Search Results (161)

As a key process subsequent to continuous casting, the cooling of cast slabs is of central importance for achieving desirably low internal stresses, thereby minimizing the risk of crack formation and structural breakage. Although the primary and secondary cooling process in continuous casting are well-established in research, studies on the thermo-metallurgical-mechanical phenomena during slab yard cooling remain critically limited. In this work, a coupled thermo-metallurgical-mechanical model is presented that elucidates the process of slab cooling, addressing the combined effects of specific alloys and cooling conditions. Three universal stages of stress accumulation are identified: the pre-transformation stage (1), the transformation stage (2), and the post-transformation stage (3). Specifically, the early ferrite transformation—which is key to many concepts of cracking susceptibility—is carefully analyzed. While stress accumulation in the transformation stage is substantially driven by the intrinsic material physics, it is shown that the potential for reducing room-temperature residual stresses resides in the application of innovative process designs in the post-transformation stage. Accordingly, a stress reduction of 50% can be achieved in critical locations. The developed model represents a versatile tool for process design and optimization, thereby contributing to the production of advanced, next-generation high-strength steels. Full article

This study proposes a deep-notched precast concrete slab system with post-cast connections for modular construction, aiming to improve on-site assembly efficiency while maintaining flexural continuity. A total of 22 full-scale slab specimens, including monolithic cast-in-place slabs and precast slabs with different notch depths, anchorage lengths, reinforcement diameters, and notch geometries, were tested under positive and negative bending conditions. The experimental results showed that, for the investigated reinforcement layout and loading conditions, the connected slabs with adequate anchorage achieved approximately 85% and 95% of the flexural capacity of the corresponding cast-in-place slabs under positive and negative bending, respectively. Anchorage length was found to be a key factor governing failure mode and load-transfer efficiency, while reinforcement diameter had a significant influence on ultimate capacity. Within the tested range, notch depth and notch geometry showed comparatively limited effects on flexural capacity, although their influence should be interpreted in relation to the adopted reinforcement arrangement and anchorage conditions. Finite element models based on the concrete damage plasticity approach were developed to interpret the load-transfer mechanism and parameter sensitivity. The models predicted the ultimate load with acceptable accuracy, while larger discrepancies were observed in some displacement estimates because of the simplification of interface behavior, bond-slip response, and local cracking. The experimental and numerical results indicate that load transfer across the joint was mainly achieved through reinforcement bridging, whereas the contribution of concrete bonding at the joint was limited under the investigated conditions. Based on these findings, a modified analytical model was proposed to predict the ultimate flexural capacity of the connected slabs. The model showed reasonable agreement with the test results for specimens with adequate anchorage. The proposed connection provides a feasible detailing solution for precast concrete slab connections in modular construction, but its application should be limited to configurations with comparable reinforcement layout, anchorage conditions, material properties, and monotonic bending behavior. Full article

Internal cracks during slab bending and straightening are continuous-casting defects. Existing caster curves rely on plastic deformation, while curvature variation is concentrated within short sections, causing excessive strain rates and increasing the risk of internal straightening cracks. This study proposes a novel method for slab straightening through creep deformation and develops a curve for an R9300 caster by connecting cubic transition curves with cycloidal main segments. High-temperature tensile and constant-stress creep tests of Q345C steel were combined with transient thermal simulation and geometric strain-rate calculations. Under constraints on caster height, minimum curvature radius, and steady-state creep rate, the optimized parameters were a = 2600 mm and t = 3.6 rad. The curve eliminates the circular-arc section and ensures continuous position, tangent, and curvature. Its bending and straightening sections are each 9379 mm long, increases of 8349 and 7859 mm, respectively, while caster height increases by only 0.47 m. At the internal 1200 °C isotherm, the maximum strain rates are $6.75\times {10}^{-5} {\mathrm{s}}^{-1}$ and $5.19\times {10}^{-5} {\mathrm{s}}^{-1}$, reductions of 82.2% and 81.1% relative to the conventional caster. Both remain below the steady-state creep rate of $7.45\times {10}^{-5} {\mathrm{s}}^{-1}$ under ±10% secondary-cooling and ±10 °C casting-temperature fluctuations. The curve alleviates deformation concentration and enables the slab region at 1200 °C and above to bend and straighten through creep deformation. Full article

