Ductile Iron Research Articles

Optimizing Wear Resistance in Carbidic Austempered Ductile Iron through Austempering Parameter Variation

Austempered ductile iron (ADI), as implied by its name, is a variant of ductile iron known for its enhanced strength and toughness compared to cast iron. Distinguishing itself from cast iron, ductile iron exhibits higher strength and toughness, particularly in tensile tests. The nomenclature "Austempered" in ADI stems from its unique heat treatment process called Austempering. While numerous research journals delve into the wear resistance of Compacted Graphite Iron (CGI) materials, there is a notable gap in understanding the correlation between Austempering temperature and abrasion properties. Material wear is influenced by various factors within the application environment, broadly categorized as time, load, and speed. This journal provides a comprehensive exploration of how these variables collectively impact the wear characteristics of Austempered ductile iron..

Influence of distribution and size of graphite particle on the machinability of nodular cast iron

Nodular cast iron (NCI), also known as particulate metal matrix composites (PMMCs), is extensively utilized in the manufacturing of pistons for high-power engines. However, poor machinability is a significant problem due to the inherent microstructural inhomogeneity of the NCI. Therefore, this study aims to investigate influence of graphite particle distribution and size on the machinability of NCI. Microstructure of NCI is experimentally examined and quantitatively analyzed, and NCI is treated as a three-phase composite (i.e., matrix-interface-graphite particles). Graphite particles are considered as a plastic material, and debonding of interfaces is taken into account. Based on average particle size and volume fraction of graphite nodules, four microstructural models with different particle sizes and distributions are discussed, and turning experiments are conducted to validate simulation results. The findings reveal that graphite particles of different sizes and distributions affect stress–strain distribution in the cutting region of the material. As the distance between the graphite particles and the cutting tool increases, their influence on the stress–strain distribution becomes less significant. Furthermore, random distribution of graphite particles is more likely to result in complex crack initiation and expansion, leading to more pronounced serrated chips. The distribution of graphite particles has a more significant impact on the stability of cutting forces compared to the particle size. Both experiments and simulation results show that cavities and burrs are appeared along the cutting path because of graphite nodules, which reduces the surface quality and affects the subsequent use of the parts. On the one hand, the present work provides guidance for the finite element modelling of NCI, which is helpful to improve the precision of cutting simulation. On the other hand, by integrating advanced manufacturing technology to regulate the microstructure and cutting parameter of NCI, the present study can provide data basis and numerical analysis support for improving the machinability of NCI.

THE EFFECT OF HARDENING TECHNIQUES ON WEAR RESISTANCE AND FATIGUE LIFE OF DUCTILE CAST IRON

Many hardening methods have been developed and proposed as an effective technology to produce microstructural modification and improvement of mechanical properties of variety metallic materials. In this experimental study, the effects of applying laser peening (LP) and friction stir processing (FSP) methods on wear resistance and fatigue properties of selected cast iron ASTM A536, grade (80-55-06) with ferrite/pearlite microstructure were investigated. Microscopic study revealed evident refinement and crashing of graphite nodules as 50% of the basic size with FSP and 32% with LP within the processed surfaces hence improving average microhardness by 100% and 48% respectively. The wear resistance and fatigue life were increased by 33% and 122% after FSP whereas, the corresponding increments were 15% and 22% after LP in comparison with the basic ductile iron. These improvements were linked to surface hardening, compressive stresses and structural modification by the employed processes.

Impact of Quenching and Aluminium on Si-Segregation and B2 Superstructure Formation in Solid Solution Strengthened Ferritic Ductile Cast Iron

Solid solution strengthened ferritic ductile iron proves to have a better ratio of tensile strength to elongation than conventional ductile iron grades. This applies up to a maximum silicon content of 4.3 wt%, beyond which it leads to an abrupt decrease in ultimate tensile strength and elongation at fracture. During solidification of high silicon ductile iron, negative segregation of silicon occurs, and the highest silicon concentration is observed near the graphite nodules. This high silicon concentration leads to long-range ordering of iron and silicon, and this ordering results in formation of superstructures like BCC_B2 and D03. The presence of super structures restricts the mobility of dislocations and leads to abrupt fracture of the material. This research focuses on the investigation of silicon homogenization by the addition of aluminium and heat treatments to avoid the formation of brittle iron–silicon superstructure. Thermodynamic–kinetic simulations as well as experimental investigations, including variation in alloy composition and quenching, are performed. The results provide a promising understanding to control the micro-segregation of silicon in ductile cast iron based on heat treatments and alloy composition.

