categories

Abstract Having good information about parameters that impact water quality can improve the management of water distribution systems in the short-term (optimising disinfection) and the long-term (planning rehabilitation). Full-scale data on the degradation of the residual disinfectant for various pipe characteristics are difficult to obtain but necessary. As the most common disinfectant is chlorine, this paper aims to determine the most important pipe and/or hydraulic system characteristics in the chlorine degradation coefficients. Such characteristics were identified based on statistical analyses that relate them with range values of bulk and pipe wall degradation coefficients estimated in full-scale conditions in a real distribution system. The results showed that among pipe characteristics, the period of installation impacts significantly kw and kt. Results of kw for three different materials confirmed that residual chlorine degradation at the pipe walls for grey-cast iron, which is older and metallic, is much higher than that for ductile cast iron and PVC pipes. In older pipes, up to 97% of residual chlorine can be degraded at the pipe walls, while the role of bulk reactions can reach about 35% in newer pipes. The obtained information can be integrated to identify pipes for rehabilitation/renewal and locations for booster rechlorination.

Effects of honing process parameters on residual stress fields of grey cast iron engine cylinder liners: Experimental and numerical study

Super polishing methods are widely employed to improve the surface integrity of machined parts. These methods not only improve the surface texture of the machined parts, but also modify the residual stresses induced at the outer layer of the machined surface. In this study, the effects of honing process parameters on the distribution of residual stresses at the surface of grey cast iron investigated numerically and experimentally. To this aim, a finite element (FE) model developed to evaluate the effects of process parameters, including cutting speed, grain size, and pressure of honing tools, on the residual stresses induced at the surface of samples. The friction coefficient introduced as an updating parameter in the model to get the best correlation between the results of FE and experiments. In addition, the X-ray diffraction method used to experimentally measuring the distribution of residual stresses at the honing surface of the samples. The experimental and numerical results showed that in majority of combinations of the process parameters, the maximum compressive residual stress occurs at a depth of approximately 0.03 mm from the cutting surface of the sample. Additionally, it was seen that decreasing the size of abrasive grains and cutting speed and increasing the pressure on the cutting tool result in higher levels of induced compressional stresses at the surface of samples. However, the depth at which the maximum residual stress occurs can proceed up to 0.06 mm by an increase in the diameter of abrasive grains and cutting speed.

Investigation of the Tribological Behaviour of Various AMC Surfaces against Brake Lining Material.

AlSi7Mg/SiCp aluminium matrix composites (AMCs) with a high ceramic content (35 vol.%) that were produced by using the field-assisted sintering technique (FAST) were subjected to tribological preconditioning and evaluated as a potential lightweight material to substitute grey cast iron brake discs. However, since an uncontrolled running-in process of the AMC surface can lead to severe wear and thus to failure of the friction system, AMC surfaces cannot be used directly after finishing and have to be preconditioned. A defined generation of a tribologically conditioned surface (tribosurface) is necessary, as was the aim in this study. To simulate tribological conditions in automotive brake systems, the prepared AMC samples were tested in a pin-on-disc configuration against conventional brake lining material under dry sliding conditions. The influence of the surface topography generated by face turning using different indexable inserts and feeds or an additional plasma electrolytic treatment was investigated at varied test pressures and sliding distances. The results showed that the coefficient of friction remained nearly constant when the set pressure was reached, whereas the initial topography of the samples studied by SEM varied substantially. A novel approach based on analysing the material ratio determined by 3D surface measurement was developed in order to obtain quantitative findings for industrial application.