In CSP thin slab casting, high casting speeds promote excessive columnar grain growth, leading to low equiaxed grain ratios in non-oriented silicon steel and resulting in wrinkling defects. This study employs a box-type electromagnetic stirrer (B-EMS) to address this issue. A multiphysics model was established, in which grain transformation and its associated effects were neglected. The effects of B-EMS on the flow of molten steel, temperature distribution and evolution of solidified shell were analyzed, and industrial trials were conducted to verify the influence of B-EMS on grains. Results show that B-EMS generates asymmetric magnetic fields and electromagnetic forces, driving width-directional flow that enhances scouring of the solidification front. Compared with the experiment and simulation, the error in the magnetic field excited by B-EMS is within 5%. Under 800 A current, narrow-face center shell thickness increased from 22.88 mm (no stirring) to 23.62 mm (starting side) and 23.21 mm (pushing side). The central mushy zone area and liquid fraction decreased significantly, indicating accelerated solidification and more uniform shell growth. Industrial trials confirmed that the equiaxed grain ratio increased to approximately 30%, with significantly improved internal strand quality. This study demonstrates B-EMS’s metallurgical effects in regulating solidification structure, optimizing shell morphology, and improving continuous casting slab quality. The numerical simulation can be correlated with the industrial production process to better guide manufacturing practices. Full article

The mechanism by which Sb influences the hot ductility and fracture behavior of corrosion-resistant steel within the temperature range of 650–1200 °C was systematically investigated using scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The temperature interval of the ductility trough and the underlying mechanisms responsible for its occurrence were elucidated. The results indicated that ductility troughs for the 0.09Sb and 0.15Sb steels occurred at 726–949 °C and 736–995 °C, respectively. Increasing Sb content broadened the ductility trough temperature range and shifted the minimum ductility temperature to higher values. The ductility trough was attributed to the combined effects of grain boundary ferrite films, coarse precipitates, and non-equilibrium grain boundary segregation of Sb. During deformation in the austenite–ferrite two-phase region at 800 °C, the hot ductility is primarily governed by the thickness of the grain boundary ferrite film. These ferrite films are prone to stress concentration, thereby reducing the hot ductility of both the 0.09Sb steel and the 0.15Sb steel. In the single-phase austenite region at 900 °C, coarse Ti(C,N) and MnS precipitates readily act as crack initiation sites, leading to intergranular fracture in the 0.15Sb steel. Non-equilibrium Sb grain boundary segregation further weakens grain boundary cohesion, thereby deteriorating the hot ductility of the steel. Moreover, increasing Sb content enhanced the magnitude of non-equilibrium grain boundary segregation and elevated its peak temperature, thereby raising the minimum ductility temperature. This work provides a theoretical basis and technical guidance for optimizing the continuous casting of Sb-containing corrosion-resistant steel in industrial production, thereby contributing to improved surface quality of continuously cast slabs. Full article

In slab continuous casting, the internal hydrodynamics of the submerged entry nozzle (SEN) play a determining role in mold flow stability and product quality, particularly when external electromagnetic flow-control technologies are not employed. This study analyzes a novel bifurcated SEN design intended to promote stable, highly symmetric outlet jets under asymmetric inlet flow conditions produced by typical flow-control devices. The proposed configuration combines three geometric modifications: a square-section bore, a flow-divider bottom wall derived from a rotated mountain-type geometry, and two bell-shaped protrusions that act as flow modulators positioned immediately above the outlet ports. The hydrodynamic behavior inside the nozzle was investigated using complementary experimental and numerical approaches. Physical modeling was conducted in a scaled water model using particle image velocimetry (PIV) to characterize time-averaged velocity fields and flow fluctuations. In parallel, three-dimensional large-eddy simulations (LESs) were performed to resolve transient flow structures and quantify jet characteristics at the nozzle exits. Both approaches show consistent results. The combined action of the flow modulators and the flow-divider bottom wall robustly induces the formation of two nearly identical counter-rotating vortices in the lower region of the SEN. This flow structure suppresses stagnation and recirculation zones near the outlet ports, mitigates inlet-induced asymmetries, and enhances flow evacuation efficiency. Quantitative analysis of the outlet jets indicates a significant reduction in angular dispersion and a flow-rate imbalance below 0.2%, markedly lower than that observed in conventional SEN configurations. The results demonstrate that appropriate internal geometric design can effectively stabilize SEN hydrodynamics without active control systems, offering a feasible and scalable strategy for improving mold flow stability in industrial continuous casting operations. Full article

