Search Results (314)

The microstructural characteristics and fracture behavior of a magnetic pole screw were investigated here. The screw threads were produced by cold thread rolling. Microstructural analysis (OM, SEM, EBSD), mechanical testing (tensile, hardness, fastening), and fracture morphology observation were conducted. The results indicate that work hardening and microstructural deformation were introduced by the gradient plastic deformation in the screw thread. The elongated microstructure of ferrite and pearlite was obtained in the deformation zones, resulting in increased hardness and decreased plasticity. The thread root subsurface experienced severe localized indentation deformation and exhibited the highest hardness. The distinct forming stress states led to a notable difference in the hardened layer depth between the thread crest and root. The torsional overload fracture was initiated at the stress-concentrated thread root, where the work-hardened microstructure exhibited a limited capacity to accommodate large plastic deformation. The crack propagation was influenced by the gradient microstructure, following three primary propagation paths: transgranular through ferrite, along the ferrite–pearlite phase interface, and cracking through lamellar pearlite. The results provide theoretical support for material design and process optimization to achieve the production of high-performance screws with high strength and hardness at the thread surface and high plasticity in the center. Full article

The influence of Zn²⁺, Ca²⁺ and Co²⁺ doping on the thermal, structural, morphological, and magnetic characteristics of CdBi_0.1Fe_1.9O₄ nanoparticles synthetized via the sol–gel technique and calcined at 300, 600, 900 and 1200 °C was investigated. Thermal analysis revealed the initial formation of metallic glyoxylates up to 300 °C, followed by their decomposition into metal oxides and subsequent ferrite formation. X-ray diffraction revealed that the ferrites were poorly crystallized at lower temperatures, whereas at higher calcination temperatures all nanocomposites exhibited well-crystalized ferrites coexisting with the SiO₂ matrix, except for the Co_0.1Cd_0.9Bi_0.1Fe_1.9O₄@SiO₂ nanocomposite, which formed a single, well-defined crystalline phase. Atomic force microscopy images revealed spherical ferrite particles encapsulated within an amorphous layer, with particle size, surface area, and coating thickness influenced by both the type of dopant ion and the calcination temperature. The structural parameters estimated by X-ray diffraction, as well as the magnetic characteristics, were strongly influenced by the dopant type and thermal treatment. These results demonstrate that the structural and magnetic characteristics of CdBi₀.₁Fe₁.₉O₄ ferrites can be effectively tuned through controlled doping and calcination, providing insights for the design of tailored functional applications. Full article

This study investigates the synergistic effects of an electropulsing (EP) and ultrasonic impact treatment (UIT) hybrid process on the mechanical and corrosion properties of D36 low-carbon steel. Conventional UIT has been shown to enhance surface hardness and induce compressive residual stress but is limited by a shallow affected depth and potential for increased surface roughness, which can exacerbate corrosion. In this work, we integrate high-energy electropulsing with UIT to overcome these limitations. The EP-UIT process leverages the combined effects of acoustoplasticity, thermal softening, and electroplasticity to achieve a significantly deeper hardened layer, extending beyond 2 mm, which is an order of magnitude thicker than that obtained by UIT alone. Microstructural analysis reveals that the process induces continuous dynamic recrystallization (CDRX), resulting in a gradient nanostructured layer with equiaxed grains near the surface and submicron ferrite grains at greater depths. Additionally, cementite dissolution and reprecipitation lead to a dual-phase microstructure comprising a supersaturated ferrite matrix and spheroidized Fe₃C particles. The EP-UIT treatment also forms a dense oxide scale composed primarily of magnetite (Fe₃O₄) and hematite (α-Fe₂O₃), significantly enhancing corrosion resistance. Potentiodynamic polarization tests demonstrate that EP-UIT reduces the corrosion current density by 68% compared to UIT-treated samples, while electrochemical impedance spectroscopy confirms the improved barrier properties of the oxide layer. This innovative approach offers a promising strategy for significantly extending the service life of welded marine structures by concurrently enhancing their mechanical properties and corrosion resistance. Full article

Aimed at improving the mechanical performance of welded joints in stainless steel composite materials, this research investigates the evolutionary characteristics of microstructure at the interface between the transition layer weld and base layer weld through electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) analytical techniques. In addition, molecular dynamics simulation methods are employed to conduct an in-depth study on the atomic diffusion behavior during the welding process. The results show that carbon and chromium atoms undergo asymmetric diffusion at the interface, forming a decarburized and a carburized zone. The diffusion coefficient of carbon atoms was the largest, with the diffusion mechanism being interstitial diffusion. Followed by chromium atoms, the diffusion coefficient of Fe was the smallest. On the base layer weld side, two structural zones with different grain sizes were formed; the zone close to the interface was a coarse ferrite microstructure with the lower geometrically necessary dislocation density, the zone far from the interface was a finer-grained ferrite and pearlite microstructure. As the welding heat input of the transition layer weld increases, the average density of geometrically necessary dislocations, the decarburized layer thickness, the average grain size, and the diffusion coefficients of Cr and C atoms at the interface all exhibit a concomitant upward trend. Concurrently, a carbon–chromium compound precipitates at the interface. Full article

