Active learning-guided design of TiB2-reinforced 316L stainless steel via additive manufacturing: Process optimization and experimental validation

Seismic performance and design of L-shaped multi-partition steel–concrete shear walls under weak-axis loading

To elucidate the evolution of dynamic recrystallization (DRX) mechanisms in cold-worked Cr4Mo4Ni4V martensitic steel, tensile tests were conducted on a 50% cold-deformed material at 600–850 °C at a fixed strain rate of 0.001 s−1, combined with systematic microstructural characterization. Under this specific strain rate, the results reveal a temperature-dependent transition from continuous dynamic recrystallization (CDRX) to discontinuous dynamic recrystallization (DDRX). At 600 °C, CDRX dominates, producing recrystallized grains with orientations close to the parent matrix and relatively strong texture. At 750 °C, CDRX and DDRX coexist, while DDRX is significantly enhanced, characterized by grain boundary nucleation and random orientations, leading to a marked reduction in texture intensity; simultaneously, the fraction of recrystallized grains and high-angle grain boundaries reaches a maximum. At 850 °C, DDRX becomes dominant. This transition in DRX mechanism governs the high-temperature plasticity, with optimal superplasticity achieved at 800 °C, corresponding to an elongation of 748%. Cavities are primarily initiated at carbide/matrix interfaces, and their growth and coalescence dominate the fracture process. These findings clarify the temperature-dependent DRX evolution and its role in regulating superplasticity, providing guidance for microstructure design and superplastic forming of martensitic steels.

Copper-bearing low-carbon high-strength steels are widely employed in marine engineering. However, the microstructural homogeneity, strength–toughness matching, and low-temperature toughening mechanisms of such steels at high copper contents remain unclear. Existing studies have predominantly focused on the Cu content range of 1–2 wt.%, lacking systematic comparisons regarding microstructural evolution and property regulation throughout the entire rolling-heat treatment process at higher Cu levels. To clarify the influence of Cu content on the microstructural evolution and mechanical properties of CuxNi2.7Mn steels during processing and heat treatment, and to fully exploit the Cu precipitation strengthening effect while suppressing its embrittlement drawback, this study investigates CuxNi2.7Mn steels with Cu contents of 1.35 wt.%, 3.1 wt.%, and 6 wt.%. The specimens were fabricated via vacuum melting and two-stage rolling. Combining in situ observation using a high-temperature laser confocal microscope, optical microscopy, scanning electron microscopy, X-ray diffraction, and mechanical property tests, the effects of different Cu contents on the microstructure, conventional mechanical properties, and low-temperature toughness at −40 °C of the steels in both as-rolled and optimally heat-treated states (solid solution at 900 °C for 1 h + aging at 540 °C for 2 h) were systematically investigated. The results demonstrate that in the as-rolled condition, with increasing Cu content, the Vickers microhardness (HV1) of the steel increases from 183.9 HV1 to 271.9 HV1, the yield strength rises from 556.55 MPa to 852.87 MPa, and the tensile strength increases from 758.53 MPa to 1162.59 MPa. Nevertheless, excessive Cu content induces austenitic grain coarsening, aggregation of Cu-rich precipitates, and stress concentration, resulting in significant deterioration of ductility and toughness. Following optimal heat treatment, the banded structure is completely eliminated, the microstructural homogeneity is substantially improved, and the ductility and toughness are remarkably enhanced compared with the as-rolled state. Meanwhile, the strength continues to increase with rising Cu content, with the 6 wt.% Cu steel achieving a yield strength of 922.51 MPa and a tensile strength of 955.17 MPa. In terms of low-temperature toughness, the 3.1 wt.% Cu steel exhibits the poorest performance (90.8 J), whereas the 6 wt.% Cu steel presents a sharply increased low-temperature impact energy of 152.6 J. This is attributed to the precipitation of particulate phases such as TiC and MnS, which effectively disperse low-temperature stress and hinder crack propagation. Overall, the CuxNi2.7Mn steel with 6 wt.% Cu possesses the highest strength as well as excellent low-temperature toughness after optimal heat treatment, providing theoretical and experimental foundations for the composition design and heat treatment process optimization of high-copper steels for marine applications.