This study systematically investigated the mechanism of micro-segregation reduction in a high-Mn austenitic cryogenic steel continuous casting slab using thermodynamic calculations and homogenization experiments. The high-Mn austenitic cryogenic steel continuous casting slab exhibits obvious non-equilibrium solidification characteristics, with severe interdendritic segregation of C and Mn. The solidus temperatures of equilibrium, Scheil, and Scheil–Back solidification are 1324 °C, 953 °C, and 1272 °C, respectively. According to thermodynamic calculations, there is only a slight decrease in the highest segregation C content when the homogenization temperature is 900 °C. When the specimens were homogenized at 1000 °C, the segregation of C and Mn was significantly alleviated, and the segregation degree further decreased when the homogenization temperature was 1100 °C. Two feasible and industrially applicable strategies for alleviating the micro-segregation of a high-Mn steel continuous casting slab are proposed. First, reduce the cooling intensity of the secondary cooling stage during continuous casting, slow down the cooling rate around 1000 °C, and promote the limited diffusion of solute elements to reduce initial segregation. Second, introduce a holding stage at around 1000 °C during slab reheating prior to hot rolling, eliminating residual segregation and stabilizing the local solidus temperature above 1200 °C. Full article

Accurate thermal analysis of steel solidification and heat transfer in the continuous casting mold is essential for understanding and controlling solidification, shell thickness uniformity, interfacial gap phenomena, and defects such as cracks and breakouts. This study investigates heat transfer in a funnel mold slab caster using the in-house thermal model, Con1D. A new methodology is introduced to predict the slag layer roughness, and its effect on interface resistance. To account for the multidimensional thermal behavior near water channels and thermocouples, finite-element models are developed in Abaqus to calibrate Con1D to match three-dimensional calculations of mold heat transfer. After calibration to match plant measurements for one set of casting conditions, Con1D predictions are validated with plant measurements at different casting speeds and mold plate thicknesses. Key outputs analyzed include the heat flux profile, mold and shell temperatures, shell thickness, shell shrinkage, and interfacial parameters such as slag layer thickness. Increasing casting speed causes higher heat flux, higher shell surface and mold temperatures, and decreased shell and slag layer thicknesses. Decreasing mold plate thickness increases heat flux slightly due to reduced thermal resistance of both the mold and interfacial gap. The modeling approach presented here is a powerful methodology to gain quantitative fundamental understanding of mold heat transfer in continuous casting, especially including phenomena in the interfacial gap. Full article

The stability of mold level fluctuations (MLFs) is crucial for product quality and process efficiency in continuous casting. Abnormal mold level fluctuations, which are typically associated with multiple factors including stopper rod opening, casting speed, and mold width, are known to lead to slab quality defects. In this paper, an Informer-based prediction framework is proposed for the early detection of abnormal MLF. A threshold-based labeling method is developed to quantify the future likelihood and severity of anomalies across different time horizons. Considering the importance of frequency-domain features in mold level prediction, power spectral density (PSD) features are incorporated and smoothed using the exponential moving average (EMA) to enhance predictive performance. Through the integration of temporal and processed spectral features, early indicators of abnormality can be captured, and proactive warnings can be issued. The proposed architecture is validated using approximately 32.5 million data points from a real-world continuous casting process. This approach provides a robust and data-driven solution for predicting and diagnosing abnormal MLF events in continuous casting. Experimental results show that the mean ROC-AUC and PR-AUC reach 0.821 and 0.418, respectively. Full article

