Study on the synergistic control of interface structure and wear properties in nodular cast iron by Mo-Cr-Nb ternary microalloying

Abstract This study examines the combined effects of molybdenum (Mo) alloying and deep cryogenic treatment (DCT) on the microstructure and mechanical response of austempered ductile iron (ADI). Ductile irons with three Mo contents (0.388, 0.671, and 0.990 wt.%) were produced, austempered at 400 °C, and subsequently subjected to DCT at −196 °C for 360 min. Microstructural and phase analyses were conducted using optical microscopy (OM), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD). Austempering resulted in a typical ausferritic matrix, while the subsequent cryogenic step was associated with further microstructural refinement and features indicative of partial transformation of retained austenite (RA). In addition, fine secondary features were observed locally and attributed to carbide-like precipitates. Quantitative XRD analysis revealed the presence of α and γ reflections in all heat-treated conditions. Detailed diffraction scans exhibited a distinct peak shift toward lower 2 angles following DCT, indicating an expansion of the lattice parameters and a corresponding enrichment of carbon within the austenite phase. In terms of mechanical response, the integration of austempering and DCT led to a 16.6% increase in hardness compared to the as-cast state. Furthermore, the combined heat treatment cycle resulted in a 42.3% enhancement in impact energy relative to the initial cast condition, highlighting the potential of DCT to optimize the structural integrity and toughness of Mo-alloyed ADI.

Mechanism of corrosion, scaling and failure of valves in drinking water distribution systems.

Numerous methods have been suggested to quantify fatigue-initiating defect size on fracture surfaces, the most prevalent are based on the Murakami-Endo a r e a -parameter. However, there is an ambiguity in how to systemically determine defect areas. For instance, in literature on high-cycle fatigue of ductile cast irons the several different methods have been suggested: i) the traced contour, ii) the convex hull, iii) the minimum circumscribed circle, and iv) the minimum bounding rectangle. This work focuses on comparing and evaluating these methods by assessing the fatigue-initiating defect area distributions, and the influence on fatigue assessment using the a r e a -parameter. To this end, very high cycle fatigue data on ductile cast irons with different microstructures is used, where complex shaped defects are the root-cause for fatigue failures. It is shown that there is a significant difference in the area distributions, originating from the applied area measurement method. In addition, to enable and include fatigue assessment of high strength ausferritic ductile irons, two improved Murakami-Endo type models are proposed, which show satisfactory prediction capabilities over a wide range of ductile cast iron microstructures. To further evaluate the different area measurement methods, the suggested models are validated against ductile cast iron high-cycle fatigue data from literature having artificial defects and notches. Finally, it is concluded that the traced contour defect measurement method yields the best agreement between artificial and natural defects, and overall, the least prediction errors. • Several defect area measurement methods compared. • Extended fatigue strength prediction models for ductile cast iron. • Evaluation of influence on area distributions and fatigue assessment.

An investigation into the uncertainties in the crack resistance curves of nodular cast iron

Mechanical response of FRP liner-reinforced ductile iron pipe joints under normal faulting

Field evidence for the impact of aged cast iron pipes on emerging DBPs in drinking water distribution systems.

This study experimentally investigates the subsequent yield surfaces of thin-walled tubular ductile cast iron (QT600-7) specimens under various pre-deformation histories and elucidates their evolution patterns. The effects of pre-deformation level, unloading position, and loading path on the subsequent yield surfaces are examined, with particular attention to the concave phenomenon observed in the measured yield surfaces. The results show that the subsequent yield surfaces of QT600-7 translate towards the pre-loading direction. Translation and distortion are more pronounced at smaller offset strains and gradually diminish with increasing offset strains. Under different pre-loading paths, a sharp corner appears in the pre-loading direction and a concave or flattened shape forms in the opposite direction when the offset strain is small; this concave phenomenon tends to disappear under larger offset strains. A higher pre-deformation level leads to more noticeable distortion of the yield surface corresponding to small strains. After pre-tension and unloading, if reverse compression occurs, the subsequent yield surface under small offset strains exhibits a complex shape in the opposite direction.