To achieve high-frequency inductance and impedance enhancement for effective electromagnetic interference (EMI) mitigation in power electronics, this paper presents an electromagnetic analysis and experimental study of laminated Mn-Zn toroidal ferrite cores. The electromagnetic field is analyzed using a 2D analytical solution based on a simplified Cartesian approximation. Although neglecting curvature, this approach enables efficient eigenfunction expansion and is rigorously validated against cylindrical finite difference (FDM) and 3D finite element (FEM) benchmarks. The results demonstrate that lamination effectively interrupts eddy current loops; notably, a four-layer structure increases the resonant frequency by approximately 2.8 times compared to a monolithic core. Experimental measurements confirm that this design significantly mitigates the skin effect and extends the stable frequency bandwidth. This study establishes a validated, computationally efficient methodology for optimizing core geometries to prevent impedance degradation. Full article

Laser surface texturing (LST) is an effective method for enhancing surface functionality, but its effect on corrosion resistance highly depends on texture design and processing parameters. This study investigates the influence of two LST patterns—orthogonal ellipses and concentric octo-donuts—applied with 1 to 20 repetitions on the corrosion resistance of AISI 430 ferritic stainless steel. Corrosion behavior was evaluated using potentiodynamic polarization in a 3.5 wt.% NaCl solution at room temperature, complemented by SEM and EDS analysis. The results indicate that while a single laser pass can maintain good corrosion resistance, increasing the number of repetitions significantly degrades performance. This is attributed to the disruption of the protective oxide layer, the introduction of residual stress, and the creation of localized sites for galvanic corrosion. Consequently, the study concludes that a low number of laser repetitions is crucial for preserving the corrosion resistance of LST-processed AISI 430 steel. Full article

With the growing demand for durable and corrosion-resistant materials in advanced Li-ion battery cases, super duplex stainless steels (SDSSs) have emerged as promising candidates due to their excellent mechanical and electrochemical properties. This study aims to investigate how the ferrite and austenite phase balance in SDSS EN 1.4501 affects the microstructural and electrochemical behavior of Ag coatings, tailored for next-generation battery enclosure applications. Ag coatings were deposited to PVD (to 1 μm) on SDSS EN 1.4501 substrates with varying ferrite (from 32 vol.% to 70 vol.%) and austenite ratios (from 56 vol.% to 30 vol.%) to evaluate the influence of phase balance on coating performance. Microstructural analysis was performed using field emission scanning electron microscopy (FE-SEM, mag x 1000), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD, from 20° to 80°), which provided insights into surface morphology, crystallographic texture, and phase distribution. Electrochemical characteristics were assessed through open circuit potential (OCP), and potentiodynamic polarization in a simulated corrosive environment. The results showed that a balanced duplex microstructure promoted superior Ag coating adhesion, grain refinement, and uniform phase distribution. Furthermore, the electrochemical analyses indicated enhanced corrosion resistance and passivation layer stability in volume fraction balanced substrates, as evidenced by more noble OCP values (form −0.06 V to −0.11 V), and potentiodynamic polarization value (higher corrosion potential (from 0.08 V to 0.10 V), and lower corrosion current densities (from 3 × 10⁻⁷ A/cm² to 4 × 10⁻⁷ A/cm²)). These findings demonstrate that optimizing the phase balance in SDSS is critical for achieving high-performance Ag coated surfaces, offering significant potential for durable and corrosion-resistant Li ion battery casing applications. Full article