The Compact Strip Production (CSP) process is the latest version of thin-slab continuous casting, combining both casting and rolling, thus improving the CSP process’s energy efficiency and the strip quality. Modeling the combined phenomena of fluid flow, heat transfer and solidification in CSP casting remains an unresolved multiphysics problem, particularly when boron and other alloying elements enter the system and modify the thermal properties and solidification behavior. In this study, we propose a more integrated approach by executing a computational fluid dynamics (CFD) model at different scales, blending macroscale fluid flow and heat transfer with meso-solidification that is molten in a CSP casting model. For the macroscale model, we solve the Reynolds-Averaged Navier–Stokes (RANS) equations with one of the energy equations, while the mesoscale model uses the solid fraction evolution algorithm to model the multiphase latent heat of solidification and the motion of solid and liquid phases of a non-equilibrium system. Mold heat flux, free surface cooling and secondary spray zones were used to set the boundary conditions. The model simulates temperature distributions at different times, the solid fraction below the liquidus and the trends in shell growth for different process parameters and the time profile of the solidification. The improved prediction capability of the model, demonstrated by the results, opens the opportunity to reduce the process parameters of casting speed and cooling to defect-free results. Comparisons with the most recent studies on continuous casting processes (including CSP and thin slabs) demonstrate alignment with the thermal gradient and solidification behavior characteristics. The thermal gradients and solidification behavior characteristics were obtained. The research yields the basis for developing microstructure and segregation models with boron-alloyed steels. Full article

Macrosegregation in continuous casting slabs remains a critical defect that adversely affects the homogeneity and mechanical properties of the final rolled products. Industrial experiments were conducted on E355 steel continuous casting slabs to investigate the effects of electromagnetic stirring (EMS) and soft reduction (SR) on the evolution of slab macrosegregation. Furthermore, the inheritance of segregation from the slab to the rolled plate was analyzed. The results indicate that the equiaxed crystal ratio increases and the centerline segregation decreases with increasing stirring intensity. The application of both secondary EMS and SR minimized the centerline segregation in the slab. When the current intensity was increased from 0 A to 320 A in continuous stirring mode, the equiaxed crystal fraction increased from 22.52% to 32.52%, and the centerline segregation index decreased from 1.23 to 1.17. Compared with the continuous stirring mode, the alternating stirring mode promoted a more pronounced increase in the equiaxed crystal ratio and a further reduction in the centerline segregation. The centerline segregation in the slab correlates with the banded structure observed in the rolled plate. A higher degree of slab centerline segregation corresponds to a more severe banded structure and greater fluctuations in the mechanical properties of the plate. Through parameter optimization, the recommended settings are an alternating stirring mode with a current of 320 A at 5 Hz and an SR amount of 3 mm. Under these optimized conditions, the equiaxed crystal ratio of the slab increased to 35.22%, the centerline segregation index dropped to 1.15, and the banded structure in the rolled plate was reduced to grade 2.0. Consequently, the standard deviations of the tensile strength and elongation were 8.03 MPa and 1.1%, respectively. Full article

The surface quality and production efficiency of continuous-casting steel slabs are predominantly determined by the performance of the mold. To address slab corner defects and enhance operational stability, this study systematically optimized two key components: the broad-face clamping mechanism and the narrow-face copper plate. A disk spring–hydraulic composite clamping mechanism was designed and subjected to mechanical analysis to ensure sufficient and reliable clamping force under high-load casting conditions. Meanwhile, based on the principle of solidification shrinkage, an external chamfer structure for the narrow-face copper plate was proposed to improve heat transfer uniformity at the slab corner. Engineering design calculations and practical application in an export-oriented wide-and-heavy slab continuous-casting project (specification: 250 mm × 2500 mm) demonstrated that the optimized clamping mechanism provides enhanced structural rigidity, while the new narrow-face copper plate effectively mitigates corner cracks and reduces wear. This integrated design approach significantly improves slab surface quality and extends component service life, yielding substantial economic benefits. Full article

