Search Results (187)

Steel is an important product in many engineering sectors; however, steelmaking remains one of the largest ${\mathrm{CO}}_2$ emitters. Therefore, new governmental policies drive the steelmaking industry toward a cleaner and more sustainable operation such as the gas-based direct reduction–electric arc furnace process. To become carbon neutral, utilizing more scrap is one of the feasible solutions to achieve this goal. Addressing knowledge gaps regarding scrap heterogeneity (size, shape, and composition) is essential to evaluate the effects of increased scrap ratios in basic oxygen furnace (BOF) operations. This review systematically examines heat and mass transfer correlations relevant to scrap melting in BOF steelmaking, with a focus on low Prandtl number fluids (thick thermal boundary layer) and dense particulate systems. Notably, a majority of these correlations are designed for fluids with high Prandtl numbers. Even for the ones tailored for low Prandtl, they lack the introduction of the porosity effect which alters the melting behavior in such high temperature systems. The review is divided into two parts. First, it surveys heat transfer correlations for single elements (rods, spheres, and prisms) under natural and forced convection, emphasizing their role in predicting melting rates and estimating maximum shell size. Second, it introduces three numerical modeling approaches, highlighting that the computational fluid dynamics–discrete element method (CFD–DEM) offers flexibility in modeling diverse scrap geometries and contact interactions while being computationally less demanding than particle-resolved direct numerical simulation (PR-DNS). Nevertheless, the review identifies a critical gap: no current CFD–DEM framework simultaneously captures shell formation (particle growth) and non-isotropic scrap melting (particle shrinkage), underscoring the need for improved multiphase models to enhance BOF operation. Full article

The initial reactivity of a multiphase ZnAlMgSi coating with an Al content > 30 wt.% was studied by in situ reflective microscopy under alternating applied potentials +50 mV/−50 mV vs. open-circuit potential in 5 wt.% NaCl and 5 wt.% Na₂SO₄ aqueous solutions. In both environments, galvanic coupling between different coating phases and the anodic behavior decreased in the order binary ZnAl > binary Zn/Zn₂Mg > Zn₂Mg > Al(Zn); dendrites were evidenced for the coating exposed alone as well as in galvanic coupling with steel. Contrary to the observations known for Zn-rich ZnAlMg coatings, pure Zn₂Mg was less reactive than the pure ZnAl phase, underlining the importance of the microstructure for reactivity. Si-needles were systematically cathodic, and Al(Zn) dendrites have shown cathodic behavior in some couplings. In the configuration of coupling with steel, corrosion started at the interfaces “binary ZnAl/steel substrate” or “binary ZnAl/Si particle”. The distribution and nature of the corrosion products formed during the experiment were assessed using X-ray microanalysis in scanning electron microscopy and confocal Raman microscopy. In the sulfate environment, a homogenous and stable corrosion product layer formed from the first steps of the degradation; this was in contrast to the chloride environment, where no surface film formed on the dendrites. Full article

Ni–P–WC–BN(h) nanocomposite coatings were fabricated on 20CrMnTi substrates using ultrasonic-assisted pulsed electrodeposition. 20CrMnTi is a low-carbon steel that is commonly used in the manufacturing gears and shaft components. To enhance the wear resistance and extend the service life of such mechanical parts, ultrasonic-assisted pulsed electrodeposition was employed as an effective surface modification technique. The microhardness, phase structure, surface morphology, and wear behavior of the coating were also characterized. An orthogonal experimental design was employed to examine the effects of current density, bath temperature, ultrasonic power, and pulse duty cycle on the microhardness and wear behavior of the coatings, aiming to optimize the deposition parameters. The optimal process combination was identified as a current density of 3 A·dm⁻², a bath temperature of 55 °C, an ultrasonic power of 210 W, and a duty cycle of 0.7. Under these conditions, the coatings exhibited enhanced hardness and wear resistance. Based on the optimized parameters, additional tribological tests were conducted under various operating conditions to further evaluate wear performance. The results showed that the dominant wear mechanisms were chemical wear and adhesive wear. This study offers new insights into the fabrication of high-performance nanocomposite coatings and expands the application scope of ultrasonic-assisted pulsed electrodeposition in multiphase composite systems. Full article