The corrosion inhibition performance of 5-amino-1,3,4-thiadiazole-2-thiol (5ATT) toward ductile iron in 1.0 M HCl solution was systematically investigated using complementary experimental and theoretical approaches, including weight loss measurements, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and surface characterization (SEM/EDX), supported by density functional theory (DFT) calculations and Monte Carlo (MC) simulations. The results show that the inhibition efficiency increases markedly with inhibitor concentration, reaching ~ 81%, which indicates effective adsorption of 5ATT molecules on the ductile iron surface. Electrochemical measurements revealed a marked decrease in corrosion current density and a significant increase in charge transfer resistance, confirming the formation of a protective adsorbed film, which was further supported by surface analysis. Importantly, the present study provides a clear correlation between the molecular electronic properties and adsorption behavior of 5-ATT and its experimentally observed inhibition performance. Adsorption studies indicated strong interaction between the inhibitor molecules and the metal surface, while thermodynamic parameters suggested a mixed physisorption–chemisorption mechanism. Furthermore, theoretical calculations supported the experimental findings, demonstrating that both the electronic structure and adsorption configuration of 5-ATT play a key role in its corrosion inhibition efficiency. Therefore, 5-ATT exhibits high inhibition performance and strong adsorption capability, highlighting its potential as an effective corrosion inhibitor for ductile iron in acidic environments.

Industrial textile wastewater containing synthetic dyes cause serious environmental and health risk, whereas ductile cast iron (DCI) foundries generate over 500 000 tons of waste annually. This study utilizes DCI solid waste as an adsorbent to remove the crystal violet (CV) dye from wastewater. Techniques (XRF, XRD, BET, SEM-EDX, FTIR, TGA-DTG, zeta potential) proved that the waste contains 88.0 wt% periclase (MgO) with nanoscale, high surface area, and abundant surface hydroxyl groups. Response surface methodology showed that the most significant parameters were the adsorbent dose and time contact. The optimal conditions give 93.7% removal efficiency at initial concentration: 38.7 mg L-1, adsorbent dose: 6.2 g L-1, shaking rate: 150 rpm, and contact time: 30 min. The isotherm model was the Freundlich model suggesting surface heterogeneity with dispersed binding energies; multilayer coverage supports this, but the Freundlich fit by itself cannot establish it. The maximum physisorption capacity was 116.85 mg g-1, and the mean free energy, E = 3.34 kJ mol-1. Kinetic study demonstrated that the reaction follows pseudo-first-order kinetics (k 1 = 0.1654 min-1) and showed three diffusion phases: the external film diffusion (0-30 min), the intraparticle diffusion (30-120 min), and the equilibration phase (>120 min). The thermodynamic investigation showed that the adsorption is an endothermic process (ΔH° = +22.15 kJ mol-1), accompanied by a positive entropy change (ΔS° = +85.3 J mol-1 K-1) and a negative Gibbs free energy change (ΔG° = -2.94 to -5.68 kJ mol-1), which means spontaneous, entropy-driven physisorption. Post-adsorption XRD showed that MgO was hydroxylated to Mg(OH)2. The pH optimization revealed maximum removal at pH 7-9. The regeneration technique employing acid and thermal methods yielded a desorption efficiency rate of 95.4%, a cumulative adsorption capacity recovery rate of 78.5% following 15 cycles, and magnesium release lower than all permissible standards (USEPA, WHO, Egyptian Law 4/1994). The initial techno-economic analysis yields a unit treatment cost of approximately $1.09 m-3 for a hypothetical 1000 m3 d-1 plant; nevertheless, further confirmation based on scale up and continuous flow operation is essential prior to actual commercialization. This study proves that DCI solid waste is not only economically feasible but also environmentally adsorbent in the context of a circular economy.

