Ductile Iron Research Articles

Density functional investigation of the heterogeneous nucleation of graphite on divalent metal oxides and sulfides

Controlling the nucleation of graphite during solidification of spheroidal and lamellar graphite irons is achieved through minor additions of certain active elements such as Mg, Ca, Sr, Ba and Mn. In the present work, interfaces of graphite with alkaline earth oxides, sulfides and MnS are investigated by density functional simulations of model structures where interfacial strain has been optimized by controlling the twisting angle between the two materials. The bulk stabilities, surface energies and interfacial energies between the nucleant phases, graphite and iron are calculated. A new graphite nucleation model for estimating undercooling based on interfacial energies is proposed. It is found that CaS is the most potent nucleant particle in spheroidal graphite iron and MnS in lamellar graphite iron. The main driver of nucleation potency is found to be of chemical nature rather than related to lattice misfit.

Research on microstructure evolution of laser surface quenching of ductile cast iron

Abstract Ductile cast iron is widely used in the manufacturing of components and dies due to its excellent performance and low cost. Laser surface quenching can further improve its performance and extend its service life. This article uses scanning electron microscopy, electron backscattered scattering detection and microhardness tester to systematically analyse the microstructure evolution of the melted zone, hardened zone, and matrix of ductile cast iron with laser surface quenching. The hardening zone can be divided into two layers: one layer contains a large amount of martensite, graphite, and bits of residual austenite, and the other layer contains a composite structure of graphite, ferrite, layered martensite+austenite+Fe3C. On the basis of microstructure research, the determination and optimization methods of the depth of the laser surface hardening zone and the process are formed, providing a basis for the selection and optimization of the laser surface hardening process for ductile cast iron.

High temperature oxidation of inoculated high Si/SiMo ductile cast irons in air and combustion atmospheres

High temperature oxidation of inoculated high Si/SiMo ductile cast irons in air and combustion atmospheres

Design of a test rig for the characterization of friction and wear in hot-metal gas-forming of AA 5083 aluminium sheets

Advanced aluminium sheet-forming processes such as the hot-metal gas-forming represent a challenging solution for producing small lots in the high-end car bodies industry, and the adoption of single cavity moulds made from low-cost, easily machinable materials such as cast iron reduces the overall sheet-forming costs. The tribological properties of the mould-sheet tribopair are of great interest for optimizing the sheet forming obtaining an acceptable esthetic surface finishing. This study presents the design and construction of a lab-scale experimental test rig for the tribological characterization at high temperatures of the mould-sheet tribopair. The proposed test method reproduces the sliding at the mould-sheet interface with contemporary sheet straining up to ε = 0.8 at strain rates in the 1.2*10-3 to 2*10-2 s-1 range. A series of experiments were carried out in dry and lubricated conditions for a ductile iron EN-GJS grade sliding against a AA 5083 aluminium alloy while straining. After comparing the experimental results with the literature data from other test rigs, comparable results were obtained as COF regards, ranging between 1.2 to 2.5 in dry sliding and between 0.05 to 0.2 in lubricated sliding. The morphological characterization of the sliding surfaces and cross-sections highlights the strong tendency to galling in dry sliding conditions expecially for low strain rates.

The sewer advances: How to select eco-friendly pipe materials for environmental protection

Sewer pipe materials exhibit diverse inner-surface features, which can affect the attachment of biofilm and influence microbial metabolic processes. To investigate the role of the type of pipe material on the composition and metabolic capabilities of the adhering microorganisms, three sets of urban sewers (High-Density Polyethylene Pipe (HDPE), Ductile Iron Pipe (DIP), and Concrete Pipe (CP)) were constructed. Measurements of biofilm thickness and environmental factors revealed that the thickest biofilm in CP pipes reached 2000 μm, with ORP values as low as −325 mV, indicating a more suitable anaerobic microbial habitat. High-throughput sequencing showed similar relative abundances of genera related to carbon and sulfur metabolism in the DIP and CP pipes, whereas HDPE exhibited only half the relative abundance compared to that found in the other pipes. To explore the impact of pipe materials on the mechanisms of microbial response, a metagenomic approach was used to investigate the biological transformation of carbon and sulfur in wastewater. The annotations of the crucial enzyme-encoding genes related to methyl coenzyme M and sulfite reductase in DIP and CP were 50 and 110, respectively, whereas HDPE exhibited lower counts (25 and 70, respectively). This resulted in significantly lower carbon and sulfur metabolism capabilities in the HDPE biofilm than in the other two pipes. The stability of wastewater quality during the transmission process in HDPE pipes reduces the metabolic generation of toxic and harmful gases within the pipes, favoring the preservation of carbon sources for sewer systems. This study reveals the variations in carbon and sulfur metabolism in wastewater pipe systems influenced by pipe materials and provides insights for designing future sewers.