Characterising and quantifying complex multiphase steels is a challenging and time-consuming process, which is often open to subjectivity when based on image analysis of optical metallographic or SEM images. The properties of multiphase steels are highly sensitive to their individual phase properties and fractions, necessitating the development of robust characterisation tools. This paper presents a method for classifying nanoindentation maps into proportional fractions of up to five distinct microstructural regions in dual-phase and complex-phase steels. The phases/regions considered are ferrite, ferrite containing mobile dislocations, bainite, tempered martensite, and untempered martensite. A range of microstructures with varying fractions of phases were evaluated using both SEM/EBSD and nanoindentation. A machine learning (ML) approach applied to EBSD data showed good consistency in characterising a two-phase system. However, as the microstructural system complexity increased, variations were observed between different analysts and the sensitivity to the ML training data increased when four phases were present (reaching up to ~11% difference in the ferrite phase fraction determined). The proposed nanoindentation mapping technique does not show operator sensitivity and enables the quantification of additional microstructural features, such as identifying and quantifying ferrite regions with a high density of mobile dislocations and the degree of martensite tempering. Full article

This work introduces a 0.6-scale water model of the continuous slab-casting process and a MATLAB-based model to study the effects of non-primed and multiphase flow on pressure and flow rate. The water model uses stopper-rod flow control and features pressure and velocity measurements at multiple locations. The new computational model, PFSR V4 (Pressure-drop Flow-rate model of Stopper Rod metal delivery systems, Version 4), improves upon a prior one-dimensional Bernoulli-based framework by incorporating a bubble accumulation zone. This zone represents a region of bubbly flow with an intermediate gas fraction between constant-pressure gas pockets below the stopper tip and the downstream bubbly flow regime. Parametric studies with the water model show that flow remains fully primed at low gas flow rates but transitions to non-primed flow as the gas flow rate exceeds 10–16 SLPM. Three different flow regions are observed inside the water model nozzle: air pocket, bubble accumulation, and bubbly flow, which are also captured by the new computational model. Above a critical gas flow rate, the flow becomes unstable and difficult to control, though higher hot gas flow rates are expected for similar transitions in a real steel caster due to gas expansion at high temperatures. Pressure changes are minimal in the air pocket region and increase significantly in the upper bubble accumulation zone, where liquid velocity is much higher than in the classic bubbly-flow region, found lower in the nozzle. The new model was successfully calibrated to match the observed flow regimes and shows good agreement with the water-model measurements. Full article

A new combined analysis of SEM-BSE and EDX images using Aphelion^TM software was proposed to describe the quantitative microstructure (quantity and neighborhood of sacrificial phases) of Al-Zn-Si-(Mg) coatings on steel. Three materials with different Al/Zn ratios and Mg content were analyzed. The quantitative microstructure allowed us to describe their corrosion behaviors in a chloride environment and understand their ranking for sacrificial protection of steel in accelerated corrosion tests. For the analyses, interdendritic Zn-rich or Mg-rich phases were expected to be more sacrificial to steel than Al-rich dendrites. Without Mg (AZ coating), Al-rich dendrites created a percolating network, but interdendritic phases did not, suggesting their sacrificial protection to steel to be very limited. Additionally, significant Zn gradients inside dendrites led to a premature coating consumption on the surface, creating new zones of naked steel. In the coatings with Mg (AZM), sacrificial interdendritic phases created a percolating network, which is expected to improve long-time sacrificial protection and contribute to a more uniform formation of Zn corrosion products. For Al content between 30 wt.% and 45 wt.%, a lowering of the Al/Zn ratio (L-AZM) increased the connectivity of the sacrificial interdendritic phases, which is expected to improve the long-term sacrificial effect. Accelerated corrosion tests of scratches in the steel coatings validated the hypotheses. Full article

In the continuous casting of special steel blooms, low casting speeds result in slow renewal of the molten steel surface in the mold, adversely affecting mold flux melting and liquid slag layer supply, which may lead to surface cracks, slag entrapment, and breakout incidents. To optimize the flow and heat transfer behavior in the mold, a three-dimensional numerical model was developed based on the VOF multiphase flow model, $k-ϵ$ RNG turbulence model, and DPM discrete phase model, employing the finite volume method with SIMPLEC algorithm for solution. The effects of casting speed, argon injection rate, and mold flux properties were systematically investigated. Simulation results demonstrate that when casting speed increases from 0.35 m·min⁻¹ to 0.75 m·min⁻¹, the jet penetration depth increases by 200 mm and meniscus velocity rises by 0.014 m·s⁻¹. Increasing argon flow rate from 0.50 L·min⁻¹ to 1.00 L·min⁻¹ leads to 350 mm deeper bubble penetration, 10 mm reduction in jet penetration depth, 0.002 m·s⁻¹ increase in meniscus velocity, and decreased meniscus temperature due to bubble cooling. When mold flux viscosity increases from 0.2 Pa·s to 0.6 Pa·s, the average liquid slag velocity decreases by 0.006 m·s⁻¹ with a maximum temperature drop of 10 K. Increasing density from 2484 kg·m⁻³ to 2884 kg·m⁻³ results in 0.005 m·s⁻¹ higher slag velocity and average 8 K temperature reduction. Comprehensive analysis indicates that optimal operational parameters are casting speed 0.35–0.45 m·min⁻¹, argon flow ≤ 0.50 L·min⁻¹, mold flux viscosity 0.2–0.4 Pa·s, and density 2484–2684 kg·m⁻³. These conditions ensure more stable flow and heat transfer characteristics, effectively reducing slab defects and improving casting process stability. Full article