Numerical studies and design of cold-formed steel battens subject to pull-through failures under bushfire conditions

Multi-scheme seismic optimization design of steel–concrete structures utilized multimodal multi-objective differential evolution algorithm

The hydrogen supply pipelines can lead to failure behaviors such as hydrogen-induced cracking and reduced plasticity when it is exposed to hydrogen-containing media during service, which is related to the migration feature of hydrogen atoms within the matrix. In this contribution, the tensile property evolution of X52MS pipeline steel before and after hydrogen charging is investigated by combining electrochemical hydrogen charging test with slow stretching experiment. The results show that as the per-charging time increases, the number and size of hydrogen blisters rise, which is caused by hydrogen accumulation on the surface. For the test steel with the thickness of 7.1 mm, the hydrogen blister size reaches about 3 mm after 12 h of pre-charging, and the hydrogen embrittlement sensitivity index is the highest of 54.6%. In contrast, the test steel with the thickness of 6.3 mm has the lowest index of 14.7%, indicating the better resistance to hydrogen embrittlement. It can be concluded that the hydrogen blister size is positively correlated with the hydrogen embrittlement sensitivity index, and surface hydrogen accumulation is the key reason for hydrogen-induced crack initiation. Furthermore, the tensile strengths of the three test specimens change little after pre-charging, but the elongation gradually decreases. The shear lips on the side of the fracture are all featured by a zigzag shape, and the cracks appear in the necking area, with a relatively large fracture diameter, showing the obvious hydrogen damage features. The fracture center morphology gradually changes from dimple one to cleavage surface one after hydrogen charging. These insights provide theoretical basis and experimental guidance for the design and development of pipeline steel for hydrogen energy transportation.

This paper introduces a data-driven framework designed to accelerate the property prediction, and hence the discovery and development of steels. The study leverages natural language processing and machine learning techniques to analyse a dataset containing steel compositions, (thermo)mechanical processing, and mechanical properties. By integrating unsupervized machine learning for process classification (via natural language processing-assisted clustering) and supervised regression models for property prediction, the framework enables an efficient exploration method to study steels. A predictive accuracy of R2 > 0.85 was achieved, with mean absolute errors <15MPa for both yield and ultimate tensile strength. A cloud-based graphical user interface was developed to facilitate user interaction, allowing researchers to input steel processing and composition to receive predictive insights on mechanical properties. The findings demonstrate the framework to support circular economy principles by reducing trial-and-error experimentation, with a view to accelerating the design of steels, and promoting sustainable steel innovation.

Multi-constraint slag design and dephosphorization modeling for 65Mn steel at a high-carbon end point in a single-slag BOF process

Technological advancements have driven the use of new computational techniques and tools in structural engineering, enabling the accurate simulation of the behavior of increasingly slender and complex structures. Making use of such tools, a Python routine was developed for the design of steel beams with non-slender webs, covering welded, rolled profiles, and mixed steel-concrete beams, in accordance with the NBR 8800:2008 standard. The routine incorporates a genetic algorithm (PyGad) for discrete parametric optimization, selecting the most suitable profile among commercial options. The weighting function considers parameters such as inertia, mass, modulus of elasticity, radius of gyration, and bending strength, with weights adjusted by the algorithm. The verification of serviceability limit states and vibration frequencies is also part of the process, offering a comprehensive approach to design and optimization. After ensuring compliance with the NBR 8800:2008 standard requirements, it was possible to perform several additional analyses with the selected beam, such as cost, weight/performance ratio, boundary conditions, degree of utilization, as well as comparisons between different profile types and beam models. The case study involved the analysis of distinct beam models, allowing an effective comparison between different types of profiles and their characteristics. The results highlighted the program’s ability to provide optimized solutions, considering criteria such as price, weight, boundary conditions and utilization.

