Search Results (1,251)

To reveal the controlling mechanism of cooling rate on the continuous cooling transformation, microstructure evolution and mechanical performances of Q580R low-temperature pressure vessel steel, this study took industrial-scale Q580R steel as the research object. The JMatPro thermodynamic software was utilized for simulating and calculating its equilibrium phase diagram, TTT diagram, CCT diagram and mechanical property evolution. Continuous cooling experiments with a wide range of cooling rates between 0.1 and 50 °C/s were executed on a Gleeble-3500 thermal simulator. Combined with optical microscopy, scanning electron microscopy and Vickers hardness tester for microstructure characterization and property testing, the measured CCT diagram was constructed and contrasted with the simulation results for verification. Experimentally, the phase composition of Q580R steel evolves at regular intervals with cooling rate. As the cooling rate rises, the ferrite content constantly decreases, the bainite content first increases and subsequently decreases, and the martensite content constantly increases. When the cooling rate reaches 30 °C/s, the martensite proportion can exceed 90%, and the microstructure is significantly refined. The hardness of the material first increases rapidly and subsequently trends to be steady as the cooling rate rises, reaching 308 HV₁₀ at 50 °C/s. The measured transformation law, microstructure evolution and hardness change exceedingly corresponds to the JMatPro simulation results. This validates the credibility of the simulation prediction. This study clarifies the quantitative relationship among “cooling rate-microstructure-properties” of Q580R steel, which can provide theoretical basis and data support for the precise design of heat treatment process and the optimization of strength and toughness. The established relationship can directly guide the formulation of controlled cooling parameters during hot rolling and off-line quenching and tempering production of Q580R pressure vessel plates, helping manufacturers optimize industrial heat-treatment procedures to satisfy low-temperature toughness requirements for petrochemical and cryogenic pressure vessel service. Full article

In this study, manual welding electrodes with varying niobium (Nb) contents (0, 0.05, and 0.1 wt%) were developed for 960 MPa grade low-alloy high-strength steel, and deposited metals were produced through multilayer multipass welding. Microstructural characterization and mechanical testing were performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and a universal testing machine to investigate the influence of Nb content and elucidate the strengthening mechanisms. The results demonstrate that under identical welding conditions, multipass thermal cycles induced a primary microstructural transformation from martensite to tempered martensite in all deposited metals, which predominantly comprised tempered martensite with minor fractions of bainite and second-phase particles. Increasing Nb content led to significant grain refinement. The second-phase particles exhibited sizes of 0.158 μm, 0.176 μm, and 0.168 μm, respectively, with volume fractions of 5.69%, 5.82%, and 5.90%. Nb addition substantially enhanced hardness and strength while causing a noticeable reduction in low-temperature impact toughness, though the values remained within acceptable limits. The deposited metal containing 0.05 wt% Nb exhibited optimal comprehensive mechanical properties, with a hardness of 386.7 HV, tensile strength of 1060 MPa, yield strength of 962 MPa, and Charpy impact energies of 41.95 J and 33.17 J at −40 °C and −60 °C, respectively. Theoretical calculations revealed that the dislocation strengthening contribution in martensite increased from 526 MPa to 600 MPa with increasing Nb content, representing the dominant strengthening mechanism, while grain refinement strengthening increased from 135.5 MPa to 157.6 MPa. Full article

To enhance the fidelity of the DEM representation of sugar beet roots, the root geometry was reconstructed from three-dimensional scanning data and represented in EDEM2024 as a multi-sphere clump. The Hertz–Mindlin (no slip) model was used to describe particle contact behavior. The root–Q235 steel contact parameters were determined by drop-rebound, inclined-plane sliding, and inclined-plane rolling experiments. For root–root interactions, the parameters were further refined through cylinder-lifting repose-angle simulations combined with the steepest-ascent method and a three-factor quadratic orthogonal rotatable regression scheme. The optimized inter-root restitution coefficient, static friction coefficient, and rolling friction coefficient were 0.534, 0.728, and 0.080, respectively. With this parameter set, the deviation between the simulated and measured angles of repose was 0.86%, and the error obtained in the independent validation test was 1.5%. These results demonstrate that the proposed DEM model and calibrated parameter set can accurately represent the motion and contact behavior of sugar beet roots. Full article