• Pore–notch competition quantified using energy-based stressed volume and strain energy. • Pearlitic and high-silicon ferritic irons show fatigue reversal with notch severity. • Computed tomography and extreme-value statistics inform defect-sensitive fatigue. • High-silicon ferritic iron shows greater pore tolerance in blunt, large stressed volumes. • Simplified strain-energy method enables fatigue design without tomography or FE. Heavy-section castings of ductile cast iron (DCI) unavoidably contain micro shrinkage porosity due to non-uniform, slow cooling, and service components also feature geometric stress raisers. This study quantifies how these two realities—intrinsic defects and notches—jointly control fatigue resistance and formalizes a design approach that accounts for their interaction. We compare a pearlitic EN-GJS-600–3 (GJS-600–3) and a high-silicon solid solution strengthened ferritic (HSi) DCI, which exhibit different matrix ductility and distinct pore populations. Pore size distributions are characterized (via X-ray computed tomography, CT), and extreme-value statistics are used to estimate the most critical defect expected in the highly stressed region of notched specimens. This defect measure is then coupled to a strain energy density (SED) criterion to predict fatigue limits. Fatigue tests on plain and V-notched specimens with varying notch severity reveal a systematic transition from pore-dominated initiation (plain and mildly notched) to notch-dominated initiation (severe notches). The proposed CT–statistics–SED framework reproduces both the fatigue limits and the observed switch in the governing initiation site. Compared with GJS-600–3, the HSi grade shows lower intrinsic fatigue strength but greater tolerance to distributed microporosity, leading to improved reliability in geometries with large highly stressed volumes. The approach provides a practical route to defect-aware fatigue design of DCI components, suggesting material-and-geometry selection: pearlitic grades for smaller, sharper features where notch control prevails; high-silicon ferritic grades for large, blunt features where defect tolerance is paramount. Overall, the method supports lighter, more reliable cast designs without resorting to overly conservative safety factors.

In-situ CLSM observation and interface diffusion behavior of the pearlitic phase transformation in ductile iron

Experimental and numerical characterization of Johnson–Cook plasticity and damage models for spheroidal graphite cast irons at high strain rates and elevated temperatures

Optimization of Ductile Iron Casting Using Simulation

Abstract The long-term integrity of buried ductile iron pipelines is increasingly compromised by external corrosion, especially where protective coatings are damaged or direct soil contact occurs. While coatings and cathodic protection remain essential for corrosion control, their long-term performance is strongly governed by the surrounding soil environment. In highly corrosive or moisture-retentive backfills, these conventional systems can degrade rapidly, leading to reduced protection efficiency and frequent maintenance. However, backfill design in current practice is primarily driven by mechanical considerations, such as providing adequate stiffness rather than corrosion resistance. To maximise the effectiveness of both structural support and corrosion protection, backfill properties should be understood from an integrated geotechnical and materials perspective; a connection that remains poorly understood. This review synthesises existing knowledge in both fields to demonstrate how key soil parameters such as moisture content, resistivity, pH, ion concentration, gradation, and compaction collectively influence the corrosion kinetics. Complementing the literature review, industry survey data from Australia provide insight into practical challenges and maintenance strategies. Findings highlight the need for performance-based backfill design to extend pipeline service life, reduce maintenance frequency, and support carbon-reduction goals in civil infrastructure.

The present study plays a crucial role in enhancing the safety and perceived quality of life for users of bone-anchored prostheses. It focuses on developing an innovative protective component using various metallic materials to identify and mitigate potential risks during use, thereby reducing the likelihood of sudden fracture and maintaining the system’s structural integrity. The protective element is manufactured from Ti6Al4V alloy, while the safety pin is made from ductile cast iron. This combination allows controlled fracture of the protective element without complete separation of the prosthesis, thereby reducing the risk of falls. To optimise the numerical analysis, a 3D model of the prosthesis and its protective component was created using SolidWorks software. Loading conditions were simulated to reflect two critical phases of the gait cycle: heel strike and toe-off. The analysis revealed that the highest stress occurred during the toe-off phase, reaching 248 MPa, with a safety factor of 1.6, demonstrating the design’s ability to prevent sudden failure. Tensile testing showed that ductile cast iron is a suitable material for the safety component. Although Ti6Al4V alloy surpasses it in tensile strength, ductile cast iron’s lower strength ensures a controlled and less catastrophic failure under excessive loading. Numerical results confirmed a high safety factor for the protective system, indicating improved reliability and mechanical load resistance. This study presents a novel approach aimed at improving the safety of bone-anchored prostheses by minimising injury risks due to mechanical overload, ultimately enhancing user comfort and confidence.