Thermal Parameter Optimization for Enhanced Graphite Nodular Properties in Ductile Cast Iron: A Comprehensive Analysis of Cooling Rates and Its Effect on Microstructure

Thermal Parameter Optimization for Enhanced Graphite Nodular Properties in Ductile Cast Iron: A Comprehensive Analysis of Cooling Rates and Its Effect on Microstructure

Effect of welding parameters on microstructure and mechanical properties of dissimilar AISI 304/ductile cast iron fusion welded joints

Problems associated with dissimilar fusion welding are mainly originated from the differences in melting points, coefficients of thermal conductivity and thermal expansion, …etc., and carbon content when welding dissimilar ferrous materials. In this study, the problems associated with dissimilar fusion welding of stainless steel AISI304 with ductile cast iron DCI grade A536 were investigated. Using shielded metal arc welding (SMAW) process, various welding parameters were studied to investigate the successful/accepted dissimilar welded joint(s). Welding electrodes and welding techniques were the main studied parameters. Microstructural and mechanical investigations were carried out for welded joints under different welding parameters. Tensile, impact and hardness tests coupled with optical and scanning electron microscopic examinations with EDX analysis were made for metallurgical and mechanical evaluations of welded joints. This extensive study could solve the problem of dissimilar welding between ductile cast iron and 304 stainless steel. The main results showed that joints welded by ENiCrFe-3 electrode in root pass and ENiFe-CI in filling passes were the successful dissimilar welded joints with 422 MPa tensile strength which represents 104% of annealed DCI base metal and without any changes in toughness properties, where toughness at HAZ of DCI was 18 J. High Ni content in weld metal increased the strength, ductility and reduced the weld metal dilution.

In-situ formed Ni2Si into lightweight SiC(rGO) nanocomposite PDCs to boost load bearing-microwave absorption integration for complex environments

As contemporary aerospace and radar-detecting technologies evolve, load bearing-microwave absorption integration of thermal protection materials for complex environment requirements are urgent. Well known for low density, good high-temperature resistance and superior tunable dielectric properties, polymer-derived ceramics (PDCs) promisingly meet most needs of high-performance aircraft thermal protection system (TPS). Aimed at promoting practical application, we integrate in-situ formed Ni2Si into lightweight SiC(rGO) nanocomposite PDCs via re-pyrolyzing coassembled nano-Ni/SiC(rGO)p/polycarbosilane-vinyltriethoxysilane-graphene oxide (PVG) blends to enhance their mechanical and electromagnetic wave (EMW) absorbing performances. Size effect on phase transition of Ni into Ni2Si (as brazing bonding agents) accompanied by volumetric expansion, ingeniously eliminates stretching stress from PVG precursor inward shrinkage for compact framework during re-pyrolysis. In-situ generated Ni/Ni2Si/C core-shell nanostructure (similar to nodular cast iron) has good chemical compatibility with β-SiC/SiOxCy/Cfree(rGO), thereby enables composites improved compactness and toughness. More interestingly, heterogeneous interfaces/defects among Ni, Ni2Si, carbon shell, β-SiC and SiOxCy/Cfree(rGO) matrix, effectively facilitate interfacial/dipole polarization for robust EMW absorption, and lightweight SiC(rGO, Ni2Si)Ni=4% nanocomposite PDCs exhibit outstanding fracture toughness of 6.56 MPa·m1/2 and high compressive strength of 119.25 MPa. Such composite with structure-function integration maintain stable under butane blowtorch at ∼1300 °C, shedding light on a new route to mass-manufacture aerospace vehicle components.