Due to climate change, corrosive conditions, and hydrogen-rich environments, steel energy pipelines inevitably develop a variety of defects. These deficiencies compromise pipeline safety and reliability, and neglecting them may result in pipeline leaks, fractures, and even potentially catastrophic explosions. Although a considerable body of literature reviews the effects of metal-loss defects like corrosion and cracks on pipeline safety and reliability, the impact of geometric deformation, like dents, lacks a comprehensive review. This work employs a hybrid systematic literature review (SLR) and bibliometric analysis (BA) to investigate the current research status of pipeline dent assessment. Four questions are answered: (1) What are the publication distribution characteristics, active journals, production organizations, and production authors related to research on pipeline dents? (2) What criteria have been employed for evaluating the pipeline dent? (3) From what perspective has the integrity of dented pipelines been assessed, and what research approaches have been used? (4) What are the future challenges and prospects of pipeline dent studies? The findings demonstrate that depth-, strain-, and damage-based evaluation criteria are widely employed to assess pipeline dents, each with merits and limitations. Despite the simplicity and ease of use of depth- and strain-based criteria, they are prone to underestimation flaws. In contrast, damage-based criteria, which consider multiple factors, are limited by their complexity and high computational resource requirements. The reliability of dented pipelines is predicted with remaining strength, fatigue life, and failure pressure using theoretical modeling, experimental testing, numerical simulation, or a combination of these methods. Future dent studies should involve refining numerical models, full-scale testing under varied loading conditions, and integrating advanced sensing techniques for real-time inspection. Full article

This study presents a novel in situ reinforcement strategy for 17-4PH stainless steel by using Nb and Cr₃C₂ powders as precursors, addressing the challenge of poor particle dispersion and interfacial bonding in conventional ex situ ceramic additions. The coatings were systematically compared with 17-4PH coatings without the addition of a reinforcing phase. The results show that the coating without Nb addition is dominated by α-Fe martensite, exhibiting a coarse columnar/dendritic microstructure. After adding Nb and Cr₃C₂, the coating successfully forms in situ face-centered cubic NbC, with a significantly refined and uniformly distributed microstructure. The 10 wt.% Nb+Cr₃C₂ coating exhibits a refined microstructure with an average grain size reduced from 1.12 μm to 0.85 μm and a microhardness of 495.5 HV, representing an 86% increase over the substrate and a 34% improvement compared to the unreinforced coating. Friction–wear tests demonstrate that the composite coating reduces wear track width and depth by approximately 50% and 45%, respectively, compared to the substrate, with the wear mechanism transitioning from severe adhesive and fatigue wear to mild abrasive wear and localized micro-delamination. In situ synthesized NbC effectively optimizes the coating microstructure, enhances interfacial bonding, and markedly improves the hardness and wear resistance of 17-4PH coatings, providing theoretical and technical support for their engineering application under severe service conditions. Full article

This study was conducted to explore how varying the concentration of nano-La₂O₃ particles in the plating bath influences the morphology, constitution, and corrosion resistance of Ni-B composite coatings deposited on N80 carbon steel via electroless plating. The novelty of this work lies in the systematic investigation on the co-deposition behavior and grain refinement mechanism of nano-La₂O₃ in electroless Ni-B system, which has been rarely reported in previous studies. The microstructure and chemical composition of the coatings were characterized through a combination of SEM, EDS, XPS and XRD analyses. SEM confirmed that a dense Ni-B/La₂O₃ composite coating was formed, with a uniform thickness of approximately 10 μm, and the nano-La₂O₃ particles were evenly distributed. XPS analysis verified the presence of B, C, O, Ni and La, while XRD analysis revealed a refinement in crystalline size due to the addition of the nanoparticles. The corrosion resistance enhancement mechanism is attributed to the triple synergistic effect: nano-La₂O₃ pins grain boundaries and refines Ni-B grains to the minimum average size of 12.943 nm at the optimal concentration of 8 g·L⁻¹; the refined grain structure promotes the formation of a continuous and dense Ni(OH)₂ passive film; the uniformly dispersed nanoparticles act as physical barriers to block the penetration of corrosive media. Electrochemical measurements demonstrated that this coating exhibited outstanding anti-corrosion performance, as confirmed by a remarkably positive corrosion potential (E_corr = −0.37189 V) and a minimal corrosion current density (I_corr = 3.7524 μA/cm²). The results conclusively show that nano-La₂O₃ reinforcement effectively enhances the corrosion protection performance of electroless Ni-B alloy coatings. Full article