Medium manganese steels provide a good combination of tensile strength and ductility due to their multiphase microstructure produced during the multi-step heat treatment process. This study primarily focused on testing and analyzing the tensile properties of 0.17C-5Mn-0.76Al-0.9Si-Nb medium manganese quenching and partitioning (QP) steel using both the experimental and finite element method (FEM) in the multilinear isotropic hardening material model. The 7 mm and 12 mm thick plates exhibited a similar microstructure of tempered primary martensite, lath-type retained austenite, and secondary martensite. The experiments measured tensile strengths of 1400 MPa for 12 mm round specimens and 1325 MPa for 7 mm flat specimens, with total elongations of 15% for round specimens and 11% for flat specimens. The results indicated that the sample’s geometry has some effect on the UTS and ductility of the studied medium-Mn QP steel. However, the more important is the complex relationship between the plate thickness and yield stress and ductility, which are affected by finishing hot rolling conditions. The FEM results showed that the von Mises stresses for flat and round specimens were 1496 MPa and 1514 MPa, respectively, and were consistent with the calculated true stresses of experimental results. This shows that numerical modeling, specifically a multilinear isotropic hardening material model, properly describes the material properties beyond the yield stress and accurately predicts the plastic deformation of the investigated multiphase QP steel. Full article

In this study, numerical modeling and experimental tests of the sheet metal cutting process were carried out in order to determine the shape of the cutting knives for a roller shear, ensuring the minimization of burr on the cut edge. A rolling mill was used for the tests, enabling the replication of the cutting process in a roller shear (demonstrating the possibility of using cutting rollers). The cutting edges of the sheets were examined using light microscopy and then compared with the results of numerical simulations to determine the cutting quality. The tests were performed for multiphase Complex Phase (CP) grade steel. The initial thicknesses of sheets were equal to 1 and 2 mm. Based on the results of theoretical research, four shapes of cutting rollers were designed, of which two shapes were selected for experimental tests. The analysis of the test results shows that the lowest burr values were obtained for straight and beveled rollers. Analyzing the size of burr obtained in experimental tests, it can be concluded that for each of the two variants of the roller shape, a reduction in burr was achieved. Greater reductions in burr were achieved for shaped (cut) rolls. Full article

The Magnetic Barkhausen Noise (MBN) is a non-destructive testing method, which, due to its high sensitivity to changes in the microstructure of the material, is increasingly being applied with success as a tool for evaluation of magnetic material state and properties. However, it is no less difficult to analyze the measurement signals and their correct interpretation due to the complex, non-deterministic and stochastic nature of the Barkhausen phenomenon. Depending on the material to be examined, a signal with different characteristics can be observed. Frequently, a signal with multi-phase Barkhausen activity characteristics is obtained, like in the case of grain-oriented electrical steels. Due to the increased computational capabilities of computers, more and more advanced signal analysis methods are being used and artificial intelligence is being involved as well. Recently, the time–frequency (TF) approach for MBN signal analysis was introduced and discussed in several papers, where short-time Fourier Transform (STFT) found frequent application with promising results. Due to the automation of the search for diagnostic patterns, the stage of selecting transformation parameters becomes extremely important in the process of preparing training data for evaluation algorithms. This paper investigates the influence of the STFT computational window size on the material state evaluation results obtained using convolutional neural network (CNN). The studies were performed for MBN signals obtained from grain-oriented electrical steel with anisotropic properties. The carried out work made it possible to draw connections on the importance of the choice of the window during the implementation of CNN network training. Full article

With the advancement of tunnel construction, the load-bearing capacity of shield tunnel segments is diminishing, while issues of deformation and fissuring are becoming more conspicuous, posing direct threats to structural integrity and functionality. Steel fiber reinforced concrete (SFRC) is considered a prevalent material, endowed with high strength, excellent crack control, fracture toughness, and remarkable economic advantages. This paper surveys the state-of-the-art research on SFRC, systematically encapsulating key aspects regarding its composition, attributes, methods of segment reinforcement, constitutive models for SFRC segments, and performance enhancements of SFRC segments. By optimizing steel fiber content, aggregate preparation, and selection of chemical admixtures, the mechanical performance of SFRC can be augmented, among which the aspect ratio (l/d) and volume fraction (V_f) of steel fibers exert the most significant influence. Compared with conventional reinforcing materials, SFRC possesses benefits of low cost, uncomplicated fabrication, and superior durability. As a heterogeneous multiphase composite, SFRC exhibits high strength, stiffness, and excellent crack resistance, which can amplify the load-bearing capacity and deformation resistance of the segments, defer damage inception, and thereby enhance the safety and durability of tunnel-lining segments. This study assists in redressing the deficiencies of current shield tunnel segment reinforcement technologies and further facilitates the extensive employment of SFRC in tunnel segment strengthening and restoration. Full article