Ferrate(VI) green oxidant: electrochemical generation, self‐decomposition, and application for reactive red 195 azo dye treatment

AbstractBACKGROUNDFerrate(VI), an environmentally friendly oxidant, has recently emerged as one of the most promising chemicals for water and wastewater treatment due to its versatile application as an oxidant, coagulant, and disinfectant. In this paper, the factors affecting the electrosynthesis process of ferrate using ductile iron anode were studied. Besides, the obtained ferrate was used to remove reactive red 195 (RR195).RESULTSThe optimal ferrate electrochemical synthesis conditions were determined, including 14 mol L−1 NaOH electrolyte solution, a current density of 40 mA cm−2, and electrolysis time of approximately 5–6 h. Furthermore, the kinetics of the ferrate's self‐decomposition reaction was also studied at different temperatures. The decomposition process of ferrate in a 14 mol L−1 NaOH environment followed second‐order kinetics, with reaction rate constants of 4.70 × 10−9, 7.31 × 10−8, 1.95 × 10−7, and 4.70 × 10−7 (L mol−1 s−1) at temperatures of 4, 10, 20, and 30 °C, respectively. RR195 treatment efficiency by ferrate reached 96.3% in a short time of 3 min at pH 3 with a ferrate/RR195 molar ratio of 30/1.CONCLUSIONThis study identified the optimal conditions for the electrochemical synthesis of ferrate using a ductile iron anode. Ferrate was stable at a low temperature of 4 °C, so unused ferrate needs to be stored at low temperatures to avoid decomposition of ferrate. The ferrate green oxidant demonstrated high efficiency in the treatment of RR195 in a short time. © 2024 Society of Chemical Industry (SCI).

Tribological properties of ductile cast iron with in-situ textures created through abrasive grinding and laser surface ablation

This paper discusses the proposed abrasive grinding (AG) and laser surface ablation (LSA) method for creating in-situ textures on ductile cast iron (DCI) surfaces. LSA method removes spherical graphite of DCI’s surface, forming martensite and high residual stress on the matrix, thus increasing hardness. AG method uses Al2O3 abrasives to disrupt spherical graphite and form grinding-layer. Compared to LSA, AG method avoids residual stress and burrs, simplifies the processing technology. Tribological tests show that LSA-treated samples have a lower coefficient of friction (COF) and specific wear rate, especially under dry friction conditions, due to increased surface hardness. AG-treated samples have a more stable COF because the oxide layer reduces adhesive wear, grinding-layer provides solid lubrication and reduces localized contact stress.

Investigation on effect of different types of inoculants on the solidification of ductile cast iron using thermal analysis

PurposeProducing superior-quality ductile cast iron demands the use of various intricate inoculants. In addition to iron and silicon, these materials also include alloying elements like calcium, barium, cerium, bismuth and zirconium. These elements are effective in minimizing carbide solidification and enhancing the formation of eutectic cells, thereby resulting in improved cast iron quality.Design/methodology/approachThis article discusses the findings of an investigation on how various inoculants impact critical thermal analysis parameters such as undercooling, recalescence and their correlation with the nucleation of graphite nodules and shrinkage tendency.FindingsFor the study, five distinct inoculants with varying active components in their chemical composition were utilized. The particular formulation of the inoculant has a notable impact on the extent of undercooling during the solidifying process of ductile cast iron. Investigation indicates that incorporating inoculant reduces the temperature at which austenite dendrites form and raises the eutectic freezing temperature. Upon analyzing the microstructure, it is found that the inclusion of inoculation led to a rise in the nodule count from 103 to 272 nodules.Originality/valueAn increased graphite factor, which denotes the growth of graphite nodules during the subsequent stage of the eutectic reaction, supports the benefits of inoculation. Ce and Bi-inoculation have increased the growth of graphite nodules in the cast area during solidification compared to other inoculant formulations. This enhanced production helps in decreasing the size of macroporosity.