This industrial-scale study investigates cerium’s effect on inclusions, microstructure, and mechanical properties in Ti-bearing high-strength steel BT700L through comparative trials of two production batches (with/without 0.0035% Ce). Characterization via SEM/EDS, automatic inclusion analysis, and Factsage thermodynamic simulations revealed that Ce addition reduced spherical Al-Mg-Ca-O-S inclusions (from 24 to 7 per 2 mm²; size decreased from 17 μm to 10 μm) while promoting composite inclusions with AlCeO₃-Ca(Mn)S cores and Ce-containing Ti(C)N shells. Although square Ti(C)N inclusion numbers remained stable, their average size increased from 8 μm to 11 μm. Ce addition eliminated banded microstructure and refined grains through heterogeneous nucleation (Ce₂O₃ exhibits low misfit of 4.00% with α-Fe). Mechanically, yield strength increased marginally (<5%) with unchanged tensile strength and reducing elongation. However, −20 °C impact toughness decreased by 22%. This duality—beneficial grain refinement versus detrimental coarsening of angular TiN inclusions acting as stress concentrators—provides critical insights for optimizing Ce addition in industrial Ti-bearing high-strength steel BT700L. Full article

This paper presents a preliminary numerical investigation on the mechanical behavior under eccentric compression of T-shaped steel tube-steel reinforced concrete columns. A refined finite element (FE) model was developed in ABAQUS 2021 and validated against published axial compression test results. The effects of three key parameters (eccentricity, outer steel tube thickness, and built-in steel skeleton size) on the bearing capacity, failure mode, stiffness degradation, and stress distribution of the studied members were systematically analyzed via finite element analysis, followed by comparative calculations and an applicability analysis of the calculation of eccentric compression bearing capacity. All eccentric compression results presented herein were obtained through numerical simulation and have not been directly verified by physical tests. The results show that the ultimate bearing capacity decreases by more than 57% as the eccentricity increases from 0 mm to 75 mm, with the failure mode transitioning from axial compression failure to flexural failure. Within the studied parameter range, the 4 mm-thick outer steel tube exhibits superior comprehensive performance, including bearing capacity, stiffness, and ductility. Increasing the built-in steel skeleton size effectively enhances the flexural stiffness and ductility, and delays stiffness degradation. The existing code-specified formula demonstrates good accuracy (relative error < 6%) for e ≤ 50 mm but yields significant errors for e = 75 mm. An empirical expression for the equivalent eccentricity influence coefficient α is proposed, which reduces the overall average error from 4.89% to 2.26% within the parameter scope of this study. Full article

Sulfate attack is a major cause of deterioration in tunnel lining concrete under aggressive underground conditions. This study investigates the sulfate resistance of fiber-reinforced ferroaluminate cement concrete incorporating steel slag powder through combined experimental and numerical approaches. Specimens with different fiber contents (0, 0.2%, and 0.4%) were subjected to dry–wet cycles in a 5% sodium sulfate solution. The results show that fiber incorporation significantly enhances sulfate resistance, with the optimal performance achieved at 0.2% fiber content. Compared with ordinary Portland cement concrete, ferroaluminate cement-based concrete exhibits improved durability, including lower mass variation, reduced strength degradation, and more stable dynamic elastic modulus. Microstructural analyses indicate that hydration products refine the pore structure, while fibers effectively inhibit crack propagation and expansion damage. Numerical simulation of tunnel lining structures further demonstrates that the optimized material reduces stress concentration, displacement, and crack development. Overall, the proposed material shows superior performance and promising application potential for tunnel linings in sulfate-rich environments. Full article