This study focuses on a critical issue in Heterotrophic Prestressed Concrete Pavement (HPCP), the closure pour, which is prone to weak interfacial bonding, stress concentration, and cracking under repeated aircraft loads. To overcome these shortcomings, a novel prefabricated integrated anchorage (PIA) device is designed, integrating the functions of both a tensioning end and an anchoring end. Based on the PIA, a continuous tensioning construction process is introduced, which eliminates the traditional closure pour by utilizing the casting space of the subsequent slab to tension the preceding one. Finite element analysis demonstrates that the PIA device exhibits complex stress alternation under prestressing, with the most critical cross sections located at depths of 100 to 150 mm. A parametric study further reveals a linear relationship between the tension angle and the maximum principal stress in the PIA. In the HPCP system, prestressing establishes a predominant compressive stress field in the slab, effectively enhancing crack resistance. However, localized stress concentration and tension–compression alternation occur not only around the PIAs but also notably at the slab corners. These results confirm that the PIA device and its associated continuous construction method not only overcome the drawbacks of closure pours but also provide an innovative, efficient, and sustainable technical pathway for improving the quality and performance of airfield pavement engineering. Full article

Hypo-peritectic steels are susceptible to interfacial cracking during thin-slab continuous casting, in which non-metallic inclusions play a critical role. This study systematically investigates the effects of inclusion type and morphology on interface cracking behavior in the steel matrix, with the aim of improving billet shell quality. Hot tensile experiments were conducted using a Gleeble 3800 thermal simulator, and a finite element–based cohesive zone model was developed to simulate inclusion-induced crack nucleation and propagation. The results demonstrate that inclusions markedly influence interfacial stress distribution and damage evolution. The maximum interfacial stresses associated with MnS, Al₂O₃, and composite inclusions are 20.7, 23.4, and 30.5 MPa, respectively. Owing to severe stress concentration at sharp corners, composite inclusions exhibit the earliest crack nucleation at an applied stress of 11.3 MPa and the highest energy dissipation. In all cases, cracks initially nucleate at the location of maximum tensile stress (α = 90°), propagate along the interface, and subsequently penetrate into the matrix, ultimately leading to failure. The strong agreement between numerical simulations and experimental results confirms that angular inclusions accelerate damage by disrupting matrix continuity. These findings provide theoretical guidance for improving hypo-peritectic steel quality through inclusion morphology control during continuous casting. Full article

The utilization of recycled steel is essential for achieving carbon neutrality and sustainable engineering, yet repeated recycling inevitably leads to the accumulation of residual elements that are difficult to remove during conventional refining. Among them, copper (Cu) readily enriches in scrap-based steels and is a primary cause of surface hot shortness during high-temperature processing due to its segregation at the oxide/steel interface. While the compositional effects of Cu have been extensively studied, the influence of thermo-history associated with different industrial processing routes remains poorly understood. In this work, Cu enrichment during high-temperature oxidation was systematically investigated under thermo-histories representative of conventional hot rolling, thin slab continuous casting and rolling (TSCR), and strip casting. Plain carbon steels containing 0.05–0.30 wt.% Cu were oxidized at 1000–1200 °C, and interfacial microstructures were characterized using SEM–EDS. The results show that Cu enrichment is highly sensitive to both temperature and thermal exposure time, with a critical temperature range of 1100–1150 °C promoting the formation of continuous Cu-rich liquid films. Prolonged thermo-history in conventional hot rolling markedly enhances Cu enrichment, TSCR partially suppresses interfacial segregation, whereas strip casting effectively inhibits Cu enrichment even at elevated Cu contents. These findings highlight thermo-history as a dominant factor controlling Cu-induced surface hot shortness and provide guidance for process optimization in recycled steels. Full article