Abstract This study employed molecular dynamics (MD) simulations to investigate the effects of Bismuth (Bi) inclusions on the anisotropy and microstructural evolution of FeNiCr alloy (a model for Bi-containing free-cutting steels) during nanoindentation. Single-crystal systems with [100], [110], [111] orientations and polycrystalline systems were constructed, with spherical Bi inclusions (radius: 25 Å) embedded in the face-centered cubic (FCC) FeNiCr matrix (atomic ratio Fe:Ni:Cr = 7:1:2).Key characterizations included nanoindentation load-displacement curve analysis (validated against Hertzian elastic theory in the initial elastic stage), dislocation evolution quantification via Dislocation Extraction Analysis (DXA), and stress/defect distribution visualization using OVITO (with common neighborhood analysis, CNA, for atomic structure classification). Results demonstrated that Bi inclusions significantly suppressed dislocation nucleation and expansion, reduced matrix stress concentrations, and thereby enhanced material machinability. Additionally, single-crystal matrices exhibited more favorable nanoindentation mechanical properties (higher hardness, stronger strain hardening) compared to polycrystalline matrices; among single-crystal orientations, [111] stood out with distinct advantages, characterized by the shortest total dislocation length (4847 Å at maximum indentation depth) and the highest stair-rod dislocation density.This work reveals the atomic-scale mechanism underlying the anisotropy of Bi-containing free-cutting steels under nanoindentation, providing critical theoretical support for the design and optimization of high-machinability steels.

Effect of multiscale microstructure on tensile properties and deformation behavior of 304 austenitic stainless steel

• An economic routine for fabricating Al 2 O 3 -IMMC and its TMP design were investigated. • Distinct mechanical and microstructural response during hot compression were studied. • Hierarchical DRX mechanism triggered by multi-scale Al 2 O 3 particles was proposed. • Grain refinement induced by nano-Cu was observed and discussed. Iron-based metal matrix composites (IMMCs) have gained tremendous research interest for their potential to replace traditional steels through economic fabrication routes combined with thermomechanical processing (TMP). Dynamic recrystallization (DRX) plays a decisive role during TMP, and further determines microstructural evolution and mechanical performance. In this study, the mechanical response and microstructural evolution of a novel in-situ fabricated Al 2 O 3 reinforced IMMCs processed by TMP were investigated, focusing on the hierarchical regulation of DRX by multiscale reinforcements. Isothermal compression was conducted at 900–1200 ℃ with a strain rate of 0.1 s −1 to true strain of 0.36–2.30. The as-cast microstructure consisted of microscale Al 2 O 3 particles (0.1–2 μm, ∼10.4 %), nanoscale particles (20–40 nm, ∼1.29 %), and dispersed Cu precipitates. The flow curves exhibit four-stage deformation responses with a yield-point-like feature which weakens at elevated temperatures. Microscale Al 2 O 3 particles promote DRX initiation through particle-stimulated nucleation (PSN), whereas nanoscale Al 2 O 3 particles impose Zener pinning to restrict growth of DRX grains. Concurrently, deformation-induced Cu precipitates facilitate grain-boundary evolution through dislocation interactions, jointly governing the temperature-dependent DRX behavior during TMP. It is envisioned that the results gained from the present study provide insightful guidance for the TMP design of low-density steels and other MMCs.

The room-temperature tensile deformation behavior of an ultra-coarse-grained duplex low-density Fe–30Mn–9Al–0.07C steel (wt.%) was investigated under quasi-static strain rates of 10 −1 -10 −5 s −1 . The alloy exhibited a non-monotonic strain-rate sensitivity: positive sensitivity was observed between 10 −1 and 10 −4 s −1 , whereas a reversal toward negative sensitivity occurred at 10 −5 s −1 . EBSD analyses reveal that high strain rates promote ferrite-dominated substructure development and a rotation toward <111>-type orientations, leading to enhanced hardening and ductility. At low strain rates, ferrite shows a weaker texture change and austenite become increasingly involved in strain accommodation, evidenced by enhanced <110>-type orientations and local γ to α transformation signatures. The results highlight a competition between ferrite substructure hardening at high strain rates and transformation-/load-transfer-assisted deformation at low strain rates, providing insight for microstructure design of lightweight steels under variable-rate loading.