Post-rotation jacking is a critical construction stage for load-path reconstruction and alignment adjustment in rotation-constructed bridges, particularly for ultra-wide double-deck composite girder systems. Taking a two-span continuous steel truss–concrete composite girder bridge with spans of 2 × 85 m as the engineering background, this study investigates the mechanical behavior during post-rotation jacking through theoretical derivation, finite element simulation, and on-site monitoring. Based on the force method of structural mechanics, a linear relationship between vertical synchronous jacking force and displacement is derived, and an analytical formulation for bearing reaction redistribution under laterally asynchronous jacking is established by considering the coupling effects of vertical bending, torsion, and transverse multi-bearing support. A full-bridge spatial finite element model was developed in MIDAS Civil NX 2024 V1.1 to analyze the redistribution of bearing reactions and the stress response of the concrete crossbeam under different jacking conditions. The results show that, for the investigated bridge, the jacking force–displacement response remains highly linear during synchronous jacking. The B-axis middle bearing is more sensitive to jacking displacement than the two side bearings, with its fitted stiffness being approximately 2.19 times the average stiffness of the side bearings. Eccentric jacking causes reaction concentration at the jacked point and reaction reduction at adjacent supports, and the magnitude of reaction variation increases approximately linearly with jacking displacement. When the transverse non-uniform jacking magnitude reaches 20 mm, a tensile stress of 0.3 MPa appears at the bottom flange of the concrete crossbeam; therefore, a project-specific stroke-difference limit of 20 mm is recommended for this bridge, while the actual construction achieved a stroke control accuracy of ±0.5 mm and a transverse elevation difference within 1 mm. Field monitoring results validate the proposed analytical and numerical methods. The Pearson correlation coefficients of the measured jacking forces with the finite element and theoretical results are 0.9987 and 0.9988, respectively, and the corresponding mean relative errors are 3.84% and 4.23%. For stress responses, the measured and calculated values show a strong correlation, with a Pearson correlation coefficient of 0.9980 and a mean relative error of 12.77%; the critical mid-span monitoring point shows a relative error of only 0.65%. The final bridge alignment deviation is controlled within ±3 cm. The overall mean verification coefficient is 0.968, with a 95% empirical agreement range of [0.888, 1.048], indicating that the proposed mechanical analysis framework and combined force–displacement control strategy can provide a useful reference for refined construction control of similar ultra-wide double-deck composite girder bridges with comparable span arrangement and transverse bearing layout. Full article

In hybrid rolling bearings operating under extreme high-temperature and high-load conditions, steel rolling elements are prone to early failure, which has accelerated the widespread adoption of ceramic materials. To address the limitations of conventional studies, which have focused mainly on macroscopic wear parameters while neglecting subsurface failure mechanisms and the relationship among sintering process, microstructure, and fatigue performance, this work systematically compares the tribological behavior of Si₃N₄ ceramic balls fabricated by high-pressure electric resistance hot-pressing (REHP) and B₄C ceramic balls prepared by conventional hot pressing (HP) against 52100 steel counterparts. The central innovation of this study lies in clarifying, based on Hertzian contact theory and Lundberg-Palmgren life theory, that subsurface orthogonal shear stress, rather than surface compressive stress, is the fundamental driving force for contact fatigue failure of ceramic balls. In addition, two distinct damage evolution modes are revealed: B₄C exhibits early-stage brittle fracture and large-scale spalling, whereas REHP-Si₃N₄ is characterized by microcrack initiation and slow crack propagation. Moreover, the intrinsic mechanism by which the REHP process significantly enhances the contact fatigue life of ceramics is elucidated; namely, it refines grain size, eliminates residual porosity, and increases densification. The results show that, under the same high-load conditions, the mass loss of REHP-Si₃N₄ ceramic balls is only 35.7% of that of HP-B₄C, while the service life is extended by 20%. This work provides a key theoretical basis for ceramic material selection and sintering process optimization in high-performance hybrid bearings. Full article

Volatilization of alloying elements during vacuum refining of high-Cr die steel can cause fume generation, resource loss and increased dust-collection burden. Here, D2 high-carbon high-chromium die steel was melted in a vacuum induction furnace and held at 15 Pa and 1600 °C for 60 min, while CO and CO₂ evolution was monitored online. The collected volatile matter and the used magnesia crucible were characterized by XRF, XRD, Micro-CT, SEM-EDS, and XPS. The volatile matter mainly consisted of Fe-Cr-Mn metallic solid-solution phases and nanoscale agglomerates with partial surface oxidation. XRF results showed that the collected metallic volatile matter contained 49.96 wt.% Mn, 32.58 wt.% Fe, and 13.23 wt.% Cr. The enrichment factors of Cr and Mn relative to Fe were calculated to be 2.78 and 3.91 × 10², respectively, indicating strong selective volatilization of Mn. Micro-CT revealed that the deposition layer was confined to the inner surface of the upper crucible, while the bulk MgO crucible remained dense. Thermodynamic calculations showed that at 10 Pa, the calculated volatilization amounts of Fe, Cr, and Mn reached 3.32 g, 1.05 g, and 0.31 g per 100 g of molten steel, respectively, whereas element volatilization was markedly suppressed when the pressure was increased. A vacuum level above 20 Pa is therefore proposed as a practical process window to reduce fume generation and alloy loss during vacuum processing of high-Cr die steels. Full article