A comparative investigation on wear behaviors of physical and chemical vapor deposited bronze coatings for hydraulic piston pump

The cylinder block/valve plate interface is one of the most critical frictional interfaces of the swashplate-type axial piston pump. However, the poor lubrication interface caused rapid wear and high friction loss in an elastohydrodynamic lubrication system, decreasing the pump lifetime. Wear resistant bronze coatings were fabricated on 38CrMoAl substrate by Physical Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD), respectively. Ball-on-disc wear tests were performed to comparatively investigate the wear behaviors of the coatings and bulk ductile iron samples. It can be found that the PVD-bronze coating exhibited better wear resistance than the other two samples. This enhanced wear resistance was attributed to the unique composite microstructure and desired mechanical strength, which could resist to mechanical shear and spallation, decreasing friction loss. The appropriate hardness of (1.33 ± 0.07) GPa could be beneficial for enhancing its wear resistance. The PVD-bronze coating possessed a much lower and stable coefficient of friction (about 0.1) and wear rate (about 6000 μm3·N−1·m−1) under the loading forces of about 100 N after 20 min. The wear mechanism was the abrasive wear.

A continuum damage coupled unified viscoplastic model for simulating the mechanical behaviour of a ductile cast iron under isothermal low-cycle fatigue, fatigue-creep and creep loading

A novel continuum damage coupled unified viscoplastic model is used for simulating the stress–strain responses of SiMo 4.06 cast iron under Low-Cycle Fatigue (LCF), fatigue-creep and creep loading for temperatures up to 650 °C. The advanced constitutive model that is developed within the framework of the Chaboche model allows the simulation of various effects including strain rate sensitivity, cyclic hardening and softening, static recovery and strain range dependency. The hyperbolic sine flow rule and the static recovery of kinematic hardening rule are proposed in order to effectively simulate both stress relaxation and creep strains. The isotropic damage variable is introduced into the constitutive equations to represent the effects of material degradation. Three main damage mechanisms are considered: fatigue, creep and ductile damage. In addition, the model is further modified to take into account the progressive microdefects closure effect. Finally, the prediction capability of the proposed model is illustrated for the experimental data obtained from the various uniaxial material tests. A good correlation was achieved between the simulated and the experimental results.

Thermal Analysis of Ductile Iron: A New Way to Predict the Mechanical Properties

Thermal analysis is characterized by the recording and evaluation of the temperature curve over time. Due to the correlation between transformation temperatures and chemical composition, thermal analysis is used to determine the carbon and silicon content. Furthermore, the aim is to be able to predict mechanical properties by thermal analysis. However, all current prediction methods refer to the cooling conditions in the investigated casting area and do not allow any transfer to other cooling conditions. There is a lack of a direct and automatic prediction of the mechanical properties from the thermal analysis before casting and transfer to other cooling conditions. For this study, cooling curves from the last 10 years at the Foundry Institute at RWTH Aachen University were evaluated and correlated with the mechanical properties from castings with three different thermal modules. The results of this empirical regression analysis are equations for the investigated mechanical parameters, which can be automatically filled with the characteristic times and temperatures of a thermal analysis in the casting process and the thermal modulus from the casting. For this modulus, the user can insert a corresponding value of the structural casting part that is relevant to the quality requirements in the foundry.

Influence of Cooling Rate and Alloying by “Cr, V, and Ni” on Microstructure and High-Temperature Wear Behavior of SiMo Ductile Iron

AbstractSiMo ductile irons, typical heat-resistant materials, are subjected to varied wear environments during operation in high-temperature applications. SiMo ductile iron castings of different thicknesses were cast in investment and greensand molds, achieving a wide range of cooling rates. The present work aims to investigate the effect of the cooling rate and alloying elements (Cr, V, and Ni) on the microstructure and the abrasive wear behavior of these grades of SiMo ductile iron at high-temperature 700 °C under different loads. Thermodynamic calculations were used to propose the phase diagrams, critical transformation temperatures, and phase volume fractions in all SiMo alloys by using the Thermo-Calc software then verified by and Differential Scanning Calorimetry (DSC). The microstructure of unalloyed SiMo ductile cast iron consists of graphite nodules and carbides embedded in the precipitates at the grain boundary regions in a ferrite matrix. The alloyed SiMo microstructure contains nodular graphite and the carbides promoted by the alloying elements (Cr and V). The alloyed SiMo alloys exhibit higher wear resistance than unalloyed ones. These wear results support that the microstructure plays a chief role in wear loss. The combination of M6C, VC, and M7C3 carbides embedded in a ferrite-pearlite matrix (alloyed SiMo) seems to be more resistant to wear than the ferritic matrix with lamellar pearlite and eutectic M6C carbides (unalloyed SiMo).