This study addresses the characterization of the particular microstructural constituents of multiphase transformation-induced plasticity (TRIP)-aided steels belonging to the first and third generations of Advanced High Strength Steels (AHSS) to explore the possibilities of the EBSD method. Complex microstructures composed of ferrite, bainite, retained austenite and martensite were qualitatively and quantitatively assessed. Microstructural constituents with the same crystal structure were distinguished using characteristic EBSD parameters like confidence index (CI), image quality (IQ), kernel average misorientation (KAM) and specific crystallographic orientation relationships. A detailed linear analysis of the IQ parameter and misorientation angles was also performed. These tools are very helpful in linking different symmetric or asymmetric features of metallic alloys with a type of their structure and morphology details. Two types of samples were investigated: thermomechanically processed and subjected to 10% tensile strain to study the microstructural changes caused by plastic deformation. Full article

It has been reported that the multiphase structure with martensite and a mixed structure obtained by the quenching and tempering of bearing steel shows high strength and ductility. However, there appears to be no study on the effects of very-high-cycle fatigue (VHCF) and ultrasonic nanocrystal surface modification (UNSM) of a new bearing steel required for the durability design of next-generation bearing steel. This study analyzed the characteristics of microstructure transformation associated with heat treatment cycles and studied and evaluated the fatigue strength characteristics by the UNSM. Fisheye cracks occur from small inclusions inside the specimen only in martensitic microstructure materials in the long-life range. And the characteristic of a double S-N curve in which the fatigue limit decreased in two stages appeared. However, fisheye cracks and double S-N curves did not appear in pearlite and mixed-structure materials. Full article

To address the issue of high fracture and wear failure rates caused by the lack of toughness and abrasion resistance in the steel used for soil-engaging components of tillage machinery, a novel composite heat treatment process, “normalizing and intercritical quenching and tempering (NIQT)”, is proposed. By regulating the austenitizing heating temperature in the intercritical area (ferrite/austenite two-phase area), the type, content, and distribution of phases in the 27MnCrB5 test sample could be precisely controlled, which further influenced the mechanical properties of the material. The results demonstrated that a multiphase composite microstructure, predominantly consisting of martensite and ferrite, could be obtained in the 27MnCrB5 steel treated by the NIQT process. The results of an EBSD test indicated that the predominant type of grain boundary following the NIQT heat treatment was a high-angle grain boundary (approximately 59.5%), which was favorable for hindering crack propagation and improving the impact toughness of the material. The results of the mechanical tests revealed that, when the quenching temperature was set to 790 °C, the 27MnCrB5 steel attained excellent comprehensive mechanical properties, with a tensile strength of 1654 MPa, elongation of 10.4%, impact energy of 77 J, and hardness of 530 HV30. Compared with conventional heat treatment processes for soil-engaging components, this novel process has the potential to enhance the performance of soil-engaging components and prolong their service life. Full article

This study examined a newly developed environmentally friendly plant-based corrosion inhibitor (Xanthium sibiricum). The natural potential method, linear polarization method, steel weight loss method, and corrosion area method were employed to verify the inhibitor’s effectiveness in chloride-containing concrete. The results indicated that Xanthium sibiricum elevated the natural potential of reinforcing steel in concrete, increased its self-corrosion potential, and reduced the self-corrosion current. After three months of curing, the corrosion rate of steel without an inhibitor was approximately 47.5% faster than the experimental group, with the steel loss rate about 40% more severe. The effectiveness of the inhibitor was influenced by increased chloride content in concrete. A two-dimensional multiphase ion transport model of reinforced concrete with realistic aggregate distribution was established using the finite element method (FEM). This model simulated chloride ion transport under typical civil engineering service environments—the coupled effects of a stray current and chloride environment. A predictive formula for the residual compressive strength of reinforced concrete was derived after corrosion under various voltages and chloride ion concentrations for a specific duration. In conjunction with a pump station project operating in a similar environment, the optimal dosage of the Xanthium sibiricum inhibitor for practical engineering was determined to be 2 g/L. At this dosage, the strength of reinforced concrete specimens increased by approximately 31.1%. Finally, a predictive formula for the residual compressive strength of reinforced concrete with an added inhibitor was obtained after corrosion under various voltages and chloride ion concentrations for a specific duration. The conclusions can enhance the durability and safety of concrete structures in similar projects, showing promising application prospects. Full article