Ductile iron suffers from insufficient wear resistance under heavy-load service conditions. Surface engineering technologies offer effective solutions to this problem. However, current research on the application of atmospheric plasma-sprayed (APS) CoCrFeNiNbx high-entropy alloy (HEA) coatings on ductile iron and the systematic study of compatible heat treatment processes with the substrate are still insufficient. In this study, CoCrFeNiNbx HEA coatings (x = 0.25, 0.50, 0.75, 1.00) were deposited on QT800-5 ductile iron by APS, and the effects of Nb content and low-temperature annealing (400-600 °C) on coating microstructure and properties were investigated. The x = 0.25 coating exhibited a single face-centered cubic (FCC) solid solution structure, while coatings with x ≥ 0.50 comprised an FCC solid solution and Cr2Nb-type Laves phase; hardness increased with Nb content, and as-sprayed wear resistance peaked at x = 0.75. Post-deposition annealing at 500 °C yielded a peak hardness of 477.45 HV and reduced the wear rate by 45% relative to the as-sprayed condition, with no measurable degradation of the substrate. These findings offer a practical reference for developing wear-resistant coatings on ductile iron components.

Understanding and optimizing high-CE DCI is key to meeting future demands for large, high-performance cast components. The microstructures obtained in ductile cast iron (DCI) processing are closely linked to the resulting mechanical properties. Both the graphite distribution and morphology, as well as the structure prevalent of the Fe-rich matrix, impact toughness and ductility. Although some studies in the literature address these aspects, few advances have been made in modeling cooling rates in high-Carbon Equivalent (CE) DCI solidified in green sand-based molds. Furthermore, establishing correlations between microstructures, morphologies, cooling rates, and carbon transport in the melt during the solidification process is essential for optimizing the as-cast properties. This study explores various methods for measuring and calculating solidification cooling rates, defining two distinct cooling rates based on the Flemings’ model —one at the center (70 mm from the surface) and another at 20 mm from the surface of the DCI casting after testing this model against experiments. By using a thermocouple at 20 mm from the casting surface to support models and methods for determining the cooling rate, the cooling rates have been determined as well as correlate them with the graphite nodules morphometric parameters. It becomes evident that in a high-CE DCI (Equivalent carbon of 4.86), segregation occurs towards the central region, resulting in a manifest bimodal distribution containing both primary and eutectic graphite, with an increased quantity of finely refined eutectic graphite particles. The microstructure optimized for higher toughness and ductility (according to Inglis' stress concentration criterion) is that corresponding to samples taken 20 mm from the surface with smaller graphite particle density (205 nodules/mm 2 ), more uniform graphite size, and a smaller overall aspect ratio of 1.45 (i.e., less elongated ellipses), particularly for eutectic graphite nodules. In sum, both regions show similar tensile strengths (∼500 MPa), but the 20 mm sample exhibits higher elongation and toughness, reflecting its more uniform microstructure.

• A strong correlation was found between the representative cooling rate of eutectoid phase transformation and the characteristics of the pearlite matrix in a fully pearlitic ductile cast iron. • The yield limit found to be strongly dependent on the interlamellar spacing of the pearlite matrix, following a modified Hall-Petch relationship. • In regions of higher strain, the graphite morphology is the dominant factor influencing mechanical properties under static loading. • Microstructure-informed simulation provides insights into how interlamellar spacing affects yield strength, highlighting the crucial role of pearlite fineness in yielding behavior. Microstructural features of ductile cast iron (DCI), including graphite morphology and the pearlitic matrix, are influenced by solidification and subsequent eutectoid transformation and can be effectively tailored through the cooling conditions. While the relationship between pearlite characteristics and mechanical properties is well established for pearlitic steels, the specific contribution of the pearlitic matrix to the mechanical response of DCI has received limited attention. In this study, fully pearlitic DCIs were cast under various cooling rates between 0.1 to 0.34 K/s, enabling systematic variations in microstructure to be correlated with changes in mechanical properties. The resulting interlamellar spacing (ILS) of the pearlite matrix ranged from 291 to 564 nm and was associated with an approximately 70 MPa difference in yield strength. A modified Hall-Petch-type relationship was formulated to describe the dependence of yield strength on ILS. To support predictive capability, representative volume elements were generated from optical micrographs and micromechanical simulations were conducted to isolate the effect of varying ILS on yield strength. The simulation results showed excellent agreement with the experiments, confirming that the ILS predominantly governs the onset of plastic deformation and that pearlite refinement is a key controlling factor for the yield strength of pearlitic DCI.

Effect of repair welding-induced residual stresses on fatigue crack growth and life of ductile cast iron: Application to a full-scale wind turbine hub