Effect of regular thicknesses on the microstructural and quantitative analysis for a hypo-eutectic ductile iron alloyed with Ni and V

Ductile iron contains free graphite nodules within the metallic matrix, which generally consists of ferrite and pearlite in the as-cast condition. The casting thicknesses have a great influence on the size, shape, and quantity of the microconstituents of the metallic matrix and the graphite nodules and thus on the mechanical properties. In this study the cooling rate (caused by the casting thicknesses) on the metallic matrix and the nodular characteristics of a low alloyed ductile iron with 0.8 %Ni and 0.15 %V was investigated. The ductile iron was produced in a sandwich process with ladle inoculation. Six plates of different thicknesses, from 4.3 mm to 25.4 mm, were produced in a green sand mold. The microstructural characterization was performed by optical microscopy (OM), scanning electron microscopy (SEM), and the image J software using different quantification methods. The area method to determine the average nodule size and nodular structure provided more reliable results than the perimeter and total particle count methods. The hardness test on the Rockwell C scale was used for the mechanical characterization. The low content of vanadium added to the ductile cast iron had a negligible effect on the solidification pattern, which was mainly due to the graphitizing impact of the nickel and silicon addition. The results of the microstructural characteristics are therefore primarily due to the cooling rate, which is determined by the casting thickness. The thinnest casting section significantly improved the number of nodules (414 Nod/mm2), sphericity (0.96), and nodularity (96.21 %). In contrast, the thickest casting plate obtained the highest volume fraction of graphite (10.85 %) and the lowest volume fraction of unwanted particles (0.36 %). The high cooling rate in the thinnest casting plate resulted in the highest hardness of 31.56 HRC due to the higher volume fraction of the pearlite (33.7 %) and carbides (4.5 %).

Corrosion resistance and other utility properties of selected austenitic nodular cast irons

This study deals with the evaluation of corrosion resistance and other utility properties of selected austenitic nodular cast irons and their comparison with other (non-austenitic) nodular cast irons. For the investigations, two types of austenitic nodular cast iron were selected: nickel-manganese nodular cast iron EN-GJSA-XNiMn13-7 and nickel-chromium nodular cast iron EN-GJSA-XNiCr20-2. Basic mechanical properties, such as yield strength, tensile strength, elongation, absorbed energy and hardness, were evaluated using mechanical tests. The fatigue limit was determined using low-frequency fatigue tests. Corrosion properties, such as average corrosion rate, corrosion potential and corrosion current density, were determined by the exposure immersion test and the electrochemical potentiodynamic polarisation test. Both corrosion tests were performed in a 3.5% NaCl solution (to simulate seawater) at room temperature. The results of mechanical, fatigue and corrosion tests show that austenitic nodular cast irons have lower strength and fatigue properties but significantly higher plastic properties and corrosion resistance compared to non-austenitic nodular cast irons.

Graphite nucleation on (Al, Si, Mg)-nitrides: Elucidating the chemical interactions and turbostratic structures in spheroidal graphite cast irons

The ubiquitous (Al,Si,Mg)-nitride has been the focus of recent investigations of spheroidal graphite irons. In particular, because they have been systematically found in the nucleus of graphite spheroids. Despite having a similar crystal structure as graphite, their lattice parameter is vastly different. Since the crystallographic match is mainly used to justify the potential of nucleation sites, challenges have been encountered to explain the mechanism of graphite nucleation in this type of inclusion (microparticle). The present work reports the structure, composition, and interactions of these (Al,Si,Mg)-nitrides with graphite and other compounds, such as (Zr,Ti,Nb)-carbonitrides. The latter were the only inclusions with Zr that could be found, while the former inclusion could also be found in the core of graphite. The results confirm that the graphite layers close to the surface of the (Al,Si,Mg)-nitrides have a turbostratic structure. Organized graphite layers are only observed far away from the nitride nucleus. Density functional theory simulations of this interface showed that the interaction between the first graphene layers and the (Al,Si,Mg)-nitrides has a covalent nature, which could explain the turbostratic structure of the inner part of the graphite nodule. Therefore, nucleation of graphite on nuclei with a large lattice mismatch (low planar misfit) may be facilitated by the covalent bonding of carbon atoms on this substrate. These results explain the observed disorder at the interface as well as the deformation of the graphene layers.