Multi-Load Topology Optimization Design for the Structural Safety Maintenance of Low- and Intermediate-Level Radioactive Waste Packaging Containers in the Case of a Collision.

This paper presents an optimized design approach using nonlinear dynamic analysis and finite element methods to ensure the structural integrity of square-shaped containers made from ductile cast iron for intermediate- and low-level radioactive waste packaging. Ductile cast iron, with its spherical graphite structure, effectively distributes stress throughout the material, leading to a storage capacity increase of approximately 18%. Considering the critical need for containers that maintain integrity under extreme conditions like earthquakes, the design focuses on mitigating stress concentrations at the corners of square structures. Nonlinear dynamic analyses were conducted in five drop directions: three specified by ASTM-D5276 standards and two additional directions to account for different load patterns. Fractures were observed in four out of the five scenarios. For each direction where fractures occurred, equivalent loads causing similar displacement fields were applied to linear static models, which were then used for multi-load topology optimization. Three optimized models were derived, each increasing the volume by 1.4% to 1.6% compared to the original model, and the design that best met the structural integrity requirements during drop scenarios was selected. To further enhance the optimization process, weights were assigned to different load conditions based on numerical analysis results, balancing the impact of maximum stress, average stress, and plastic deformation energy. The final model, with its increased storage capacity and enhanced structural integrity, offers a practical solution for radioactive waste management, overcoming limitations in previous designs by effectively addressing complex load conditions.

Comparative Analysis of Water Hammer Performance in Different Pipe Parameters with FSI

Water hammer (WH) is a critical phenomenon in fluid-filled piping systems that can lead to severe pressure surges and structural damage. The characteristics of the pipe material, geometry, and support conditions play a crucial role in the fluid–structure interaction (FSI) during WH events. This study investigates the impact of various pipe parameters, including material, length, thickness, and diameter, on the WH behavior using an FSI-based numerical approach. A comprehensive computational model was developed based on the algorithm presented in Delft Hydraulics Benchmark Problem (A) to simulate the WH phenomenon in pipes made of different materials, such as steel, copper, ductile iron, PPR (polypropylene random copolymer), and GRP (glass-reinforced plastic). This study examines the influence of pipe parameters on WH performance in pipelines, utilizing FSI to analyze the phenomenon. The results show that the pipe material has a significant influence on the pressure wave speed, stress wave propagation, and the overall system response during WH. Pipes with lower modulus of elasticity, such as PPR and GRP, exhibit lower pressure wave speeds but higher stress wave speeds compared with steel pipes. Increasing the elastic modulus, pipe wall thickness, length, and diameter enhances the pipe’s stiffness and impacts the timing, magnitude of pressure surges, and the likelihood of cavitation. The findings of this study provide valuable insights into the design and mitigation of WH in piping systems.

Thermal analysis of laser fabricated new composite brake drums in each orientation

In this study, a Fe-based alloy material was fabricated by laser on the inner shell of a brake drum. The thermal conductivity of the composite brake drum was analyzed and discussed by conducting experiments on the shell nodular cast iron substrate, laser manufacturing materials, and their composites, as well as different heat transfer directions of laser manufacturing materials. At 500 °C, the thermal conductivity of the matrix was 21.434 W/(m·K), the Fe-base alloy was 15.271 W/(m·K), and the composite sample was 17.442 W/(m·K), which was close to the average value of the two. The grain characteristics and microstructure of the alloy were different in different directions. The thermal conductivities of the samples in the x-, y-, and z-directions were 17.047 W/(m·K), 16.665 W/(m·K), and 15.271 W/(m·K), respectively; the diffusion was slower in the z direction and fastest in the x direction.