Duplex-phase low-density steels are attracting interest for lightweight structural applications, as reducing vehicle mass is an effective route to lower fuel consumption and emissions. This review summarizes recent progress in alloy design, processing, microstructure control, and performance of duplex-phase low-density steels. The roles of major alloying elements are discussed in terms of phase stability and precipitation tendency, followed by an overview of typical processing routes from melting to hot and cold rolling and subsequent heat treatments used to tailor phase fractions and defect structures. Strengthening mechanisms are reviewed with emphasis on precipitation control, including the beneficial contribution of fine intragranular κ' precipitates and the ductility penalty associated with coarse intergranular κ* films, as well as the use of B2-based particles for high specific strength. Deformation behavior is then discussed in terms of transformation-/twinning-induced plasticity (TRIP/TWIP), planar versus wavy slip, and strain partitioning between ferrite and austenite. Finally, key challenges are outlined, including quantitative interface-based mechanism description, gaps in service property data, stable industrial production and compositional uniformity, and the development of forming and welding windows for engineering implementation.

To address the limitations of existing design specifications for laterally unrestrained stainless steel I-section beam-columns, new design rules are proposed in this study. A comprehensive parametric study was conducted using finite element modelling to investigate the member behaviour and generate benchmark member resistances, covering Class 1–3 cross-sections and considering a range of material grades, member geometries and combined loading conditions. It was observed that the numerically derived compression-bending interaction factor for out-of-plane buckling checks decreases with more pronounced bending moment gradients, indicating their beneficial influence on member resistances. Thus, calibrated against the numerical results, a new formulation of the interaction factor is proposed, covering combined compression and uniform or non-uniform bending and ensuring alignment between member buckling and cross-section resistance checks. The new proposals are shown to provide accurate and consistent member resistance predictions for all load cases, and can be applied with the partial safety factor of 1.1 as specified in EN 1993–1–4:2025. These proposals have been included in the new version of the European structural stainless steel design standard EN 1993–1–4:2025. • Out-of-plane stability and design of stainless steel beam-columns under combined compression and bending are investigated. • A comprehensive parametric study is conducted to generate benchmark member resistances and investigate member behaviour. • Interaction factors for the out-of-plane buckling check in the design of stainless steel beam-columns are proposed. • The new proposals are shown to provide accurate and consistent member resistance predictions for all load cases. • Proposals are suitable for use with the partial safety factor of γ M1 = 1.1 and have been included in EN 1993–1–4:2025.

Pre-Engineered Buildings (PEBs) are widely used in industrial and commercial construction because of their structural efficiency, faster erection, and economic advantages. However, due to their large spans, lightweight steel sections, and relatively flexible framing systems, PEBs are highly vulnerable to lateral loads such as wind and earthquake forces. Hence, the selection of an appropriate bracing system becomes essential to improve stiffness, stability, and overall seismic performance. The present study presents a comparative assessment of a steel PEB structure incorporating five different bracing configurations: Conventional X-bracing, Harp bracing, and Perimetral bracing. The structure is modelled and analysed using ETABS software in accordance with IS 800:2007 for steel design, IS 875 (Parts 1, 2 and 3):2015 for gravity and wind loads, and IS 1893 (Part 1):2020 for seismic analysis. Wind and earthquake loads are considered, and seismic effects are evaluated using the Response Spectrum Method. The investigation focuses exclusively on the distribution of translational (UX, UY) and rotational (RX, RY, RZ) mass participation across vibration modes for Conventional X bracing, Harp bracing, and Perimetral bracing systems. The results indicate significant variation in modal mass distribution depending on the bracing configuration. The Conventional X bracing system exhibits mass participation distributed over multiple modes in the longitudinal direction, along with noticeable torsional coupling, indicating the influence of higher modes on seismic response. Harp bracing demonstrates improved dynamic efficiency by concentrating mass participation within fewer lower-order modes, thereby reducing higher-mode dominance and torsional irregularities. The Perimetral bracing system shows the most desirable behaviour, with nearly complete mass participation captured in the fundamental modes of both principal directions, ensuring predictable and stable seismic response. The findings confirm that advanced bracing systems enhance dynamic performance by minimizing higher-mode effects and controlling torsional response, thereby improving the overall seismic reliability of PEB structures