Failure analysis of inner wall of X-10 brake discs for urban rail vehicles

Some X-10 type brake discs for urban rail vehicles were examined by fluorescent magnetic particle inspection test, and the magnetic trace accumulation was observed at the root of the connecting claw of the brake discs. In this work, the causes of failure for the brake discs are analyzed and discussed. The chemical composition, metallographic structure, and mechanical property of the failure samples were characterized by means of X-ray energy dispersive spectrometry, metallographic microscope, scanning electron microscopy, and an electronic universal material-testing machine. At the same time, the stress and crack propagation states were analyzed by numerical simulation, braking dynamic and fatigue tests, respectively. Based on the fracture mechanics theory, the residual fatigue life was also predicted. The failure reason of the inner wall of brake disc was that the fatigue crack occurred at the root of the connecting claw of the brake disc body, and the crack source was taken from graphite sheets exposed on the surface of the grey cast iron matrix. The results of the numerical simulation showed that the larger thermal stress acted on the graphite sheets at the root of the connecting claw, and promoted the crack to expand along the path of the graphite sheets. The results of the braking force and fatigue tests showed that there was stability propagation of the crack. Finally, some suggestions and prevention for brake discs are provided.

Temperature during Repetitive Short-Term Operation of a Brake with Functionally Graded Friction Element.

The object of study is the temperature of a braking system, operating in repetitive short-term (RST) mode. One element of the considered friction pair is made of a functionally gradient material (FGM), and the other of a homogeneous material. To determine the temperature on the friction surfaces of both elements, the previously obtained, exact solution of the boundary value problem of heat conduction was adopted, with account of the heat generation due to the friction. A calculation scheme was proposed that takes into consideration thermal sensitivity of materials and variations of the friction coefficient under the influence of temperature. Calculations were performed for two-component FGM (ZrO2-Ti-6Al-4V) in combination with gray cast iron (ChNMKh). It was found that for selected friction pair materials, consideration of their thermal sensitivity reduces the time of braking and the value of temperature achieved on the friction surfaces. At the same time, the whole process was characterized by a good stability of braking with a slight decrease in efficiency in each subsequent cycle.

Coaxial laser cladding of cobalt-base alloy StelliteTM6 on gray cast iron/investigations on friction, wear versus commercial brake pad, and corrosion characteristics

Environmental legislation and the electrification of vehicles place increased requirements on brake disks in terms of wear and corrosion resistance. Departing from a preliminary study, the present investigation examined the friction and wear behavior as well as the corrosion properties of Stellite™ 6 coatings on gray cast iron, which were deposited by laser cladding. The friction and wear experiments were conducted on a pin-on-disk tribometer at contact pressures of 1.0 and 2.0 MPa as well as rotation speeds of 0.2, 0.4, 0.6, 0.8, and 2.0 m/s. The pins are manufactured from an automotive semi-metallic brake pad. The friction behavior of gray cast iron and Stellite™ 6 coatings is similar under changing test conditions. The tribological behavior is strongly influenced by the microstructural and mechanical properties of the coatings and the brake pad material. A third body layer of contact patches is formed on Stellite™ 6, which mainly consists of brake pad components. The transformation of the Co-matrix (fcc → hcp), subsurface fatigue, and tribo-oxidation are the main wear mechanism for Stellite™ 6. The electrochemical characteristics were analyzed by potentiodynamic polarization, and the corrosion rate was determined with Tafel plots in 3.5% NaCl solution, respectively. Compared to gray cast iron, Stellite™ 6 coatings have a pronounced corrosion resistance due to the formation of a protective passive layer of Co and Cr oxides. This corrosion resistance is mainly influenced by the microstructure. The corrosion rate of the coatings increases in parallel with the Fe dilution.

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.

A novel path towards limiting non-exhaust particulate matter emissions of a commercial friction material through the addition of metallurgical slag

Keeping recycling and the circular economy in mind, this study explores the reduction in emission of a highly optimized, commercially employed friction material formulation through the addition of metallurgical slags from a basic oxygen furnace in varying quantities from 6 to 38 wt%. The various compositions were paired with a pearlitic grey cast iron counterface and tested on a pin on disc tribometer. The friction coefficient and pin wear increased with the slag addition but were still within the permissible limit when compared to the original formulation. Specimens with higher slag content observed extremely compacted and extended secondary contact plateaus, which also recorded significant slag presence. The extended plateaus detached in the form of chunks from the mating surfaces, which settled on the equipment hardware and restricted the production of airborne particles. From an industrial symbiosis perspective, the addition of metallurgical slags proved to be a promising way of obtaining green friction materials with reduced emissions.