Fabrication of gradient nanostructure on metal surfaces is recognized as an effective approach for enhancing mechanical and surface properties, as well as serving as a pretreatment for subsequent surface engineering. Unfortunately, their fabrication on high-strength and low-ductility metal surface poses a significant challenge due to the prevalent issue of process-induced surface damage. In this study, we report the successful fabrication of a gradient nanostructured surface layer with low roughness (Ra ~ 0.17 μm) on high-strength 38CrMoAl steel through an optimized ultrasonic severe surface rolling (USSR) processing. By systematically varying the tempering temperature of quenched-and-tempered samples, the strength and ductility of the 38CoMoAl steel are tailored to facilitate gradient nanostructure formation. Microstructural analysis via advanced electron microscopy reveals the gradient nanostructure features progressively coarser martensite/ferrite grains and decreasing dislocation density along the depth. As the tempering temperature increases from 600 °C to 700 °C, the yield strength of 38CrMoAl steel decreases from 915 ± 16 MPa to 815 ± 16 MPa, while the elongation increases from 18.7 ± 0.6 to 27.3 ± 1.2%, resulting in an increase in the thickness of the gradient nanostructured surface layer from 300 μm to 400 μm. Following USSR processing, samples tempered at 600 °C, 650 °C, and 700 °C exhibit significant enhancements in surface hardness by 7.3%, 22.7%, and 21.5%, respectively, along with substantial reduction in wear volume by 73%, 78%, and 60%. USSR processing also leads to a reduction in coefficient of friction. This work provides valuable insights into the fabrication of high-quality gradient nanostructures on high-strength, low-ductility metallic materials. Full article

In this study, two types of submerged arc welding (SAW) wires were prepared—one without cerium (Ce) and another containing 0.14 wt.% Ce. Deposition experiments were carried out on corrosion-resistant crude oil storage tank steel plates using a multi-layer, multi-pass welding process. Through a combination of microstructural characterization techniques, including optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM), along with mechanical property testing, a systematic investigation was conducted to evaluate the influence of Ce on the weld metal microstructure and its impact toughness at −20 °C. The results reveal that Ce introduced via the welding wire into the weld seam refines and disperses inclusions, leading to the formation of composite inclusions primarily composed of Ce₂O₃, Ce₂O₂S, and CeS. These Ce-enriched inclusions serve as heterogeneous nucleation sites, increasing the area fraction of acicular ferrite (AF) within the weld columnar grain region from 52% to 83%, and within the heat-affected zone from 20% to 37%. Correspondingly, the proportions of blocky and polygonal ferrite decrease, while the size of martensite/austenite (M/A) constituents is reduced. The addition of Ce thus diminishes the size of hard phase inclusions and M/A constituents in the weld metal, enhancing the critical fracture stress and increasing the energy required for crack initiation. Meanwhile, the higher proportion of AF elevates the density of high-angle grain boundaries, thereby improving crack propagation resistance. These combined effects raise the −20 °C impact energy of the weld metal from 117 J to 197 J. Full article

With the growing demand for efficiency, low consumption, and environmental sustainability in the iron and steel industry, ultra-high bed sintering technology emerges as a research hotspot due to its advantages in significantly reducing fuel consumption and pollutant emissions. However, studies on the influence of fuel on mineralization behavior under ultra-high bed sintering conditions remained limited. This study systematically analyzes the effects of particle size, chemical composition, alkalinity, and MgO/Al₂O₃ ratio on mineralization behavior using a 500 m² sintering machine, while evaluating the tumbler strength and phase composition of the sinter. The results reveal that particle size segregation in the mixture was primarily caused by the upper layer, with the lower layer having a lesser impact on overall segregation. Chemical composition also exhibited significant segregation, particularly in TFe and fuel distribution along the bed height. Fuel segregation was pronounced vertically but negligible horizontally. Under the current fuel distribution, uneven heat distribution was observed, with excessive heat in the lower layer leading to increased liquid phase formation, reduced porosity, and improved sinter strength downward along the bed. Additionally, the phase composition varied markedly across layers: hematite content gradually increases from top to bottom, calcium ferrite (SFCA) content peaks in the middle layers, and magnetite decreases with bed depth. Full article

This study investigated the electrolytic-plasma hardening (EPH) of cast 20GL steel, used for railway spring beams. The main objective was to analyze the spectral characteristics of the cathodic discharge and establish correlations between the plasma parameters, processing regimes, and resulting surface properties. Optical emission spectroscopy revealed that the plasma at 260 V exhibited a high-energy state with an electron density of ~5.3 × 10¹⁶ cm⁻³ and an electron temperature of 10,031 K. Using these parameters, the heat flux from the plasma to the steel surface was estimated at ~1.5 × 10⁷ W/m², confirming that the discharge provides sufficient energy for surface austenitization. Microstructural analysis demonstrated that the electrolyte flow rate, which determines the cooling rate, is the key parameter controlling phase transformations. At low flow rates, ferrite–pearlite and bainitic structures formed, while a fully martensitic structure and maximum hardness (1046 HV) were achieved at 10 L/min. Tribological tests confirmed the superior wear resistance of the martensitic layers, showing a friction coefficient of 0.454 and a wear volume 3.4 times lower than in the as-cast state. These findings verify that EPH offers an energy-efficient, low-cost method for improving the surface performance and service life of 20GL steel components in heavy-duty railway applications. Full article