Permanent magnet linear synchronous motors (PMLSMs) used in high precision applications demand both high thrust density and minimal thrust ripple. This paper presents a novel tooth-wise rolling direction design using grain-oriented electrical steel (GOES) to create a spatially tailored permeance profile in the mover core. The core principle is to strategically assign the GOES easy axis to enhance fundamental, thrust producing flux paths while utilizing the hard axis to suppress the specific spatial harmonics responsible for thrust ripple. A theoretical framework linking spatial harmonics to thrust ripple is established. Based on this, both a conventional uniform direction GOES model and the proposed tooth-wise design were optimized using a multi objective genetic algorithm (NSGA-II) to ensure a fair comparison. Finite element analysis results demonstrate that the proposed design reduces the simulated thrust ripple from 3.60% to 1.79% while maintaining average thrust. Analysis of the no-load voltage waveform and the local force density at minimum thrust points reveals that this improvement stems from the strategic rebalancing of the air gap flux density components, which mitigates causes of ripple. Furthermore, acknowledging the manufacturing complexity of the ideal segmented core, a practical implementation method using stacked sets of non-segmented laminations, termed Stacked Heterogeneous Anisotropy Core (SHAC), is proposed and validated. This approach aims to approximate the performance benefits of the tooth-wise design with a more scalable manufacturing process. This study, therefore, introduces an effective structural design methodology that leverages material anisotropy to actively control electromagnetic performance in high precision PMLSMs and presents a practical strategy for its implementation.

Softening in the heat-affected zone (HAZ) of high-strength pipeline welds compromises its service safety but the corresponding softening mechanism is not well-understood. Softening behavior in the HAZ of two X80 pipeline girth welds with different base metal microstructures, i.e., acicular ferrite (AF)-dominated (X80-AF) and granular bainite (GB)-dominated (X80-GB), were investigated through microhardness tests and detailed microstructure characterization. The results showed that softening in the HAZ of two girth welds primarily occurred in the fine-grained (FG) HAZ, while hardening was found in the coarse-grained (CG) HAZ. X80-AF showed higher softening resistance than X80-GB, with softening ratios of 3.44% vs. 12.46%, and softened zone widths of 2.1 mm vs. 3.9 mm, respectively. Due to its high dislocation density and refined interlocking structure, AF could effectively inhibit phase transformation and grain coarsening during reheating, which resulted in smaller grains and a lower fraction of polygonal ferrite (PF) in the FGHAZ (28%). In contrast, coarse GB was more prone to grain coarsening and hence engendered higher PF proportion (68%). Therefore, for the microstructural design of high-strength pipeline steels, increasing the proportion of refined AF is beneficial to the softening resistance and thereby elevates the service safety of pipelines.

This study presents an optimum design methodology for laminated semi-elliptic steel leaf springs used in vehicle suspension systems, with the primary objective of minimizing spring weight while satisfying structural, geometric, and dynamic requirements. Analytical expressions for bending stress, mid-span deflection, stiffness, and natural frequency are derived based on classical beam theory and expressed in non-dimensional form to enable a generalized and systematic optimization framework. The design variables considered include strip thickness, strip width, and number of leaves, while constraints are imposed on allowable bending stress, maximum deflection, bounded geometry, and natural frequency to ensure structural safety and acceptable ride comfort. The resulting nonlinear optimization problem is solved using MATLAB for a carbon steel (AISI 1020) leaf spring subjected to a specified vertical load. The optimized design consists of four steel strips with a width of approximately 75 mm and a thickness of about 7.5 mm, yielding a total spring weight of approximately 19 kg. The results demonstrate that significant weight reduction can be achieved without compromising stress limits, deflection requirements, or dynamic performance. The proposed methodology provides a reliable and efficient tool for the optimal design of steel laminated leaf springs and can be extended to other materials, loading conditions, and vehicle applications. The results obtained from this study have been compared with available numerical results obtained by FEA and a good agreement is aobtained.