Fatigue behavior of a nodular cast iron subjected to a variable amplitude strain-based load spectrum applied in bench tests of an Off-highway axle

Nodular cast irons are commonly adopted in off-highway applications, owing to the possibility to shape complex components and to guarantee good mechanical properties. In the fatigue strength assessment of axles made of nodular cast irons, engineers have to deal with external loads that turn into local strain spectra at the fatigue crack initiation zones, which are usually located in areas weakened by notched geometrical details. Moreover, off-highway axles are subjected to variable amplitude load histories during their service life; during the design phase, the field load histories are usually applied to the axles in the form of simplified bench load spectra. In this paper, the mechanical properties of EN-GJS-500-7 have been investigated through static tensile tests and strain-controlled fatigue tests performed on specimens with machined surface extracted from an axle. Furthermore, a local strain-based spectrum has been derived by means of strain gauges which have been applied at the failure location of the axle during the bench tests. Finally, the damage index to failure relevant to the simplified bench load spectrum has been calculated by adopting Miner's linear damage rule and the Smith, Watson and Topper mean stress corrected life equation.

The stress response mechanisms and resistance change of chlorine-resistant microbial community at multi-phase interface under residual antibiotics in drinking water distribution system

The presence of multiple trace amounts of antibiotics in drinking water has recently drawn much attention. However, synergistic effects between disinfectants and antibiotics often occur in pipeline due to the presence of residual disinfectants. How this interaction affects the drinking water microbial community remains unknown. Herein, reactors with 2 h of hydraulic retention time (HRT) were constructed to simulate the drinking water distribution system (DWDS), and the antibiotics were continuously discharged to the reactor. Sulfamethoxazole (SMX) was used as a representative antibiotic, and treatment protocols with and without disinfectants were compared. High-throughput sequencing and metagenome were used to study the microbial community and function in polyethylene (PE) and ductile cast iron (DI) (protected by cement mortar lining) pipes. By measuring the enzyme activity and ATP content, we found that disinfectant exposure could not only increase the secretion of biofilm EPS, but also improve the bacterial activity to a certain extent. The synergistic effect of antibiotics and disinfectants could increase the activity of oxidative stress-related enzymes in microbial communities, and the main effect was antibiotic stress. This study not only provides insights into how to inhibit the transmission process of antibiotic resistance genes (ARGs) in biofilm in DWDS, but also provides enlightenment for the harm of ARGs in all carriers where biofilms may exist in water plants.

Certain investigation on feasibility of developing riser less ductile iron castings

The solidification mechanism of ductile iron is a bit complex due to the precipitation of graphite and silicon. These elements change the solidification pattern of cast iron. Density of these elements is less than iron leads to occupying more volume consequently increase the overall metal volume. There are two aspects on this increase in metal volume. One is, reducing this volume increase to reduce the creation of porosities at the earlier stage of solidification and second is, using this volume increase to remove porosity at the later stage of solidification. Proper understanding of this graphite expansion in cast iron solidification will bring insights on reducing or removing of the risers. The current study focus on correlating the net contraction and austenitic liquidus point with shrinkage. The average contraction found through this study is 1.36 % which is more than the net expansion of 0.25 % (without riser) reported in literature. The study found that properly balancing graphite precipitation, pouring temperature and mold strength can enable riserless casting of ductile iron by compensating for liquid contraction through graphite expansion.