In this study, the microstructure and mechanical properties of ductile cast iron subjected to a novel austempering treatment were investigated. The methodology was based on prolonged isothermal annealing within the low-temperature range of the bainitic transformation. The experiments were carried out on samples with two different initial microstructures: pearlitic–ferritic and ausferritic. Two long-term austempering treatment variants were designed and tested: single (AT-1) and double (AT-2). In both cases, the heat treatment led to the production of a nanoausferritic microstructure, characterized by exceptionally thin plates of bainitic ferrite separated by thin layers of retained austenite. Compared to conventional austempering, the new method produced a much finer microstructure and a reduced amount of retained austenite. Moreover, the AT-2 variant further enhanced the homogeneity of the microstructure, promoting a higher fraction of thin ferrite plates. Mechanical tests revealed that the new heat treatment significantly improved the performance parameters of the material: hardness increased from 27 HRC to 32–35 HRC, tensile strength rose from 1027 MPa to 1220–1296 MPa, and yield strength from 683 MPa to 1033–1054 MPa. It was proved that, regardless of the initial microstructure of ADI, new processes exhibited comparable, enhanced mechanical properties, confirming their efficiency and universality. Full article

In this study, the J-integral method was used to evaluate the fracture toughness (J_Q) of the isolation layer at the top of SA508-III-309L/308L-316L dissimilar metal welded joints (DMWJs) of a pressure vessel. Tests were carried out at varying temperatures, from room temperature to 320 °C, to study the mechanism underlying temperature effects on unstable crack propagation. The results show that failure occurs in the middle position of the weld isolation layer of the welded joint at all test temperatures. The J_Q of the inner diameter of the joint decreases with increased temperature, with a maximum decrease of 31.8%. The analysis shows that the lath ferrite structure in the isolation layer provides a favorable path for crack propagation. The increase in temperature enlarges the difference in thermal expansion between SA508-III steel and the isolation layer, making it easier for second-phase particles in the isolation layer to induce crack initiation and propagation, thus reducing the J_Q of the steel. In addition, at high temperatures, the dislocation density of the isolation layer, the deformation resistance of the material, and the difference in the yield ratio of the joint weld all decrease, which is not conducive to the redistribution of the stress field at the tip of the fatigue crack, leading to further reduction in the J_Q. Full article

Thick steel plates in bridges exhibit mechanical property gradients along their thickness, yet the underlying micro-mechanisms remain unclear. This study investigates an 80 mm thick 420 MPa-grade HSLA steel plate, and also quantitatively investigates the mechanism of its mechanical gradient behavior in the thickness direction through layered tensile tests combined with multi-scale microstructural characterization. The unique contribution of this work lies in establishing a quantitative correlation between the gradient in the dislocation density and the transition in yielding behavior. The results show that the surface layer area of the tested steel exhibited continuous yield characteristics, while all core layers exhibited pronounced discontinuous yielding. The mechanical properties showed a gradient distribution along the thickness direction, with the yield strength and tensile strength decreasing from 512.4 MPa and 545.9 MPa at the surface to 419.5 MPa and 520.4 MPa at the center (1/2t). Microstructural analysis shows that the full-thickness structure was composed of granular bainite (GB) and polygonal ferrite (PF). With respect to increases with depth, the average grain size increased from 6.86 µm at the surface to 11.57 µm at the center. Moreover, the surface region exhibited a broader grain size distribution range and higher size dispersity. The second-phase precipitates in the full thickness were mainly of two types, namely, Fe₃C and (Nb, Ti) (C, N) composite precipitates, and the precipitates in the surface layer had smaller sizes and higher distribution densities. Crucially, the dislocation density decreased sharply from the surface to 1/8t, then stabilized. While quantitatively elucidating the contributions of various strengthening mechanisms to the strength gradient, the mechanistic analysis also reveals a dislocation microstructure synergistic mechanism underlying the yield behavior differences. Full article

The γ ⟶ α′-transformation under implantation of austenitic-ferritic steel CF8 with ⁵⁷Fe ions to fluences of 1 × 10¹⁶, 5 × 10¹⁶ and 1 × 10¹⁷ ion/cm², as well as the reverse α′ ⟶ γ–transformation under thermal treatment, was studied using transmission Mössbauer spectroscopy (MS), conversion electron Mössbauer spectroscopy (CEMS), and X-ray diffraction (XRD) methods. It was found that implantation, which causes radiation damage with 36 dpa, results in the formation of α′-martensite. At higher fluences of implanted ions, the amount of α′-martensite increased, reaching 86 at.% within the irradiated layer. Annealing in the temperature range of 600–850 °C resulted in the observed reverse transformation of α′-martensite to γ-austenite. The dependence of the average effective magnetic field on the annealing temperature was established. Full article