Hydrogen energy represents a crucial clean energy carrier and plays a critical role in achieving the national strategic goals of carbon neutrality and peak carbon emissions. Pipeline transportation is currently the most economical and efficient method for hydrogen delivery. However, most existing hydrogen pipelines worldwide utilize low-alloy steels, which are prone to hydrogen embrittlement (HE) during hydrogen transportation, leading to degradation of mechanical properties in pipeline steels. Since material composition and microstructure directly govern pipeline steel performance, this study systematically investigates the effects of compositional variations among three X65-grade pipeline steels on their microstructural evolution and hydrogen embrittlement resistance. Key findings include reducing Mn content enhances hydrogen embrittlement resistance by refining grain size and increasing the proportion of low-angle grain boundaries (LAGBs); cementite phases act as preferential hydrogen trapping sites, significantly reducing hydrogen resistance; and strain rate dependency of HE susceptibility is confirmed, as under slower strain rates, hydrogen interacts with dislocations, promoting brittle fracture mechanisms. This work provides practical mechanism insights for optimizing hydrogen-resistant pipeline steel design through compositional regulation and microstructural engineering. Full article

With the rapid expansion of urban underground space in China, anti-floating has become a critical challenge, and uplift piles are a key solution. Previous studies on composite anchor-cable uplift piles have primarily focused on small-diameter single-pipe types (≤600 mm), often simplifying the pile as an integral component, leaving the multi-interface stress transfer mechanisms of large-diameter piles inadequately understood. This study proposes a back-analysis method based on orthogonal experiments, implemented using Abaqus 3D finite element software, to determine interfacial mechanical parameters for three critical contact pairs (strand-grout, grout-steel pipe, steel pipe-concrete) in large-diameter multi-pipe composite anchor-cable uplift piles. These parameters are then implemented in a refined 3D finite element model to simulate the load-deformation behavior of such piles. Quantitative results show that the back-calculated parameters are highly reliable, with maximum simulation errors for pile head displacement limited to 13.0% and 9.6% for fully bonded and semi-bonded piles, respectively. Unlike conventional piles, stress and strain in this new pile type transfer progressively from the inner steel strands outward and from the top downward, resulting in reduced pile-soil displacement mismatch, fuller mobilization of side interfacial strength, and effective mitigation of concrete cracking. This study provides a systematic parameter-calibration framework and numerical platform, offering theoretical and technical support for optimized design and engineering application of large-diameter composite uplift piles. Full article

This study focuses on a 155 mm 32CrNi3MoV steel barrel and presents a thermochemically coupled phase transformation and diffusion dynamics model. The model leverages the significant disparity between radial and axial temperature gradients to simplify the heat conduction problem to a one-dimensional transient formulation. The temperature field distribution during firing sequences is solved analytically, accounting for the dynamic shift in critical phase transformation temperatures under high heating rates. The evolution of the martensitic layer thickness under repeated thermal shock is subsequently calculated. A numerical model for the pulsed diffusion of C and N is established based on Fick’s second law, incorporating the competitive diffusion–phase transformation mechanisms that govern martensite/austenite interface migration. To quantitatively evaluate the synergistic contribution of C and N to austenite stabilization, a carbon equivalent (Ceq) model is introduced, with the weight coefficient of N relative to C determined to be 0.68 and the critical Ceq required to lower the martensite start temperature below 25 °C calculated as 1.15 wt%. Concurrently, the microstructure and elemental distribution within the austenite layer of the retired barrel are systematically characterized using multi-scale techniques. The results indicate that the austenite layer on the inner bore surface arises from the synergistic effects of cyclic thermal-shock-induced phase transformation and elemental diffusion. Based on the Ceq criterion, the austenite layer thickness increases rapidly during the initial ~100 firing cycles, after which the growth rate slows significantly: it reaches approximately 1.27 μm after the first cycle and 2.94 μm after 1000 cycles, with only 0.2 μm of additional thickening between 100 and 1000 cycles—consistent with the experimentally observed range of 1.52–4.16 μm. The martensitic layer formed during the first firing cycle exhibits low thermal conductivity, which impedes subsequent heat transfer and leads to stabilization of its thickness at a characteristic depth. Grain refinement induced by repeated thermal shock provide short-circuit diffusion paths for elemental diffusion, accelerating compositional homogenization within the austenite layer and resulting in a stepped concentration profile at the interface. This study provides a representative example of non-equilibrium coupled phase transformation–diffusion phenomena under extreme transient loading. The established thickness prediction model can provide guidance for service life assessment of large-caliber barrels, offering both theoretical foundations and practical engineering guidance for their material design and performance optimization. Full article