Experimental investigation of buried flexible HDPE pipe

Buried pipes are used mainly for water supply and drainage, among many other applications such as oil, liquefied natural gas, coal slurries, and mine tailings. The pipes used may be rigid (reinforced concrete, vitrified clay, and ductile iron) or flexible (steel, UPVC, aluminum, fiberglass, and high-density polyethylene), although the distinction between them is blurring. Deflection or buckling determines the design of flexible pipes. HDPE pipes are preferred due to their light weight, long term chemical stability and cost efficiency. This project aims to design and fabricate an experimental setup of the model trench as a steel tank filled with the desired type of soil and flexible pipe with the required depth and loading provisions to simulate uniform loading and record the behavior, i.e., deflection of the flexible plastic pipe, compare the observation with the theoretical results, and infer the findings. The deflection characteristics were to be measured with the help of a dial gauge fixed inside the pipe. Additionally, the objective is to study the load deformation behavior of the buried pipe and stress variation across the cross section of the pipe under static loading, along with the influence of depth of embedment and density of backfill on the deformation and stresses in the pipe and the deformation behavior of the buried pipe when soil is reinforced with geogrid reinforcement, and evaluate the structural performance of the pipe. Based on the conclusions, various recommendations can be made in terms of the application of buried flexible HDPE pipes in place of conventional pipes and thereby reducing the risk of leakage and damage and also compensating the cost of pipe systems economically.

Efficiency of Aloe Vera as a bioinhibitor in the treatment of corrosion in water pipes made of ductile cast iron

RESUMO As adutoras de abastecimento de água estão constantemente susceptíveis a corrosão, por agentes internos e externos, causando fissuras e rupturas das estruturas, ocasionando prejuízos econômicos e ambientais. Os processos que causam corrosão são químicos ou eletroquímicos, resultando na oxidação do material na presença de substâncias que sofrem redução, o que degrada suas propriedades químicas, físico-químicas ou mecânica. Uma alternativa para prevenir ou retardar o processo corrosivo, é a utilização de inibidores naturais em revestimentos para proteção contra a corrosão. Propõe-se o uso de inibidores naturais, como o extrato glicólico de Aloe Vera, para mitigar a corrosão. O estudo avaliou o desempenho desse inibidor por meio de ensaios eletroquímicos, perda de massa e análise de espectroscopia no infravermelho por transformada de Fourier - IVTR do extrato. Resultados indicam que a concentração do Bioinibidor de Aloe Vera em 0,3 ml apresentou melhor eficiência de 45,05%, com redução na taxa de corrosão de 31,84% nos ensaios de perda de massa, em relação as demais concentrações. A análise IVTR revelou grupos funcionais (OH; C-H; C=C) no extrato associados às propriedades inibitórias. Conclui-se que o extrato de Aloe Vera tem potencial como inibidor de corrosão para ferro fundido dúctil.

2D and 3D Microstructural Reconstruction of Nodular Cast Iron

2D and 3D Microstructural Reconstruction of Nodular Cast Iron

Erratum to: The Effect of Heat Treatment on the Structure and Properties of VCh 35 Ductile Cast Iron

Erratum to: The Effect of Heat Treatment on the Structure and Properties of VCh 35 Ductile Cast Iron

The influence of modifiers, alloying with copper and nickel on the structure, mechanical and performance properties of pearlitic ductile iron

The influence of modifiers, alloying with copper and nickel on the structure, mechanical and performance properties of pearlitic ductile iron

Study of fractography of ferritic ductile iron at different temperatures and loading conditions

This study characterizes the fractography of ferritic ductile iron under various loads, including tensile, fatigue and bending, and impact conditions. The results indicate that ductile fracture is the primary mechanism observed during tensile testing at room temperature. The fractography resulting from fatigue testing exhibits characteristics similar to cleavage fracture, and explains the formation of fatigue striations caused by the joint effects of dislocation slip and oxidation under crack tip stress. Under impact testing, the main fracture mechanism transitions from ductile to brittle with decreasing temperature. At high temperatures, fractography is mainly characterized by elliptical dimples with graphite nodules at the center that deform along the stress direction. In the ductile-brittle transition temperature range, a mixed fracture mechanism involving both dimples and cleavage patterns is observed. At low temperatures, the fracture mechanism is cleavage fracture, cleavage fracture is mainly caused by the deformation twin, inducing crack nucleation. These findings further validate D.O.Frenandino’s quantitative analysis method for determining the main crack propagation direction of ductile fracture and brittle fracture. By employing larger statistical datasets, it is shown that this method yields high accuracy in determining the main crack propagation direction of ferritic ductile iron, thereby promoting its application as a general method for impact fractography analysis.