Mechanical and metallurgical characterization of contact fatigue mechanisms in ADI spur gears

Surface pitting of gear teeth flanks is one of the most common causes of gear failure. The increase of the contact fatigue strength of gears is usually achieved through the development of new combinations of materials and heat-treatment processes. Austempered Ductile Iron (ADI) is one of the results of this research field that leaded to a material which is replacing conventional steel in many mechanical applications. This paper shows the experimental results obtained from tests performed on ADI spur gears in order to characterize the contact fatigue crack nucleation and growth and understand the possible interaction with the graphite spheroids and casting defects. Using a four-square test rig, it was carried out a systematic monitoring of the evolution of the damage, collecting several images concerning crack development at gear surfaces. At the end of the tests several metallurgical analyses of surface and sub-surface areas were performed to understand the fracture mechanism at the base of the pitting failure in ADI. All experimental analyses were complemented by theoretical calculations, useful for a better understanding of the phenomenon.

Nodular Graphite Dissolution and Nucleus Observation: High-Temperature Dynamics of Ductile Iron Recycling

This investigation examines the dynamic behavior of the nodular graphite structure in ductile cast iron at elevated temperatures during the recycling process. It comprises a systematic analysis of the impact of high temperature on the change in chemical composition, followed by a set of examinations of the nodular graphite structure dissolution mechanism at the early phase of the remelting process. The results indicate that prolonged holding at higher temperatures affects the carbon or silicon concentration due to oxidation, which correlates with the operating temperature and the dynamic concentration proportion of those two main alloying elements. It is also substantiated that the dissolution of nodular graphite, the only carbon source during the ductile cast iron remelting process, does not occur primarily in the liquid state but has already started during the solid phase because of austenitization. This dissolution is governed mainly by a surface reaction, as indicated by the residual graphite structure with preserved nonmetallic nuclei. Hence, this approach also provides an alternative method for observing the nodular graphite core by intentionally partially dissolving the graphite structure.

Leak detection and localization of fluid-filled pipeline using accelerometer pairs and mode separation method

Acoustic methods are commonly used to detect and locate leaks in pipelines, but they often overlook important multimodal characteristics of acoustic waves, limiting their applicability. Based on propagation theories regarding F(1,1) mode signal extraction, a new and easy-to-use method for leak detection and localization in pressurized pipelines is proposed. The F(1,1) mode signals are obtained using accelerometer pairs and mode separation method, which are then used to train detection models and to estimate the time difference of arrival (TDOA) for leak localization. Mode separation empowers the data-driven models with physically meaningful samples, aiming to broaden their applicability. The mode consistency between TDOA and velocity is achieved to ensure accurate leak localization. Experiments in buried water-filled ductile iron pipe (experiment A) and in fuel-filled iron pipe (experiment B) are conducted and the longest test distance reaches 72 m. The results validate that the employment of mode separation notably improves current leak detection and localization methods which primarily rely on original signals. The recognition rates rise about 3 %∼11 %, and the false alarm rates reduce about 1 %∼2 %, even when confronted with pipe junction interferences. Also, the leak localization errors are overall lower, with absolute errors below 2 m and relative errors less than 5 % of the test segment length for most cases.

Hollow Connecting Rod Thin Wall Austempered Ductile Iron (TWADI) for Manufacturing Light Weight Components

Hollow Connecting Rod Thin Wall Austempered Ductile Iron (TWADI) for Manufacturing Light Weight Components

Evaluation of scale invariance in fatigue crack growth in metallic materials

The length-scale dependence of fatigue crack growth is evaluated for a set of metallic materials, namely titanium Ti-6Al-4V, ductile iron EN-GJS-500-7 and tool steel AISI H13, by performing fatigue crack growth tests on geometrically similar compact C(T) specimens of different sizes. With references to length-scale-invariant variables, notably the crack growth rate normalised by the specimen width, it is demonstrated that fatigue crack growth is not a length-scale-invariant process for the tested conditions. In particular, the length-scale dependence is less significant for larger specimens and at longer crack lengths. The test results also contradict the hypothesis of similitude, i.e., that the growth rate is uniquely related to the stress-intensity-factor range, as smaller specimens manifest a higher growth rate when compared at the same stress-intensity-factor range. The observations are in line with presented fracture-mechanical demonstrations, which show that the Paris–Erdogan law depends on the length scale whenever fatigue crack growth is anticipated to be scale invariant.

Wear behaviors of PcBN milling insert in high-speed dry milling nodular cast iron

Wear behaviors of PcBN milling insert in high-speed dry milling nodular cast iron